24

Collections and Software Development Using Java

24.1 Introduction

While well-designed algorithms improve the efficiency of programs, the data structures will allow a programmer to use the underlying hardware and supporting language features to enhance the throughput of the programmers. J2SE 5.0 and later versions have provided collection framework that provides several interfaces such as Set<T>, List<T>, Queue<T>, and Map<k,s>. This chapter introduces you to these concepts so that you can deliver programs by efficiently using collections rather than developing programs yourself, thereby enhancing productivity.

In industry, databases are used extensively because of ease with which they provide answers to queries without resorting to elaborate programming through a software called sql query. The most popular databases in the industry are Oracle, MySql (open source by MySql.com), and, of course, MS Access that is within easy reach through all prevalent MS Office. This chapter shows you ways to handle these databases through Java programs by using drivers such as JDBC, JDBC-ODBC, and MySql connectivity tools. Servlets are important implementation in Java to handle client server programs. Servlets extend the functionality of web servers to any user on the net just like applets extend the functionality of the web browser. Java Beans is designed for reusability. In this chapter, you will learn the procedures to deploy java beans.

This chapter will put you through various skills that are required to become highly productive and make you ready to take up a job in the industry or enhance your skills. We teach you the methodologies through step-by-step procedures and programs and reflect these steps thereby making learning permanent and easy.

24.2 Collection Framework of Java

How do we store a group of objects in an array? J2SE 5.0 has provided a collection framework. Collection framework provides an API that makes programming using data structures easy and thereby enhances the productivity of the programmer. This is somewhat similar to the container of C++ but has quite a number of differences. Collection framework is implemented in java.util package. The concept is make a collection object, store group of objects in collection object. The collection framework of Java is shown in Figure 24.1

 

Collection class provides several interfaces such as Collection, Map, and Iterator. These are shown in Figure 24.2.

 

The Collection Framework classes and interfaces have been derived from meta class Object provided by Java. The hierarchy of classes of Collection framework is shown in Figure 24.3.

 

Interfaces and their implementing class are shown in Table 24.1.

 

Table 24.1 Collection class interfaces and implementing classes

Interface	Implementing Class	Description
List	ArrayList	Implementation based on resizable array
List	LinkedList	Implementation based on linked list
Set	HashSet	Implementation based on Hash table
Set	TreeSet	Implementation based on balanced binary tree
Map	HashMap	Implementation based on Hash table
Map	TreeMap	Implementation based on balanced binary tree

24.3 Collection Interface

The Collection Interface is the main interface from which the List and Set Interfaces are derived. It specifies the methods that are common to all Collections. The methods defined in the Collection Interface and their descriptions are listed in Table 24.2.

 

Table 24.2 Collection Interface and their descriptions

Method	Remark
boolean add(Object o)	Add a new object
boolean addAll(Collection c)	Usage: t.addAll(c) Mimics union operation. Result: Collection t contains all the objects in both t and c
void clear()	Remove All elements in the collection
boolean contains(Object o)	Checks if object is present in collection
boolean containsAll(Collection c)	Usage: t.containsAll(c) Mimics subset operation Result: returns true if Collection c is subset collection t
boolean isEmpty()	Returns true if collection is empty
Iterator iterator()	Used to traverse the collection
boolean remove(Object o)	Remove object from collection
boolean removeAll(Collection c)	Usage: t.removeAll(c) Result: All objects in Collection t which are also contained in collection c are removed
boolean retainAll(Collection c)	Usage: t.retainAll(c) Mimics intersection operation. Result: Collection t has objects common to both t and t
int size()	Number of objects in the collection
Object[] toArray() Object[] toArray(Object[] a))	The array operations allow the contents of a Collection to be translated into an array

24.4 Set Interface

Important features of Set interface are as follows:

• Defined in java.util.Set
• Set extends the Collection Interface but does not add any new methods
• The interface models the mathematical set abstraction
• Set cannot contain duplicate elements
• Collection framework provides two implementations of Set Interface: HashSet and TreeSet

We demonstrate some basic set operations in Example 24.1 using the HashSet implementation of the Set interface.

 

1. import java.util.Set;
2. import java.util.HashSet;
3. public class SetDemo {
4. public static void main(String[] args) {
5. Set<String> PoolA=new HashSet<String>();
6. PoolA.add(“India”);
7. PoolA.add(“Australia”);
8. PoolA.add(“South Africa”);
9. System.out.println(“PoolA: “ +PoolA);
10. Set<String> PoolB=new HashSet<String>();
11. PoolB.add(“England”);
12. PoolB.add(“India”);
13. PoolB.add(“New Zealand”);
14. System.out.println(“PoolB: “ +PoolB);
15.
16. PoolA.retainAll(PoolB);
17. System.out.println(“Intersection Operation PoolA: “ +PoolA);
18. PoolA.addAll(PoolB);
19. System.out.println(“Union Operation PoolA: “ +PoolA);
20. System.out.println(“Subset Operation: “
21. +PoolA.containsAll(PoolB));
22. }
23. }
24. /* Output
25. PoolA: [Australia, South Africa, India]
26. PoolB: [England, New Zealand, India]
27. Intersection Opeartion PoolA: [India]
28. Union Operation PoolA: [England, New Zealand, India]
29. Subset Operation: true
30. */

Lines Nos. 1 & 2:	import Set and HashSet defined in the java.util package. Line 5 defines a set of strings called PoolA.
Lines Nos. 6, 7 & 8:	show how to populate the Set PoolA using the add method.
Line No. 9:	demonstrates how we can print the elements to PoolA on the console.
Lines Nos. 11–15:	create a new Set PoolB and populate them with elements.
Line No. 17:	demonstrates the intersection operation between sets, Line 19 union operations and Lines 21–22 the subset operations.

24.5 Iterators

Iterator allows us to iterate over a collection such as Set. The iterator interface is defined in java.util.Iterator. The interface defines three methods as seen below:

public interface Iterator {
public boolean hasNext();
public object next();
public void remove();
}

The hasNext( ) method returns true is the iteration has more elements. The next( ) method returns the next element in the collection and the remove( ) method is used to remove the last element returned by the iterator. Example 24.2 demonstrates usage of an iterator on a Set

 

import java.util.Set;
import java.util.HashSet;
import java.util.Iterator;
public class SetDemo {
  public static void main(String[] args) {
    Set<String> set=new HashSet<String>();
    set.add(“Gautam”);
    set.add(“Ramesh”);
    set.add(“Anand”);
  System.out.println(“HashSet Output”);
  for(Iterator it = set.iterator(); it.hasNext(); ){
  System.out.println(“String: “ + it.next());
    }
  }
}
/*Output
HashSet Output String: Gautam String: Ramesh String: Anand */

Line No. 12:

shows how to obtain an iterator for the Set using the iterator( ) methods. We use the hasNext( ) method as the breaking condition for the loop as shown in Line 12. To get the value of the element we use the next( ) method as shown in Line 13.

24.6 List Interface

Important features of List interface are as follows:

• Defined in java.util.List
• List extends the Collection Interface and adds a few new methods
• The elements are stored in a linear fashion with a beginning and an end.
• List can contain duplicate elements
• Collection framework provides two implementations of List Interface: ArrayList and LinkedList
• Lists have the capability to expand to accommodate the addition of new elements

Table 24.3 describes the additional methods defined by the List interface

 

Table 24.3 Additional methods defined by List Interface

Method	Remark
E get(int index)	Returns element at given index
E set(int index, E element)	Replace value at given index with new element
boolean add(E element)	Adds element at the end of the list
void add(int index, E element)	Adds element at the given index
E remove(int index)	Removes element at the given index
int indexOf(Object o)	Returns index of object o in the list
int lastIndexOf(Object o)	Returns index of last found occurrence of Object o
ListIterator<E> listIterator()	List Iterator extends the iterator it has ability to traverse the list in both directions, modify the list and provide positional information such as current index
List<E> subList(int from, int to)	Returns a view of the list between indices from (inclusive) and to (excluded). Changes done in the sublist are reflected in the main list

We demonstrate some of the important methods of the List Interface and also usage of the List Iterator in Example 24.3:

 

1. import java.util.ArrayList;
2. import java.util.LinkedList;
3. import java.util.ListIterator;
4. public class ListDemo {
5. public static void main(String[] args) {
6. ArrayList<String> AList = new ArrayList<String>();
7. LinkedList<String> LList = new LinkedList<String>();
8. AList.add(new String(“Ramesh”));
9. AList.add(new String(“Anand”));
10. AList.add(new String(“Gautam”));
11. System.out.println(“ArrayList: “ +AList);
12. DemoArrayList(AList);
13. LList.add(new String(“Ramesh”));
14. LList.addFirst(new String(“Anand”));
15. LList.addLast(new String(“Gautam”));
16. System.out.println(“LinkedList: “ +LList);
17. System.out.print(”Reversed LinkedList: ”);
18. ListIterator<String> it = LList.listIterator(LList.size());
19. while(it.hasPrevious())
20. System.out.println(it.previous());
21. }
22. private static void DemoArrayList(ArrayList<String> list){
23. String s = new String(”Gautam“);
24. System.out.println(”index: ” +list.indexOf(s));
25. list.remove(s);
26. System.out.println(”ArrayList: ” +list);
27. list.set(0, ”Thunder“);
28. System.out.println(”ArrayList: ” +list);
29. }
30. }
31. /* Output
32. ArrayList: [Ramesh, Anand, Gautam]
33. index: 2
34. ArrayList: [Ramesh, Anand]
35. ArrayList: [Thunder, Anand]
36. LinkedList: [Anand, Ramesh, Gautam]
37. Reversed LinkedList: Gautam Ramesh Anand
38. */

We instantiate two lists one is of the type ArrayList(AList) and the other is of the type LinkedList(LList) in Lines 6 and 7. Both the Lists hold Strings. Lines 9, 10, and 11 demonstrate how to add elements to an ArrayList. The function DemoArrayList( ) further demonstrates some of the important methods of the List Interface. Lines 15, 16, and 17 show the methods that can be used to add elements to a LinkedList as seen in addition to the add method LinkedList provides the addFirst( ) and addLast( ) methods which enable us to add elements to the starting and ending of the list easily. Line 21 shows how to create a List iterator and set to the last element in the list by passing the LList.size( ) parameter during instantiation. Lines 22 and 23 show how to iterate backwards.

24.7 Collection Algorithms

Java platform provides a number of useful algorithms. The algorithms are implemented as static methods in the Collections class. Many of the algorithms can be used only with Lists while some can be used with all the Collections. The algorithms are polymorphic in nature, i.e., the same method can be used on different implementations of a Collection interface. The algorithms can be used by importing the java.util.Collections class. In Table 24.4, we list some of the most widely used algorithms present in the collection class.

 

Table 24.4 Collection algorithms description

Algorithm	Remark
sort	Sorts the input list using an optimized merge sort algorithm. Worst case time complexity is nlog(n).
binarySearch	The binarySearch algorithm searches for a specified element in a List. The input list must be sorted before using the binaryserach algorithm
shuffle	Shuffles the order of elements in the list
reverse	Reverses the order of elements in a List
fill	Fills the List with the specified value.
copy	Copies elements in a source list to a destination list. The size of the destination list must be equal or greater than the source list.
swap	Swaps the elements at the specified positions in a List
addAll	Adds all the specified elements to a Collection. Generally elements are appended to the end of the Collection
frequency	Returns the number of instances of a specified element in a collection
disjoint	Used to determine if two collections have no elements in common

We demonstrate the usage of some the algorithms in Example 24.4.

 

1. import java.util.Collections;
2. import java.util.ArrayList;
3. public class ListAlgorithmDemo {
4. public static void main(String[] args) {

5. ArrayList<Integer> IList = new ArrayList<Integer>();
6. ArrayList<String> SList = new ArrayList<String>();
7. IList.add(new Integer(7));
8. IList.add(new Integer(5));
9. IList.add(new Integer(9));
10. Collections.sort(IList);
11. System.out.println(“Ascending Order: “ +IList);
12. System.out.println(“Index of Integer 9 in sorted list: “
13. +Collections.binarySearch(IList, 9));
14. Collections.reverse(IList);
15. System.out.println(“Descending Order: “ +IList);
16. Collections.shuffle(IList);
17. System.out.println(“Shuffled List: “ +IList);
18. System.out.println(“Min: “ +Collections.min(IList));
19. System.out.println(“Max: “ +Collections.max(IList));
20. SList.add(new String(“Ramesh”));
21. SList.add(new String(“Anand”));
22. SList.add(new String(“Gautam”));
23. Collections.sort(SList);
24. System.out.println(“Ascending Order: “ +SList);
25. }
26. }
27. /* Output
28. Ascending Order: [5, 7, 9]
29. Index of Integer 9 in sorted list: 2
30. Descending Order: [9, 7, 5]
31. Shuffled List: [5, 9, 7]
32. Min: 5
33. Max: 9
34. Ascending Order: [Anand, Gautam, Ramesh]
35. */

Line Nos. 5 & 6:	create two List objects: one of Integer type and the other of String type.
Lines Nos. 8, 9, & 10:	populate the Integer list.
Line No. 12:	demonstrates how to apply sort algorithm on Integer list.
Lines Nos. 14 & 15:	demonstrate binarysearch. Please note that binarysearch works only on sorted lists so we call it only after sorting the integer list.
Lines Nos. 16 & 18:	demonstrate usage of shuffle and reverse algorithms.
Lines Nos. 23–28:	sort algorithm on string list.

24.8 Map Interface

Important features of Map interface are as follows:

• Map is similar to a dictionary.
• Each entry in the Map involves a pair of elements called keys and values. They are collectively referred to as key–value pairs.
• Each key maps to a particular value. For example, the roll number (key) maps to a name (value) in an attendance register.
• Map cannot contain duplicate keys, but can contain duplicate values.
• The association between key and value is one to one, i.e., each key should map to only one value.
• Collection framework provides two implementations of Map Interface: HashMap and TreeMap.

Table 24.5 describes the methods defined in the Map interface.

 

Table 24.5 Map Interface description

Method	Remark
V put(K key, V value)	Create a new map for key and value
V get(Object key)	Returns the value associated with key
V remove(Object key)	Removes the mapping for key
boolean containsKey(Object key)	Checks if collection contains a mapping for key
boolean containsValue(Object value)	Checks if collection contains a mapping to value
int size()	Returns the number of key–value pairs present in the collection
boolean isEmpty()	Returns true if collection is empty
void clear()	Clears all the mappings in the collection
Set<K> keySet()	The method returns a Set which contains all the keys in the Map
Collection<V> values()	The method returns a Collection which contains all the values in the Map. The method returns Collection and not a Set as values can be duplicate whereas Keys are unique
Set<Map.Entry<K,V>> entrySet()	The method returns a Set which is populated with Map. Entry objects, key–value pairs can be obtained simultaneously by using methods defined in Map. Entry objects

24.9 Collection View of Map

It is not possible to attach an iterator directly to a Map. So in order to iterate over a Map, the Map interface provides methods which allow the Map to be viewed as a Collection. Example 24.5 demonstrates two such methods: keySet() and values(). Please note that Map stores only object references so it is not possible to use primitive data types like double or int. Instead we can use wrapper class such as Integer or Double.

 

1. import java.util.Collection;
2. import java.util.Map;
3. import java.util.HashMap;
4. import java.util.Iterator;
5. import java.util.Set;
6. public class MapDemo{
7. public static void main(String[] args){
8. Map<Object,String> map=new HashMap<Object,String>();
9. map.put(new Integer(120400), “Ramesh”);
10. map.put(new Integer(120401), “Anand”);
11. map.put(new Integer(120402), “Gautam”);
12. System.out.println(“Printing Keys: “);
13. Set s = map.keySet();
14. for(Iterator itr = s.iterator();itr.hasNext();)
15. System.out.println(itr.next());
16. System.out.println(“Printing Values: “);
17. Collection c = map.values();
18. for(Iterator itr = c.iterator();itr.hasNext();)
19. System.out.println(itr.next());
20. }
21. }
22. /* Output
23. Printing Keys: 120401 120400 120402
24. Printing Values: Anand Ramesh Gautam
25. */

Line No. 8:	instantiates a Map object with Keys defined as Objects and Values defined as Strings. The Map uses the HashMap implementation.
Line Nos. 9, 10, & 11:	populate the Map with an Integer object and String.
Line No. 14:	demonstrates how to use the keyset( ) method to get a Collection view of the keys. We use the Set Interface as Set cannot have duplicates like keys. Similarly, Line 19 shows how to get a collection view of Values.

Sometimes, we would like to modify the value associated with a key during iteration. Map interface provides a method entrySet() and a nested interface called Map.Entry to accomplish this. The method entrySet () returns a collection view of all the key–value pairs present in the Map. The nested interface Map.Entry is defined as follows:

public interface Entry {
K getKey(); V getValue(); V setValue(V value);}

As seen from the above, the interface provides methods through which we can access and modify the Value associated with a key. Example 24.6 demonstrated how to use method entrySet() and Map.Entry to iterate and access values associated with keys.

 

1. import java.util.Map;
2. import java.util.HashMap;
3. import java.util.Set;
4. import java.util.Iterator;
5. public class MapDemo {
6.   public static void main(String[] args) {
7.     Map<Object,String> map=new HashMap<Object,String>();
8.     map.put(new Integer(120400), “Ramesh”);
9.     map.put(new Integer(120401), “Anand”);
10.    map.put(new Integer(120402), “Gautam”);
11.  Set s=map.entrySet();
12.  for(Iterator it=s.iterator();it.hasNext();){
13.    Map.Entry m =(Map.Entry)it.next();
14.    int rollno=(Integer)m.getKey();
15.    String name=(String)m.getValue();
16.    System.out.println(“Roll No:”+ rollno + “ Name:” +name );
17.    }
18.  }
19. }
20. /* Output
21. Roll No:120401 Name:Anand
22. Roll No:120400 Name:Ramesh
23. Roll No:120402 Name:Gautam
24. */

Line No. 12:

creates a Set s that contains all the key–value pairs contained in the map. We associate an iterator to the Set in Line 13. Line 14 demonstrates how to create a Map.Entry object. Lines 15 and 16 show how to get the key and value using the Map.Entry methods. The for loop used in the program can be simplified using a for each loop as follows:

for (Map.Entry< Object, String > e : map.entrySet()){
System.out.println(“Roll No:”+ e.getKey() + “ Name:” +e.getValue());
}

When using the above for loop line 12 Set s=map.entrySet() is also not required.

24.10 JDBC Database Connectivity

In order to connect to a database you will need Drivers. Firstly, as you will be requesting connection from Java program, you will need JDBC Manager to act as interface between Java components such as Applet or Application and Drivers.

Then to work with databases such as Oracle, MS Access, and MySQL which are third party database you will need drivers such as ODBC (Open Database Connectivity) which takes calls supplied by JDBC and converts them into formats suitable for proprietary databases such as MS Access and Oracle 10g, etc. This means that Database and ODBC must be available in your machine. ODBC is shipped along with Windows OS. JDBC is a part of JDK which we have installed. Finally, MySQL also provides a connector mysql-connector-java-5.1.3 and mysql-5.1.51-win32.msi. First download these databases as per your choice and install them. Paths are to be set by you in case it has not prompted you during installation. Procedure for setting path is provided in Section 16.6.2. Figure 24.4 describes this arrangement. Applet and application are from client side and Database is from the server side. The server side also can reside in the same machine for testing in which case its called local host.

 

 

Type 1: JDBC-ODBC Driver: Receives JDBC calls and hands over to ODBC driver. ODBC hands over these calls to manufacturers to library. This type is most widely used since ODBC drivers are available for almost all databases. This connector is a general connector and applicable to a wide variety of databases.

Type 2: Same as Type 1 but connector connects to a specific database. Hence, it is a specific connector. These are not popular since they are vendor specific.

Type 3: This is a net-based Data Connector in which JDBC converts the calls into middle tier server calls and, based on the actual server, the middle tier calls are converted to specific server. Obviously, as there is an additional conversion, this type is a slow connector.

Type 4: This is a pure Java driver that converts to vendor-specific database directly. It is machine independent since it is a pure Java product but the disadvantage is that you will need vendor-specific drivers.

24.11 Access Database Records Using MS Access Database

MS Access is the most popular and easily available database available along with MS office package. Students have easy access to MS Access and can gain knowledge of the process involved and easily migrate to Oracle and MySql. The application we will select is to create a database with fields idNum, Name, and Dept and Salary of Employees. Once the database is created, we will use Sql query to access the records and display the result. There are three distinct phases for retrieving data from MS Access Database using JDBC-ODBC Bridge. They are:

• Phase 1 : Create the MS Access database File
• Phase 2 : Create Data Source Name(DSN)
• Phase 3 : Write Java Application to access the MS Access database

Phase 1: Create MS Access database Table called oopsemp

Step 0: Start --- MicroSoft Office---- MS Access- create a new file-Blank Database enter filename to save as oops.mdbcreate in The Directory you are working. For example c:oopsjavaworkspaceoopstech2comoopschap24

 

 

Step 1: Choose option 3 i.e. create table by entering data

 

 

Step 2: Right click on field and select rename column and change field names to id, name, dept, salary. Then enter data in the relevant fields

 

 

Step 3: File save as oopsemp24.mdb ok. Click no for entering primary key

Step 4: Create Data Source Navigator DSN for JDBC ODBC connectivity Start settings control panel Administrative ToolsData Sources(ODBC)MS Access DataBasesAdd

 

 

Step 5: Select the database for which we want to create DSN

 

 

Step 6: Enter data Source Name as oopsemp and description oopstech company employees. Press ok.

 

 

Step 7: Select the file form your directory, i.e., oops.mdb and press ok

 

 

Step 8: The control will return to ODBC Microsoft Access screen at Step 6. Press ok

Step 9: The control will return to ODBC Data Source Administrator screen at Step 4 - press ok.

DSN has been created. Now we are ready for phase 3, i.e., write a Java program.

Phase 3: Write Java Program

We will show the methodology in steps

Step 0: import java.sql.*;

Step 1: Load and register the Driver by using Class.forName()

Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);

Step 2: Establish connection to a database

Connection con = DriverManager.getConnection
		(“jdbc:odbc:oopsemp”,””,””);
		oopsemp is the data source name we have selected while creating access table. User Name and Pass word field are empty strings.

Step 3: Create a statement : Statement stmt = con.createStatement();

Step 4: Execute the statement : ResultSet rs = stmt.executeQuery (“select * from oopsemp24”);

Step 5: Work on ResultSet

	while (( rs.next()))
	{ System.out.print(rs.getInt(reccount)+” “);
	System.out.print(rs.getString(reccount+1)+ “ “);
	System.out.print(rs.getString(reccount+2)+” “);
	System.out.println(rs.getFloat(reccount+3)+” “);
	}

In our next example, we will put all the above steps into practice.

 

1. package com.oops.chap24;
2. import java.sql.*;
3. public class AccessJDBCODBC {
4. public static void main(String[] args) throws SQLException {
5. int reccount=1;
6. //Register the Driver
7. try{
8. Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);
9. }catch ( Exception e ){System.out.println(“Unable to load Driver”);}
10.	Connection con = DriverManager.getConnection(“jdbc:odbc:oopsemp”,””,””);
11.	//create sql statement
12.	Statement stmt = con.createStatement();
13.	ResultSet rs = stmt.executeQuery(“select * from oopsemp24”);
14.	System.out.println(“
id name Dept Salary”);
15.	while (( rs.next()))
16.	{System.out.print(rs.getInt(reccount)+” “);
17.	System.out.print(rs.getString(reccount+1)+ “ “);
18.	System.out.print(rs.getString(reccount+2)+” “);
19.	System.out.println(rs.getFloat(reccount+3)+” “);
20.	}
21.	}
22. }

 

Output: id name Salary
id name Dept Salary
50595 Ramesh laptops 24000.0
50596 Usha internet 22000.0
50597 Anand automobile 80000.0
50598 gautam cellphones 75000.0

24.12 Access Database Records Using MySql Open Source Database

The reason for choosing MySql is free and open source being provided by MySql.com. For running the JDBC connectivity using MySql, you will need mysql-5.1.51-win32.msi and mysql-connector-java-5.1.13. These are software for using mysql and connecting to databases through Java programs. Let us say that you have installed them in Directory d:Directory sql. The path is automatically set by installer. In this case also, we would follow a two-step strategy:

• Phase 1: Create the mysql database File
• Phase 2: Use JDBC connector and Write Java Application to access the MySql database

Phase 1: Create the mysql database File

Step 1:To create database file : Start programs- MySql Server 5.1 >MySql command line client <enter> Enter password mysql command prompt appears.

 

 

mysql> show databases; command shows databases available

To see what tables are available in oopsemp2:

mysql> use oopsemp2; Database changed
mysql> show tables;
+--------------------+
| Tables_in_oopsemp2 |
+--------------------+
| oopsemp2 |
| oopsemp3 |
+--------------------+
2 rows in set (0.06 sec)

To create a table called: oopsemp4 :

mysql> create table oopsemp4 ( id int,name char(10),dept char(10),salary float);
uery OK, 0 rows affected (0.17 sec)

To verify the field created: mysql> desc oopsemp4;

+--------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+----------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | char(10) | YES | | NULL | |
| dept | char(10) | YES | | NULL | |
| salary | float | YES | | NULL | |
+--------+----------+------+-----+---------+-------+

To enter data in to table oopsemp4

mysql> insert into oopsemp4 values (50595,”Ramesh”,”laptops”,20000.00);
Query OK, 1 row affected (0.09 sec). Enter further records as required.

To see the records we have just entered:

mysql> select * from oopsemp4;
+-------+------------+---------------+----------+
| id | name | dept | salary |
+-------+--------+-------------------+----------+
| 50595 | Ramesh | Laptops | 20,000 |
| 50596 | Usha | Internet | 20,000 |
| 50597 | Anand | Automobiles | 80,000 |
| 50597 | Gautam | Cell phones | 80,000 |
+-------+--------+------------+--------+
4 rows in set (0.05 sec)

To set a query: to see id and names of employees whose salary is more than 20000.00

mysql> select name from oopsemp4 where salary >20000.00;
+----------+
| name |
+----------+
| Anand |
| Gautam|
+--------+

You have seen that we set queries and got the answers. Now will write a java program to connect to database and get the same answers.

Phase 2: Use JDBC connector and access the MySql database

 

1. package com.oops.chap24;
2. import java.sql.*;
3. public class Connect{
4. public static void main(String args[]){
5. try{
6. String userName = “”;
7. String password = “”;
8. String url = “jdbc:mysql://localhost/oopsemp2”; //database name
9. Class.forName (“com.mysql.jdbc.Driver”).newInstance ();
10. Connection conn=DriverManager.getConnection (url, userName, password);
11. System.out.println (“Database connection established”);
12. Statement st = conn.createStatement();
13. ResultSet rs=st.executeQuery(“select * from oopsemp3”);// table name
14. System.out.println(“
 output from table :oopsemp3…”);
15. System.out.print(“--------------------------
”);
16. System.out.println(“| Sur Name | Last Name |”);
17. System.out.println(“--------------------------”);
18. while(rs.next())
19. {
20. String username=rs.getString(1);
21. String password2=rs.getString(2);
22. System.out.print(“
| “+username);
23. System.out.print(“ | “+password2);
24. System.out.print(“ | “);
25. } // while
26. System.out.println(“
--------------------------”);
27. //Handle oopsemp4 table
28. rs=st.executeQuery(“select id,name from oopsemp4 where salary>20000.0”);// table name
29. System.out.println(“
 id & name for salary>20000.00 from table :oopsemp4…”);
30. System.out.print(“--------------------------
”);
31. System.out.println(“|Employee id no | Name |”);
32. System.out.println(“--------------------------”);
33. while(rs.next())
34. {int userid=rs.getInt(1);
35. String name =rs.getString(2);
36. System.out.print(“
| “+userid);
37. System.out.print(“ | “+name);
38. System.out.print(“ | “);
39. } // end of while
40. System.out.println(“
--------------------------”);
41. } catch(Exception ex){ex.printStackTrace();}
42. } //main
43. } // class
Output : Database connection established
output from table :oopsemp3…
--------------------------
| Sur Name | Last Name |
--------------------------
| ramesh | vasappanavara |
| Usha | vasappanavara |
| Anand | vasappanavara |
| Gautam | vasappanavara |
--------------------------
id & name for salary>20000.00 from table :oopsemp4…
--------------------------
|Employee id no | Name |
--------------------------
| 50597 | Anand |
| 50597 | Gautam |
--------------------------

24.13 Access Database Records Using Oracle Database

There are three distinct phases for retrieving data from Oracle database using JDBC-ODBC Bridge. They are:

• Phase 1: Create the Oracle database File
• Phase 2: Create Data Source Name (DSN)
• Phase 3: Write Java Application to access the MS Access database

Phase 1: Create Oracle database file

We are assuming that you have Oracle installed in your computer system and SQL>prompt is available. We will show only in command prompt usage, while web-based approach is also allowed by Oracle 10 and later versions. All Oracle databases file in Oracle 10g and later will have User name: system and password: oracle. Other older oracle versions use username: scott and password: tiger. Get SQL prompt on the screen.

   SQL> connect system; Enter password:oracle<enter> Connected. SQL>
   SQL> select * from cat ; will list out all tables in system
   -----------------------------------------
   PRODUCT_USER_PROFILE SYNONYM
   HELP TABLE
   OOPSEMP5 TABLE
   179 rows selected.
   SQL>
SQL> SQL> create table oopsemp6( idNum int, name varchar2(10),dept varchar2(10),salary float);
   Table created.
   OOPSEMP6 TABLE
   OOPSEMP5 TABLE
   180 rows selected.
SQL> desc oopsemp6; will show the field in table oopsemp6
   Name Null? Type
   --------------------------------------------------------------
   IDNUM NUMBER(38)
   NAME VARCHAR2(10)
   DEPT VARCHAR2(10)
   SALARY FLOAT(126)
   SQL> insert into oopsemp6 values(&idNum,’&name’,’&dept’,&salary);
   Enter value for idnum: 50595
   Enter value for name: Ramesh
   Enter value for dept: laptops
   Enter value for salary: 20000.00
   old 1: insert into oopsemp6 values(&idNum,’&name’,’&dept’,&salary)
   new 1: insert into oopsemp6 values(50595,’Ramesh’,’laptops’,20000.00)
   1 row created.
   We can create further records.
   SQL > SELECT * FROM OOPSEMP6; will show you the data we have entered
   IDNUM NAME DEPT SALARY
   ----------------------------------------
   50595 Ramesh laptops 20000
   50596 Usha Internet 22000
   Now we are ready to proceed to Phase 2

Phase 2: Create a Data Source Name (DSN)

Step 1: Create Data Source Navigator DSN for JDBC ODBC connectivity

       Start- settings - control panel  Administrative ToolsData Sources(ODBC)-Add

 

 

Step 2: Select the database for which we want to create DSN-Press Finish.

 

 

Step 3: Enter data Source Name as oopsempdsn and description oops employees. Description system and Press ok.

 

 

Step 4: The control will return to ODBC Data Source Administrator screen at Step 1 you can see oopsempdsn1 listed press ok.

 

 

DSN has been created. Now we are ready for phase 3, i.e., write a Java program.

Phase 3: Write Java Application to access the Oracle database

 

1. package com.oops.chap24;
2. import java.sql.*;
3. public class accessoracle{
4. public static void main(String args[]){
5. try{
6. String userName = “system”;
7. String password = “oracle”;
8. String url = “jdbc:odbc:oopsempdsn”; //database name
9. Class.forName (“sun.jdbc.odbc.JdbcOdbcDriver”);
10. Connection conn=DriverManager.getConnection (url,userName,password);
11. System.out.println (“Database connection established”);
12. Statement st = conn.createStatement();
13. //Handle oopsemp5 table
14. ResultSet rs=st.executeQuery(“select idNo ,name from oopsemp5 where
15. salary>20000.0”);// table name
16. System.out.println(“
 idNo & name for salary>20000.00 from table :oopsemp5…”);
17. System.out.print(“--------------------------
”);
18. System.out.println(“|Employee id no | Name |”);
19. System.out.println(“--------------------------”);
20. while(rs.next())
21. { int userid=rs.getInt(1);
22. String name =rs.getString(2);
23. System.out.print(“
| “+userid);
24. System.out.print(“ | “+name);
25. System.out.print(“ | “);
26. } // end of while
27. System.out.println(“
--------------------------”);
28. } catch(Exception ex){ex.printStackTrace();}
29. } //main
30. } // class
Output : Database connection established
idNo & name for salary>20000.00 from table :oopsemp5…
------------------------------
|Employee id no | Name |
-------------------------------
| 50596 | Usha |
| 50597 | Anand |
| 50599 | Gautam |
-------------------------------

 

1. package com.oops.chap24;
2. import java.sql.*;
3. public class InsertDB{
4. public static void main(String args[]){
5. try{String userName = “system”;
6. String password = “oracle”;
7. String url = “jdbc:odbc:oopsempdsn”; //database name
8. Class.forName (“sun.jdbc.odbc.JdbcOdbcDriver”);
9. Connection conn = DriverManager.getConnection (url, userName, password);
10. System.out.println (“Database connection established”);
11. Statement st = conn.createStatement();
12. //Handle oopsemp5 table
13. System.out.println(“
 Inserting a record in to database”);
14. st.executeUpdate(“insert into oopsemp5 values(50600,’Prahlad’,’Toys’,40000.00)”);
15. ResultSet rs=st.executeQuery(“select idNo ,name from oopsemp5”);// table name
16. System.out.println(“
 idNo & name from table :oopsemp5…”);
17. System.out.print(“--------------------------
”);
18. System.out.println(“|Employee id no | Name |”);
19. System.out.println(“--------------------------”);
20. while(rs.next())
21. {int userid=rs.getInt(1);
22. String name =rs.getString(2);
23. System.out.print(“
| “+userid);
24. System.out.print(“ | “+name);
25. System.out.print(“ | “);
26. } // end of while
27. System.out.println(“
--------------------------”);
28. } catch(Exception ex){ex.printStackTrace();}
29. } //main
30. } // class
Output : Database connection established
Inserting a record in to database
idNo & name from table :oopsemp5…
--------------------------
|Employee id no | Name |
--------------------------
| 550595 | ramesh |
| 50596 | Usha |
| 50597 | Anand |
| 50599 | Gautam |
| 50600 | Prahlad |
--------------------------

 

package com.oops.chap24;
import java.sql.*;
public class UpdateDB{
public static void main(String args[]){
try{
String userName = “system”;
String password = “oracle”;
String url = “jdbc:odbc:oopsempdsn”; //database name
Class.forName (“sun.jdbc.odbc.JdbcOdbcDriver”);
Connection conn = DriverManager.getConnection (url, userName, password);
System.out.println (“Database connection established”);
Statement st = conn.createStatement();
//Handle oopsemp5 table
System.out.println(“
 Updating a record in to database”);
st.executeUpdate(“update oopsemp5 set salary = 35000 where idNo=50595”);
ResultSet rs=st.executeQuery(“select idNo ,name, salary from oopsemp5”);// table name
System.out.println(“
 idNo&name&salary from table :oopsemp5…”);
System.out.print(“----------------------------------------
”);
System.out.println(“|Employee id no | Name | Salary |”);
System.out.println(“--------------------------------------”);
while(rs.next())
{int userid=rs.getInt(1);
String name =rs.getString(2);
float sal = rs.getFloat(3);
System.out.print(“
| “+userid);
System.out.print(“ | “+name);
System.out.print(“ | “+ sal);
} // end of while
System.out.println(“
--------------------------”);
} catch(Exception ex){ex.printStackTrace();}
} //main
} // class

 

Output: Database connection established
Updating a record in to database
idNo & name from table :oopsemp5…
----------------------------------------
|Emp idno | Name | Salary |
----------------------------------------
| 50595 | ramesh | 35000.0 |
| 50596 | Usha | 22000.0 |
| 50597 | Anand | 80000.0 |
| 50599 | Gautam | 85000.0 |
| 50600 | Prahlad | 40000.0 |
---------------------------------------

 

package com.oops.chap24;
import java.sql.*;
public class DeleteDB{
  public static void main(String args[]){
try{String userName = “system”;
String password = “oracle”;
String url = “jdbc:odbc:oopsempdsn”; //database name
Class.forName (“sun.jdbc.odbc.JdbcOdbcDriver”);
Connection conn = DriverManager.getConnection (url, userName, password);
System.out.println (“Database connection established”);
Statement st = conn.createStatement();
//Handle oopsemp5 table
System.out.println(“
 Deleting records to database”);
st.executeUpdate(“delete oopsemp5 where idNo=50600”);
} catch(Exception ex){ex.printStackTrace();}
  }
}

You can use module presented at Ex1 to view the database records. You can observe that records with idNo=50600 have been deleted.

24.14 Prepared Statement and Callable Statements

We have used Statement Object: Statement st = conn.createStatement(); where conn is an object : Connection conn = DriverManager.getConnection (url, userName, password);

Finally we have used st : st.executeUpdate(“delete oopsemp5 where idNo=50600”);

24.14.1 PreparedStatement

Statement carries out parsing every time statement gets executed. So far there are no repetitions of statements. What is if there is loop in which a statement gets executed several times thus wasting compiler time.

PreparedStatement, on the other hand, is a pre-parsed and compiled statement that needs not be compiled every time a statement gets executed. Thus, it is beneficial to use PreparedStatement if multiple executions are expected.

//Handle oopsemp5 table
  PreparedStatement st = conn.prepareStatement (“update oopsemp5 set salary=? where idNo=?”);
  System.out.println(“
 Updating a record in to database”);
  st.setFloat(1,50000.00f); // applies to first ? mark
  st.setInt(2,50595); // applies to second ?
  st.executeUpdate(“update oopsemp5 set salary = 35000 where idNo=50595”);

 

1. package com.oops.chap24;
2. import java.sql.*;
3. public class PreparedDB{
4. public static void main(String args[]){
5. try{
6.     a. String userName = “system”;
7. String password = “oracle”;
8. String url = “jdbc:odbc:oopsempdsn”; //database name
9. Class.forName (“sun.jdbc.odbc.JdbcOdbcDriver”);
10. Connection conn = DriverManager.getConnection (url, userName, password);
11. System.out.println (“Database connection established”);
12. //Handle oopsemp5 table
13. System.out.println(“Updating a record in to database”);
14. PreparedStatement st = conn.prepareStatement(“update oopsemp5 set salary = ? where idNo = ?”);
15. st.setFloat(1,50000); // applies to first ? mark
16. st.setInt(2,50595); // applies to second ?
17. st.executeUpdate();
18. Statement st1 = conn.createStatement();
19. ResultSet rs=st1.executeQuery(“select idNo ,name ,salary from oopsemp5”);// table name
20. System.out.println(“idNo & name & salary :oopsemp5…”);
21. System.out.print(“------------------------------------
”);
22. System.out.println(“|Employee id no | Name |Salary |”);
23. System.out.println(“------------------------------------”);
24. while(rs.next())
25. {
26. int userid=rs.getInt(1);
27. String name =rs.getString(2);
28. float sal = rs.getFloat(3);
29. System.out.print(“
| “+userid);
30. System.out.print(“ | “+name);
31. System.out.print(“ | “+ sal);
32. } // end of while
33. System.out.println(“
--------------------------”);
34. } catch(Exception ex){ex.printStackTrace();}
35. } //main
36. } // class

 

Output: Database connection established
Updating a record in to database
idNo & name & salary from table :oopsemp5…
----------------------------------------
|Employee id no | Name | Salary |
--------------------------------------
| 50595 | ramesh | 50000.0
| 50596 | Usha | 22000.0
| 50597 | Anand | 80000.0
| 50599 | Gautam | 85000.0

24.14.2 Callable Statements

Callable statements are statements in a Java program that call a stored procedures and functions. Stored procedures are a set of statements executed on database and the result is sent to calling Java program.

Step 0: We have to create a stored procedure say sutti.sql. Go to sql prompt and enter

      SQL> select * from oopsemp7;
  IDNO NAME SALARY
  ------------------------------
  50595 Ramesh 20,000
  50596 Usha 22,000

Step 1: Enter at SQL Prompt

    SQL> create or replace procedure sutti( no in int, pay out float) as sal float;
    2 begin
	3 select salary into sal from oopsemp7 where idno=no;
	4 pay:=sal+10000;
	5 end;
	6 / press enter
	Procedure created.
	SQL>

Alternatively, you can open notebook anywhere, enter the program, and save it as sutti.sql. The contents can be :

create or replace procedure sutti1(no in int, pay out float) as sal float;
begin
select salary into sal from oopsemp5 where idNo=no;
pay := sal + 10000; // observe it is :=
end;
/ // after pasting code in SQL prompt press enter
Copy the content of file using copy and paste it on to SQL> prompt line. It will appear as
SQL> create or replace procedure sutti1
2 (no in int, pay out float) as sal float;
3 begin
4 select salary into sal from oopsemp5 where idNo=no;
5 pay := sal + 10000;
6 end;
7 /
Press Enter. You will see procedure created message on the sql prompt screen. You are ready.

 

package com.oops.chap24;
import java.sql.*;
public class StoredDB{
  public static void main(String args[]){
try{String userName = “system”;
String password = “oracle”;
String url = “jdbc:odbc:oopsempdsn”; //database name
Class.forName (“sun.jdbc.odbc.JdbcOdbcDriver”);
Connection conn = DriverManager.getConnection (url, userName, password);
System.out.println (“Database connection established”);
//Handle oopsemp5 table
System.out.println(“Using a callable statement”);
CallableStatement st2 = conn.prepareCall(“{ call sutti(?,?)}”);
st2.setInt(1,50596); // applies to first ? mark
//Register the output as float data type
st2.registerOutParameter(2,Types.FLOAT);
st2.execute();
float incrPay = st2.getFloat(2);
 System.out.println(“
 enhanced pay “ + incrPay);
conn.close();
} catch(Exception ex){ex.printStackTrace();}
} //main
} // class
Output : Database connection established
Using a callable statement
enhanced pay 32000.0

How to update fields in a record of database?

In the above example , the stored procedure did not update the record; instead it returned up dated salary to calling procedure. What should we do in case we need to update the database. Ex 4 at the end of the chapter gives the program.

24.15 Servlets

We are aware that applets are dynamic and that they reside embedded on to web browser and can extend the functionality of the web browser across the Internet. Servlets like applets are small server side programs that reside on the web servers and extend the web servers functionality across the Internet. Hence, the name Servlets. As an example, consider a server is hosting an application for centralized inventory control system for its multi-country multi-location branches. The company provides information about Inventory on real time through web pages to all its branch offices. The information must reflect the latest position of the stock in the database. Servlets offer best possible means to extend the web server to client and in addition provide advantages such as platform independency, ability to interact with applets, databases and sockets, etc.

What environment we need to put Servlets to work?

To host a servlet you need a server. The best server widely used in industry is Tomcat Apache Server. This software can be downloaded :Jakarta.apache.org and can be downloaded to: C:Program Files Apache Soft FoundationTomcat 5.0. To start the server go to bin directory and click on C:Program FilesApache Software FoundationTomcat 6.0in> tomcat6.exe. You will also be able to start the tomcat server by using startprogramsTomcat6.0- tomcat6 or by permanently setting tomcat server to be worked each time you switch on the system by selecting tomcat6 by running config command from startrun config

Servlet libraries-servlet-api.jar: Note that Servlets is not part of pure java. Hence, you need to include servlet-api.jar which is present c:Program FilesApache Software FoundationTomcat 6.0commonlibserver.jar file as part of class path. The procedure for doing so is: start settingscontrolpanelsystemadvanced environment variables select class path from bottom- edit enter the class path shown above press ok

 

Step 0:

Write servlet code ServletWelcome.java in the directory called Demo1 and place the directory Demo1 C:Program FilesApache Software FoundationTomcat 6.0webapps. The content of directory Demo1 should be as shown in Figure 24.5.

 

 

 

1. import java.io.*;
2. import javax.servlet.*;
3. public class ServletWelcome extends GenericServlet {
4. public void service(ServletRequest req,ServletResponse res) throws i. ServletException,IOException{
5. res.setContentType(“text/html”);
6. PrintWriter pw = res.getWriter();
7. pw.println(“<B>Hello Students! Welcome to Servlet Chapter”);
8. }
9. }

Compile javac ServletWelcome.java into C:Program FilesApache Software FoundationTomcat 6.0webappsdemo1WEB-INFclasses. Note that loading class file into the specified directory is mandatory for Tomcat to pick up the class file.

Step 1: Add servlet name and mapping to web.xml file in the following C:Program FilesApache Software FoundationTomcat 6.0webappsdemo1WEB-INF.Web.xml file can be opened by notepad or wordpad for editing. Servlets are embedded onto web.xml file. A typical web.xml file would look like:

 

<?xml version=”1.0” encoding=”ISO-8859-1”?>
<!DOCTYPE web-app
  PUBLIC “-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN”
“http://java.sun.com/dtd/web-app_2_3.dtd”>
<web-app>
 <servlet>
   <servlet-name>ServletWelcome</servlet-name>
   <servlet-class>ServletWelcome</servlet-class>
 </servlet>
 <servlet-mapping>
   <servlet-name>ServletWelcome</servlet-name>
   <url-pattern>/ServletWelcome</url-pattern>
 </servlet-mapping>
</web-app>

Step 2: Start the tomcat server

Step 3: Send request on web browser

http://localhost:8080/demo1/ServletWelcome

Output: Hello Students! Welcome to Servlet Chapter

Line No. :2	imports javax.servlet.* ; a package essential to run servlet programs. Make sure you have included Servlets-api.jar file in your class path.
Line No. 3:	creates a class ServletWelcome as subclass of GenericServlet. That provides init(), destroy() methods. We will override service() method for our own implementation. Service() method takes care of clients requests by accepting ServletRequest object res and gives out ServletResponse object res.
Line No. 5:	sets the content type to html/text. It is an indication that browser to interpret the data in html.
Line Nos. 6 & 7:	use getWriter() that obtains PrintWriter object pw. In Line No. 7, the object pw writes the string to web browser to display the message.

 

 

24.15.1 Servlets API and javax.servlet Package

Servelt API contains javax.servlet and javax.setvlet.http. These are part of Tomcat wservlet-api.jar and not part of J2SE 5. javx.servlet package supplies all the interfaces required for the implementation and is shown in Table 24.6, while the important classes in the package are shown at Table 24.7. Interfaces are shown in Table 24.8.

Table 24.6 Interfaces provided javax.servlet package

Javax.servlet package interfaces	Remarks
Servlet	Life cycle methods of servlets included
ServletRequest	Gets data from the client request
ServletResponse	Sends data to client request
ServletConfig	Initial params are set
ServletContext	Servlets can log events & can get environment info

Table 24.7 Classes provided javx.servlet package

Javax.servlet package Classes	Remarks
GenericServelet	Implements servlets * config interfaces
ServletInputStream	InputStreamfor the client request
ServletOutputStream	OutputStream for sending data
ServletException	Servlet error
ServletUnavailableException	Servlet unavailable

Table 24.8 Servlet interface−Methods

Javax.servlet interface Methods	Remarks
void service(ServiceRequest req, ServiceResonse res) throws Sevlet Exception,IOException	Attends request from client and sends the response
void init( ServletConfig config)	Initialization params are set
ServletConfig getServletConfig()	Servlets config information & ServletsContext for accessing environment params
String getServletInfo()	Returns servlet author 7version
void destroy()	Called when servlet is unloaded
ServletException	Servlet error
ServletUnavailableException	Servlet unavailable

ServletRequest and ServletResponse interphases shown above receive the request object from client and prepares response to be sent. Servlet packages define two types of abstract classes. One is GenericServlet belonging to javax.servlet and the other is HttpServlet belonging to package javax.servlet.http. In our next example, we will show a program extending to GenericServlet. In this example, we would read the parameter names and values contained in clients request by copying them into object enm of Enumeration class of Javas Utility Package.

 

1. import java.io.*;
2. import java.util.*;
3. import javax.servlet.*;
4. public class PostParamServlet extends GenericServlet {
5. public void service(ServletRequest req , ServletResponse res)
6. throws ServletException,IOException{
7. // print writer
8. PrintWriter pwtr = res.getWriter();
9. Enumeration enm = req.getParameterNames();
10. // Display Parameter names and values
11. while( enm.hasMoreElements()){
12. String stg = (String) enm.nextElement();
13. pwtr.print(stg + “ = “);
14. String pval= req.getParameter(stg);
15. pwtr.println(pval);
16. }
17. pwtr.close();
18. }
19. }

Step1: Compile javac PostParamServlet.java into C:Program FilesApache Software FoundationTomcat 6.0webappsdemo2WEB-INFclasses. Load the html file PostParamServlet.html also in the same directory.

Line No. 5:	shows that PostParamServlet extends to GenericServlet class.
Line No. 9:	creates a PrintWriter Object pwtr to send data to client
Line No. 10:	Enumeration enm = req.getParameterNames(); pushes the names and values contained in client message into enumeration object enm. Using Line No. 12: while( enm.hasMoreElements()){
Line Nos. 14 & 15:	send name and roll number to client through pwtr object

HTML File: PostParamServlet
<html>
<body>
<center>
<form name=”Form1”
method =”post”
action =”http://localhost:8080/demo2/PostParamServlet”>
  <table>
<tr>
  <td><B>StudentName</td>
<td><input type = textbox name=”studentname” size=”24” value =””></td>
</tr>
<tr>
  <td><B>RollNumBer</td>
  <td><input type=textbox name=”studentnumber” size=”24” value =””></td>
</tr>
</table>
<input type=”submit” value = “Submit”>
</body>
</html>
Web.xml: As shown in Example 24.16b

Step 2: Start the Tomcat Server

Step 3: Send request on web browser

http://localhost:8080/demo2/PostParamServlet

 

 

OUTPUT from server
studentname = ShraddaPandey
studentnumber = 50596

24.15.2 HttpServletRequest

Out of the two abstract classes, namely, GenericServlet and HTTPServlet, HttpServlet provides better interface and is widely used. The important methods are:

• Service() receives ServletRequest and ServletResponse object that provide access to stream inputs of type character based or byte based.
• Service requests for HttpServlet are get and post. Get request gets the information from the server and post sends data to a server such as information from form or authentication details, etc. HttpServelet defines doGet() and doPost() methods which are called by service() method. Interfaces HttpServletrequest and HttpservletResponse handle doGet() and DoPost() and organize client server interaction.

Whenever doGet() or doPost() methods are called, object of HttpServletRequest is created by the server and passed on to service() method as an argument. The service() method executes the service request and makes the response ready for dispatch to client. A few of the important methods supported by HttpServletRequest interface are shown in Table 24.9.

 

Table 24.9 HttpServletRequest interface

HttpServletRequest interface	Remarks
String getName()	Gets the argument sent to servlet byget or post requests
Enumeration getParameterNames()	Returns manes of all parameters
String[] getParameterValues( String names)	Names of all parameters sent to servlet
Cookie[] getCookies()	Return an array of cookie object
HttpSession getSession(boolean create)	Returns current session of the client. Helps in unique identification of the client

24.15.3 HttpServletResponse

The main job of HttpServletResponse is to prepare the response to be sent to the client on receipt of HttpServletRequest Object. The web servers that is executing the servlet makes an object of HttpServletResponse and hands it over to service() method. A few of the important methods are presented in Table 24.10.

 

Table 24.10 HttpServletRequest methods interface

HttpServletResponse interface	Remarks
ServletOutputStream getOutputStream()	Gets a Byte-based output stream to be sent to client
PrintWriter getWriter()	Gets a character-based output stream for sending text data
void setContentType	Sets Multipurpose Internet Mail Extensions (MIME) type. Ex “text/html”
void addCookie(cookie cookie)	Returns an array of cookie object
HttpSession getSession(boolean create)	Returns current session of the client. Helps in unique identification of the client

24.15.4 HttpServlet Class−Get Request with Data from Client

HttpServlet class provides several methods to perform tasks of receiving client request and sending servers response. The important methods are doGet() and doPost(). The other methods include doDelete(), doPut() and, of course, service() method. These methods all handle HTTP functions. In our next example, we will show Http Get Request. In this model, we present a form for the user to select his favourite subject by offering options and a submit button. The action statement in the html file links the servlet to be called by the server. Server calls the prescribed servlet and prepares the response and sends them to client. The client selects a preferred subject and submits the choice to servlet at server. The Http request is received by the servlet and prepares the response.

 

Step 1: Create HTML File: SubjectGetServlet.html in the Directory C:PROGRA~1APACHE~1TOMCAT~1.0webappsDemo3WEB-INFclasses>

1. <html>
2. <body>
3. <center>
4. <form name=”Form1”
5. action=”http://localhost:8080/Demo3/SubjectGetServlet”>
6. <B>Subject:</B>
7. <select name=”subject” size=”1”>
8. <option value=”Maths”>Mathematics</option>
9. <option value=”Physics”>Physics</option>
10.    <option value=”Chemistry”>Chemistry</option>
11.	</select>
12.	<br><br>
13.	<input type=submit value=”Submit”>
14.	</form>
15.	</body>
16.	</html>

 

 

DropDown List. User selects any one subject from options at Line Nos. 7, 8, and 9.

Step 2: Create Servlet program SubjectGetServlet.java in the directory: C:PROGRA~1APACHE~1TOMCAT~1.0webappsDemo3WEB-INFclasses>

1. import java.io.*;
2. import javax.servlet.*;
3. import javax.servlet.http.*;
4. public class SubjectGetServlet extends HttpServlet {
5. public void doGet(HttpServletRequest req,HttpServletResponse res)
6. throws ServletException, IOException {
7. String subject=req.getParameter(“subject”);
8. res.setContentType(“text/html”);
9. PrintWriter pwtr=res.getWriter();
10. pwtr.println(“<B>The selected subject is: “);
11. pwtr.println(subject);
12. pwtr.close();
13. }
14. }

Line No. 4:	shows SubjectGetServlet extending to HttpServlet
Line No. 5:	uses doGet() with arguments HttpServletRequest req, HttpServletResponseres.
Line No. 7:	uses getParameter() method with “subject” being passed as argument from html file. The program will receive mathematics or physics or chemistry as argument.
Line No. 8:	sets the content as html and Line Nos. 9, 10, 11 send the response to client

Step 3: Compile the code:

C:PROGRA~1APACHE~1TOMCAT~1.0webappsDemo3WEB-INFclasses>javac SubjectGetServlet.java

Step 4: create web.xml file in the directory: As per example, 24.16b

Step 5: Start the Tomcat server C:Program FilesApache Software FoundationTomcat 6.0in

Step 6: Send request on web browser by double clicking on the html icon

Servlet OUTPUT: The selected subject is: Mathematics

24.15.5 HTTP Post Requests

We have seen doGet() method by HttpServlet which is used to get the client request. In this section, we will study doPost() method which is used just like doGet() when fetching input through Form. Html file SubjectPost.html and HttpServlet program called SubjectPostServlet.java. Post request is identical to Get Request except that Form method will have “post” specified explicitly.

 

The program uses Post method to send client request and receive response from the server. The application is a simple coding of text in which capital letter is added 13 to get a new character. For example, character ‘A’ will be coded as 65 + 13 =78, i.e., character ‘B’. If the resultant character goes beyond ‘Z’, then 26 is subtracted. These values are so chosen that characters wrap around when they overflow beyond ‘Z’. Further, observe that we would also shape the response using html document as shown in Apcode.java so that result is displayed using the same form format. We have included coding only for capital letters. There are three distinct files. One is an html file, Apcode.html, and the second file is Apcode.java. These files are created in the directory: C:Program FilesApache Software FoundationTomcat 6.0webappsexamples WEB-INFclasses

Web.xml file is in Directory: FilesApache Software FoundationTomcat 6.0 webapps examples WEB-INF

Step 1: Create Apcode.html file in directory C:Program FilesApache Software FoundationTomcat 6.0webappsexamples WEB-INFclasses

1. <html>
2. <body>
3. <head><title>Apcode Coder</title></head>
4. <h1>Apcode Coder</h1>
5. <p>Text to code:
6. <form name=”Form1”
7. method=”post”
8. action=”http://localhost:8080/examples/Apcode”>
9. <textarea name=”text” rows=”8” cols=”55”>
10. </textarea>
11. <p><input type=submit value = “code”>
12. </form>
13. </body>
14. </html>

Line No. 7:

indicates that we are using post method. The action part of the form specifies that the Servlet resource is at examples/web-inf/classes.

 

 

Step 2: Create Servlet program Apcode.java in the directory: C:Program FilesApache Software FoundationTomcat 6.0webappsexamples WEB-INFclasses

Apcode.java

1. import java.io.*;
2. import javax.servlet.*;
3. import javax.servlet.http.*;
4. public class Apcode extends HttpServlet {
5. public void doPost(HttpServletRequest req, HttpServletResponse res)
6. throws ServletException, IOException {
7. String text = req.getParameter(“text”);
8. String translation = translate(text);
9. res.setContentType(“text/html”);
10. ServletOutputStream out = res.getOutputStream();
11. out.println(“<html>”);
12. out.println(“<body>”);
13. out.println(“<head><title>Apcode Coder</title></head>”);
14. out.println(“<h1>Apcode Coder</h1>”);
15. out.println(“<p>Text to code:”);
16. out.println(“<form action=”Apcode” method=”post”>”);
17. out.println(“<textarea name=”text” ROWS=8 COLS=55>”);
18. out.println(translation);
19. out.println(“</textarea>”);
20. out.println(“<p><input type=”submit” value=”code”>”);
21. out.println(“</form>”);
22. out.println(“</body>”);
23. out.println(“</html>”);
24. }
25. public void doGet(HttpServletRequest req, HttpServletResponse res)
26. throws ServletException, IOException {
27. doPost(req, res);
28. }
29. String translate(String input) {
30. StringBuffer output = new StringBuffer();
31. if (input!= null) {
32. for (int i = 0; i < input.length(); i++) {
33. char inChar = input.charAt(i);
34. if ((inChar >= ‘A’) & (inChar <= ‘Z’)) {
35. inChar += 13;
36. if (inChar > ‘Z’)
37. inChar -= 26;
38. }
39. output.append(inChar);
40. }
41. }
42. return output.toString();
43. }
44. }

Line No. 4:	specifies that Apcode extends to HttpServlet interface.
Line No. 5:	shows that doPost() method is used to get the request of the client and send the response.
Line No. 7:	shows usage of req.getParameter(“text”); to get the client request.
Line No. 9:	sets the content to text / html type.
Line No. 10:	obtains ServletOutputStream object out for sending response to client.
Line Nos. 11 to 23:	show that we are sending response to client using out object and in the same format as that used by Apcode.html
Line No. 16:	Shows use of escape character for setting up of action part of response out.println(“<form action=”Apcode” method=”post”>”);
Line No. 24:	uses doGet()method and which in turn calls doPost() method at Line No. 27

Step 3: Compile the code : C:Program FilesApache Software FoundationTomcat 6.0webappsexamplesWEB-INFclasses >javac SubjectPostServlet.java

Step 4: create web.xml file in the directory: As per example, at 24.16b

Step 5: Start the Tomcat server from C:Program FilesApache Software FoundationTomcat 6.0in directory.

Step 6: Send request on web browser by double clicking on the html icon

OUTPUT form Servlet Apcode:

 

 

24.16 Java Beans

Java's strong point is its reusability feature and java beans is a feature available in Java for providing this feature. Java bean is a portable, platform-independent component model to facilitate writing highly reusable components. For this, we would use Java Beans API. Once these components are developed, we can embed them in applets or applications. Java beans can be visual or non-visual components. Beans are dynamic in that they can be changed or customized. We can use property of beans component to customize the bean and save the bean using the bean's persistence property.

Introspection

• A Java program can discover the beans property through a process known as introspection.
• A class called Introspector uses core reflection API For introspection to work; we need to follow certain naming conventions and some specific rules so that introspection can identify these properties.
• A bean information class implements the BeanInfo interface. ABeanInfo class explicitly lists those bean features that are to be exposed to application builder tools.
• Properties are the appearance and behaviour characteristics of a bean. Beans expose properties so they can be customized at design time. Properties can be changed at design time by customizers or property editors.
• Bean events can be used for communication between bean components. A listener bean receiving information has to register with source bean.
• Persistence enables beans to save and restore their state.

Java Bean API and Important Classes and Interfaces

• Class Introspector provides interface and method such as getBeanInfo(Class<type> bean) throws IntrospectionException.
• PropertyDescriptor class describes the property of the bean. It supports methods such as getName().
• EventSetDescriptor class describes events associated with the bean. It supports methods such as getAddListenerMethod() to get names of all addlisteners that bean supports.getName() gets you the name of the event.
• MethodDescriptor class gives data about methods and supports such as Method getMethod().

Normally, several beans are developed by programmers and the third part by developers. In order to reuse them in your applications, you need to know these properties. Hence, these are provided. We can summarize the java beans as:

• Java beans is like a java class.
• Java beans will have properties. In such cases, only the bean class must have get() and set() methods.
• Java beans must be serializable.
• As beans are part of server side programming, the bean need not be a visual component at client side.

Let us attempt our first bean example. In this example, the instructor welcomes the class. For this, he calls the beans adds, his own message, and fires the beans. It is a traditional welcome students example, used here to highlight the procedures involved. For executing beans programs you will need a good builder toll like NetBeans 6.1, free downloadable from the net or enterprise version of eclips that supports beans components. For our example, we have chosen NetBeans 6.1. The concept diagram is shown in Figure 24.6.

 

We have to use jsp connection because html file is not allowed to call any server components like beans directly. JSP in turn calls for Bean component registered with server like WelcomeBean class. WelcomeBean class is from a normal java class program.

In an application that does not require any input from html form from the user, you can directly start with jsp module and call class file.

Step 0: install NetBean 6.9 version from the net on to your system. Choose the version with full features.

Step 1: Create a new project

FileNew-javaWeb--webapplication1nextnext-GlashFishServer next-Finish.

Step 2: Create Welcome.html file

WebApplication1 webpage Rightclick-newhtmlfileenter in name field :Welcome -finish

1. <html>
2. <body>
3. <form method=post action=Welcome.jsp>
4. <input type=text name=’text1’>
5. <input type=submit>
6. </form>
7. </body>
8. </html>

Line No. 3:

html file calls Welcome.jsp.

Output of html

 

 

Step 3: Create a jsp file

WebApplication1 webpage Rightclick-new  JSP  enter in name field :Welcome -finish.
Welcome.jsp
1. <%--
2. Document : Welcome
3. Created on : 14 Jan, 2011, 6:28:39
4. Author : Ramesh
5. --%>
6. <%@page contentType=”text/html” pageEncoding=”UTF-8”%>
7. <!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 01 Transitional//EN”
8. “http://www.worg/TR/html4/loose.dtd”>
9. <html>
10. <head>
11. <meta http-equiv=”Content-Type” content=”text/html; charset= UTF-8”>
12. <title>JSP Page</title>
13. </head>
14. <body>
15. <jsp:useBean id=”Welcomebean” class=”jchap24beans.Welcombean” />
16. <%
17. String stg = request.getParameter(“text1”);
18. String addlstg = Welcomebean.welcomeStudents(s);
19. out.println(addlstg);
20. %>
21. </body>
22. </html>

Line Nos. 1–14:	are NetBeans generated system document information.
Line No. 15:	Enter user bean id as :”Welcomebean” class = “jchap24beans.Welcombean” />
Line No. 17:	uses getParameter(String msg) format to obtain the request of the client and stores it in String stg.
Line No. 18:	attaches additional string to the String object addlstg by calling a method welcomeStudents(stg) method of Welcomebean class.
Line No. 19:	sends out addlstg which is concatenated strings comprising clients request + response i.e. Welcome to Java Beans Students!

Step 4: Create Package

WEB-INF new-java packagejchap24beans save

Step 5: create class

Jchap24beans new-java class-Welcomebean-finish
1. package jchap24beans;
2. public class Welcomebean
3. {
4. public Welcomebean() { }
5. public String WelcomeStudents(String s)
6. {return “Welcome to Java Beans First Programme….”+s; }
7. }
Welcome to Java Beans.Students!

Line No. 4:	Nil argument constructor
Line No. 5:	defines a bean method: WelcomeStudents()

Step 6: Save and compile the files in the package.

Step 7: Select Welcome.html file -- rightclick-run the file Output on the browser screen: Welcome to Java Beans Students!

24.17 Summary

1. J2SE 5.0 has provided a collection framework. Collection framework is implemented in java.util package.
2. Collection class provides several interfaces such as Collection, Map, and Iterator.
3. The Collection Interface is the main interface from which the List and Set Interfaces are derived. It specifies the methods that are common to all the Collections.
4. Set is defined in java.util.Set. Set cannot contain duplicate elements.
5. Iterator allows us to iterate over a collection such as Set.
6. List can contain duplicate elements. It supports ArrayList and LinkedList.
7. The algorithms are implemented as static methods in the Collections class.
8. Each entry in the Map involves a pair of elements called keys and values. They are collectively referred to as key–value pairs.
9. Map cannot contain duplicate keys, but can contain duplicate valuesCollection framework providing two implementations.
10. JDBC Manager acts as interface between Java programs and database.
11. ODBC (Open Database Connectivity) is provided by Microsoft Corporation. ODBC is shipped along with windows OS. JDBC is a part of JDK which we have installed. It takes calls supplied by JDBC and converts it into formats suitable for proprietary databases such as MS Access and Oracle 10g.
12. MySQL also provides a connector mysql-connector-java-5.1.3 and mysql- 5.1.51-win32.msi.
13. DSN stands for Data Source Navigator. The programmers need to create a DSN name to facilitate access to database using ODBC-JDBC Bridge.
14. Oracle database also uses ODBC-JDBC bridge and hence DSN needs to be created.
15. PreparedStatement is a pre-parsed and compiled statement that need not be compiled every time statement gets executed. Thus, it is beneficial to use PreparedStatement if multiple executions are expected.
16. Callable statements are statements in a java program that call stored procedures. Stored procedures are a set of statements executed on database and results are sent to calling Java program.
17. Servlets like applets are small server side programs that reside on the web servers and extend the web servers functionality across the Internet.
18. Servelt API contains javax.servlet and javax.setvlet.http. These are part of Tomcat servlet-api.jar.
19. ServletRequest and ServletResponse interphases shown above receive the request object from client and prepares response to be sent.
20. Servlet packages define two types of abstract classes: One is GenericServlet belonging to javax.servlet and the other is HttpServlet belonging to package javax.servlet.http.
21. Java beans is a feature available in java for providing this feature. Java bean is a portable, platform-independent component model to facilitate writing highly reusable components.
22. A Java program can discover the beans property through a process known as introspection.
23. A bean information class implements the BeanInfo interface. A BeanInfo class explicitly lists those bean features that are to be exposed to application builder tools.
24. Properties are the appearance and behaviour characteristics of a bean.
25. Bean events can be used for communication between bean components.
26. Persistence enables beans to save and restore their state.
27. Java beans must be serializable.

Objective Questions

1. Which of the following statements are true in respect of JDBC Connectivity?
   1. JDBC-ODBC bridge is required to connect java program to third party databases like MS Access, Oracle, etc.
   2. JDBC-ODBC bridge works for MySql database.
   3. JDBC-ODBC Bridge is a type 2 Driver
   4. Connectivity classes and interfaces are provided by JDBC API
   1. i and ii
   2. i and iii
   3. i and iv
   4. iii and iv
2. Which of the following statements are true in respect of JDBC Driver types?
   1. Type 1 are vendor specific
   2. JDBC-ODBC is a type 2 and vendor independent
   3. mysql connector is a type 2 and vendor specific
   4. type 4 is a pure java driver and connects directly to database
   1. i and ii
   2. i and iii
   3. i and iv
   4. iii and iv
3. Which of the following statements are true in respect of JDBC Driver types?
   1. java.sql package contains interfaces and classes for databases
   2. Connection Object manages connection between java and database
   3. Connection object is used to submit the query
   4. Object of statement is used to obtain the result
   1. i and ii
   2. i and iii
   3. i and iv
   4. iii and iv
4. Which of the following statements are true in respect of JDBC statements?
   1. If repetitive and multiple execution is involved, statement object is inefficient.
   2. Prepared statement obviates the need to compile every time in a loop.
   3. Callable statement calls procedures and not functions.
   4. output by callable statement needs to be registered in order to use it
   1. i and ii
   2. i, ii and iv
   3. i and iv
   4. iii and iv
5. Which of the following methods is used by HttpResponse interface to dispatch the response to client.
   1. doPost()
   2. getWriter()
   3. doGet()
   4. getResponse()
6. The action parameter in Form attribute specifies
   1. Method at server
   2. A procedure at server
   3. Servlets at server
   4. Applet at server
7. Which of the following statements are true in respect of Java Beans?
   1. Platform independent
   2. Client side components
   3. Server side components
   4. Uses JSP (java server pages)
   1. i, ii and iii
   2. i, ii and iv
   3. ii, iii and iv
   4. i, iii and iv
8. Which of the following statements are true in respect of Collection Framework of Java?
   1. Collection framework has been included in java.lang package
   2. Collection framework has been included in java.util package
   3. Iterator is an interface provided by Collections class
   4. Collection classes are derived from Collection Object which is derived from Collection class
   1. i and ii
   2. i and iii
   3. i and iv
   4. ii, iii and iv
9. Set interface can contain duplicates     TRUE/FALSE

   Short-answer Questions

10. What is ODBC–JDBC Bridge Driver?
11. Distinguish JDBC net driver and pure java driver.
12. Why are type 3 connectors called slow connectors?
13. What is the role of DSN for JDBC-ODBC Connector?
14. Give Java statement for loading and registering Driver by using Class.forName().
15. Give Java statement for establishing the connection.
16. Give an example statement to execute a query.
17. Give Java program statement to insert a record into database.
18. Give java program statement to update a record into database.
19. Give syntax for PreparedStatement.
20. Give syntax of callable statement.
21. Distinguish the Statement and Prepared Statement.
22. Distinguish a Servlet and an Applet.
23. What are the major interfaces of servlet package?
24. What are added to web.xml regarding a servlet?
25. What are the interfaces provided by javax.servlet interface?
26. If java bean file is required to be serializable then what conditions are to be met?
27. What are the features of java beans?
28. What are java beans?
29. What are the features of Set interface?
30. What are Iterators?
31. What are the methods supported by List interface?
32. Explain the Map interface.

    Long-answer Questions

33. Explain the JDBC framework. Explain the usage of various types of database drivers. With explanation, which type is best suited for which type of database?
34. Explain the procedure for creating a DSN for any database like MS Access or Oracles.
35. Explain with Java statements the procedures for loading the Driver, establishing the connection, getting the result through ResultSet.
36. Explain the java statements for accessing MySql databases.
37. Explain the JDBC statements required to insert, update, and delete records from Oracle database.
38. Explain the procedure to use Prepared statement.
39. Explain with suitable examples for using callable statements.
40. Explain HttpServletRequest and HttpServletResponse interfaces provided by javax.servlet.http package.
41. Explain the procedure for obtaining database connection in respect of servlet.
42. Explain the differences and similarities between java class file and beans file.
43. What are the requirements for java bean file?
44. Give out the procedure for executing a java bean.
45. Explain the class and interface and methods of Collection framework of java.
46. What are the important methods supported by Collection Interface?
47. Explain Algorithms interface provided by Collection framework.

    Assignment Questions

48. Write a JDBC connectivity program to connect to Students database at server. The client HTML interface obtains the rollNo from the user and approaches the server. Server to formulate the result marks sheet comprising name Roll No, college name and college code, student name and subject marks.
49. Write a java connectivity program, in which a teacher updates the attendance particulars of the class. A table at Server called attendance has the attendance detail against roll No of the student such as name and dates on which attendance is being taken. The teacher to be able to record attendance either by noting only absentees or by not noting those who are present. The output to be as per format:

    
    Class                Subject Name     subject Code
    Teacher Code         Teacher Name
    Roll No Student Name     date1    date2       date3……………………date60

50. Modify the problem at 1 for handling the problem with the use of HttpServlet Request and Response.
51. Write a program with JDBC Connectivity using Servlet to obtain the marks in two sessional examinations and attendance percentage as on particular date. The program to accept roll no from the client and send back response in html document.
52. Write a program with servlet connectivity to display phone book in which client enters the idNo and gets name, number, class, branch , and cell number, email number of both students and parents.
53. Write a servlet-based program to facilitate student registration for a semester. On entering the roll number, program to validate the eligibility and payment of fees and then offer subjects both mandatory and optional and complete the formalities.
54. Write a java beans application in which the user can enter the data about rollNo, name, semester, and server to return registration detail. Use java application.
55. Write a Java program to show the usage of search algorithms provided by Collection framework.
56. Write a program to accept the url from the user. While sourcing the urls, look for other link web pages listed in the url. Store these in the stack and visit each url in turn. Store all the urls visited in a Hash File in the local disk. On demand from the user, perform hash search and provide the url from local HashTable.

Solutions to Objective Questions

1. c
2. d
3. a
4. b
5. b
6. c
7. d
8. d
9. False