API Start Process Error : Could not write JSON: Cannot get process model: no current command context is active;

[dongwenting]

flowable 6.3.1

runtimeService.startProcessInstanceByKey(processDefinitionKey, variables);

Error message is

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: Cannot get process model: no current command context is active; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Cannot get process model: no current command context is active (through reference chain: org.flowable.engine.impl.persistence.entity.ExecutionEntityImpl["currentFlowElement"])
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:293)

I figure out the reason.

I return processInstance in the controller like fellow, and the error is thrown
@RestController
public class Controller {
@RequestMapping
public ProcessInstance start(Map<String, Object> model){
return runtimeService.startProcessInstanceByKey(processDefinitionKey, variables);
}
}

so please close the issue

[tijsrademakers]

Thanks for updating the issue with your findings.

[dongwenting]

You can not return ProcessInstance in Controller, because Spring MVC convert ProcessInstance to JSON which causes the error. So I change the return to boolean. Sorry for my pool English, I try my best to explain. ^ ^!

       @PostMapping(value = "/start")
	public Boolean start(@RequestBody Map<String, Object> model) {

[filiphr]

Why don't you use the REST API from Flowable? You can start a process instance and do much more with it if you want to.

On top of that there are mappings that would return a clean Response back

[dongwenting]

@filiphr In addition to start a process instance, I do need to do a lot of extra work, like add attachments, set businessKey, set variables, set Initiator etc. I don't know how to do those only by REST API, so I invoke the api
`

@Override
public ProcessInstance startProcessInstance(String processDefinitionKey, String businessKey, List<AttachmentVO> attachments, Map<String, Object> variables, Boolean isCommit) {
	if(StringUtils.isEmpty(processDefinitionKey)) {
		throw new JxBizException("没有流程Id");
	}
	//从ThreadLocal中获得申请人
	String userCode = UserUtils.getUser();
	if(StringUtils.isEmpty(userCode)) {
		throw new JxBizException("没有发起人");
	}
	
	//往流程变量中添加创建人和创建人部门
	UserVO userVO = candidateService.findCandidateByUserCode(userCode);
	variables.put("CREATE_USER_CODE", userVO.getUserCode());
	variables.put("CREATE_USER_NAME", userVO.getUserName());
	variables.put("CREATE_USER_DEPT_CODE", userVO.getOrgCode());
	variables.put("CREATE_USER_DEPT_NAME", userVO.getOrgName());
	
	//设置流程发起人Initiator
	identityService.setAuthenticatedUserId(userCode);
	
	//启动流程
	ProcessInstance processInstance = runtimeService.startProcessInstanceByKey(processDefinitionKey, businessKey, variables);
	log.info("用户{}启动流程{}{}", userCode, processInstance.getProcessDefinitionName(), processDefinitionKey);
	
	Task task = taskService.createTaskQuery().processInstanceId(processInstance.getId()).singleResult();
	for(AttachmentVO att: attachments) {
		String name = att.getName();
		String type = name.substring(name.lastIndexOf(".")+1);
		taskService.createAttachment(type, task.getId(), processInstance.getId(), att.getName(), userVO.getUserName(), att.getUrl());
	}
	
	if(isCommit) {
		//获得第一个任务，第一个任务一般都是发起人填写单据，如果isCommit为true，则点击提交直接通过，isCommit为false，则保存草稿
		taskService.complete(task.getId());
	}
	return processInstance;
}

[filiphr]

@dongwenting makes sense. Thanks for giving the example.

I would suggest you to create your own DTO that would be returned on your REST call. Something like ProcessInstanceResponse. This is the one returned by the Flowable REST API