If you define an XML validation task within an Ant build script like so:

<xmlvalidate lenient="true">
   <fileset dir="${config.dir}" includes="**/*.xml" />

This will normally work fine, even if the XML file does not validate against the DTD or XSD.

However, this task will fail if the DTD cannot be downloaded, for example if you are behind a proxy, or the DTD is badly formed or missing.

This is a known bug: see https://issues.apache.org/bugzilla/show_bug.cgi?id=35657#c4

There are three solutions that I’ve played around with.

Download the DTD locally

One solution is to download the DTD locally, and define it explicitly as a local DTD within the xmlvalidate task:

<xmlvalidate ...>
   <dtd publicId="-//Apache Software Foundation//DTD Struts Configuration 1.0//EN"

Of course this means that you will now have to maintain a repository of DTDs.

Add the -autoproxy option for Ant

As described by Ant documentation, the -autoproxy option will allow Ant to use the system proxy settings, meaning that it should be able to download the DTD as necessary.

You can also add this to the environment variable ANT_ARGS, so that you don’t need to define it for every ant build.

However, I couldn’t work out how to add this environment variable to an instance of Eclipse – adding it to the Windows environment variables would not pass the variable or option along to Ant, when executing Ant within Eclipse.

Use the setproxy task

The final option that I’ve found is using the setproxy task of Ant to manually set the proxy itself.

This can be done as an optional extra to an existing script, like so:

<target name="set-proxy" if="PROXY_ENABLED"
      description="Optionally set the proxy for the xml-lint target">
   <fail unless="PROXY_HOST" message="PROXY_HOST property not set." />
   <fail unless="PROXY_PORT" message="PROXY_PORT property not set." />
   <setproxy proxyhost="${PROXY_HOST}" proxyport="${PROXY_PORT}" />

<target name="xml-lint"
      ... />

You can now define, within Eclipse, the properties PROXY_ENABLED, PROXY_HOST and PROXY_PORT.