code: @Override
     public void execute() throws BuildException 
     {
        ClassLoader oldCL = SecurityActions.getThreadContextClassLoader();
        try 
        {
           SecurityActions.setThreadContextClassLoader(SecurityActions.getClassLoader(ValidatorTask.class));
  
           Validation.validate(new File(getRarFile()).toURI().toURL(), 
              getOutputDir(), getCommandLine().getClasspath().list());
        }
        catch (Throwable t) 
        {
           throw new BuildException(t.getMessage(), t);
        }
        finally
        {
           SecurityActions.setThreadContextClassLoader(oldCL);
        }
     }
docs: Execute
  @exception BuildException If the build fails