<dependency>
    <groupId>org.activiti</groupId>
    <artifactId>activiti-image-generator</artifactId>
    <version>5.19.0.2</version>
</dependency>

@RequestMapping("getPiImage")
    public void xx(String processInstanceId, HttpServletResponse response)
            throws IOException {
        if (processInstanceId == null) {
            throw new ActivitiIllegalArgumentException(
                    "No process instance id provided");
        }

        ExecutionEntity pi = (ExecutionEntity) runtimeService
                .createProcessInstanceQuery()
                .processInstanceId(processInstanceId).singleResult();

        if (pi == null) {
            throw new ActivitiObjectNotFoundException(
                    "Process instance with id" + processInstanceId
                            + " could not be found", ProcessInstance.class);
        }

        ProcessDefinitionEntity pde = (ProcessDefinitionEntity) ((RepositoryServiceImpl) repositoryService)
                .getDeployedProcessDefinition(pi.getProcessDefinitionId());

        if (pde != null && pde.isGraphicalNotationDefined()) {
            BpmnModel bpmnModel = repositoryService.getBpmnModel(pde.getId());
            ProcessDiagramGenerator ge = new DefaultProcessDiagramGenerator();
            InputStream resource = ge.generateDiagram(bpmnModel, "png",
                    runtimeService.getActiveActivityIds(processInstanceId),
                    new ArrayList<String>(), "宋体", "宋体", null, 1.0d);

            int len = 0;
            byte[] b = new byte[1024];
            while ((len = resource.read(b, 0, 1024)) != -1) {
                response.getOutputStream().write(b, 0, len);
            }

        } else {
            throw new ActivitiException("Process instance with id "
                    + processInstanceId + " has no graphic description");
        }

    }