Maven and Ant Can't run Java - CreateProcess error=206, The filename or extension is too long

Maven creates lengthy classpaths due to the structure and location of the local maven repo. We need to use a pathing jar.

• Convert Classpath into string
• Escape windows drive letter (C: = bad \C: = good)
• Create manifest only jar with class path attribute
• Use the pathing jar instead of the maven compile classpath

<mkdir dir="${classpath-compile.dir}"/>

<!-- Convert into usable string .   -->
<pathconvert property="compile_classpath_raw" pathsep=" ">
    <path refid="maven.compile.classpath"/>                        
</pathconvert>

<!-- escape windows drive letters (remove C: from paths -- need to wrap with a condition os.family="windows")-->
<propertyregex property="compile_classpath_prep" 
  input="${compile_classpath_raw}"
  regexp="([A-Z]:)"
  replace="\\\\\1"
  casesensitive="false"
  global="true"/>

<!-- Create pathing Jars -->
<jar destfile="${classpath-compile.jar}">
  <manifest>
    <attribute name="Class-Path" value="${compile_classpath_prep}"/>
  </manifest>                      
</jar>

<java classname="com.me.api" failonerror="true" fork="true" maxmemory="128m" output="${wsdlFile}.out">
  <arg value="${className}" />
  <arg value="${name}" />
  <arg value="${wsdlFile}" />
  <classpath>
    <pathelement location="${classpath-compile.jar}" />
  </classpath>

Extending the answer provided by @user4386022: You can define (starting with Ant 1.8) this macro which can help you if you have the same problem in different places in your build process (and you cannot just copy-paste the same snippet everywhere because Ant does not allow re-defining properties, so you will get an error saying that "manifest.classpath" is already defined.)

<macrodef name="create-classpath-jar" description="Create classpath Jar, to avoid getting the error about CreateProcess error=206, The filename or extension is too long">
    <attribute name="classpathjar"/>
    <attribute name="classpathref"/>
    <sequential>
        <!-- Turn the classpath into a property formatted for inclusion in a MANIFEST.MF file -->
        <local name="manifest.classpath.property"/>
        <manifestclasspath property="manifest.classpath.property" jarfile="@{classpathjar}">
            <classpath refid="@{classpathref}" />
        </manifestclasspath>
        <!-- Create the Jar -->
        <jar destfile="@{classpathjar}">
            <manifest>
                <attribute name="Class-Path" value="${manifest.classpath.property}"/>
            </manifest>                      
        </jar>
    </sequential>
</macrodef>

To use the macro in your targets or tasks, then simply use it like this:

<path id="myclasspath">
   .........
</path>
<create-classpath-jar classpathjar="classpath-compile.jar" classpathref="myclasspath" />

If using Ant 1.7 or newer you can utilize the manifestclasspath task to generate a manifest file then include it in a jar for use on the javac classpath

<!-- turn the classpath into a property formatted for inclusion in a MANIFEST.MF file -->
<manifestclasspath property="manifest.classpath"
                   jarfile="${classpath-compile.jar}">
  <classpath refid="maven.compile.classpath" />
</manifestclasspath>

<!-- Create pathing Jars -->
<jar destfile="${classpath-compile.jar}">
  <manifest>
    <attribute name="Class-Path" value="${manifest.classpath}"/>
  </manifest>                      
</jar>

<java classname="com.me.api" failonerror="true" fork="true" maxmemory="128m" output="${wsdlFile}.out">
  <arg value="${className}" />
  <arg value="${name}" />
  <arg value="${wsdlFile}" />
  <classpath>
    <pathelement location="${classpath-compile.jar}" />
</classpath>