Flowable BPMN2.0 Workflow Engine Tutorial: From Basics to Practical Implementation

1. Introduction to Workflow

Workflow abstracts business steps and rules into a model that can be executed by a computer, reducing complex code logic for approval processes.

1.1 Why Use Workflow

Traditional field‑based state handling becomes cumbersome for multi‑stage approvals; a workflow engine decouples business logic from implementation.

1.2 What Is a Workflow

A workflow is a generalized state machine that models business processes using a dedicated language such as BPMN.

2. BPMN 2.0 Specification

BPMN 2.0 provides a standard, human‑readable and machine‑parsable notation for modeling processes.

2.2 BPMN Elements

Gateways : Exclusive, Parallel, Inclusive – control flow branching.

Tasks : User Task, Service Task, Receive Task, Call Activity – represent work units.

3. Flowable Overview

Flowable is a lightweight Java implementation of the BPMN 2.0 engine, capable of embedding in Spring Boot applications or running as a standalone server.

3.2 Flowable vs. Activiti

Flowable forks from Activiti‑6.0.0.Beta4 and fixes many bugs, allowing zero‑cost migration.

4. Practical Flowable Project

Steps to build an employee leave request workflow:

Create a flowable-ui Spring Boot project to design the process diagram.

Export the diagram as an XML file and place it under resources/processes in a second Spring Boot project.

Configure application.yml (server port, datasource, Flowable settings).

Include required Maven dependencies (spring‑boot‑starter, flowable‑spring‑boot‑starter‑ui‑idm, modeler, JPA, MySQL).

Key XML snippets:

<process id="leave" name="Company Employee Leave Process" isExecutable="true">
  <startEvent id="startEvent1" name="Start"/>
  <userTask id="apply" name="Leave Application" flowable:assignee="${studentUser}"/>
  <userTask id="teacherPass" name="Leader Approval" flowable:candidateGroups="a"/>
  <exclusiveGateway id="judgeTask" name="Is >2 days?"/>
  <userTask id="principalPass" name="Boss Approval" flowable:candidateGroups="b"/>
  <endEvent id="end" name="End"/>
  ...
</process>

Sample Java test code (SpringBootTest) demonstrates how to start a process, query tasks, complete approvals, and retrieve historic activity data:

@SpringBootTest
class JavaSkillPointApplicationTests {
    @Autowired RuntimeService runtimeService;
    @Autowired TaskService taskService;
    @Autowired HistoryService historyService;

    @Test
    void startLeave() {
        Map
vars = new HashMap<>();
        vars.put("day",5);
        vars.put("studentUser","XiaoMing");
        ProcessInstance pi = runtimeService.startProcessInstanceByKey("leave",vars);
        Task task = taskService.createTaskQuery().processInstanceId(pi.getId()).singleResult();
        taskService.complete(task.getId());
    }
    // Additional tests for leader, boss approvals and history queries
}

4.4 Flowable Database Tables

Flowable tables are prefixed with ACT_ and grouped by purpose:

ACT_RE_* – repository (static definitions, resources).

ACT_RU_* – runtime (variables, active tasks, jobs).

ACT_HI_* – history (completed instances, tasks).

ACT_ID_* – identity (users, groups).

ACT_GE_* – generic data.

Diagrams of the table structures are provided in the original article.

The article concludes with a reminder that the content is intended for technical discussion and not for advertising.