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service：让程序更健壮和可维护

1、实现PostService

grails create-service com.grailsinaction.post

 1 package com.grailsinaction
 2 
 3 class PostService {
 4     /*如果发生错误，数据库回滚*/
 5     boolean transactional = true
 6 
 7     Post createPost(String userId, String content) {
 8         def user = User.findByUserId(userId)
 9         if (user) {
10             def post = new Post(content: content)
11             user.addToPosts(post)
12             if (user.save()) {
13                 return post
14             } else {
15                 throw new PostException(message: "Invalid or empty post", post: post)
16             }
17         }
18         throw new PostException(message: "Invalid User Id")
19     }
20 }
21 
22 class PostException extends RuntimeException {
23     String message
24     Post post
25 }

2、修改PostController，引入PostService，改写addPost闭包

 1 package com.grailsinaction
 2 
 3 class PostController {
 4     
 5     def postService
 6 
 7 ......
 8     
 9     def addPost = {
10         try {
11             def newPost = postService.createPost(params.id,    params.content)
12             flash.message = "Added new post: ${newPost.content}"
13         } catch (PostException pe) {
14             flash.message = pe.message
15         }
16         redirect(action: 'timeline', id: params.id)
17     }
18 }