構建一個Flowable命令列應用

官網連結

[(https://flowable.com/open-source/docs/bpmn/ch02-GettingStarted/#building-a-command-line-application)]

簡介

Flowable是Activity5.0的一個分支，本身是用kava開發的一個業務流程引擎，可以用來部署BPMN2.0標準流程定義。

案例

• 員工(employee)發出請假的請求
• 管理者(manager)同意或拒絕請假請求
• 我們會模擬把請求註冊到外部的系統，傳送郵件來通知流程的結果
  
  其中，左邊的圈圈是一個開始事件（start event），第一個長方形是使用者任務（user task），中間的菱形是一個排他閘道器（exclusive gateway），對應的xml檔案holiday-request.bpmn20.xml放在
  src/main/resources目錄下。

<?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:xsd="http://www.w3.org/2001/XMLSchema"
             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"
             xmlns:flowable="http://flowable.org/bpmn"
             typeLanguage="http://www.w3.org/2001/XMLSchema"
             expressionLanguage="http://www.w3.org/1999/XPath"
             targetNamespace="http://www.flowable.org/processdef">

    <process id="holidayRequest" name="Holiday Request" isExecutable="true">

        <startEvent id="startEvent"/>
        <sequenceFlow sourceRef="startEvent" targetRef="approveTask"/>

        <userTask id="approveTask" name="Approve or reject request" flowable:candidateGroups="managers"/>
        <sequenceFlow sourceRef="approveTask" targetRef="decision"/>

        <exclusiveGateway id="decision"/>
        <sequenceFlow sourceRef="decision" targetRef="externalSystemCall">
            <conditionExpression xsi:type="tFormalExpression">
                <![CDATA[
          ${approved}
        ]]>
            </conditionExpression>
        </sequenceFlow>
        <sequenceFlow  sourceRef="decision" targetRef="sendRejectionMail">
            <conditionExpression xsi:type="tFormalExpression">
                <![CDATA[
          ${!approved}
        ]]>
            </conditionExpression>
        </sequenceFlow>

        <serviceTask id="externalSystemCall" name="Enter holidays in external system"
                     flowable:class="org.flowable.CallExternalSystemDelegate"/>
        <sequenceFlow sourceRef="externalSystemCall" targetRef="holidayApprovedTask"/>

        <userTask id="holidayApprovedTask" name="Holiday approved" flowable:assignee="${employee}"/>
        <sequenceFlow sourceRef="holidayApprovedTask" targetRef="approveEnd"/>

        <serviceTask id="sendRejectionMail" name="Send out rejection email"
                     flowable:class="org.flowable.SendRejectionMail"/>
        <sequenceFlow sourceRef="sendRejectionMail" targetRef="rejectEnd"/>

        <endEvent id="approveEnd"/>

        <endEvent id="rejectEnd"/>

    </process>

</definitions>

java專案中的配置

pom檔案

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.happen</groupId>
    <artifactId>holidayrequest</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.flowable</groupId>
            <artifactId>flowable-engine</artifactId>
            <version>6.6.0</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.21</version>
        </dependency>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.30</version>
        </dependency>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.30</version>
        </dependency>

    </dependencies>


    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

</project>

flowable使用了log4j作為debug工具，需要在resources資料夾下配置log4j.properties檔案

log4j.rootLogger=DEBUG, CA

log4j.appender.CA=org.apache.log4j.ConsoleAppender
log4j.appender.CA.layout=org.apache.log4j.PatternLayout
log4j.appender.CA.layout.ConversionPattern= %d{hh:mm:ss,SSS} [%t] %-5p %c %x - %m%n

主函式在HolidayRequest類下

import org.flowable.engine.*;
import org.flowable.engine.history.HistoricActivityInstance;
import org.flowable.engine.impl.cfg.StandaloneProcessEngineConfiguration;
import org.flowable.engine.repository.Deployment;
import org.flowable.engine.repository.ProcessDefinition;
import org.flowable.engine.runtime.ProcessInstance;
import org.flowable.task.api.Task;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;

public class HolidayRequest {
    public static void main(String[] args) {

        // 配置一個StandaloneProcessEngine，連線資料庫
        ProcessEngineConfiguration cfg = new StandaloneProcessEngineConfiguration()
                .setJdbcUrl("jdbc:mysql://localhost:3306/holiday_request?useUnicode=true&characterEncoding=utf8&autoReconnect=true&serverTimezone=GMT%2B8")
                .setJdbcUsername("root")
                .setJdbcPassword("WHP199617whp")
                .setJdbcDriver("com.mysql.cj.jdbc.Driver")
                // 資料表不存在的時候，自動生成
                .setDatabaseSchemaUpdate(ProcessEngineConfiguration.DB_SCHEMA_UPDATE_TRUE);

        // 工作引擎
        ProcessEngine processEngine = cfg.buildProcessEngine();

        // 讀取一個工作流並部署
        RepositoryService repositoryService = processEngine.getRepositoryService();
        Deployment deployment = repositoryService.createDeployment()
                .addClasspathResource("holiday-request.bpmn20.xml")
                .deploy();

        // 建立一個查詢，嘗試讀取工作流的名字
        ProcessDefinition processDefinition = repositoryService.createProcessDefinitionQuery()
                .deploymentId(deployment.getId())
                .singleResult();
        System.out.println("Found process definition : " + processDefinition.getName());


        // 提交一個流程
        RuntimeService runtimeService = processEngine.getRuntimeService();

        Map<String, Object> variables = new HashMap<String, Object>();
        variables.put("employee", "happen");
        variables.put("nrOfHolidays", 12);
        variables.put("description", "go home");

        // 使用key開啟一個流程
        ProcessInstance processInstance =
                runtimeService.startProcessInstanceByKey("holidayRequest", variables);


        // manager查詢過程
        TaskService taskService = processEngine.getTaskService();
        List<Task> tasks = taskService.createTaskQuery().taskCandidateGroup("managers").list();
        System.out.println("You have " + tasks.size() + " tasks:");
        for (int i=0; i<tasks.size(); i++) {
            System.out.println((i+1) + ") " + tasks.get(i).getName());
        }

        Scanner scanner= new Scanner(System.in);
        // manager處理請求
        System.out.println("Which task would you like to complete?");
        int taskIndex = Integer.valueOf(scanner.nextLine());
        Task task = tasks.get(taskIndex - 1);
        Map<String, Object> processVariables = taskService.getVariables(task.getId());
        System.out.println(processVariables.get("employee") + " wants " +
                processVariables.get("nrOfHolidays") + " of holidays. Do you approve this?");

        boolean approved = scanner.nextLine().toLowerCase().equals("y");
        variables = new HashMap<String, Object>();
        variables.put("approved", approved);
        taskService.complete(task.getId(), variables);


        HistoryService historyService = processEngine.getHistoryService();
        List<HistoricActivityInstance> activities =
                historyService.createHistoricActivityInstanceQuery()
                        .processInstanceId(processInstance.getId())
                        .finished()
                        .orderByHistoricActivityInstanceEndTime().asc()
                        .list();

        for (HistoricActivityInstance activity : activities) {
            System.out.println(activity.getActivityId() + " took "
                    + activity.getDurationInMillis() + " milliseconds");
        }
    }
}

其中，manager如果批准，在xml流程中的表述如下：

<serviceTask id="externalSystemCall" name="Enter holidays in external system"
             flowable:class="org.flowable.CallExternalSystemDelegate"/>
<sequenceFlow sourceRef="externalSystemCall" targetRef="holidayApprovedTask"/>

其中的org.flowable.CallExternalSystemDelegate類需要我們自己編寫，這是需要執行的步驟，我們簡單的列印下：

package org.flowable;

import org.flowable.engine.delegate.DelegateExecution;
import org.flowable.engine.delegate.JavaDelegate;

public class CallExternalSystemDelegate implements JavaDelegate {

    public void execute(DelegateExecution execution) {
        System.out.println("Calling the external system for employee "
                + execution.getVariable("employee"));
    }

}

最終的專案結構如下：

執行結果（與官網不同，做了些修改）

結論

一個flowable工作流首先需要一個標準的BPMN2.0檔案，檔案中需要指明每個process、startEvent、userTask、exclusiveGateway等的id，並通過sequenceFlow指明流向，需要儲存的變數可以為${approved}的形式，如果需要具體執行什麼任務，通過serviceTask標籤的flowable:class類指明呼叫的類實現功能，比如發郵件、http請求等。在命令列應用中使用時，首先需要一個StandaloneProcessEngineConfiguration例項配置連線的資料庫，然後生成對應的引擎ProcessEngine，之後使用對應的service執行具體的任務。