Flowable6.4 - Behavior的用途分析

Flowable和Activiti里面有一个很重要的部分 - Behavior，接下来分析一下这部分的主要作用是什么。

首先，要找一个切入点，看一下在调用TaskServiceImpl.complete()时发生了什么。下面是该函数的源码：

@Overridepublic void complete(String taskId) { commandExecutor.execute(new CompleteTaskCmd(taskId, null));}

这里可以看到执行了CompleteTaskCmd，进入这个类的内部，基于以前的文章，看一看这个命令的execute()方法发生了什么，这里主要关注以下的方法：

TaskHelper.completeTask(task, variables, transientVariables, localScope, commandContext);

追踪下去，可以在completeTask()的最末尾找到一段代码：

// Continue process (if not a standalone task)if (taskEntity.getExecutionId() != null) { ExecutionEntity executionEntity = CommandContextUtil.getExecutionEntityManager(commandContext).findById(taskEntity.getExecutionId()); CommandContextUtil.getAgenda(commandContext).planTriggerExecutionOperation(executionEntity);}

继续追踪下去，就进入了TriggerExecutionOperation这个类，在这个类的run()方法内就可以看到Behavior出现了。

@Overridepublic void run() { FlowElement currentFlowElement = getCurrentFlowElement(execution); if (currentFlowElement instanceof FlowNode) { ActivityBehavior activityBehavior = (ActivityBehavior) ((FlowNode) currentFlowElement).getBehavior(); if (activityBehavior instanceof TriggerableActivityBehavior) { if (currentFlowElement instanceof BoundaryEvent || currentFlowElement instanceof ServiceTask) { // custom service task with no automatic leave (will not have a activity-start history entry in ContinueProcessOperation) CommandContextUtil.getActivityInstanceEntityManager(commandContext).recordActivityStart(execution); } if(!triggerAsync) { ((TriggerableActivityBehavior) activityBehavior).trigger(execution, null, null); } else { //此处省略代码若干 } } }}

当跟踪((TriggerableActivityBehavior) activityBehavior).trigger()的实现时，会发现一堆实现类：

挑选一个最简单的UserTaskActivityBehavior进入，看看发生了什么。会发现调用了一个最关键的方法leave()。然后看看leave()的实现：

@Overridepublic void leave(DelegateExecution execution) { FlowElement currentFlowElement = execution.getCurrentFlowElement(); Collection boundaryEvents = findBoundaryEventsForFlowNode(execution.getProcessDefinitionId(), currentFlowElement); if (CollectionUtil.isNotEmpty(boundaryEvents)) { executeCompensateBoundaryEvents(boundaryEvents, execution); } //关键在这里，如果没有loop的关键字，就不是多实例，直接调用super.leave if (!hasLoopCharacteristics()) { super.leave(execution); } else if (hasMultiInstanceCharacteristics()) { multiInstanceActivityBehavior.leave(execution); }}

再看看super.leave()的实现，如下：

/** * Default way of leaving a BPMN 2.0 activity: evaluate the conditions on the outgoing sequence flow and take those that evaluate to true. */public void leave(DelegateExecution execution) { bpmnActivityBehavior.performDefaultOutgoingBehavior((ExecutionEntity) execution);}

到这里，通过这些关键字就大体可以猜测出接下来的实现了，同时也应该大概明白Behavior的作用了。

如果再看一下多实例用户节点的Behavior也许就会更加清晰，比如ParallelMultiInstanceBehavior，关键的代码如下：

/** * Called when the wrapped {@link ActivityBehavior} calls the {@link AbstractBpmnActivityBehavior#leave(DelegateExecution)} method. Handles the completion of one of the parallel instances */@Overridepublic void leave(DelegateExecution execution) { //代码略..... int loopCounter = getLoopVariable(execution, getCollectionElementIndexVariable()); int nrOfInstances = getLoopVariable(execution, NUMBER_OF_INSTANCES); int nrOfCompletedInstances = getLoopVariable(execution, NUMBER_OF_COMPLETED_INSTANCES) + 1; int nrOfActiveInstances = getLoopVariable(execution, NUMBER_OF_ACTIVE_INSTANCES) - 1; //代码略..... if (zeroNrOfInstances) { return; } ExecutionEntity executionEntity = (ExecutionEntity) execution; if (executionEntity.getParent() != null) { //代码略..... //只有满足跳出条件时，才会调用super.leave if (nrOfCompletedInstances >= nrOfInstances || isCompletionConditionSatisfied) { //代码略..... if (isCompletionConditionSatisfied) { //代码略..... sendCompletedWithConditionEvent(leavingExecution); } else { sendCompletedEvent(leavingExecution); } super.leave(leavingExecution); } } else { sendCompletedEvent(execution); super.leave(execution); }}

所以综上分析，我个人觉得，Behavior就是控制节点是否跳转的，每一次流转，都会进入到这里，然后在此判断是否满足离开此节点的条件，如果满足就离开此节点，进入到下一个节点，否则的话仍旧保持处于此节点。

以上，就是关于Behavior的分析，欢迎指正和讨论。