Using Java to Write an Event Handler

Creating a Java event handler is slightly more complex than creating a JavaScript event handler. You cannot simply enter Java code directly in the BIRT Report Designer.

To create a Java event handler class, you must compile the source for the Java class and make certain that the class is visible to BIRT. Creating a Java event handler for BIRT is simplified, however, by the fact that Eclipse is a robust Java development environment and supports integrating a Java project with a BIRT project.

How to create an event handler class and add it to the Java project

This section describes the process for using the Eclipse Java development environment to create an event handler class for a scriptable BIRT element.

1	Add org.eclipse.birt.report.engine_<version>.jar to your Java project, as outlined in the following steps:

1	Select your Java project and choose File →Properties→Java Build Path→Libraries. Java Build Path appears, as shown in Figure 23‑1.

Figure 23‑1

Adding a JAR file to the compiler’s classpath

2	Choose Add External JARs. JAR Selection appears.

3	Navigate to Eclipse /plugins directory. In a default Eclipse installation, this directory is in the following location:

<ECLIPSE_INSTALL>\eclipse\plugins

4	Select org.eclipse.birt.report.engine_<version>.jar. Choose Open. Java Build Path reappears.

5	Choose OK.

2	Select your Java project and choose File →New→Other. Select a wizard appears.

3	Expand Java and select Class, as shown in Figure 23‑2.

Figure 23‑2

The Select a wizard dialog

Choose Next. New Java Class appears, as shown in Figure 23‑3.

Figure 23‑3

New Java Class

4	Navigate to the folder where you want the Java source file to reside by choosing the Browse button beside Source Folder.

5	If your new Java class is a part of a package, type the fully qualified package name in Package.

6	In Name, type a name for your class.

7	In Modifiers, choose Public.

8	Choose the Browse button beside Superclass. Superclass Selection appears, as shown in Figure 23‑4.

Figure 23‑4

Superclass Selection

9	In Choose a type, type the name of the adapter class for the ROM element. For example, enter Label EventAdapter for the Label element. Choose OK. New Java Class reappears.

10	Select Generate comments. Choose Finish. A Java editor view appears, similar to the one shown in Figure 23‑5.

Figure 23‑5

The Java editor

11	Add the event handler method for your new event handler class. Figure 23‑6 shows the addition of an onPrepare( ) method that sets the background color of the label to red.

Figure 23‑6

The onPrepare( ) method in the Java editor

How to associate a Java class with a report element

The example in this procedure makes the following assumptions:

n	The report design includes a scriptable report item, such as a label.

n	A Java class containing event handler methods for the scriptable report item is visible to BIRT.

1	In Outline, select the report element for which an event handler class is visible to BIRT, as shown in Figure 23‑7.

Figure 23‑7

Selecting a report element

2	In Property Editor for the selected report element, select Event Handler and enter the fully qualified name of the event handler class, as shown in Figure 23‑8.

Figure 23‑8

The event handler class name