topic Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ? in Alfresco Forum

What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

viorelhojda — Wed, 18 Jan 2017 12:51:42 GMT

I'm trying to use a simple ServiceTask with a delegateExpression (a Spring bean) and to inject simple Expressions using activiti fields, I'm following the tutorial from official page : Activiti User Guide .The Spring bean is correctly initialized by Spring and I have other beans and services correc

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

gdharley — Wed, 18 Jan 2017 17:43:59 GMT

Please provide a unit test to demonstrate your problem.

Thanks,

Greg

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Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

viorelhojda — Thu, 19 Jan 2017 10:11:42 GMT

Hello, thank you for the interest. I haven't configured a JUnit environment (yet) , so I can't provide on the spot the use case scenario, but I can lay down all the needed data, it will certainly contain all the needed data.

So:

1.a Spring bean in the Spring context availlable and instantiated by Spring

2.The Activiti BPM process:

<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:activiti="http://activiti.org/bpmn" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlnsmgdc="http://www.omg.org/spec/DD/20100524/DC" xmlnsmgdi="http://www.omg.org/spec/DD/20100524/DI" typeLanguage="http://www.w3.org/2001/XMLSchema" expressionLanguage="http://www.w3.org/1999/XPath" targetNamespace="http://activiti.org/bpmn20" id="definitions">
   <process id="sone_email" name="Send Sone Email" isExecutable="true">
   <startEvent id="theStart"></startEvent>
   <endEvent id="theEnd"></endEvent>
   <serviceTask id="servicetask1" name="Simple Service Task"       activiti:delegateExpression="${simpleServiceTaskDelegate}">
      <extensionElements>
         <activiti:field name="fieldA">
            <activiti:string><![CDATA[AAA]]></activiti:string>
         </activiti:field>
      </extensionElements>
   </serviceTask>
   <sequenceFlow id="flow1" sourceRef="theStart" targetRef="servicetask1"></sequenceFlow>
   <sequenceFlow id="flow2" sourceRef="servicetask1" targetRef="theEnd"></sequenceFlow>
</process>
</definitions>

3.The delegate: SimpleServiceTaskDelegate.java class

public class SimpleServiceTaskDelegate implements JavaDelegate {

private Expression fieldA;

   @Override
   public void execute(DelegateExecution execution) {
      System.out.println("FIELD:" + this.fieldA);// null
   }
}

4.Just deploy and start the process

//deploy

InputStream is = this.getStream(workflowResourceName);

this.activitiBpmService.getRepositoryService().createDeployment().addInputStream(workflowResourceName, is).deploy()

//start

this.activitiBpmService.getRuntimeService().startProcessInstanceByKey("sone_email");

Basically, in the simpleServiceTaskDelegate bean I inject an Expression fieldA, which is null always. If I use the class to inject expressions, then it works:

If needed, I will setup the JUnit along with Spring context, h2 DB and Activiti and came up with a more functionl test.

Thanks in advance for all the help !

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

nikmenke — Thu, 19 Jan 2017 10:56:50 GMT

Hi,

maybe you should define the scope of your bean as prototype.

Niklas

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

viorelhojda — Thu, 19 Jan 2017 12:11:15 GMT

Hello, I tried that already, that "only" means the bean won't be a Singleton with the implications regarding instantiating objects and therefore thread-safety. This doesn't solve the problem , the fields (Expressions) won't be injected in the bean, they will still be null.

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

nikmenke — Thu, 19 Jan 2017 12:30:36 GMT

Hi,

yes i know. My thought was that the setter might not be called because the object was initialized before. The behaviour with a prototyped bean should be the same as using the class attribute of the service task.

I have tested your code now with my engine. With version 6.0.0.Beta4 there is no problem getting your inserted value. Maybe you should consider to update your engine to a newer version than 5.9.

Niklas

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

viorelhojda — Thu, 19 Jan 2017 12:42:13 GMT

Thank you again for the interest, I will consider upgrading to 6 (I did try that also), the problem is I have to refactor a lot. Thanks again !

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

viorelhojda — Thu, 19 Jan 2017 12:48:40 GMT

Hello again, I did find a "workaround" though:

1.create a "dummy" Spring Bean simpleServiceBean with a method with 2 params, let's say callMethod(Object a, Object b); also, make sure the object t's serializable

2.add the bean to the process instance variables map when starting the process

Object simpleServiceBean = this.getApplicationContext().getBean("simpleServiceBean");
vars.put("simpleServiceBean", simpleServiceBean);

3.use the delegate class as before, SimpleServiceTaskDelegate

4.in the execute method in SimpleServiceTaskDelegate, take the injected Expressions (members of the class), extract the SimpleServiceTaskDelegate from the execution and call the method with params:

Object fa = this.fieldA.getValue(execution);
Object fb = this.fieldB.getValue(execution);

Object obj = execution.getVariable("simpleServiceBean");
SimpleServiceBean ssb = (SimpleServiceBean) obj;
ssb.callMethod(fa, fb);

This works, but it isn't so pretty

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

nikmenke — Thu, 19 Jan 2017 13:13:03 GMT

I think the better workaround would be to use the expression attribute of the servicetask. There you could call the method with the two parameters of the spring bean. Something like this:

Niklas

Re: What are the reasons when expressions are not injected (null) in a service task delegate expression (Spring bean) ?

viorelhojda — Thu, 19 Jan 2017 13:53:06 GMT

Yes, I think it's a better approach, it's lighter since I don't have to put the Spring bean in the process instance variables.

It seems I have 3 options:

1.Activiti 6 with Java class delegate

2.Facade Spring Bean with Expression delegate and delegate Java class

3.Call Spring bean code with Expression

Thanks again !