activiti源码解读之心得整编

activiti采取了command模式，completeTask会被包装成一个CompleteTaskCmd，一个Cmd执行的时候需要一些外围处理，如：log日志。activiti定义了一个拦截器链，链上的每个拦截器都有个next，会一直next执行下去。以CompleteTaskCmd为例，拦截器链为：

logger拦截器–>spring事务拦截器–>CommandContext拦截器–>CommandInvoker拦截器

其中CommandContext拦截器的工作主要是设置Context：

      // Push on stack
      Context.setCommandContext(context);
      Context.setProcessEngineConfiguration(processEngineConfiguration);      return next.execute(config, command);

这边push，另外有地方pop，CommandInvoker就干的此事：

  public <T> T execute(CommandConfig config, Command<T> command) {
    return command.execute(Context.getCommandContext());
  }

答案是TaskEntity.completeTask()方法会调用execution.signal()–>activityBehavior.signal()–>activityBehavior.leave()方法，该方法最终会激活AtomicOperationTransitionNotifyListenerStart的eventNotificationsCompleted()方法，该方法会创建当前Transition的destination，代码如下：

  protected void eventNotificationsCompleted(InterpretableExecution execution) {
    TransitionImpl transition = execution.getTransition();
    ActivityImpl destination = null;
    if(transition == null) { // this is null after async cont. -> transition is not stored in execution
      destination = (ActivityImpl) execution.getActivity();
    } else {
      destination = transition.getDestination();
    }
    ActivityImpl activity = (ActivityImpl) execution.getActivity();
    if (activity!=destination) {
      ActivityImpl nextScope = AtomicOperationTransitionNotifyListenerTake.findNextScope(activity, destination);
      execution.setActivity(nextScope);
      execution.performOperation(TRANSITION_CREATE_SCOPE);
    } else {
      execution.setTransition(null);
      execution.setActivity(destination);
      execution.performOperation(ACTIVITY_EXECUTE);
    }
  }
}

多实例任务会启动多个任务和execution，调用execution.signal()–>activityBehavior.signal()–>activityBehavior.leave()，ParallelMultiInstanceBehavior.leave()其中包含如下代码：

    List<ActivityExecution> joinedExecutions = executionEntity.findInactiveConcurrentExecutions(execution.getActivity());
    if (joinedExecutions.size() == nrOfInstances || completionConditionSatisfied(execution)) {      // Removing all active child executions (ie because completionCondition is true)
      List<ExecutionEntity> executionsToRemove = new ArrayList<ExecutionEntity>();
      for (ActivityExecution childExecution : executionEntity.getParent().getExecutions()) {
        if (childExecution.isActive()) {
          executionsToRemove.add((ExecutionEntity) childExecution);
        }
      }
      for (ExecutionEntity executionToRemove : executionsToRemove) {
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Execution {} still active, but multi-instance is completed. Removing this execution.", executionToRemove);
        }
        executionToRemove.inactivate();
        executionToRemove.deleteCascade("multi-instance completed");
      }
      executionEntity.takeAll(executionEntity.getActivity().getOutgoingTransitions(), joinedExecutions);

completionConditionSatisfied()方法将用来判断是否该结束，takeAll()方法将结束当前子执行，并将主执行设置为active。

当然可以！但是记住，标注有当前activity的execution在后续执行和结束的时候会用到这个activity！如果发生程序关闭等情况，execution会尝试从ProcessDefinition里重新根据ID加载activity，如下所示：

  protected void ensureProcessDefinitionInitialized() {
    if ((processDefinition == null) && (processDefinitionId != null)) {
      ProcessDefinitionEntity deployedProcessDefinition = Context
        .getProcessEngineConfiguration()
        .getDeploymentManager()
        .findDeployedProcessDefinitionById(processDefinitionId);
      setProcessDefinition(deployedProcessDefinition);
    }
  }    protected void ensureActivityInitialized() {
    if ((activity == null) && (activityId != null)) {
      activity = getProcessDefinition().findActivity(activityId);
    }
  }

再来看看execution的set方法，就能明白它为什么会保留一堆id：

  public void setActivity(ActivityImpl activity) {
    this.activity = activity;
    if (activity != null) {
      this.activityId = activity.getId();
      this.activityName = (String) activity.getProperty("name");
    } else {
      this.activityId = null;
      this.activityName = null;
    }
  }

所以，要完全保证程序认识被改造的activity的途径是：自定义ProcessDefinition，重写其findActivity()方法！

不知道！真的不知道activiti为什么这么做！是想支持flex里面的JSON建模么？（如上结论主要是针对于activiti-modeler的实现，经仔细验证，activiti-engine对model的editorsource是没有任何限制的~~~）

答案是AtomicOperationTransitionCreateScope.execute()，代码摘录如下：

  public void execute(InterpretableExecution execution) {
    InterpretableExecution propagatingExecution = null;
    ActivityImpl activity = (ActivityImpl) execution.getActivity();
    if (activity.isScope()) {
      propagatingExecution = (InterpretableExecution) execution.createExecution();
      propagatingExecution.setActivity(activity);
      propagatingExecution.setTransition(execution.getTransition());
      execution.setTransition(null);
      execution.setActivity(null);
      execution.setActive(false);
      log.debug("create scope: parent {} continues as execution {}", execution, propagatingExecution);
      propagatingExecution.initialize();    } else {
      propagatingExecution = execution;
    }    propagatingExecution.performOperation(AtomicOperation.TRANSITION_NOTIFY_LISTENER_START);
  }

其中的activity就是当前的节点。

魅力在于activity的executionListeners，代码如下：

public class ActivityInstanceEndHandler implements ExecutionListener {  public void notify(DelegateExecution execution) {
    Context.getCommandContext().getHistoryManager()
      .recordActivityEnd((ExecutionEntity) execution);
  }
}