基于redis的mybatis二级缓存的实现(springboot)

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本文介绍如何在SpringBoot项目中整合Mybatis和Redis实现二级缓存，通过自定义RedisCache类实现Mybatis的Cache接口，提高数据查询效率。

Springboot + Mybatis + Redis+mysql
Mybatis的二级缓存是多个SqlSession共享的，作用于是mapper配置文件中同一个namespace，不同的SqlSession两次执行相同namespace下的sql语句且参数如果也一样则最终执行的sql语句是相同的。每次查询都会先看看缓存中是否有对应查询结果，如果有就从缓存拿，如果没有就执行sql语句从数据库中读取，从而提高查询效率。

maven配置

<?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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.domcj.seccache</groupId>
    <artifactId>secache</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>secache</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.0.0</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.7</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>

    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

#配置mybatis
mybatis:
  mapper-locations: mapper/UserMapper.xml
  type-aliases-package: com.domcj.seccache.seccache.entity

#配置redis
spring:
  datasource:
      url: jdbc:mysql://localhost:3306/chenjian
      username: root
      password: chenjian
      driver-class-name: com.mysql.jdbc.Driver
      type: com.alibaba.druid.pool.DruidDataSource
  redis:
    host: localhost
    port: 6379
    database: 0
    password:

SpringContextHolder
组件，实现了Spring的ApplicationContextAware来获取ApplicationContext，从中获取容器的bean

package com.domcj.seccache.seccache.util;

import java.util.Map;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

/**
 * @description: This is a class!
 * @author: chenjian
 * @date: 2019/03/07 11:33
 */

@Component
public class ApplicationContextHolder implements ApplicationContextAware {

   private static ApplicationContext applicationContext;

   @Override
   public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
      ApplicationContextHolder.applicationContext = applicationContext;
   }
   public ApplicationContext getApplicationContext() {
      return applicationContext;
   }
   @SuppressWarnings("unchecked")
   public static <T> T getBean(String beanName) {
      checkApplicationContext();
      return (T) applicationContext.getBean(beanName);
   }
   @SuppressWarnings("unchecked")
   public static <T> Map<String, T> getBean(Class<T> clazz) {
      checkApplicationContext();
      return applicationContext.getBeansOfType(clazz);
   }
   private static void checkApplicationContext() {
      if (applicationContext == null) {
         throw new IllegalStateException("applicaitonContext未注入,请在applicationContext.xml中定义SpringContextHolder");
      }
   }

}

RedisCache
Mybatis二级缓存默认使用的是其他的缓存，这里我们需要集成Redis就需要自己自定义写一个缓存类去实现二级缓存。

自定义缓存需要实现Mybatis的Cache接口。

package com.domcj.seccache.seccache.util;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.apache.ibatis.cache.Cache;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.ValueOperations;

/**
 * @description: This is a class!
 * @author: chenjian
 * @date: 2019/03/07 11:45
 */
public class RedisCache implements Cache {

   private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
   private 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;
   }

   @Override
   public void putObject(Object key, Object value) {
      RedisTemplate redisTemplate = getRedisTemplate();
      ValueOperations opsForValue = redisTemplate.opsForValue();
      opsForValue.set(key, value, EXPIRE_TIME_IN_MINUTES, TimeUnit.SECONDS);
   }

   @Override
   public Object getObject(Object key) {
      RedisTemplate redisTemplate = getRedisTemplate();
      ValueOperations opsForValue = redisTemplate.opsForValue();
      Object obj = opsForValue.get(key);
      return obj;
   }

   @Override
   public Object removeObject(Object key) {
      RedisTemplate redisTemplate = getRedisTemplate();
      redisTemplate.delete(key);
      return null;
   }

   @Override
   public void clear() {
      RedisTemplate redisTemplate = getRedisTemplate();
      redisTemplate.execute((RedisCallback) connection -> {
         connection.flushDb();
         return null;
      });
   }

   @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.xml
mapper映射配置文件，只需要引入刚刚配置好的自定义缓存类。

<?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.domcj.seccache.seccache.mapper.UserMapper">
    <cache type="com.domcj.seccache.seccache.util.RedisCache">
        <property name="eviction" value="LRU" />
        <property name="flushInterval" value="600000" />
        <property name="size" value="1024" />
        <property name="readOnly" value="false" />
    </cache>
    <select id="getUserById" parameterType="java.lang.Long" resultType="User">
        select * from user where id=#{id, jdbcType=BIGINT}
    </select>
</mapper>

eviction：定义缓存移除机制（算法），默认为LRU（最近最少使用），它会清除最少使用的数据，还有一种FIFO（先进先出），它会清除最先进来的数据。

flushInterval：定义缓存刷新周期，单位为毫秒。

size：标识缓存cache中容纳的最大元素，默认为1024。

readOnly：默认为false，可配置为true缓存只读。

实体类
实体类需要实现Serializable

package com.domcj.seccache.seccache.entity;

import java.io.Serializable;

/**
 * @description: This is a class!
 * @author: chenjian
 * @date: 2019/03/07 11:21
 */
public class User implements Serializable {
   private Long id;
   private String name;

   public Long getId() {
      return id;
   }

   public void setId(Long id) {
      this.id = id;
   }

   public String getName() {
      return name;
   }

   public void setName(String name) {
      this.name = name;
   }
}

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