Java 工作流框架的前世今生，我从《activiti与flowable的区别》这篇文章了解到flowable是基于activiti发展而来的，官方文档中有段话：

也证明了flowable是fork自activiti

《flowable对比》这篇文章对比了业内流行框架以及它们往后的发展历程。

Activiti

快速入门

我参考了这篇文章《Spring Boot Activiti 整合工作流引擎开发》，指导你如何配置 ProcessEngineConfiguration 以及八大接口

深入

Flowable

Flowable 项目中包括 BPMN（Business Process Model and Notation）引擎、CMMN（Case Management Model and Notation）引擎、DMN（Decision Model and Notation）引擎、表单引擎（Form Engine）

资源

github:https://github.com/flowable/flowable-engine
BPMN Get Started: https://flowable.com/open-source/docs/bpmn/ch02-GettingStarted/ (重要）
Flowable BPMN 用户手册（对应上面的中文版）：https://tkjohn.github.io/flowable-userguide/#_introducti
一文看懂开源工作流引擎 Flowable：对一些概念性的东西讲解得比较深入

Get Started

创建流程引擎

引入pom.xml

<dependencies>
  <dependency>
    <groupId>org.flowable</groupId>
    <artifactId>flowable-engine</artifactId>
    <version>6.5.0.event-SNAPSHOT</version>
  </dependency>
  <dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>1.3.176</version>
  </dependency>
</dependencies>

创建 ProcessEngine

package org.flowable;
import org.flowable.engine.ProcessEngine;
import org.flowable.engine.ProcessEngineConfiguration;
import org.flowable.engine.impl.cfg.StandaloneProcessEngineConfiguration;
public class HolidayRequest {
  public static void main(String[] args) {
    ProcessEngineConfiguration cfg = new StandaloneProcessEngineConfiguration()
      .setJdbcUrl("jdbc:h2:mem:flowable;DB_CLOSE_DELAY=-1")
      .setJdbcUsername("sa")
      .setJdbcPassword("")
      .setJdbcDriver("org.h2.Driver")
      .setDatabaseSchemaUpdate(ProcessEngineConfiguration.DB_SCHEMA_UPDATE_TRUE);
    ProcessEngine processEngine = cfg.buildProcessEngine();
  }
}

ProcessEngine 是一个线程安全的对象，所以只需创建一次就好。

This is a thread-safe object that you typically have to instantiate only once in an application.

加入日志(不是必须的）

<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>slf4j-api</artifactId>
  <version>1.7.21</version>
</dependency>
<dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>slf4j-log4j12</artifactId>
  <version>1.7.21</version>
</dependency>

log4j.properties

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

定义流程

如上图所示的流程图，在flowable中实际上是以xml格式存储的。（实际工作中，画此流程图应当使用Flowable Modeler）

下面的holiday-request.bpmn20.xml 是具体内容,holiday-request.bpmn20.xml需要放在src/main/resources文件夹下

<?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"/>
    <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"/>
    <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>

具体标签的含义请参考官方文档

开启流程实例

Scanner scanner= new Scanner(System.in);

System.out.println("Who are you?");
String employee = scanner.nextLine();

System.out.println("How many holidays do you want to request?");
Integer nrOfHolidays = Integer.valueOf(scanner.nextLine());

System.out.println("Why do you need them?");
String description = scanner.nextLine();

RuntimeService runtimeService = processEngine.getRuntimeService();

Map<String, Object> variables = new HashMap<String, Object>();
variables.put("employee", employee);
variables.put("nrOfHolidays", nrOfHolidays);
variables.put("description", description);
ProcessInstance processInstance =
  runtimeService.startProcessInstanceByKey("holidayRequest", variables);

注意 key: holidayRequest 是和xml中的process id一致的。

Java通用

工作流入门