大家看看这个该怎么转换（jbpm4.0）

 ProcessDefinition pd = ((OpenExecution) processInstance).getProcessDefinition();这是错误的代码。我要得到ProcessDefinition  对象的实力怎么做啊 下面是一个方法  public InputStream getXmlByProcessInstance(HttpServletRequest request) {
        String id = getProcessInstanceId(request);        if (id != null) {
            ApplicationContext ctx = null;
            ctx = WebApplicationContextUtils.getWebApplicationContext(getServletContext());            ProcessEngine processEngine = (ProcessEngine) ctx.getBean(
                    "processEngine");            RepositoryService repositoryService = processEngine
                .getRepositoryService();
            ExecutionService executionService = processEngine
                .getExecutionService();            ProcessInstanceQuery query = executionService
                .createProcessInstanceQuery();
            query.processInstanceId(id);            Execution processInstance = (Execution) query.uniqueResult();
            ProcessDefinition pd = ((OpenExecution) processInstance).getProcessDefinition();
                
            System.out.println("这里把getDeploymentDbid()改为getDeploymentId()");
            return repositoryService.getResourceAsStream(pd.getDeploymentId(), "process.jpdl.xml");
        } else {
            return null;
        }
    }