build.xml

<?xml version="1.0"?>

<project name="opennms" default="usage" basedir=".">
  <description>OpenNMS Ant Targets</description>
  <target name="java.check">
    <condition property="java.versionokay">
      <or>
        <!-- Don't forget to update the <fail> message below -->
        <contains string="${java.version}" substring="1.6."/>
        <contains string="${java.version}" substring="1.7."/>
        <contains string="${java.version}" substring="1.8."/>
        <contains string="${java.vm.version}" substring="1.6."/>
        <contains string="${java.vm.version}" substring="1.7."/>
        <contains string="${java.vm.version}" substring="1.8."/>
      </or>
    </condition>

    <fail unless="java.versionokay">
Your Java version (java.version = ${java.version} java.vm.version = ${java.vm.version}) is not supported.  The
build system is currently designed and tested to work with Java
versions 1.8.  You can try to work around this error by
modifying the java.check target in the build.xml file.
    </fail>
  </target>
</project>