Flowable工作流之任务回退

1. 前言

有的时候，一个任务节点会存在多个候选人，例如 zhangsan 提交一个任务，这个任务既可以 lisi 处理，又可以 wangwu 处理，当一个候选人认领任务之后，但是又不想处理任务了，此时我们可以将任务回退，那么针对这种情况，我们该如何处理？今天一起来看看

2. Flowable 中的任务回退

2.1. 串行的回退

2.1.1. 流程图

我们先从最简单的串行流程来分析，案例流程图如下

完整的 xml 文件内容

<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:flowable="http://flowable.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.flowable.org/processdef" exporter="Flowable Open Source Modeler"
             exporterVersion="6.7.2">
    <process id="TaskFallback" name="TaskFallback" isExecutable="true">
        <documentation>flowable中任务的回退documentation>
        <startEvent id="sid-28824261-2B78-4304-A8A5-3C16F52D9797" flowable:formFieldValidation="true">startEvent>
        <userTask id="userTaskId1" name="用户任务1" flowable:assignee="${user1}" flowable:formFieldValidation="true">
            <extensionElements>
                <modeler:initiator-can-complete xmlns:modeler="http://flowable.org/modeler">
                    modeler:initiator-can-complete>
            extensionElements>
        userTask>
        <sequenceFlow id="sid-600A5337-2246-4AD7-A042-0936186F4327" sourceRef="sid-28824261-2B78-4304-A8A5-3C16F52D9797"
                      targetRef="userTaskId1">sequenceFlow>
        <userTask id="userTaskId2" name="用户任务2" flowable:assignee="${user2}" flowable:formFieldValidation="true">
            <extensionElements>
                <modeler:initiator-can-complete xmlns:modeler="http://flowable.org/modeler">
                    modeler:initiator-can-complete>
            extensionElements>
        userTask>
        <sequenceFlow id="sid-A816C5B2-796D-49AB-A5BB-18D3A59809A2" sourceRef="userTaskId1"
                      targetRef="userTaskId2">sequenceFlow>
        <userTask id="userTaskId3" name="用户任务3" flowable:assignee="${user3}" flowable:formFieldValidation="true">
            <extensionElements>
                <modeler:initiator-can-complete xmlns:modeler="http://flowable.org/modeler">
                    modeler:initiator-can-complete>
            extensionElements>
        userTask>
        <sequenceFlow id="sid-A5EE9D1F-5B60-4741-9CBA-3450BCD79851" sourceRef="userTaskId2"
                      targetRef="userTaskId3">sequenceFlow>
        <userTask id="userTaskId4" name="用户任务4" flowable:assignee="${user4}" flowable:formFieldValidation="true">
            <extensionElements>
                <modeler:initiator-can-complete xmlns:modeler="http://flowable.org/modeler">
                    modeler:initiator-can-complete>
            extensionElements>
        userTask>
        <sequenceFlow id="sid-62FCA0CF-0A6F-4A81-BE80-85B251DE7E40" sourceRef="userTaskId3"
                      targetRef="userTaskId4">sequenceFlow>
        <endEvent id="sid-D326808D-3133-4907-84B4-1B6CE14EACF7">endEvent>
        <sequenceFlow id="sid-E025FC2C-2857-4377-9D87-37FCC68C6781" sourceRef="userTaskId4"
                      targetRef="sid-D326808D-3133-4907-84B4-1B6CE14EACF7">sequenceFlow>
    process>
    <bpmndi:BPMNDiagram id="BPMNDiagram_TaskFallback">
        <bpmndi:BPMNPlane bpmnElement="TaskFallback" id="BPMNPlane_TaskFallback">
            <bpmndi:BPMNShape bpmnElement="sid-28824261-2B78-4304-A8A5-3C16F52D9797"
                              id="BPMNShape_sid-28824261-2B78-4304-A8A5-3C16F52D9797">
                <omgdc:Bounds height="30.0" width="30.0" x="38.0" y="108.0">omgdc:Bounds>
            bpmndi:BPMNShape>
            <bpmndi:BPMNShape bpmnElement="userTaskId1" id="BPMNShape_userTaskId1">
                <omgdc:Bounds height="80.0" width="100.0" x="135.0" y="83.0">omgdc:Bounds>
            bpmndi:BPMNShape>
            <bpmndi:BPMNShape bpmnElement="userTaskId2" id="BPMNShape_userTaskId2">
                <omgdc:Bounds height="80.0" width="100.0" x="315.0" y="83.0">omgdc:Bounds>
            bpmndi:BPMNShape>
            <bpmndi:BPMNShape bpmnElement="userTaskId3" id="BPMNShape_userTaskId3">
                <omgdc:Bounds height="80.0" width="100.0" x="495.0" y="83.0">omgdc:Bounds>
            bpmndi:BPMNShape>
            <bpmndi:BPMNShape bpmnElement="userTaskId4" id="BPMNShape_userTaskId4">
                <omgdc:Bounds height="80.0" width="100.0" x="675.0" y="83.0">omgdc:Bounds>
            bpmndi:BPMNShape>
            <bpmndi:BPMNShape bpmnElement="sid-D326808D-3133-4907-84B4-1B6CE14EACF7"
                              id="BPMNShape_sid-D326808D-3133-4907-84B4-1B6CE14EACF7">
                <omgdc:Bounds height="28.0" width="28.0" x="855.0" y="109.0">omgdc:Bounds>
            bpmndi:BPMNShape>
            <bpmndi:BPMNEdge bpmnElement="sid-600A5337-2246-4AD7-A042-0936186F4327"
                             id="BPMNEdge_sid-600A5337-2246-4AD7-A042-0936186F4327" flowable:sourceDockerX="15.0"
                             flowable:sourceDockerY="15.0" flowable:targetDockerX="50.0" flowable:targetDockerY="40.0">
                <omgdi:waypoint x="67.94999895119737" y="123.0">omgdi:waypoint>
                <omgdi:waypoint x="135.0" y="123.0">omgdi:waypoint>
            bpmndi:BPMNEdge
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