Activiti 流程启动及节点流转源码分析

本文主要是以activiti-study中的xiaomage.xml流程图为例进行跟踪分析 

具体的流程图如下： 

流程图对应的XML文件如下：

<?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:activiti="http://activiti.org/bpmn" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:omgdc="http://www.omg.org/spec/DD/20100524/DC" xmlns:omgdi="http://www.omg.org/spec/DD/20100524/DI" typeLanguage="http://www.w3.org/2001/XMLSchema" expressionLanguage="http://www.w3.org/1999/XPath" targetNamespace="http://www.activiti.org/test">    <process id="MyProcess" name="MyProcess">        <documentation>Place documentation for the 'MyProcess' process here.</documentation>        <startEvent id="startevent1" name="Start"/>        <userTask id="sss" name="ddd" activiti:assignee="fq"/>        <sequenceFlow id="flow1" name="" sourceRef="startevent1" targetRef="sss"/>        <endEvent id="endevent1" name="End"/>        <sequenceFlow id="flow2" name="" sourceRef="sss" targetRef="endevent1"/>    </process>    <bpmndi:BPMNDiagram id="BPMNDiagram_MyProcess">        <bpmndi:BPMNPlane bpmnElement="MyProcess" id="BPMNPlane_MyProcess">            <bpmndi:BPMNShape bpmnElement="startevent1" id="BPMNShape_startevent1">                <omgdc:Bounds height="35" width="35" x="340" y="150"/>            </bpmndi:BPMNShape>            <bpmndi:BPMNShape bpmnElement="sss" id="BPMNShape_sss">                <omgdc:Bounds height="55" width="105" x="305" y="250"/>            </bpmndi:BPMNShape>            <bpmndi:BPMNShape bpmnElement="endevent1" id="BPMNShape_endevent1">                <omgdc:Bounds height="35" width="35" x="340" y="370"/>            </bpmndi:BPMNShape>            <bpmndi:BPMNEdge bpmnElement="flow1" id="BPMNEdge_flow1">                <omgdi:waypoint x="357" y="185"/>                <omgdi:waypoint x="357" y="250"/>            </bpmndi:BPMNEdge>            <bpmndi:BPMNEdge bpmnElement="flow2" id="BPMNEdge_flow2">                <omgdi:waypoint x="357" y="305"/>                <omgdi:waypoint x="357" y="370"/>            </bpmndi:BPMNEdge>        </bpmndi:BPMNPlane>    </bpmndi:BPMNDiagram></definitions>

流程实例创建过程如下（下图转载自：activiti 源码笔记之startProcess）： 

流程启动跟踪分析： 
图一： 

图二： 

图三： 

图四： 

以上主要是跟踪分析了，三个节点之间的流转情况。 
在流转的时候需要注意以下两个接口： 
原子操作（AtomicOperation）接口：

public interface AtomicOperation {  AtomicOperation PROCESS_START = new AtomicOperationProcessStart();  AtomicOperation PROCESS_START_INITIAL = new AtomicOperationProcessStartInitial();  AtomicOperation PROCESS_END = new AtomicOperationProcessEnd();  AtomicOperation ACTIVITY_START = new AtomicOperationActivityStart();  AtomicOperation ACTIVITY_EXECUTE = new AtomicOperationActivityExecute();  AtomicOperation ACTIVITY_END = new AtomicOperationActivityEnd();  AtomicOperation TRANSITION_NOTIFY_LISTENER_END = new AtomicOperationTransitionNotifyListenerEnd();  AtomicOperation TRANSITION_DESTROY_SCOPE = new AtomicOperationTransitionDestroyScope();  AtomicOperation TRANSITION_NOTIFY_LISTENER_TAKE = new AtomicOperationTransitionNotifyListenerTake();  AtomicOperation TRANSITION_CREATE_SCOPE = new AtomicOperationTransitionCreateScope();  AtomicOperation TRANSITION_NOTIFY_LISTENER_START = new AtomicOperationTransitionNotifyListenerStart();  AtomicOperation DELETE_CASCADE = new AtomicOperationDeleteCascade();  AtomicOperation DELETE_CASCADE_FIRE_ACTIVITY_END = new AtomicOperationDeleteCascadeFireActivityEnd();  void execute(InterpretableExecution execution);  boolean isAsync(InterpretableExecution execution);}

注意：

void execute(InterpretableExecution execution);

InterpretableExecution接口：

public interface InterpretableExecution extends ActivityExecution, ExecutionListenerExecution, PvmProcessInstance {  void take(PvmTransition transition);  void take(PvmTransition transition, boolean fireActivityCompletedEvent);  void setEventName(String eventName);  void setEventSource(PvmProcessElement element);  Integer getExecutionListenerIndex();  void setExecutionListenerIndex(Integer executionListenerIndex);  ProcessDefinitionImpl getProcessDefinition();  void setActivity(ActivityImpl activity);  void performOperation(AtomicOperation etomicOperation);  boolean isScope();  void destroy();  void remove();  InterpretableExecution getReplacedBy();  void setReplacedBy(InterpretableExecution replacedBy);  InterpretableExecution getSubProcessInstance();  void setSubProcessInstance(InterpretableExecution subProcessInstance);  InterpretableExecution getSuperExecution();  void deleteCascade(String deleteReason);  boolean isDeleteRoot();  TransitionImpl getTransition();  void setTransition(TransitionImpl object);  void initialize();  void setParent(InterpretableExecution parent);  void setProcessDefinition(ProcessDefinitionImpl processDefinitionImpl);  void setProcessInstance(InterpretableExecution processInstance);  boolean isEventScope();  void setEventScope(boolean isEventScope);  StartingExecution getStartingExecution();  void disposeStartingExecution();}

注意：

void performOperation(AtomicOperation etomicOperation);

单独摘出来的两个方法是图一中： 

上下文、原子操作、执行器实体三者相互调用的关键。 
上图的具体调用情况如下： 
ExecutionEntity类中的：

public void performOperation(AtomicOperation executionOperation) {    if (executionOperation.isAsync(this)) {        scheduleAtomicOperationAsync(executionOperation);    } else {        performOperationSync(executionOperation);    }}protected void performOperationSync(AtomicOperation executionOperation) {    Context    .getCommandContext()    .performOperation(executionOperation, this);}

performOperation函数中调用上下文CommandContext类中的：

public void performOperation(AtomicOperation executionOperation, InterpretableExecution execution) {    nextOperations.add(executionOperation);    if (nextOperations.size()==1) {        try {            Context.setExecutionContext(execution);            while (!nextOperations.isEmpty()) {                AtomicOperation currentOperation = nextOperations.removeFirst();                if (log.isTraceEnabled()) {                    log.trace("AtomicOperation: {} on {}", currentOperation, this);                }                if (execution.getReplacedBy() == null) {                    currentOperation.execute(execution);                } else {                    currentOperation.execute(execution.getReplacedBy());                }            }        } finally {            Context.removeExecutionContext();        }    }}

performOperation函数调用原子操作（AtomicOperation）接口中的void execute(InterpretableExecution execution)来处理。 
该处的处理分为两种情况： 
1、根据AtomicOperation接口标识来继续进行流转 
（再次调用ExecutionEntity类中的performOperation(AtomicOperation executionOperation)方法） 
比如： 
PROCESS_START=》PROCESS_START_INITIAL=》ACTIVITY_EXECUTE。。。。。。 
具体可以参考本文图一到图四的代码跟踪中的标识。 
2、根据节点上的ActivityBehavior类进行不同的处理 

Activiti节点（开始、结束、任务、网关等等）都是Activity类型的，只是其挂的ActivityBehavior不同，通过不同的ActivityBehavior来实现相应的操作。