Question

I wanted to have a look which system properties are set here (and to which values), so the easiest way (if not writing a new Java program here) would be adding some lines to my ant build script:

  <target name="properties">
    <echoproperties/>
  </target>

But running ant gives my this error message:

/u/ebermann/projektoj/stackoverflow-examples/build.xml:19: Problem: failed to create task or type echoproperties
Cause: the class org.apache.tools.ant.taskdefs.optional.EchoProperties was not found.
        This looks like one of Ant's optional components.
Action: Check that the appropriate optional JAR exists in
        -/usr/share/ant/lib
        -/u/ebermann/.ant/lib
        -a directory added on the command line with the -lib argument

Do not panic, this is a common problem.
The commonest cause is a missing JAR.

This is not a bug; it is a configuration problem

Okay, so I don’t panic, but wonder what to do.

I have Ant 1.7.1 here (an OpenSUSE system), and sadly no documentation for this version, and I’m not root to install either a current ant version or the documentation for the old version (I just downloaded it and it still does not say which jar file is needed here). Of the directories listed above, only /usr/share/ant/lib exists, but it contains nothing like optional.

I would want to download the necessary jar file and put it in my home directory, but where to find it? The ant download archive contains nothing like that, and I have no idea where else to search. (I did google a bit, but did not find anything.

So, can someone give me some pointers where to find the right jar file?

(I suppose the solution is quite easy, and something is just blocking my view.)

---

After vahapt‘s answer, I downloaded the file from the apache repository, and put it into the directory /u/ebermann/.ant/lib mentioned by the error message. Running ant properties again – the same result as above.

$ jar -tf /u/ebermann/.ant/lib/ant-nodeps-1.7.1.jar | grep 'EchoProperties.class'
org/apache/tools/ant/taskdefs/optional/EchoProperties.class

This looks like it should work – is the error message simply wrong?

If I put it directly into the CLASSPATH, it works:

$ CLASSPATH=/u/ebermann/.ant/lib/ant-nodeps-1.7.1.jar ant properties 
Buildfile: build.xml

properties:
[echoproperties] #Ant properties
[echoproperties] #Thu Mar 10 00:46:22 CET 2011
...
[echoproperties] user.name=ebermann
[echoproperties] user.timezone=

BUILD SUCCESSFUL
Total time: 0 seconds

I don’t want to change my normal CLASSPATH variable, and it should work by putting it into this directory, or did I understand something wrong?

Any ideas, or is this an ant bug?

(Also, why is this file nowhere mentioned in the ant documentation?)

---

Edit:

After the answer from vahapt, my ant build-file looks like this:

<project name="stackoverflow-examples" basedir=".">

  <target name="echoproperties.prepare">
    <available property="echoproperties.works"
               classname="org.apache.tools.ant.taskdefs.optional.EchoProperties"
               />
  </target>

  <target name="echoproperties.init"
          depends="echoproperties.prepare"
          unless="echoproperties.works">
    <taskdef name="echoproperties" classname="org.apache.tools.ant.taskdefs.optional.EchoProperties">
      <classpath>
        <fileset dir="${user.home}/.ant/lib">
          <include name="ant-nodeps.jar" />
        </fileset>
      </classpath>
    </taskdef>
  </target>


  <target name="properties" depends="echoproperties.init">
    <echoproperties/>
  </target>

</project>

This re-registers the task only if it is not already in the ant classpath. (Thus it should also work for complete ant installations which do not have this file in the home directory).

I would still say that This is not a bug; it is a configuration problem is not totally right, even more as putting the file in the indicated directory does not help.

---

One more interesting observation: The nodeps.jar in ${user.home}/.ant/lib (i.e. now /u/ebermann/.ant/lib/ant-nodeps.jar) is already in the class path (the one shown by ${java.class.path}, but this seems not to help for <echoproperties> to work without this taskdef.

So, this works too:

  <target name="echoproperties.init"
          depends="echoproperties.prepare"
          unless="echoproperties.works">
    <taskdef name="echoproperties"
             classname="org.apache.tools.ant.taskdefs.optional.EchoProperties"
             classpath="${java.class.path}" />
  </target>

Answer 1

When you make a google search, results point to ant-nodeps-1.7.1.jar
Make sure that jar exists and you’ve added it into the classpath

For the second part of your question:
SOLUTION 1. You do not need to modify your CLASSPATH variable. Instead you might add it by adding the parameter -cp [JAR FILE LOCATION] (-cp is for “java” executable)
SOLUTION 2. Jar files are simply zip files, open ant-nodeps.jar copy its content to ant.jar throw away ant-nodeps.jar
SOLUTION 3. See the sample below. taskdef is a ant feature that loads a jar or a class into ClassLoader hierarchy. (You load the class before using it, works like a charm)

<?xml version="1.0" encoding="ASCII"?>
<project name="Test" default="properties" basedir=".">

    <target name="properties" depends="init">
        <echoproperties/>
    </target>

    <target name="init">
        <taskdef name="echoproperties" classname="org.apache.tools.ant.taskdefs.optional.EchoProperties">
            <classpath>
                <fileset dir="${ant.library.dir}">
                    <include name="ant-nodeps.jar" />
                </fileset>
            </classpath>
        </taskdef>
    </target>
</project>