开启 MyBatis 二级缓存
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
private static final long serialVersionUID = -1438690827318640624L;
IDEA 提示生成序列号
File -> Settings -> Inspections -> Serialization issues -> Serialization class without 'seralVersionUID`
创建相关工具类
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 idprivate 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;}@Overridepublic String getId() {return id;}/*** Put query result to redis** @param key* @param value*/@Overridepublic 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*/@Overridepublic 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*/@Overridepublic 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*/@Overridepublic int getSize() {return 0;}@Overridepublic ReadWriteLock getReadWriteLock() {return readWriteLock;}private RedisTemplate getRedisTemplate() {if (redisTemplate == null) {redisTemplate = ApplicationContextHolder.getBean("redisTemplate");}return redisTemplate;}
}Mapper 接口增加注解
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> {
}