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版权声明

• 本文原创作者：谷哥的小弟
• 作者博客地址：http://blog.csdn.net/lfdfhl

使用二级缓存的前期准备

在MyBatis中使用二级缓存之前，需要进行如下配置：

1、在mybatis-config.xml中开启二级缓存

2、xxxMapper.xml中使用catch标签

3、pojo实现Serializable接口

public class YourPojo implements Serializable{
    }

二级缓存的使用说明

当MyBatis中开启二级缓存，那么缓存的使用顺序如下：

• 1、当执行查询语句时候会先去二级缓存中查询数据，如果有则返回。如果二级缓存中没有则到一级缓存中查找。
• 2、如果一级缓存中有，则返回。如果一级缓存也没有则发送sql语句到数据库中去查询。
• 3、从数据库查询出数据后立马将数据保存到一级缓存中。
• 4、当SqlSession关闭的时候把一级缓存中的数据保存到二级缓存中。

请注意：如果执行增 、删、改 那么会同时清除一级缓存和二级缓存

二级缓存使用示例

数据准备

DROP DATABASE IF EXISTS mybatisDatabase;CREATE DATABASE mybatisDatabase;use mybatisDatabase;CREATE TABLE user(  id INT PRIMARY KEY auto_increment,  username VARCHAR(50),  password VARCHAR(50),  gender VARCHAR(10));INSERT INTO user(username,password,gender) VALUES("lucy","123456","female");INSERT INTO user(username,password,gender) VALUES("momo","234567","female");INSERT INTO user(username,password,gender) VALUES("xixi","345678","female");INSERT INTO user(username,password,gender) VALUES("pepe","456123","female");SELECT * FROM user;

搭建开发环境

创建普通的Java工程，结构如下：

User

package cn.com.pojo;import java.io.Serializable;/** * 本文作者：谷哥的小弟  * 博客地址：http://blog.csdn.net/lfdfhl */public class User implements Serializable{
   	private static final long serialVersionUID = 112149170027586026L;	private Integer id;	private String username;	private String password;	private String gender;	public User() {
   			}	public User(Integer id, String username, String password, String gender) {
   		super();		this.id = id;		this.username = username;		this.password = password;		this.gender = gender;	}	public Integer getId() {
   		return id;	}	public void setId(Integer id) {
   		this.id = id;	}	public String getUsername() {
   		return username;	}	public void setUsername(String username) {
   		this.username = username;	}	public String getPassword() {
   		return password;	}	public void setPassword(String password) {
   		this.password = password;	}	public String getGender() {
   		return gender;	}	public void setGender(String gender) {
   		this.gender = gender;	}	@Override	public String toString() {
   		return "User [id=" + id + ", username=" + username + ", password=" + password + ", gender=" + gender + "]";	}	}

UserMapper .java

package cn.com.mapper;import cn.com.pojo.User;/** * 本文作者：谷哥的小弟  * 博客地址：http://blog.csdn.net/lfdfhl */public interface UserMapper {
   		public User queryUserById(Integer id);		public int updateUser(User user);}

UserMapper .xml

   
   	  
      
        
        select id,username,password,gender from user where id = #{
   id}      
    
          update user set username=#{
   username},password=#{
   password},gender=#{
   gender} where id=#{
   id}  
      
   

mybatis-config.xml

log4j.properties

# Global logging configurationlog4j.rootLogger=DEBUG, stdout# Console output...log4j.appender.stdout=org.apache.log4j.ConsoleAppenderlog4j.appender.stdout.layout=org.apache.log4j.PatternLayoutlog4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

MybatisTest

package cn.com.test;import java.io.InputStream;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import org.junit.Test;import cn.com.mapper.UserMapper;import cn.com.pojo.User;/** * 本文作者：谷哥的小弟 * 博客地址：http://blog.csdn.net/lfdfhl */public class MybatisTest {
   	static SqlSessionFactory sqlSessionFactory = null;	public static SqlSessionFactory getSqlSessionFactory() {
   		try {
   			if (sqlSessionFactory == null) {
   				InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");				SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();				sqlSessionFactory = sqlSessionFactoryBuilder.build(inputStream);			}			return sqlSessionFactory;		} catch (Exception e) {
   			// TODO: handle exception		} finally {
   		}		return null;	}		public void sqlSessionCatch() {
   		//获取SqlSession		SqlSession sqlSession=getSqlSessionFactory().openSession();		//利用SqlSession得到UserMapper		UserMapper userMapper = sqlSession.getMapper(UserMapper.class);		//利用SqlSession执行数据查询		User user = userMapper.queryUserById(1);		System.out.println(user.getUsername());		//关闭SqlSession		sqlSession.close();	}	@Test	public void testSqlSessionCatch() {
   		sqlSessionCatch();		sqlSessionCatch();		sqlSessionCatch();		sqlSessionCatch();	}		public void sqlSessionCatchClean() {
   		//获取SqlSession		SqlSession sqlSession=getSqlSessionFactory().openSession();		//利用SqlSession得到UserMapper		UserMapper userMapper = sqlSession.getMapper(UserMapper.class);		//利用SqlSession执行数据查询		User user = userMapper.queryUserById(1);		System.out.println(user.getUsername());		//利用SqlSession执行数据更新		userMapper.updateUser(new User(2, "bmbm", "123456", "female"));		//关闭SqlSession		sqlSession.close();	}		@Test	public void testSqlSessionCatchClean() {
   		sqlSessionCatchClean();		sqlSessionCatchClean();		sqlSessionCatchClean();		sqlSessionCatchClean();	}}

testSqlSessionCatch测试结果如下：

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.0DEBUG [main] - Opening JDBC ConnectionDEBUG [main] - Created connection 1392425346.DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - ==>  Preparing: select id,username,password,gender from user where id = ? DEBUG [main] - ==> Parameters: 1(Integer)DEBUG [main] - <==      Total: 1lucyDEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Returned connection 1392425346 to pool.DEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.5lucyDEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.6666666666666666lucyDEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.75lucy

请注意命中率Cache Hit Ratio的变化：

• 1、第一次查询时无缓存，所以Cache Hit Ratio=0
• 2、第二次查询时有缓存，共两次查询其中一次来自于缓存；所以，Cache Hit Ratio=0.5
• 3、第三次查询时有缓存，共三次查询其中二次来自于缓存；所以，Cache Hit Ratio=0.66666666666666666666
• 4、第四次查询时有缓存，共四次查询其中三次来自于缓存；所以，Cache Hit Ratio=0.75

testSqlSessionCatchClean测试结果如下：

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - PooledDataSource forcefully closed/removed all connections.DEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.0DEBUG [main] - Opening JDBC ConnectionDEBUG [main] - Created connection 1392425346.DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - ==>  Preparing: select id,username,password,gender from user where id = ? DEBUG [main] - ==> Parameters: 1(Integer)DEBUG [main] - <==      Total: 1lucyDEBUG [main] - ==>  Preparing: update user set username=?,password=?,gender=? where id=? DEBUG [main] - ==> Parameters: bmbm(String), 123456(String), female(String), 2(Integer)DEBUG [main] - <==    Updates: 1DEBUG [main] - Rolling back JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Returned connection 1392425346 to pool.DEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.0DEBUG [main] - Opening JDBC ConnectionDEBUG [main] - Checked out connection 1392425346 from pool.DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - ==>  Preparing: select id,username,password,gender from user where id = ? DEBUG [main] - ==> Parameters: 1(Integer)DEBUG [main] - <==      Total: 1lucyDEBUG [main] - ==>  Preparing: update user set username=?,password=?,gender=? where id=? DEBUG [main] - ==> Parameters: bmbm(String), 123456(String), female(String), 2(Integer)DEBUG [main] - <==    Updates: 1DEBUG [main] - Rolling back JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Returned connection 1392425346 to pool.DEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.0DEBUG [main] - Opening JDBC ConnectionDEBUG [main] - Checked out connection 1392425346 from pool.DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - ==>  Preparing: select id,username,password,gender from user where id = ? DEBUG [main] - ==> Parameters: 1(Integer)DEBUG [main] - <==      Total: 1lucyDEBUG [main] - ==>  Preparing: update user set username=?,password=?,gender=? where id=? DEBUG [main] - ==> Parameters: bmbm(String), 123456(String), female(String), 2(Integer)DEBUG [main] - <==    Updates: 1DEBUG [main] - Rolling back JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Returned connection 1392425346 to pool.DEBUG [main] - Cache Hit Ratio [cn.com.mapper.UserMapper]: 0.0DEBUG [main] - Opening JDBC ConnectionDEBUG [main] - Checked out connection 1392425346 from pool.DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - ==>  Preparing: select id,username,password,gender from user where id = ? DEBUG [main] - ==> Parameters: 1(Integer)DEBUG [main] - <==      Total: 1lucyDEBUG [main] - ==>  Preparing: update user set username=?,password=?,gender=? where id=? DEBUG [main] - ==> Parameters: bmbm(String), 123456(String), female(String), 2(Integer)DEBUG [main] - <==    Updates: 1DEBUG [main] - Rolling back JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@52feb982]DEBUG [main] - Returned connection 1392425346 to pool.

在此测试中命中率Cache Hit Ratio=0；再次验证了：如果执行增 、删、改 那么会同时清除一级缓存和二级缓存

二级缓存策略

MyBatis二级缓存常用策略如下：

• LRU – 最近最少使用的，即移除最长时间不被使用的对象(默认策略)。

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