Java Extreme Programming Cookbook

Passing Arguments to a Buildfile

Problem

You want to pass system properties to a buildfile. Java system properties are a more portable alternative to environment variables.

Solution

Pass the system properties to Ant using the -D command-line argument. For example:

ant -Dprop1="My Property" run

Within the buildfile, refer to the property using Ant’s ${prop1} syntax. You can specify default values for properties using the <property> tag, and you can pass system properties to Java applications using the <sysproperty> tag nested within the <java> element.

Discussion

Example 3-3 shows an Ant buildfile that demonstrates system properties. It echoes the property name/value pairs to the console, and then invokes a Java application that echoes the same properties.

Example 3-3. Buildfile demonstrating system properties

<?xml version="1.0"?>
<project name="sysprops" default="run" basedir=".">
  <!-- define two properties -->
  <property name="prop1" value="Property 1 from Buildfile"/>
  <property name="prop2" value="Property 2 from Buildfile"/>

  <target name="clean">
    <delete dir="com"/>
  </target>

  <target name="compile">
    <javac srcdir="." destdir=".">
      <classpath path="."/>
    </javac>
  </target>

  <target name="run" depends="compile">
    <!-- echo each of the properties to the console -->
    <echo message="Now in buildfile..."/>
    <echo message="prop1     = ${prop1}"/>
    <echo message="prop2     = ${prop2}"/>
    <!-- The 'prop3' property must be defined on the command 
         line or it shows up like '${prop3}' -->
    <echo message="prop3 ...