In order to work with this recipe, you need to have a relational database installed on your computer. I prefer a simple and easy-to-use open source database, which makes a small footprint on your PC. That's because I am providing sample data with this recipe, so I would like to make it as easy and quick as possible for readers to import the sample data into their databases before executing the steps of this recipe.

I have used the PostgreSQL database, which fulfills these criteria. You can visit the web site (http://www.postgresql.org/) and get all the information to install and start using PostgreSQL. You may also refer to the installPostgreSQL.txt file included in the source code download for this chapter, which shows how you will install and run PostgreSQL. Make sure that PostgreSQL is up and running before you proceed.

The source code for this chapter also includes a copySampleDataIntoPGS.txt file, which will help you create a table named CustomerInvoices with five columns ( InvoiceID, CustomerName, InvoicePeriod, ProductName, and InvoiceValue) and copy sample data for all the recipes of this chapter into the table.

After inserting the required data, you will connect iReport to your database hosted on PostgreSQL using the steps described in the Creating a report from relational data recipe later in Chapter 4.

Open the XML tab of your report and you will see the following JRXML code:

<?xml version="1.0" encoding="UTF-8"?>
<jasperReport>
<parameter name="CustomerName" class="java.lang.String">
</parameter>
<queryString>
<![CDATA[SELECT * from "public"."CustomerInvoices"
WHERE "public"."CustomerInvoices"."CustomerName" =
$P{CustomerName}]]>
</queryString>
<!-- other JasperReports XML tags -->
<title>
<band height="79" splitType="Stretch">
<staticText>
<!-- other JasperReports XML tags -->
<text><![CDATA[Monthly Customer Invoices]]></text>
</staticText>
<textField>
<reportElement x="113" y="49" width="128" height="20"/>
<textElement/>
 <textFieldExpression class="java.lang.String">
<![CDATA[$P{CustomerName}]]>
</textFieldExpression>
</textField>
<!-- other static text and text field XML tags -->
</band>
</title>
<!-- other JasperReports XML tags -->
</jasperReport>

You can see that this JRXML contains<parameter>, <queryString>, and<title> tags in expanded view, whereas all other tags that are not relevant to the present discussion of the recipe are omitted.

iReport has generated the<parameter> tag (shown highlighted in the code) in response to steps 3 and 4 of the recipe. In these steps, you configured the CustomerName parameter. The<parameter> tag wraps the name of the parameter (CustomerName) and the type of data (that is, a Java string) through its name and class attributes, respectively.

Now look at the<queryString> tag (shown highlighted in the code), which wraps the SQL query you authored in step 11 of the recipe to fetch table data from your database.

Also notice from the SQL query that it contains a string $P{CustomerName} on the right of the = sign in the Where clause. This $P is not SQL syntax. This $P will be internally processed by the JasperReports engine, which resolves it to the CustomerName parameter before executing the query.

This way, the SQL query becomes part of your JRXML code and the JasperReports engine will process and execute this query to fetch the customer name from your database. JasperReports will also copy the name of the customer into the CustomerName parameter while processing your report.

Now look at the<staticText> tag whose<textFieldExpression> child is shown highlighted in the code. This<textFieldExpression> tag specifies the parameter (CustomerName) that contains the name of the customer fetched from the database. Therefore, when JasperReports processes this<staticText> tag, it will show the name of the customer in the title of your report.