mybatis的缓存机制

一级缓存:

MyBatis的一级缓存指的是在一个Session域内,session为关闭的时候执行的查询会根据SQL为key被缓存(跟mysql缓存一样,修改任何参数的值都会导致缓存失效)

package cn.itcast.mybatis.dao;

import static org.junit.Assert.*;

import java.io.IOException;
import java.io.InputStream;
import java.util.Date;
import java.util.HashMap;
import java.util.List;

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.Before;
import org.junit.Test;

import cn.itcast.mybatis.pojo.User;

public class UserDAOTest2 {

private static IUser userDAO = null;

private static SqlSession sqlSession = null;

@Before
public void init() {
try {
// 构造SqlSessionFactory
// 定义配置文件路径
String resource = "mybatis-config.xml";
// 读取配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
// 通过SqlSessionFactoryBuilder构建一个SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream,"test");

this.sqlSession = sqlSessionFactory.openSession(false);//设为false时,必须手动提交:sqlSession.commit();
//            this.sqlSession.close();
this.userDAO = sqlSession.getMapper(IUser.class);
} catch (IOException e) {
e.printStackTrace();
}
}

static{

// 构造SqlSessionFactory
// 定义配置文件路径
String resource = "mybatis-config.xml";
// 读取配置文件
InputStream inputStream;
try {
inputStream = Resources.getResourceAsStream(resource);
// 通过SqlSessionFactoryBuilder构建一个SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream,"test");

sqlSession = sqlSessionFactory.openSession(false);//设为false时,必须手动提交:sqlSession.commit();
//            this.sqlSession.close();//当关闭的时候,在下面的方法中都会报错
userDAO = sqlSession.getMapper(IUser.class);

} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

@Test
public void testQueryUserByUserName() {
User user = this.userDAO.queryUserByUserName("zhangsan");
System.out.println(user);
}

@Test
public void testQueryByTabkeName() {

List <HashMap<String, Object>> list2= this.userDAO.queryByTabkeName("tb_order");
for (HashMap<String, Object> hashMap : list2) {
System.out.println(hashMap);

}
}

@Test
public void testQueryUserByUserNameAndPassword() {
HashMap<String, Object> map = new HashMap<String, Object>();
map.put("userName", "zhangsan");
map.put("password", "123456");
//        User user = this.userDAO.queryUserByUserNameAndPassword(map);
User user = this.userDAO.queryUserByUserNameAndPassword("zhangsan","123456");
System.out.println(user);
}

@Test
public void testSaveUser() {
User user = new User();
user.setAge(20);
user.setBirthday(new Date());
user.setName("test_name_9");
user.setPassword("123456");
user.setSex(true);
user.setUserName("test_username_9");

this.userDAO.saveUser(user);

System.out.println(user);
// 提交
this.sqlSession.commit();
}

@Test
public void testUpdateUser() {
User user = new User();
user.setAge(20);
user.setBirthday(new Date());
user.setName("test_name_1");
user.setPassword("123qwe");
user.setSex(true);
user.setId(6L);

this.userDAO.updateUser(user);
this.sqlSession.commit();
}

@Test
public void testDeleteUserById() {
this.userDAO.deleteUserById(6L);
}

}

二级缓存:

Mybatis的二级缓存的作用域是一个mapper的namespace，同一个namespace中查询sql可以从缓存中命中。

二级缓存是可以跨session的。

开启二级缓存：

在mapper.xml文件中加入 <cache /> 。