activiti除了可以通过流程设计器画流程图之外，其实也可以通过代码生成流程图。
activiti的流程图核心对象就是BpmnModel，只要生成了这个BpmnModel对象，流程图就OK了。
示例代码如下：

//创建bpmn模型
  BpmnModel model = new BpmnModel();
  Process process = new Process();
  model.addProcess(process);
  process.setId("my-process");


//创建bpmn元素
  process.addFlowElement(createStartEvent());
  process.addFlowElement(createUserTask("task1", "First task", "fred"));
  process.addFlowElement(createUserTask("task2", "Second task", "john"));
  process.addFlowElement(createEndEvent());


  process.addFlowElement(createSequenceFlow("start", "task1"));
  process.addFlowElement(createSequenceFlow("task1", "task2"));
  process.addFlowElement(createSequenceFlow("task2", "end"));


  // 2.生成BPMN自动布局
  new BpmnAutoLayout(model).execute();
  
  创建task
protected UserTask createUserTask(String id, String name, String assignee) {
  UserTask userTask = new UserTask();
  userTask.setName(name);
  userTask.setId(id);
  userTask.setAssignee(assignee);
  return userTask;
}


//创建箭头
protected SequenceFlow createSequenceFlow(String from, String to) {
  SequenceFlow flow = new SequenceFlow();
  flow.setSourceRef(from);
  flow.setTargetRef(to);
  return flow;
}


protected StartEvent createStartEvent() {
  StartEvent startEvent = new StartEvent();
  startEvent.setId("start");
  return startEvent;
}


protected EndEvent createEndEvent() {
  EndEvent endEvent = new EndEvent();
  endEvent.setId("end");
  return endEvent;
}

上面的代码是上网找的，代码生成流程图其实最麻烦的就是节点的定位问题。
而代码new BpmnAutoLayout(model).execute();就帮我们自动布局了，这样只要生成想要的节点就可以生成bpmn对象了.