Java Extreme Programming Cookbook

Checking for the Existence of Properties

Problem

You want to check for the existence of several properties and/or environment variables before you perform a build.

Solution

Define a “checkProperties” target that uses the fail task to abort the build if any properties are undefined.

Discussion

Suppose that various parts of your buildfile require several environment variables. First, specify a target that checks those properties:

<target name="checkProperties">
  <fail unless="env.TOMCAT_HOME">TOMCAT_HOME must be set</fail>
  <fail unless="env.JUNIT_HOME">JUNIT_HOME must be set</fail>
  <fail unless="env.JBOSS_HOME">JBOSS_HOME must be set</fail>
</target>

This causes the build to fail if any one of these environment variables is not set. To execute this target, list it as a dependency from some other target:

<target name="compile" depends="checkProperties">
  ...
</target>

The dependency ensures that the checkProperties target executes before Ant attempts to compile your code.

See Also

The previous two recipes showed how to define environment variables and Ant properties.