MyBatis二级缓存使用

• 注意点：
• 在最新的3.x版本，实现二级缓存的配置也有了一些改变。
• 官方建议在service使用缓存，但是你也可以直接在mapper层缓存，这里的二级缓存就是直接在Mapper层进行缓存操作

  Mybatis的二级缓存实现也十分简单，只要在springboot的配置文件打开二级缓存，即

  mybatis-plus:
    configuration:
      cache-enabled: true

  缓存接口的实现

  public class MybatisRedisCache implements Cache {
  
  
      // 读写锁
      private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock(true);
  
  	//这里使用了redis缓存，使用springboot自动注入
  	@Autowired
      private RedisTemplate<String, Object> redisTemplate;
  
      private String id;
  
      public MybatisRedisCache(final String id) {
          if (id == null) {
              throw new IllegalArgumentException("Cache instances require an ID");
          }
          this.id = id;
      }
  
      @Override
      public String getId() {
          return this.id;
      }
  
      @Override
      public void putObject(Object key, Object value) {
          if (redisTemplate == null) {
          //由于启动期间注入失败，只能运行期间注入，这段代码可以删除
              redisTemplate = (RedisTemplate<String, Object>) ApplicationContextRegister.getApplicationContext().getBean("RedisTemplate");
          }
          if (value != null) {
              redisTemplate.opsForValue().set(key.toString(), value);
          }
      }
  
      @Override
      public Object getObject(Object key) {
          try {
              if (key != null) {
                  return redisTemplate.opsForValue().get(key.toString());
              }
          } catch (Exception e) {
              log.error("缓存出错 ");
          }
          return null;
      }
  
      @Override
      public Object removeObject(Object key) {
          if (key != null) {
              redisTemplate.delete(key.toString());
          }
          return null;
      }
  
      @Override
      public void clear() {
          log.debug("清空缓存");
          if (redisTemplate == null) {
              redisTemplate = (RedisTemplate<String, Object>) ApplicationContextRegister.getApplicationContext().getBean("functionDomainRedisTemplate");
          }
          Set<String> keys = redisTemplate.keys("*:" + this.id + "*");
          if (!CollectionUtils.isEmpty(keys)) {
              redisTemplate.delete(keys);
          }
      }
  
      @Override
      public int getSize() {
          Long size = redisTemplate.execute((RedisCallback<Long>) RedisServerCommands::dbSize);
          return size.intValue();
      }
  
      @Override
      public ReadWriteLock getReadWriteLock() {
          return this.readWriteLock;
      }
  }

  mapper.xml文件声明缓存，这里3.x只需要这样配置

  <?xml version="1.0" encoding="UTF-8" ?>
  <!DOCTYPE mapper
          PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
          "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
  <mapper namespace="com.zsy.mapper.CarouselMapper">
      <cache-ref namespace="com.zsy.mapper.CarouselMapper"/>
  </mapper>

  Mapper接口使用注解

  @Repository
  @CacheNamespace(implementation=MybatisRedisCache.class,eviction=MybatisRedisCache.class)
  public interface CarouselMapper extends BaseMapper<Carousel> {}