轻量级工作流引擎的设计与实现

一、什么是工作流引擎

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二、为什么要重复造轮子

开源的工作流引擎很多，比如 activiti、flowable、Camunda 等，那么，为什么没有选它们呢？基于以下几点考虑：

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* 资料、代码量、API繁多，学习成本较高，维护性较差。
* 经过分析与评估，我们的业务场景需要的BPMN元素较少，开发实现的代价不大。

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三、怎么造的轮子

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• 少依赖：代码的java实现上，除了jdk8以外，不依赖与其他第三方jar包，从而可以更好的减少依赖带来的问题。
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  [En]

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• 轻规范：并没有完全实现BPMN规范，也没有完全按照BPMN规范进行设计，而只是参考了该规范，且只实现以一小部分必须实现的元素。从而降低了学习成本，可以按照需求自由发挥。
• 工具化：代码上，只是一个工具(UTIL)，不是一个应用程序。从而你可以简单的运行它，扩展你自己的数据层、节点层，更加方便的集成到其他应用中去。

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四、Hello ProcessEngine

按照国际惯例，第一个迭代用来实现 hello world 。

1、需求

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2、分析

• 第一个流程，可以打印Hello ProcessEngine，第二个流程可以打印ProcessEngine Hello，这两个流程的区别是只有顺序不同，蓝色的节点与红色的节点的本身功能没有发生变化
• 蓝色的节点与红色的节点都是节点，它们的功能是不一样的，即：红色的节点打印Hello,蓝色的节点打印ProcessEngine
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  [En]

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  [En]

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• 需要一种表示流程的方式，或是XML、或是JSON、或是其他，而不是图片

3、设计

（1）流程的表示

相较于JSON，XML的语义更丰富，可以表达更多的信息，因此这里使用XML来对流程进行表示，如下所示

<span class="hljs-tag"><<span class="hljs-name">definitions>
    <span class="hljs-tag"><<span class="hljs-name">process <span class="hljs-attr">id=<span class="hljs-string">"process_1" <span class="hljs-attr">name=<span class="hljs-string">"hello">
        <span class="hljs-tag"><<span class="hljs-name">startEvent <span class="hljs-attr">id=<span class="hljs-string">"startEvent_1">
            <span class="hljs-tag"><<span class="hljs-name">outgoing>flow_1<span class="hljs-tag">outgoing>
        <span class="hljs-tag">startEvent>
        <span class="hljs-tag"><<span class="hljs-name">sequenceFlow <span class="hljs-attr">id=<span class="hljs-string">"flow_1" <span class="hljs-attr">sourceRef=<span class="hljs-string">"startEvent_1" <span class="hljs-attr">targetRef=<span class="hljs-string">"printHello_1" />
        <span class="hljs-tag"><<span class="hljs-name">printHello <span class="hljs-attr">id=<span class="hljs-string">"printHello_1" <span class="hljs-attr">name=<span class="hljs-string">"hello">
            <span class="hljs-tag"><<span class="hljs-name">incoming>flow_1<span class="hljs-tag">incoming>
            <span class="hljs-tag"><<span class="hljs-name">outgoing>flow_2<span class="hljs-tag">outgoing>
        <span class="hljs-tag">printHello>
        <span class="hljs-tag"><<span class="hljs-name">sequenceFlow <span class="hljs-attr">id=<span class="hljs-string">"flow_2" <span class="hljs-attr">sourceRef=<span class="hljs-string">"printHello_1" <span class="hljs-attr">targetRef=<span class="hljs-string">"printProcessEngine_1" />
        <span class="hljs-tag"><<span class="hljs-name">printProcessEngine <span class="hljs-attr">id=<span class="hljs-string">"printProcessEngine_1" <span class="hljs-attr">name=<span class="hljs-string">"processEngine">
            <span class="hljs-tag"><<span class="hljs-name">incoming>flow_2<span class="hljs-tag">incoming>
            <span class="hljs-tag"><<span class="hljs-name">outgoing>flow_3<span class="hljs-tag">outgoing>
        <span class="hljs-tag">printProcessEngine>
        <span class="hljs-tag"><<span class="hljs-name">sequenceFlow <span class="hljs-attr">id=<span class="hljs-string">"flow_3" <span class="hljs-attr">sourceRef=<span class="hljs-string">"printProcessEngine_1" <span class="hljs-attr">targetRef=<span class="hljs-string">"endEvent_1"/>
        <span class="hljs-tag"><<span class="hljs-name">endEvent <span class="hljs-attr">id=<span class="hljs-string">"endEvent_1">
            <span class="hljs-tag"><<span class="hljs-name">incoming>flow_3<span class="hljs-tag">incoming>
        <span class="hljs-tag">endEvent>
    <span class="hljs-tag">process>
<span class="hljs-tag">definitions></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

• process表示一个流程
• startEvent表示开始节点，endEvent表示结束节点
• printHello表示打印hello节点，就是需求中的蓝色节点
• processEngine表示打印processEngine节点，就是需求中的红色节点
• sequenceFlow表示连线，从sourceRef开始，指向targetRef，例如：flow_3，表示一条从printProcessEngine_1到endEvent_1的连线。

（2）节点的表示

• outgoing表示出边，即节点执行完毕后，应该从那个边出去。
• incoming表示入边，即从哪个边进入到本节点。
• 一个节点只有outgoing而没有incoming，如：startEvent，也可以 只有入边而没有出边，如：endEvent，也可以既有入边也有出边，如：printHello、processEngine。

（3）流程引擎的逻辑

基于上述XML，流程引擎的运行逻辑如下

1. 找到开始节点(startEvent)
2. 找到startEvent的outgoing边(sequenceFlow)
3. 找到该边(sequenceFlow)指向的节点(targetRef)
4. 执行节点自身的逻辑
5. 找到该节点的outgoing边(sequenceFlow)
6. 重复3-5，直到遇到结束节点(endEvent)，流程结束

4、实现

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可以看到，一个流程(PeProcess)由多个节点(PeNode)与边(PeEdge)组成，节点有出边(out)、入边(in)，边有流入节点(from)、流出节点(to)。

具体的定义如下：

<span class="hljs-keyword">public <span class="hljs-keyword">class PeProcess {
    <span class="hljs-keyword">public <span class="hljs-built_in">String id;
    <span class="hljs-keyword">public PeNode start;

    <span class="hljs-keyword">public PeProcess(<span class="hljs-built_in">String id, PeNode start) {
        <span class="hljs-keyword">this.id = id;
        <span class="hljs-keyword">this.start = start;
    }
}

<span class="hljs-keyword">public <span class="hljs-keyword">class PeEdge {
    <span class="hljs-keyword">private <span class="hljs-built_in">String id;
    <span class="hljs-keyword">public PeNode <span class="hljs-keyword">from;
    <span class="hljs-keyword">public PeNode to;

    <span class="hljs-keyword">public PeEdge(<span class="hljs-built_in">String id) {
        <span class="hljs-keyword">this.id = id;
    }
}

<span class="hljs-keyword">public <span class="hljs-keyword">class PeNode {
    <span class="hljs-keyword">private <span class="hljs-built_in">String id;

    <span class="hljs-keyword">public <span class="hljs-built_in">String <span class="hljs-keyword">type;
    <span class="hljs-keyword">public PeEdge <span class="hljs-keyword">in;
    <span class="hljs-keyword">public PeEdge out;

    <span class="hljs-keyword">public PeNode(<span class="hljs-built_in">String id) {
        <span class="hljs-keyword">this.id=id;
    }
}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

PS : 为了表述主要思想，在代码上比较”奔放自由”，生产中不可直接复制粘贴！

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:89489d1c-de6d-4cbb-941a-9793463bd955

<span class="hljs-keyword">public <span class="hljs-keyword">class <span class="hljs-title">XmlPeProcessBuilder {
    <span class="hljs-keyword">private String xmlStr;
    <span class="hljs-keyword">private final Map<string, penode> id2PeNode = <span class="hljs-keyword">new HashMap<>();
    <span class="hljs-keyword">private final Map<string, peedge> id2PeEdge = <span class="hljs-keyword">new HashMap<>();

    <span class="hljs-function"><span class="hljs-keyword">public <span class="hljs-title">XmlPeProcessBuilder(<span class="hljs-params">String xmlStr) {
        <span class="hljs-keyword">this.xmlStr = xmlStr;
    }

    <span class="hljs-function"><span class="hljs-keyword">public PeProcess <span class="hljs-title">build(<span class="hljs-params">) throws Exception {
        </span></span></span></span></span></span></span></span></span></span></string,></span></span></string,></span></span></span></span></span>

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:ed8b94ac-4a77-4e9d-8a7b-e24c4307fccf

<span class="hljs-keyword">public <span class="hljs-keyword">class <span class="hljs-title">ProcessEngine {
    <span class="hljs-keyword">private String xmlStr;

    <span class="hljs-function"><span class="hljs-keyword">public <span class="hljs-title">ProcessEngine(<span class="hljs-params">String xmlStr) {
        <span class="hljs-keyword">this.xmlStr = xmlStr;
    }

    <span class="hljs-function"><span class="hljs-keyword">public <span class="hljs-keyword">void <span class="hljs-title">run(<span class="hljs-params">) throws Exception {
        PeProcess peProcess = <span class="hljs-keyword">new XmlPeProcessBuilder(xmlStr).build();

        PeNode node = peProcess.start;
        <span class="hljs-keyword">while (!node.type.<span class="hljs-keyword">equals(<span class="hljs-string">"endEvent")) {
            <span class="hljs-keyword">if (<span class="hljs-string">"printHello".<span class="hljs-keyword">equals(node.type))
                System.<span class="hljs-keyword">out.print(<span class="hljs-string">"Hello ");
            <span class="hljs-keyword">if (<span class="hljs-string">"printProcessEngine".<span class="hljs-keyword">equals(node.type))
                System.<span class="hljs-keyword">out.print(<span class="hljs-string">"ProcessEngine ");

            node = node.<span class="hljs-keyword">out.to;
        }
    }
}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

就这？工作流引擎就这？同学们可千万不要这样简单理解啊，毕竟这还只是hello world而已，各种代码量就已经不少了。

另外，这里面还有很多可以改进的空间，比如异常控制、泛化、设计模式等，但毕竟只是一个hello world而已，其目的是方便同学理解，让同学入门。

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:28cbf83a-1e6d-4fdb-b7a2-cb7cad509789

五、简单审批

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1、需求

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[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:f58b789c-39e3-40e8-9431-1b0b9517fb10

2、分析

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:254818ba-c424-4045-8497-fbb4c5965c51

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:342cde92-22eb-48cf-9df2-d56a49b7b935

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:584df568-794d-4821-ae89-a9d6f4a0a311

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:7260c082-4690-4e61-ae90-f5f6730e2b31

3、设计

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[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:a121600a-ba65-43de-b7e2-900d00bcb0b8

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:972f747e-2b90-4b3d-a03a-1a5c618f5579

4、实现

新的XML定义如下：

<span class="hljs-tag"><<span class="hljs-name">definitions>
    <span class="hljs-tag"><<span class="hljs-name">process <span class="hljs-attr">id=<span class="hljs-string">"process_2" <span class="hljs-attr">name=<span class="hljs-string">"&#x7B80;&#x5355;&#x5BA1;&#x6279;&#x4F8B;&#x5B50;">
        <span class="hljs-tag"><<span class="hljs-name">startEvent <span class="hljs-attr">id=<span class="hljs-string">"startEvent_1">
            <span class="hljs-tag"><<span class="hljs-name">outgoing>flow_1<span class="hljs-tag">outgoing>
        <span class="hljs-tag">startEvent>
        <span class="hljs-tag"><<span class="hljs-name">sequenceFlow <span class="hljs-attr">id=<span class="hljs-string">"flow_1" <span class="hljs-attr">sourceRef=<span class="hljs-string">"startEvent_1" <span class="hljs-attr">targetRef=<span class="hljs-string">"approvalApply_1" />
        <span class="hljs-tag"><<span class="hljs-name">approvalApply <span class="hljs-attr">id=<span class="hljs-string">"approvalApply_1" <span class="hljs-attr">name=<span class="hljs-string">"&#x63D0;&#x4EA4;&#x7533;&#x8BF7;&#x5355;">
            <span class="hljs-tag"><<span class="hljs-name">incoming>flow_1<span class="hljs-tag">incoming>
            <span class="hljs-tag"><<span class="hljs-name">outgoing>flow_2<span class="hljs-tag">outgoing>
        <span class="hljs-tag">approvalApply>
        <span class="hljs-tag"><<span class="hljs-name">sequenceFlow <span class="hljs-attr">id=<span class="hljs-string">"flow_2" <span class="hljs-attr">sourceRef=<span class="hljs-string">"approvalApply_1" <span class="hljs-attr">targetRef=<span class="hljs-string">"approval_1" />
        <span class="hljs-tag"><<span class="hljs-name">approval <span class="hljs-attr">id=<span class="hljs-string">"approval_1" <span class="hljs-attr">name=<span class="hljs-string">"&#x5BA1;&#x6279;">
            <span class="hljs-tag"><<span class="hljs-name">incoming>flow_2<span class="hljs-tag">incoming>
            <span class="hljs-tag"><<span class="hljs-name">outgoing>flow_3<span class="hljs-tag">outgoing>
        <span class="hljs-tag">approval>
        <span class="hljs-tag"><<span class="hljs-name">sequenceFlow <span class="hljs-attr">id=<span class="hljs-string">"flow_3" <span class="hljs-attr">sourceRef=<span class="hljs-string">"approval_1" <span class="hljs-attr">targetRef=<span class="hljs-string">"notify_1"/>
        <span class="hljs-tag"><<span class="hljs-name">notify <span class="hljs-attr">id=<span class="hljs-string">"notify_1" <span class="hljs-attr">name=<span class="hljs-string">"&#x7ED3;&#x679C;&#x90AE;&#x4EF6;&#x901A;&#x77E5;">
            <span class="hljs-tag"><<span class="hljs-name">incoming>flow_3<span class="hljs-tag">incoming>
            <span class="hljs-tag"><<span class="hljs-name">outgoing>flow_4<span class="hljs-tag">outgoing>
        <span class="hljs-tag">notify>
        <span class="hljs-tag"><<span class="hljs-name">sequenceFlow <span class="hljs-attr">id=<span class="hljs-string">"flow_4" <span class="hljs-attr">sourceRef=<span class="hljs-string">"notify_1" <span class="hljs-attr">targetRef=<span class="hljs-string">"endEvent_1"/>
        <span class="hljs-tag"><<span class="hljs-name">endEvent <span class="hljs-attr">id=<span class="hljs-string">"endEvent_1">
            <span class="hljs-tag"><<span class="hljs-name">incoming>flow_4<span class="hljs-tag">incoming>
        <span class="hljs-tag">endEvent>
    <span class="hljs-tag">process>
<span class="hljs-tag">definitions></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:45004816-e26f-4d7a-b17b-543d4aae68e1

<span class="hljs-keyword">public <span class="hljs-keyword">class <span class="hljs-title">PeContext {
    <span class="hljs-keyword">private Map<string, object> info = <span class="hljs-keyword">new ConcurrentHashMap<>();

    <span class="hljs-function"><span class="hljs-keyword">public Object <span class="hljs-title">getValue(<span class="hljs-params">String key) {
        <span class="hljs-keyword">return info.<span class="hljs-keyword">get(key);
    }

    <span class="hljs-function"><span class="hljs-keyword">public <span class="hljs-keyword">void <span class="hljs-title">putValue(<span class="hljs-params">String key, Object <span class="hljs-keyword">value) {
        info.put(key, <span class="hljs-keyword">value);
    }
}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></string,></span></span></span></span>

每个节点的处理逻辑是不一样的，此处应该进行一定的抽象，为了强调流程中节点的作用是逻辑处理，引入了一种新的类型–算子(Operator)，定义如下：

<span class="hljs-keyword">public <span class="hljs-keyword">interface <span class="hljs-title">IOperator {
    </span></span></span>

对于引擎来讲，当遇到一个节点时，需要调度之，但怎么调度呢？首先需要各个节点算子注册(registNodeProcessor())进来，这样才能找到要调度的那个算子。

其次，引擎怎么知道节点算子自有逻辑处理完了呢？一般来讲，引擎是不知道的，只能是由算子告诉引擎，所以引擎要提供一个功能(nodeFinished())，这个功能由算子调用。

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:508566b6-0ae8-4883-922f-7ccb56f4d24f

修改后的ProcessEngine代码如下：

<span class="hljs-keyword">public <span class="hljs-keyword">class <span class="hljs-title">ProcessEngine {
    <span class="hljs-keyword">private String xmlStr;

    </span></span></span></span>

接下来，简单(简陋)实现本示例所需的三个算子，代码如下：

[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:7218ecda-4480-4e25-8c36-7007627728eb

<span class="hljs-keyword">public <span class="hljs-class"><span class="hljs-keyword">class <span class="hljs-title">ProcessEngineTest {

    </span></span></span></span>

到此，轻量级工作流引擎的核心逻辑介绍的差不多了，然而，只支持顺序结构是太单薄的，我们知道，程序流程的三种基本结构为顺序、分支、循环，有了这三种结构，基本上就可以表示绝大多数流程逻辑。循环可以看做一种组合结构，即：循环可以由顺序与分支推导出来，我们已经实现了顺序，那么接下来只要实现分支即可，而分支有很多类型，如：二选一、N选一、N选M(1

Original: https://www.cnblogs.com/Jcloud/p/16730261.html
Author: 京东云开发者
Title: 轻量级工作流引擎的设计与实现