扩展Activiti流程定义文件，实现自定义节点属性

      为了知足业务须要，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可以正常解析，咱们采用相似<activiti:formProperty>元素的方式，模式以下：

<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. 可配置属性以下:
                        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. 可配置属性以下:
                        backTo 可退回到的节点范围,能够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"(从新流转). 默认值为track;
                    -->
                    <activiti:turnback backTo="startevent1" returnBy="track" />
                    <!-- 撤销: 退回的反向操做?. 可配置属性以下:
                        gotoBy 前进方式,可选"track"(原路返回),"flow"(从新流转). 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>

流程定义文件扩展以后，扩展的属性如何存储呢？咱们知道在Activiti中ActivitiImpl对象存储的是活动节点的定义，那么咱们便可在流程文件解析时将扩展属性经过setProperty方式存储到 ActivitiImpl对象中。实现过程以下：

• 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，便可经过 activity.getProperty(ExtensionBpmnConstants.PROPERTY_OPERATIONS_DEFINITION);获取扩展的属性值。