扩展Activiti流程定义文件，实现自定义节点属性

为了满足业务需要，流程设计阶段需对设计产物流程定义文件中节点属性进行扩展，譬如：任务是否支持退回、退回方式、退回的节点，任务转派人、任务可跳转的节点范围等属性信息。为了保证扩展后的流程定义文件能够正常解析，我们采用类似<activiti:formProperty>元素的方式，模式如下：

<process id="extensionOperationProcess" name="The process which has extension operations" isExecutable="true">
<startEvent id="start" name="Start"></startEvent>
<sequenceFlow id="flow1" sourceRef="start" targetRef="operationTask"></sequenceFlow>
<userTask id="operationTask" name="User task which has extension operations" activiti:assignee="admin">
<extensionElements>
<activiti:operations>
<!-- 转派: 将当前任务转派给他人. 可配置属性如下:
transferTo 转派任务接收人. 可为具体的人,也可为表达式;
-->
<activiti:transfer transferTo="admin" />
<!-- 退回: 从当前节点退回到前序已执行的节点. 可配置属性如下:
backTo 可退回到的节点范围,可以逗号间隔可选的节点. 为any时,表示可选任意前序的已执行节点. 默认值为与该节点紧邻的上一个节点;
returnBy 返回方式,可选"track"(原路返回),"flow"(重新流转). 默认值为track;
-->
<activiti:turnback backTo="startevent1" returnBy="track" />
<!-- 撤销: 退回的反向操作?. 可配置属性如下:
gotoBy 前进方式,可选"track"(原路返回),"flow"(重新流转). 默认值为track;
-->
</activiti:operations>
</extensionElements>
</userTask>
<sequenceFlow id="flow2" sourceRef="operationTask" targetRef="usertask"></sequenceFlow>
<userTask id="usertask" name="User Task" activiti:assignee="user"></userTask>
<sequenceFlow id="flow3" sourceRef="usertask" targetRef="end"></sequenceFlow>
<endEvent id="end" name="End"></endEvent>
</process>

流程定义文件扩展之后，扩展的属性如何存储呢？我们知道在Activiti中ActivitiImpl对象存储的是活动节点的定义，那么我们即可在流程文件解析时将扩展属性通过setProperty方式存储到
ActivitiImpl对象中。实现过程如下：

自定义用户任务解析控制类，该类实现将流程定义文件中的扩展属性设置给ActivitiImpl

流程引擎配置中将自定义的用户任务解析控制类，覆盖掉默认的用户任务解析控制类

public class ExtensionUserTaskParseHandler extends UserTaskParseHandler {

@Override
protected void executeParse(BpmnParse bpmnParse, UserTask userTask) {
//调用上层的解析
super.executeParse(bpmnParse, userTask);

ActivityImpl activity = bpmnParse.getCurrentScope().findActivity(userTask.getId());
Map<String, ExtensionOperation> operationMap = parseUserTaskOperations(bpmnParse, userTask);

//将扩展属性设置给activity
activity.setProperty(ExtensionBpmnConstants.PROPERTY_OPERATIONS_DEFINITION, operationMap);
}

public Map<String, ExtensionOperation> parseUserTaskOperations(BpmnParse bpmnParse, UserTask userTask) {
Map<String, ExtensionOperation> operationMap = new HashMap<String, ExtensionOperation>();
//获取扩展属性标签元素
ExtensionElement operationsElement = userTask.getExtensionElements()
.get(ExtensionBpmnConstants.EXTENSION_ELEMENT_OPERATIONS);

if (operationsElement != null) {
for (ExtensionElement operationElement : operationsElement.getChildElements().values()) {
ExtensionOperation userTaskOperation = new ExtensionOperation(operationElement.getName());

if (operationElement != null && !operationElement.getAttributes().isEmpty()) {
for (ExtensionAttribute attributeElement : operationElement.getAttributes().values()) {
userTaskOperation.addProperty(attributeElement.getName(), attributeElement.getValue());
}
}
operationMap.put(operationElement.getName(), userTaskOperation);
}
}

return operationMap;
}
}

引擎配置：

<bean id="processEngineConfiguration" class="org.activiti.engine.impl.cfg.StandaloneInMemProcessEngineConfiguration">
<property name="processEngineName" value="activitiEngineInMemory" />
<property name="jdbcUrl" value="jdbc:h2:mem:activiti;DB_CLOSE_DELAY=1000" />
<property name="jdbcDriver" value="org.h2.Driver" />
<property name="jdbcUsername" value="sa" />
<property name="jdbcPassword" value="" />
<!-- Database configurations -->
<property name="databaseSchemaUpdate" value="true" />
<!-- job executor configurations -->
<property name="jobExecutorActivate" value="false" />
<!-- mail server configurations -->
<property name="mailServerPort" value="5025" />
<property name="customDefaultBpmnParseHandlers">
<list>
<bean class="com.cayenne.bpm.engine.kernel.activiti.extension.bpmn.ExtensionUserTaskParseHandler" />
</list>
</property>
</bean>

完成上述设置后，即可通过 activity.getProperty(ExtensionBpmnConstants.PROPERTY_OPERATIONS_DEFINITION);获取扩展的属性值。