=============
后端_线程池化
=============

1 在辅助线程中更新数据库

...
public class ArticleServiceImpl implements ArticleService {
    ...
    @Override
    public Result details(Long articleId) {
        ...
        // 每次显示文章详情，文章阅读数加一
        updateArticleViewCount(articleMapper,
            article.getId(), article.getViewCount());
        ...
    }
    ...
}

- 在这里更新t_article表的view_count字段，势必会延长业务响应时间
- 更好的处理方法是将更新数据库表的操作放到辅助线程中，并立即返回
- 每次派发都要创建全新的辅助线程同样会带来开销，借助池化提高性能

-----------------> 主线程
      派|发
 _______|________
|       |        |
|       v        |
| ----------> 辅 |
| ----------> 助 | 线程池
| ----------> 线 |
| ----------> 程 |
|________________|

2 线程池配置类

/ysdblog-api/src/main/java/com/weihome/ysdblog/config/ThreadPoolConfig.java：

@Configuration
@EnableAsync // 开启多线程
public class ThreadPoolConfig {
    @Bean("taskExecutor")
    public Executor asyncServiceExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        // 核心线程数
        executor.setCorePoolSize(5);
        // 最大线程数
        executor.setMaxPoolSize(20);
        // 队列大小
        executor.setQueueCapacity(Integer.MAX_VALUE);
        // 线程活跃时间(秒)
        executor.setKeepAliveSeconds(60);
        // 线程名称前缀
        executor.setThreadNamePrefix("YSDBLOG");
        // 所有任务结束后关闭线程池
        executor.setWaitForTasksToCompleteOnShutdown(true);
        // 初始化
        executor.initialize();
        return executor;
    }
}

3 线程服务类

/ysdblog-api/src/main/java/com/weihome/ysdblog/service/ThreadService.java：

@Component
public class ThreadService {
    /**
     * 更新文章阅读数
     * 此方法在taskExecutor线程池中执行
     */
    @Async("taskExecutor")
    public void updateArticleViewCount(
        ArticleMapper articleMapper, long id, int viewCount) {
        /*
        try {
            Thread.sleep(10000);
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
        */
        Article article = new Article();
        article.setViewCount(viewCount + 1);
        LambdaUpdateWrapper<Article> updateWrapper =
            new LambdaUpdateWrapper<>();
        updateWrapper.eq(Article::getId, id);
        updateWrapper.eq(Article::getViewCount, viewCount);
        // 只更新非空属性对应的字段
        articleMapper.update(article, updateWrapper);
    }
}

4 文章服务实现

/ysdblog-api/src/main/java/com/weihome/ysdblog/service/impl/ArticleServiceImpl.java：

...
public class ArticleServiceImpl implements ArticleService {
    ...
    @Autowired
    private ThreadService threadService;
    ...
    @Override
    public Result details(Long articleId) {
        ...
        // 每次显示文章详情，文章阅读数加一
        threadService.updateArticleViewCount(articleMapper,
            article.getId(), article.getViewCount());
        ...
    }
    ...
}

5 运行测试

Postman
    GET
        localhost:8888/article/details/1
----------------------------------------
{
    "success": true,
    "code": 200,
    "msg": "success",
    "data": {
        "id": 1,
        "commentCount": 1,
        "createDate": "2022-01-01 13:22:59",
        "summary": "summary_a",
        "title": "title_a",
        "viewCount": 2,
        "weight": 1,
        "author": "nickname_a",
        "content": {
            "content": "content_a"
        },
        "category": {
            "id": 1,
            "avatar": "category_a.png",
            "categoryName": "category_a"
        },
        "tags": [
            {
                "id": 1,
                "tagName": "tag_a"
            }
        ]
    }
}

检查数据库中t_article表特定文章记录的view_count字段。

增加睡眠延时检验线程池效果。