check for build.properties

build.xml

<!-- Check for the build.properties file and force the user to create one before compiling. -->
<available file="build.properties" filePath="." property="customBuildPropertiesExist" />
<fail unless="customBuildPropertiesExist" message="You must create a file called 'build.properties' with your local settings in order to use ant with this project." />
<property file="build.properties" />
<echo message="Successfully loaded properties." />