第一步：

在pom.xml中添加依赖

<!-- 添加Activiti 依赖 begin-->
        <dependency>  
            <groupId>org.activiti</groupId>  
            <artifactId>activiti-spring-boot-starter-basic</artifactId>  
            <version>5.21.0</version>  
        </dependency>
  <!-- 添加Activiti 依赖 end-->

第二步：

建立流程bpmn文件。
例子如下：（注：流程启动的时候key需与process id相同）

<?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:activiti="http://activiti.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" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:di="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.activiti.org/testm1510735932336" id="m1510735932336" name="">  
  <process id="leave" isExecutable="true" isClosed="false" processType="None">  
    <startEvent id="_2" name="StartEvent"></startEvent>  
    <endEvent id="_3" name="EndEvent"></endEvent>  
    <userTask id="approve" name="经理审批" activiti:assignee="${approve}"></userTask>  
    <exclusiveGateway id="_5" name="ExclusiveGateway"></exclusiveGateway>  
    <sequenceFlow id="_6" sourceRef="approve" targetRef="_5"></sequenceFlow>  
    <sequenceFlow id="_7" name="通过" sourceRef="_5" targetRef="_3">  
      <conditionExpression xsi:type="tFormalExpression"><![CDATA[${pass}]]></conditionExpression>  
    </sequenceFlow>  
    <userTask id="application" name="提交申请" activiti:assignee="${apply}"></userTask>  
    <sequenceFlow id="_9" sourceRef="_2" targetRef="application"></sequenceFlow>  
    <sequenceFlow id="_10" sourceRef="application" targetRef="approve"></sequenceFlow>  
    <userTask id="modify" name="修改申请" activiti:assignee="${apply}"></userTask>  
    <sequenceFlow id="_12" name="不通过" sourceRef="_5" targetRef="modify">  
      <conditionExpression xsi:type="tFormalExpression"><![CDATA[${!pass}]]></conditionExpression>  
    </sequenceFlow>  
    <sequenceFlow id="_13" sourceRef="modify" targetRef="approve"></sequenceFlow>  
  </process>  
  <bpmndi:BPMNDiagram id="BPMNDiagram_leave">  
    <bpmndi:BPMNPlane bpmnElement="leave" id="BPMNPlane_leave">  
      <bpmndi:BPMNShape bpmnElement="_2" id="BPMNShape__2">  
        <omgdc:Bounds height="35.0" width="35.0" x="15.0" y="60.0"></omgdc:Bounds>  
      </bpmndi:BPMNShape>  
      <bpmndi:BPMNShape bpmnElement="_3" id="BPMNShape__3">  
        <omgdc:Bounds height="35.0" width="35.0" x="630.0" y="63.0"></omgdc:Bounds>  
      </bpmndi:BPMNShape>  
      <bpmndi:BPMNShape bpmnElement="approve" id="BPMNShape_approve">  
        <omgdc:Bounds height="55.0" width="85.0" x="315.0" y="50.0"></omgdc:Bounds>  
      </bpmndi:BPMNShape>  
      <bpmndi:BPMNShape bpmnElement="_5" id="BPMNShape__5">  
        <omgdc:Bounds height="40.0" width="40.0" x="505.0" y="60.0"></omgdc:Bounds>  
      </bpmndi:BPMNShape>  
      <bpmndi:BPMNShape bpmnElement="application" id="BPMNShape_application">  
        <omgdc:Bounds height="55.0" width="85.0" x="135.0" y="50.0"></omgdc:Bounds>  
      </bpmndi:BPMNShape>  
      <bpmndi:BPMNShape bpmnElement="modify" id="BPMNShape_modify">  
        <omgdc:Bounds height="55.0" width="85.0" x="315.0" y="150.0"></omgdc:Bounds>  
      </bpmndi:BPMNShape>  
      <bpmndi:BPMNEdge bpmnElement="_6" id="BPMNEdge__6">  
        <omgdi:waypoint x="400.0" y="77.0"></omgdi:waypoint>  
        <omgdi:waypoint x="505.0" y="80.0"></omgdi:waypoint>  
      </bpmndi:BPMNEdge>  
      <bpmndi:BPMNEdge bpmnElement="_7" id="BPMNEdge__7">  
        <omgdi:waypoint x="545.0" y="80.0"></omgdi:waypoint>  
        <omgdi:waypoint x="630.0" y="80.0"></omgdi:waypoint>  
      </bpmndi:BPMNEdge>  
      <bpmndi:BPMNEdge bpmnElement="_9" id="BPMNEdge__9">  
        <omgdi:waypoint x="50.0" y="77.0"></omgdi:waypoint>  
        <omgdi:waypoint x="135.0" y="77.0"></omgdi:waypoint>  
      </bpmndi:BPMNEdge>  
      <bpmndi:BPMNEdge bpmnElement="_10" id="BPMNEdge__10">  
        <omgdi:waypoint x="220.0" y="77.0"></omgdi:waypoint>  
        <omgdi:waypoint x="315.0" y="77.0"></omgdi:waypoint>  
      </bpmndi:BPMNEdge>  
      <bpmndi:BPMNEdge bpmnElement="_12" id="BPMNEdge__12">  
        <omgdi:waypoint x="525.0" y="100.0"></omgdi:waypoint>  
        <omgdi:waypoint x="525.0" y="177.0"></omgdi:waypoint>  
        <omgdi:waypoint x="400.0" y="177.0"></omgdi:waypoint>  
      </bpmndi:BPMNEdge>  
      <bpmndi:BPMNEdge bpmnElement="_13" id="BPMNEdge__13">  
        <omgdi:waypoint x="357.0" y="150.0"></omgdi:waypoint>  
        <omgdi:waypoint x="357.0" y="105.0"></omgdi:waypoint>  
      </bpmndi:BPMNEdge>  
    </bpmndi:BPMNPlane>  
  </bpmndi:BPMNDiagram>  
</definitions>  

第三步：

在配置文件中添加配置。

#activiti
spring.jpa.hibernate.ddl-auto=update
spring.jpa.database=MYSQL

第四步：

启动流程，编写流程各个环节的处理。
示例如下：

public boolean startActivityDemo() {  
        System.out.println("method startActivityDemo begin....");  
        Map<String,Object> map = new HashMap<String,Object>();  
        map.put("apply","zhangsan");  
        map.put("approve","lisi");  
//流程启动  
        ExecutionEntity pi1 = (ExecutionEntity) runtimeService.startProcessInstanceByKey("leave",map);  
        String processId = pi1.getId();  
        String taskId = pi1.getTasks().get(0).getId();  
        taskService.complete(taskId, map);//完成第一步申请  
          
        Task task = taskService.createTaskQuery().processInstanceId(processId).singleResult();  
        String taskId2 = task.getId();  
        map.put("pass", false);  
        taskService.complete(taskId2, map);//驳回申请  
        System.out.println("method startActivityDemo end....");  
        return false;  
    }