Helper classes
A parser developer may choose to write classes that implement the interfaces described above, and also add further useful methods. But this kind of support is optional. The standard includes some recommendations for helper classes, and specifies that they appear in the following package:
org.xml.sax.helpers
Attributes list implementation
The AttributesListImpl helper class has the following constructors and methods. It implements the AttributesList interface, and adds methods for adding and removing attributes. It could be used by application developers to persistently store and manage attributes.
Constructors:
AttributeListImpl(); AttributeListImpl(AttributeList atts);
Methods:
int getLength();
String getName(int i);
String getType(int i);
String getType(String name);
String getValue(int i);
String getValue(String name);
void setAttributeList(AttributeList atts);
void addAttribute(String name, String type,
String value);
void removeAttribute(String name);
void clear();
Note that SAX 2.0 deprecates this class and introduces a replacement called AttributesImpl.
Locator implementation
The LocatorImpl helper class implements the Locator interface, and adds methods for setting its properties, so would be most likely to be used by the parser rather than the application itself. It has the following constructor and methods.
Constructor:
LocatorImpl(Locator locator);
Methods:
int getLineNumber(); int getColumnNumber(); String getSystemId(); String getPublicId(); void setColumnNumber(int columnNumber); void setLineNumber(int lineNumber); void setPublicId(String publicId); void setSystemId(String systemId);
Parser factory
The ParserFactory helper class has the following constructors. It is used to dynamically create a parser at run-time, so that application can be coded to cope with any compliant SAX parser without recompiling.
Constructors:
static Parser makeParser();
throws ClassNotFoundException,
IllegalAccessException,
InstantiationException,
NullPointerException,
ClassCastException;
static Parser makeParser(String className)
throws ClassNotFoundException,
IllegalAccessException,
InstantiationException,
ClassCastException;
There are no other methods.
The constructor with no parameter is used when the 'org.xml.sax.parser' system property holds the name of the parser.
Consider the following example:
import java.io.IOException; import org.xml.sax.*; import org.xml.sax.helpers.ParserFactory; ... String pClass = "org.apache.xerces.parsers.SAXParser"; // CREATE PARSER try { Parser mySAXParser = ParserFactory.makeParser(pClass); } catch (SAXException err) { ... } catch (NullPointerException err) { ... } catch (ClassCastException err) { ... } // REGISTER HANDLERS mySAXParser.setDocumentHandler( this ); mySAXParser.setErrorHandler( this ); mySAXParser.setEntityResolver( this ); // PARSE DOCUMENT try { mySAX2Parser.parse("file:///TestFile.xml"); } catch (SAXException err) { ... }