二级缓存是多个SqlSession共享的，其作用域是mapper的同一个namespace，不同的sqlSession两次执行相同namespace下的sql语句且向sql中传递参数也相同即最终执行相同的sql语句，第一次执行完毕会将数据库中查询的数据写到缓存（内存），第二次会从缓存中获取数据将不再从数据库查询，从而提高查询效率。Mybatis默认没有开启二级缓存需要在setting全局参数中配置开启二级缓存。

下面是使用Redis来作为Mybatis二级缓存的实例：

主要的三个class：RedisCache，RedisConfig，RedisCacheTransfer。其他的都是一些配置。

RedisCache继承mybatis的Cache接口，用于建立redis与mybatis连接关系
RedisConfig配置redis相关参数，用于建立spring中的redis client与redis服务器建立连接
RedisCacheTransfer获取依赖注入的JedisConnectionFactory类，这个类会在RedisCache中用到，很重要

application.properties

在application.properties文件中配置Redis，Mybatis，开启Mybatis二级缓存等：

#\u914D\u7F6E\u524D\u7AEF\u6A21\u5F0F
#spring.thymeleaf.mode=legacyhtml5
#\u914D\u7F6Ejdbc
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
#\u914D\u7F6E\u6570\u636E\u5E93
spring.datasource.url=jdbc:mysql://10.10.10.10:3306/sc?useUnicode=true&characterEncoding=UTF8&useServerPrepStmts=true&prepStmtCacheSqlLimit=256&cachePrepStmts=true&prepStmtCacheSize=256&rewriteBatchedStatements=truespring.datasource.username=root
spring.datasource.password=123456spring.redis.host = 10.10.10.11
spring.redis.password=123456
spring.redis.port=6379
spring.redis.database=0
spring.redis.timeout=0spring.redis.pool.ma-active=8#first.datasource.driver-class-name=com.mysql.jdbc.Driver
#first.datasource.url=jdbc:mysql://192.168.1.163:3306/testdemo1?characterEncoding=UTF-8
#first.datasource.username=root
#first.datasource.password=root
#
#second.datasource.driver-class-name=com.mysql.jdbc.Driver
#second.datasource.url=jdbc:mysql://192.168.1.163:3306/testdemo?characterEncoding=UTF-8
#second.datasource.username=root
#second.datasource.password=root#\u914D\u7F6E\u5C38\u4F53\u7C7B\u6620\u5C04\u8DEF\u5F84
mybatis.typeAliasesPackage=com.cetc.uavsystem.entity
#\u914D\u7F6EMapper\u6587\u4EF6\u6620\u5C04\u8DEF\u5F84
mybatis.mapper-locations=classpath:/mapper/*Mapper.xml
#\u914D\u7F6Emybatis\u914D\u7F6E\u6587\u4EF6
mybatis.config-location=classpath:mybatis-config.xml

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><artifactId>spring-boot-student-mybatis-redis</artifactId><packaging>jar</packaging><name>spring-boot-student-mybatis-redis</name><description>Mybatis Redis for Spring Boot</description><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-student</artifactId><version>0.0.1-SNAPSHOT</version><relativePath /></parent><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding><java.version>1.8</java.version></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId></dependency><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>1.3.0</version></dependency><!--pagehelper --><dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper-spring-boot-starter</artifactId><version>1.1.1</version></dependency><dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.31</version></dependency><dependency><groupId>org.mybatis</groupId><artifactId>mybatis-ehcache</artifactId><version>1.0.0</version></dependency></dependencies></project>

Redis配置类替换序列化实现方式以及redis获取配置文件 RedisConfig

/*** */
package com.cetc.uavsystem.redis.cache;import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.Jackson2JsonRedisSerializer;
import org.springframework.data.redis.serializer.StringRedisSerializer;import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;import redis.clients.jedis.JedisPoolConfig;/*** @author Mickle_zhang*配置文件*/
@Configuration
public class RedisConfig {//    @Value("$spring.redis.pool.maxIdle}")
//  private int maxIdle;
//  @Value("${spring.redis.pool.maxTotal}")
//  private int maxTotal;
//  @Value("${spring.redis.pool.maxWaitMillis}")
//  private long maxWaitMillis;
//  @Value("${spring.redis.pool.minIdle}")
//  private int minIdle;@Beanpublic JedisPoolConfig getRedisConfig(){JedisPoolConfig config = new JedisPoolConfig();
//        config.setMaxIdle(maxIdle);
//        config.setMaxTotal(maxTotal);
//        config.setMaxWaitMillis(maxWaitMillis);
//        config.setMinIdle(minIdle);return config;}@Value("${spring.redis.host}")private String host;@Value("${spring.redis.port}")private int port;@Value("${spring.redis.database}")private int database;@Value("${spring.redis.password}")private String password;@Value("${spring.redis.timeout}")private int timeout;@Bean(name = "jedisConnectionFactory")public JedisConnectionFactory getConnectionFactory(){JedisConnectionFactory factory = new JedisConnectionFactory();JedisPoolConfig config = getRedisConfig();factory.setPoolConfig(config);factory.setHostName(host);factory.setPort(port);factory.setDatabase(database);factory.setPassword(password);factory.setTimeout(timeout);return factory;}@Bean(name = "redisTemplate")public RedisTemplate<String, Object> redisTemplate(RedisConnectionFactory redisConnectionFactory) {RedisTemplate<String, Object> redisTemplate = new RedisTemplate<>();redisTemplate.setConnectionFactory(redisConnectionFactory);Jackson2JsonRedisSerializer<Object> jackson2JsonRedisSerializer = new Jackson2JsonRedisSerializer<Object>(Object.class);ObjectMapper om = new ObjectMapper();om.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);om.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);  jackson2JsonRedisSerializer.setObjectMapper(om);// 设置值（value）的序列化采用Jackson2JsonRedisSerializer。redisTemplate.setValueSerializer(jackson2JsonRedisSerializer);// 设置键（key）的序列化采用StringRedisSerializer。redisTemplate.setKeySerializer(new StringRedisSerializer());redisTemplate.afterPropertiesSet();return redisTemplate;}
}

Spring容器获取Bean工具类SpringContextHolder

通过Spring Aware（容器感知）来获取到ApplicationContext，然后根据ApplicationContext获取容器中的Bean。

/*** */
package com.cetc.uavsystem.redis.cache;import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;/*** @author Mickle_zhang**/
@Component
public class SpringContextHolder implements ApplicationContextAware{private static ApplicationContext applicationContext;/*** 实现ApplicationContextAware接口的context注入函数, 将其存入静态变量.*/public void setApplicationContext(ApplicationContext applicationContext) {SpringContextHolder.applicationContext = applicationContext; // NOSONAR}/*** 取得存储在静态变量中的ApplicationContext.*/public static ApplicationContext getApplicationContext() {checkApplicationContext();return applicationContext;}/*** 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.*/@SuppressWarnings("unchecked")public static <T> T getBean(String name) {checkApplicationContext();return (T) applicationContext.getBean(name);}/*** 从静态变量ApplicationContext中取得Bean, 自动转型为所赋值对象的类型.*/@SuppressWarnings("unchecked")public static <T> T getBean(Class<T> clazz) {checkApplicationContext();return (T) applicationContext.getBeansOfType(clazz);}/*** 清除applicationContext静态变量.*/public static void cleanApplicationContext() {applicationContext = null;}private static void checkApplicationContext() {if (applicationContext == null) {throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextHolder");}}
}

自定的Mybatis缓存RedisCache

自定义缓存需要实现Mybatis的Cache接口，我这里将使用Redis来作为缓存的容器。

package com.cetc.uavsystem.redis.cache;import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;import org.apache.ibatis.cache.Cache;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
import org.springframework.data.redis.serializer.JdkSerializationRedisSerializer;
import org.springframework.data.redis.serializer.RedisSerializer;
import org.springframework.stereotype.Component;import redis.clients.jedis.exceptions.JedisConnectionException;/*** * @author Mickle_zhang* redis 做二级缓存*/
public class RedisCache implements Cache {private static final Logger logger = LoggerFactory.getLogger(RedisCache.class);private static JedisConnectionFactory jedisConnectionFactory;private final String id;private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();public RedisCache(final String id) {if (id == null) {throw new IllegalArgumentException("Cache instances require an ID");}this.id = id;}@Overridepublic void clear() {RedisConnection connection = null;try {connection = jedisConnectionFactory.getConnection();RedisSerializer<Object> serializer = new JdkSerializationRedisSerializer();
//            connection.flushDb();
//            connection.flushAll();Long length = connection.lLen(serializer.serialize(id));if (0 == length) {return;}List<byte[]> keys = connection.lRange(serializer.serialize(id),0,length-1);for (byte[] key :keys) {connection.expireAt(key,0);System.out.println("删除缓存:"+serializer.deserialize(key).toString());}connection.expireAt(serializer.serialize(id),0);keys.clear();} catch (Exception e) {e.printStackTrace();} finally {if (connection != null) {connection.close();}}}@Overridepublic String getId() {return this.id;}@Overridepublic Object getObject(Object key) {Object result = null;RedisConnection connection = null;try {connection = jedisConnectionFactory.getConnection();RedisSerializer<Object> serializer = new JdkSerializationRedisSerializer();result = serializer.deserialize(connection.get(serializer.serialize(key)));logger.info("redis取数据");} catch (JedisConnectionException e) {e.printStackTrace();} finally {if (connection != null) {connection.close();}}return result;}@Overridepublic ReadWriteLock getReadWriteLock() {return this.readWriteLock;}@Overridepublic int getSize() {int result = 0;RedisConnection connection = null;try {connection = jedisConnectionFactory.getConnection();result = Integer.valueOf(connection.dbSize().toString());} catch (JedisConnectionException e) {e.printStackTrace();} finally {if (connection != null) {connection.close();}}return result;}@Overridepublic void putObject(Object key, Object value) {RedisConnection connection = null;try{
// 现在将namespace做一张单独的表即com.cetc.uavsystem.dao.Idt_user_tableDao，clear方法就寻找该list connection = jedisConnectionFactory.getConnection();RedisSerializer<Object> serializer = new JdkSerializationRedisSerializer();connection.set(serializer.serialize(key),serializer.serialize(value));// 将key保存到redis.list中connection.lPush(serializer.serialize(id), serializer.serialize(key));logger.info("redis存数据");} catch (JedisConnectionException e) {e.printStackTrace();} finally {if (connection != null) {connection.close();}}}@Overridepublic Object removeObject(Object key) {RedisConnection connection = null;Object result = null;try {connection = jedisConnectionFactory.getConnection();RedisSerializer<Object> serializer = new JdkSerializationRedisSerializer();result = connection.expire(serializer.serialize(key), 0);} catch (JedisConnectionException e) {e.printStackTrace();} finally {if (connection != null) {connection.close();}}return result;}public static void setJedisConnectionFactory(JedisConnectionFactory jedisConnectionFactory) {RedisCache.jedisConnectionFactory = jedisConnectionFactory;}}

RedisCacheTransfer

/*** */
package com.cetc.uavsystem.redis.cache;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
import org.springframework.stereotype.Component;/*** @author Mickle_zhang**/
@Component
public class RedisCacheTransfer {@Autowiredpublic void setJedisConnectionFactory(JedisConnectionFactory jedisConnectionFactory) {RedisCache.setJedisConnectionFactory(jedisConnectionFactory);}
}

Mapper文件

<?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.cetc.uavsystem.dao.Idt_user_tableDao"><!-- 开启本mapper的namespace下的二级缓存 -->
<cache  type="com.cetc.uavsystem.redis.cache.RedisCache"><property name="eviction" value="LRU" /><property name="flushInterval" value="6000000" /><property name="size" value="1024" /><property name="readOnly" value="false" /></cache><!-- useCache是否开启二级缓存，flushCache为是否刷新二级缓存 --><select id="get" resultMap="Idt_user_table" parameterType="Integer" useCache="true"  flushCache="true">select * from idt_user_table where user_id=#{nUser_id}</select><select id="getAll" resultMap="Idt_user_table" useCache="true"  flushCache="false">select * from idt_user_table</select>
</mapper >

如果还是不明白，可参照demo

地址：https://github.com/yxyyzyf/shaungseqiu

基于spring cloud，功能完善中

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