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
1 version: '3.1' 2 services: 3 master: 4 image: redis 5 container_name: redis-master 6 ports: 7 - 6379:6379 8 9 slave1: 10 image: redis 11 container_name: redis-slave-1 12 ports: 13 - 6380:6379 14 command: redis-server --slaveof redis-master 6379 15 16 slave2: 17 image: redis 18 container_name: redis-slave-2 19 ports: 20 - 6381:6379 21 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
1 version: '3.1' 2 services: 3 sentinel1: 4 image: redis 5 container_name: redis-sentinel-1 6 ports: 7 - 26379:26379 8 command: redis-sentinel /usr/local/etc/redis/sentinel.conf 9 volumes: 10 - ./sentinel1.conf:/usr/local/etc/redis/sentinel.conf 11 12 sentinel2: 13 image: redis 14 container_name: redis-sentinel-2 15 ports: 16 - 26380:26379 17 command: redis-sentinel /usr/local/etc/redis/sentinel.conf 18 volumes: 19 - ./sentinel2.conf:/usr/local/etc/redis/sentinel.conf 20 21 sentinel3: 22 image: redis 23 container_name: redis-sentinel-3 24 ports: 25 - 26381:26379 26 command: redis-sentinel /usr/local/etc/redis/sentinel.conf 27 volumes: 28 - ./sentinel3.conf:/usr/local/etc/redis/sentinel.conf 29
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
1 port 26379 2 dir /tmp 3 sentinel monitor mymaster 217.0.0.1 6379 2 4 sentinel down-after-milliseconds rmaster 30000 5 sentinel parallel-syncs mymaster 1 6 sentinel failover-timeout mymaster 180000 7 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）
1 package com.learn.hello.system.utils;
2
3 import lombok.extern.slf4j.Slf4j;
4 import org.apache.ibatis.cache.Cache;
5 import org.springframework.data.redis.core.RedisCallback;
6 import org.springframework.data.redis.core.RedisTemplate;
7 import org.springframework.data.redis.core.ValueOperations;
8
9 import java.util.concurrent.TimeUnit;
10 import java.util.concurrent.locks.ReadWriteLock;
11 import java.util.concurrent.locks.ReentrantReadWriteLock;
12
13 /**
14 * @ClassName RedisCache
15 * @Deccription 通过redis实现mybaits的二级缓存
16 * @Author DZ
17 * @Date 2020/1/12 22:41
18 **/
19 @Slf4j
20 public class RedisCache implements Cache {
21
22 private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
23 private final String id; // cache instance id
24 private RedisTemplate redisTemplate;
25
26 private static final long EXPIRE_TIME_IN_MINUTES = 30; // redis过期时间
27
28 public RedisCache(String id) {
29 if (id == null) {
30 throw new IllegalArgumentException("Cache instances require an ID");
31 }
32 this.id = id;
33 }
34
35 @Override
36 public String getId() {
37 return id;
38 }
39
40 /**
41 * Put query result to redis
42 *
43 * @param key
44 * @param value
45 */
46 @Override
47 public void putObject(Object key, Object value) {
48 try {
49 RedisTemplate redisTemplate = getRedisTemplate();
50 ValueOperations opsForValue = redisTemplate.opsForValue();
51 opsForValue.set(key, value, EXPIRE_TIME_IN_MINUTES, TimeUnit.MINUTES);
52 log.debug("Put query result to redis");
53 } catch (Throwable t) {
54 log.error("Redis put failed", t);
55 }
56 }
57
58 /**
59 * Get cached query result from redis
60 *
61 * @param key
62 * @return
63 */
64 @Override
65 public Object getObject(Object key) {
66 try {
67 RedisTemplate redisTemplate = getRedisTemplate();
68 ValueOperations opsForValue = redisTemplate.opsForValue();
69 log.debug("Get cached query result from redis");
70 return opsForValue.get(key);
71 } catch (Throwable t) {
72 log.error("Redis get failed, fail over to db", t);
73 return null;
74 }
75 }
76
77 /**
78 * Remove cached query result from redis
79 *
80 * @param key
81 * @return
82 */
83 @Override
84 @SuppressWarnings("unchecked")
85 public Object removeObject(Object key) {
86 try {
87 RedisTemplate redisTemplate = getRedisTemplate();
88 redisTemplate.delete(key);
89 log.debug("Remove cached query result from redis");
90 } catch (Throwable t) {
91 log.error("Redis remove failed", t);
92 }
93 return null;
94 }
95
96 /**
97 * Clears this cache instance
98 */
99 @Override
100 public void clear() {
101 RedisTemplate redisTemplate = getRedisTemplate();
102 redisTemplate.execute((RedisCallback) connection -> {
103 connection.flushDb();
104 return null;
105 });
106 log.debug("Clear all the cached query result from redis");
107 }
108
109 /**
110 * This method is not used
111 *
112 * @return
113 */
114 @Override
115 public int getSize() {
116 return 0;
117 }
118
119 @Override
120 public ReadWriteLock getReadWriteLock() {
121 return readWriteLock;
122 }
123
124 private RedisTemplate getRedisTemplate() {
125 if (redisTemplate == null) {
126 redisTemplate = SpringContextHolder.getBean("redisTemplate");
127 }
128 return redisTemplate;
129 }
130 }
3.在接口类增加redis缓存注解
@CacheNamespace(implementation = RedisCache.class)
例如：
1 @CacheNamespace(implementation = RedisCache.class)
2 public interface RoleMapper extends MyMapper<Role> {
3 List<Role> selectByCondition(ModelMap modelMap);
4
5 Role selectById(int id);
6
7 List<Role> selectAllRole();
8 }
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
1 spring: 2 redis: 3 lettuce: 4 # 连接池配置 5 pool: 6 # 连接池中的最小空闲连接，默认 0 7 min-idle: 0 8 # 连接池中的最大空闲连接，默认 8 9 max-idle: 8 10 # 连接池最大阻塞等待时间（使用负值表示没有限制），默认 -1ms 11 max-wait: -1ms 12 # 连接池最大连接数（使用负值表示没有限制），默认 8 13 max-active: 8 14 # 集群模式 15 # cluster: 16 # nodes: 192.168.1.12:6379,192.168.1.12:6380,192.168.1.12:6381 17 # 哨兵模式 18 sentinel: 19 master: mymaster 20 nodes: 192.168.1.12:26379,192.168.1.12:26380,192.168.1.12:26381
1 mybatis: 2 mapper-locations: classpath:mapper/*.xml 3 # 此配置的作用：xml中不用写实体类的全路径 4 type-aliases-package: com.learn.hello.modules.entity 5 # 查询的null字段也返回 6 configuration: 7 call-setters-on-nulls: true 8 # 开启二级缓存 9 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
