How can I specify the path of a JAR in an ant buildfile?

Question

I am executing lot of scp and sshexec and other remote commands from an ant build script. These commands don't work if jsch.jar isn't in the ant lib directory. To make it work, I copied the JAR into the ant lib directory, but this is not a good solution, as anyone else wanting to run the script would have to do the same thing. To run the ant target from Teamcity, we will have to explicitly set the path of the lib file.

Is there a way I can specify the path of the JAR in the ant build XML itself?

Answer 1

Thanks all for your answers. I am managed to get it work with classloader task. This is what I did.

<project basedir="." >
  <property environment="env"/>

  <taskdef resource="net/jtools/classloadertask/antlib.xml">
    <classpath>
      <fileset dir="${basedir}/lib" includes="ant-classloader*.jar"/>
    </classpath>
  </taskdef>

  <!--Add JSCH jar to the classpath-->
  <classloader loader="system">
    <classpath>
      <fileset dir="${basedir}/lib" includes="jsch*.jar"/>
      </classpath>
  </classloader>

  <target name="Test">
      <scp todir="user1:pass1@server1:/tmp" trust="true" >
        <fileset dir="dir1">
          <include name="test.txt" />
        </fileset>
      </scp>
   </target>
</project>

As you can see here, I didn't have to give any dependant target for my "Test" target, it just works. It uses classloader, which appends jsch.jar to the system classloader.

Answer 2

One possible work around would be to use the -lib command line option to tell ant where to look for additional jars. Perhaps you could create a wrapper script that calls ant with this option set.

Another way would be to move the ant-jsch.jar file (this is the jar that comes with ant that defines the tasks, not the jsch.jar file you need to download separately) out of your ant lib directory, and create a taskdef for your ssh task separate to the built in one, then set the classpath for this task to the jsch.jar and the ant-jsch.jar:

<taskdef name="sshexec"
  classname="org.apache.tools.ant.taskdefs.optional.ssh.SSHExec">
  <classpath>
    <pathelement location="jsch-0.1.44.jar"/>
    <pathelement location="ant-jsch.jar" />
  </classpath>
</taskdef>

I'm not sure this will help you though, since it also involves making changes to the lib directory.

As far as I'm aware, it's not currently possible to specify the extra jars required for the built in tasks in the build file itself in general. There are some special cases, like junit for instance.

Answer 3

To ensure your build is more cross platform I'd suggest using dependency management. The ivy plug-in can automatically install the version of your build's plugin at build-time.

This approach means the last jar you'll ever need to install into your ANT lib is ivy-2.2.0.jar :-)

First declare your project's dependencies in the file ivy.xml

<ivy-module version="2.0">
    <info organisation="com.myspotontheweb" module="demo"/>
    <configurations>
        <conf name="anttask" description="Jars implementing ANT tasks"/>
    </configurations>
    <dependencies>
        <dependency org="com.jcraft" name="jsch" rev="0.1.42" conf="anttask->default"/>
    </dependencies>
</ivy-module>

Within your build.xml run ivy and use it to populate a custom classpath based on the ivy configuration:

<target name='init' description='Resolve project dependencies and set classpaths'>
    <ivy:resolve/>
    <ivy:cachepath pathid="anttask.path" conf="anttask"/>
</target>

Finally, elsewhere in your build declare your ANT tasks using the class path now automatically populated by ivy.

<target name='dosomething' depends="init">
    <taskdef name="sshexec" 
             classname="org.apache.tools.ant.taskdefs.optional.ssh.SSHExec"
             classpathref="anttask.path"/>
    ..
    ..
</target>

This approach works for all ANT plug-ins, most of which are available in the central Maven repository. The second benefit is that it's easy to upgrade the plug-in versions across all builds.