You can't do an ANT build inside eclipse if your chosen jdk is 1.3. Here is a the error message you get...
BUILD FAILED
java.lang.NoClassDefFoundError: org/xml/sax/SAXException
at org.apache.tools.ant.ProjectHelper.getProjectHelper(ProjectHelper.java:228)
at org.eclipse.ant.internal.ui.antsupport.InternalAntRunner.parseBuildFile(InternalAntRunner.java:189)
at org.eclipse.ant.internal.ui.antsupport.InternalAntRunner.run(InternalAntRunner.java:400)
at org.eclipse.ant.internal.ui.antsupport.InternalAntRunner.main(InternalAntRunner.java:137)
nice little trick to fix that...
Inside Eclipse Go to Window->Preferences...->Ant->Runtime
In the classpath tab, add a new entry to the Ant Home Entries to the xerces jar file inside your eclipse/pluggins folder. In my case the file was org.apache.xerces_2.8.0.v200705301630.jar.
Now go ahead an run your build again successfully :)
update: When I updated my eclipse to 3.4, this again stopped working for me. The above fix did not work.I then saw a mailing list where the user executed the ant script by right clicking the ant script and choosing Run->Ant build..
Now change the JRE it runs in. It should be set to the option which says "Run in the same JRE as the workspace"
The mailing list thread is here
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