Section 12.1. Creating a Simple Custom Ant Task

12.1. Creating a Simple Custom Ant Task

Creating new Ant tasks is simple since all you need is an execute( ) method. Example 12-1 is a Java class named Greeting that displays the text "No worries.".

Example 12-1. A simple Ant task (ch12/greetingtask/src/Greeting java)

public class Greeting  {     public void execute( )      {         System.out.println("No worries.");     } }

To install this class as a new Ant task, you compile this code and use the taskdef task to declare it in Ant. The attributes of the taskdef task are shown in Table 12-1.

The taskdef task is based on the typedef task, except that the values of two attributes, adapter and adapto, are preset to fixed values ("org.apache.tools.ant.TaskAdapter" and "org.apache.tools.ant.Task", respectively).

Table 12-1. The taskdef task's attributes

Attribute	Description	Required	Default
adapter	Specifies the adapter, which adapts the defined class to another interface/class.	No	org.apache.tools.ant.TaskAdapter
adaptto	Specifies the interface/class to which to adapt. Used with the adapter attribute.	No	org.apache.tools.ant.Task
classname	Specifies the classname that will support/perform the type or task.	Yes, unless file or resource have been specified.
classpath	Specifies the classpath you want to use when searching for classname.	No
file	Specifies the name of the file from which to load definitions, if any.	No
format	Specifies the format of the file or resource pointed to by the file or resource attributes. Possible values are properties or xml.	No	properties
loaderRef	Specifies the loader that you want to use to load the class.	No
name	Specifies the name of the datatype or task you're creating.	Yes, unless the file or resource type attributes have been specified.
onerror	Specifies what to do if there is an error while defining a type. Possible values are: fail Causes a build exception. report Outputs a warning. ignore Does nothing. Since Ant 1.6.	No	fail
resource	Specifies the name of the resource from which you want to load definitions.	No
uri	Specifies the URI at which this type/task definition should be found. Since Ant 1.6.	No

The taskdef task's classpath attribute is a path-like structure and can be set with a nested classpath element.

The build file in Example 12-2 builds the simple Ant task and JARs it in greeting.jar. The taskdef task in the same build file retrieves the task from that JARfile and executes the task, which should print out the "No worries." message.

Example 12-2. Build file for a simple Ant task (ch12/greetingtask/build.xml)

<?xml version="1.0"?> <project default="main">     <property name="src" location="src"/>     <property name="output" location="output"/>     <target name="main" depends="jar">         <taskdef name="greeting" classname="Greeting" classpath="greeting.jar"/>         <greeting/>     </target>     <target name="jar" depends="compile">         <jar destfile="greeting.jar" basedir="${output}"/>     </target>     <target name="compile">         <mkdir dir="${output}"/>         <javac srcdir="${src}" destdir="${output}"/>     </target> </project>

Here's what you see when the build file runs. The execute( ) method of the task's code was indeed called, displaying the expected message:

%ant Buildfile: build.xml compile:     [mkdir] Created dir: /home/steven/ant/ch12/greetingtask/output     [javac] Compiling 2 source files to /home/steven/ant/ch12/greetingtask/output jar:       [jar] Building jar: /home/steven/ant/ch12/greetingtask/greeting.jar main:  [greeting] No worries. BUILD SUCCESSFUL Total time: 3 seconds