【微服务架构 - 12 - MyBatis Redis】01 配置 MyBatis Redis 二级缓存

阳光穿透心脏的1/2处 2022-03-12 15:26 150阅读 0赞

#### 开启 MyBatis 二级缓存 ####

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在 Spring Boot 配置文件中开启 MyBatis 二级缓存，配置代码如下：

mybatis:
      configuration:
        cache-enabled: true

#### 实体类实现序列化接口并声明序列号 ####

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private static final long serialVersionUID = -1438690827318640624L;

#### IDEA 提示生成序列号 ####

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File -> Settings -> Inspections -> Serialization issues -> Serialization class without 'seralVersionUID\`

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## 创建相关工具类 ##

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#### 实现 Spring ApplicationContextAware 接口，用于手动注入 Bean ####

创建一个名为 `ApplicationContextHolder` 的工具类，代码如下：

package com.yuu.itoken.common.context;
    
    import org.apache.commons.lang3.Validate;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.DisposableBean;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    import org.springframework.stereotype.Component;
    
    /**
     * @Classname ApplicationContextHolder
     * @Date 2019/3/6 9:04
     * @Created by Yuu
     */
    @Component
    public class ApplicationContextHolder implements ApplicationContextAware, DisposableBean {
        private static final Logger logger = LoggerFactory.getLogger(ApplicationContextHolder.class);
    
        private static ApplicationContext applicationContext;
    
        /**
         * 获取存储在静态变量中的 ApplicationContext
         *
         * @return
         */
        public static ApplicationContext getApplicationContext() {
            assertContextInjected();
            return applicationContext;
        }
    
        /**
         * 从静态变量 applicationContext 中获取 Bean，自动转型成所赋值对象的类型
         *
         * @param name
         * @param <T>
         * @return
         */
        public static <T> T getBean(String name) {
            assertContextInjected();
            return (T) applicationContext.getBean(name);
        }
    
        /**
         * 从静态变量 applicationContext 中获取 Bean，自动转型成所赋值对象的类型
         *
         * @param clazz
         * @param <T>
         * @return
         */
        public static <T> T getBean(Class<T> clazz) {
            assertContextInjected();
            return applicationContext.getBean(clazz);
        }
    
        /**
         * 实现 DisposableBean 接口，在 Context 关闭时清理静态变量
         *
         * @throws Exception
         */
        public void destroy() throws Exception {
            logger.debug("清除 SpringContext 中的 ApplicationContext: {}", applicationContext);
            applicationContext = null;
        }
    
        /**
         * 实现 ApplicationContextAware 接口，注入 Context 到静态变量中
         *
         * @param applicationContext
         * @throws BeansException
         */
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            ApplicationContextHolder.applicationContext = applicationContext;
        }
    
        /**
         * 断言 Context 已经注入
         */
        private static void assertContextInjected() {
            Validate.validState(applicationContext != null, "applicationContext 属性未注入，请在 spring-context.xml 配置中定义 ApplicationContextHolder");
        }
    }

#### 实现 MyBatis Cache 接口，用于自定义缓存为 Redis ####

创建一个名为 `RedisCache` 的工具类，代码如下：

package com.yuu.itoken.common.utils;
    
    import com.yuu.itoken.common.context.ApplicationContextHolder;
    import org.apache.ibatis.cache.Cache;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    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
     * @Date 2019/3/6 9:08
     * @Created by Yuu
     */
    public class RedisCache implements Cache {
        private static final Logger logger = LoggerFactory.getLogger(RedisCache.class);
    
        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);
                logger.debug("Put query result to redis");
            } catch (Throwable t) {
                logger.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();
                logger.debug("Get cached query result from redis");
    //            System.out.println("****" + opsForValue.get(key).toString());
                return opsForValue.get(key);
            } catch (Throwable t) {
                logger.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);
                logger.debug("Remove cached query result from redis");
            } catch (Throwable t) {
                logger.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;
            });
            logger.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 = ApplicationContextHolder.getBean("redisTemplate");
            }
            return redisTemplate;
        }
    }

#### Mapper 接口增加注解 ####

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在 Mapper 接口中增加注解，声明需要使用二级缓存

package com.yuu.itoken.common.mapper;
    
    import com.yuu.itoken.common.domain.TbPostsPost;
    import com.yuu.itoken.common.utils.RedisCache;
    import org.apache.ibatis.annotations.CacheNamespace;
    import tk.mybatis.mapper.MyMapper;
    
    @CacheNamespace(implementation = RedisCache.class)
    public interface TbPostsPostMapper extends MyMapper<TbPostsPost> {
    }

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