Spring Boot 入门（十）：集成Redis哨兵模式，实现Mybatis二级缓存

本片文章续《Spring Boot 入门（九）：集成Quartz定时任务》。本文主要基于redis实现了mybatis二级缓存。较redis缓存，mybaits自带缓存存在缺点（自行谷歌）。本文是基于docker安装redis主从模式。

1.redis安装

（1）首先安装redis集群模式，建立redis目录，并编写主从模式docker-compose.yml文件

 version: '3.1'
 services:
   master:
     image: redis
     container_name: redis-master
     ports:
       - 6379:6379

   slave1:
     image: redis
     container_name: redis-slave-1
     ports:
       - 6380:6379
     command: redis-server --slaveof redis-master 6379

   slave2:
     image: redis
     container_name: redis-slave-2
     ports:
       - 6381:6379
     command: redis-server --slaveof redis-master 6379

（2）.启动 docker-compose up -d

（3）.建立sentinel文件，并编写docker-compose.yml文件

 version: '3.1'
 services:
   sentinel1:
     image: redis
     container_name: redis-sentinel-1
     ports:
       - 26379:26379
     command: redis-sentinel /usr/local/etc/redis/sentinel.conf
     volumes:
       - ./sentinel1.conf:/usr/local/etc/redis/sentinel.conf

   sentinel2:
     image: redis
     container_name: redis-sentinel-2
     ports:
       - 26380:26379
     command: redis-sentinel /usr/local/etc/redis/sentinel.conf
     volumes:
       - ./sentinel2.conf:/usr/local/etc/redis/sentinel.conf

   sentinel3:
     image: redis
     container_name: redis-sentinel-3
     ports:
       - 26381:26379
     command: redis-sentinel /usr/local/etc/redis/sentinel.conf
     volumes:
       - ./sentinel3.conf:/usr/local/etc/redis/sentinel.conf
         

从模式需要sentinel的conf文件，我创建了3个容器，所以这里需要3份（sentinel1.conf sentinel2.conf sentinel3.conf），内容是一模一样

 port 26379
 dir /tmp
 sentinel monitor mymaster 217.0.0.1 6379 2
 sentinel down-after-milliseconds rmaster 30000
 sentinel parallel-syncs mymaster 1
 sentinel failover-timeout mymaster 180000
 sentinel deny-scripts-reconfig yes

（4）.启动：docker-compose up -d

（5）.验证redis是否已经成功启动

进入容器：docker exec -it redis-sentinel-1 /bin/bash

连接redis：redis-cli -p 26379

如下图，表示启动成功

也可以通过桌面客户端查看是否启动成功，如图，我使用的RedisDesktopManager客户端

 这里有个问题可以思考：传统的redis集群，即cluster，也有主从模式，现在为什么大家都选择sentinel主从模式？

2.编写RedisCache工具类

网上一大堆，根据自己需要选择合适的utils（有的utils中方法很全）

 package com.learn.hello.system.utils;

 import lombok.extern.slf4j.Slf4j;
 import org.apache.ibatis.cache.Cache;
 import org.springframework.data.redis.core.RedisCallback;
 import org.springframework.data.redis.core.RedisTemplate;
 import org.springframework.data.redis.core.ValueOperations;

 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.ReadWriteLock;
 import java.util.concurrent.locks.ReentrantReadWriteLock;

 /**
  * @ClassName RedisCache
  * @Deccription 通过redis实现mybaits的二级缓存
  * @Author DZ
  * @Date 2020/1/12 22:41
  **/
 @Slf4j
 public class RedisCache implements Cache {

     private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
     private final String id; // cache instance id
     private RedisTemplate redisTemplate;

     private static final long EXPIRE_TIME_IN_MINUTES = 30; // redis过期时间

     public RedisCache(String id) {
         if (id == null) {
             throw new IllegalArgumentException("Cache instances require an ID");
         }
         this.id = id;
     }

     @Override
     public String getId() {
         return id;
     }

     /**
      * Put query result to redis
      *
      * @param key
      * @param value
      */
     @Override
     public void putObject(Object key, Object value) {
         try {
             RedisTemplate redisTemplate = getRedisTemplate();
             ValueOperations opsForValue = redisTemplate.opsForValue();
             opsForValue.set(key, value, EXPIRE_TIME_IN_MINUTES, TimeUnit.MINUTES);
             log.debug("Put query result to redis");
         } catch (Throwable t) {
             log.error("Redis put failed", t);
         }
     }

     /**
      * Get cached query result from redis
      *
      * @param key
      * @return
      */
     @Override
     public Object getObject(Object key) {
         try {
             RedisTemplate redisTemplate = getRedisTemplate();
             ValueOperations opsForValue = redisTemplate.opsForValue();
             log.debug("Get cached query result from redis");
             return opsForValue.get(key);
         } catch (Throwable t) {
             log.error("Redis get failed, fail over to db", t);
             return null;
         }
     }

     /**
      * Remove cached query result from redis
      *
      * @param key
      * @return
      */
     @Override
     @SuppressWarnings("unchecked")
     public Object removeObject(Object key) {
         try {
             RedisTemplate redisTemplate = getRedisTemplate();
             redisTemplate.delete(key);
             log.debug("Remove cached query result from redis");
         } catch (Throwable t) {
             log.error("Redis remove failed", t);
         }
         return null;
     }

     /**
      * Clears this cache instance
      */
     @Override
     public void clear() {
         RedisTemplate redisTemplate = getRedisTemplate();
         redisTemplate.execute((RedisCallback) connection -> {
             connection.flushDb();
             return null;
         });
         log.debug("Clear all the cached query result from redis");
     }

     /**
      * This method is not used
      *
      * @return
      */
     @Override
     public int getSize() {
         return 0;
     }

     @Override
     public ReadWriteLock getReadWriteLock() {
         return readWriteLock;
     }

     private RedisTemplate getRedisTemplate() {
         if (redisTemplate == null) {
             redisTemplate = SpringContextHolder.getBean("redisTemplate");
         }
         return redisTemplate;
     }
 }

3.在接口类增加redis缓存注解

@CacheNamespace(implementation = RedisCache.class)

例如：

 @CacheNamespace(implementation = RedisCache.class)
 public interface RoleMapper extends MyMapper<Role> {
     List<Role> selectByCondition(ModelMap modelMap);

     Role selectById(int id);

     List<Role> selectAllRole();
 }

这里也可以直接在MyMapper父接口中增加注解，这样，所有的接口就不需要单独增加这个注解（根据业务需要自行素选择）。

4.配置application.yml

 spring:
   redis:
       # 哨兵模式推荐使用lettuce作为客户端，弃用jedis
     lettuce:
       # 连接池配置
       pool:
         # 连接池中的最小空闲连接，默认 0
         min-idle: 0
         # 连接池中的最大空闲连接，默认 8
         max-idle: 8
         # 连接池最大阻塞等待时间（使用负值表示没有限制），默认 -1ms
         max-wait: -1ms
         # 连接池最大连接数（使用负值表示没有限制），默认 8
         max-active: 8
     #    集群模式
     #    cluster:
     #      nodes: 192.168.1.12:6379,192.168.1.12:6380,192.168.1.12:6381
     #    哨兵模式
     sentinel:
       master: mymaster
       nodes: 192.168.1.12:26379,192.168.1.12:26380,192.168.1.12:26381

 mybatis:
   mapper-locations: classpath:mapper/*.xml
   #  此配置的作用：xml中不用写实体类的全路径
   type-aliases-package: com.learn.hello.modules.entity
   #  查询的null字段也返回
   configuration:
     call-setters-on-nulls: true
     #    开启二级缓存
     cache-enabled: true

5.效果

当进行CURD操作时，相关的检索sql语句就会缓存到redis，如图：

当再次对相关数据进行CRUD时，就会走缓存