/**
   * 显示图片
   *
   * @return
   */
  @RequestMapping(value = "/viewPic.do")
  public void viewPic(
      HttpServletRequest request,
      HttpServletResponse response,
      @RequestParam("executionId") String executionId)
      throws Exception {
    ProcessInstance processInstance =
        runtimeService.createProcessInstanceQuery().processInstanceId(executionId).singleResult();
    BpmnModel bpmnModel = repositoryService.getBpmnModel(processInstance.getProcessDefinitionId());
    List<String> activeActivityIds = runtimeService.getActiveActivityIds(executionId);

    // 使用spring注入引擎请使用下面的这行代码
    Context.setProcessEngineConfiguration(processEngine.getProcessEngineConfiguration());

    InputStream imageStream =
        ProcessDiagramGenerator.generateDiagram(bpmnModel, "png", activeActivityIds);

    // 输出资源内容到相应对象
    byte[] b = new byte[1024];
    int len;
    while ((len = imageStream.read(b, 0, 1024)) != -1) {
      response.getOutputStream().write(b, 0, len);
    }
  }