MyBatis架構的一級緩存機制（SqlSession級别）

 代碼：

User.java

package com.bean;

import java.io.Serializable;

public class User implements Serializable {
	private Integer id;
	private String name;
	private String sex;
	private Integer age;
	public User() {
		super();
		// TODO Auto-generated constructor stub
	}
	public User(String name, String sex, Integer age) {
		super();
		this.name = name;
		this.sex = sex;
		this.age = age;
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public Integer getAge() {
		return age;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		return "User [id=" + id + ", name=" + name + ", sex=" + sex + ", age=" + age + "]";
	}
	
}
           

FKSqlSessionFactory.java

package com.factory;

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;

public class FKSqlSessionFactory {
	
	private static SqlSessionFactory sqlSessionFactory = null;
	
	// 初始化建立SqlSessionFactory對象
	static{
		try {
			// 讀取mybatis-config.xml檔案
			InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
			sqlSessionFactory = new SqlSessionFactoryBuilder()
					.build(inputStream);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	// 擷取SqlSession對象的靜态方法
	public static SqlSession getSqlSession(){
		return sqlSessionFactory.openSession();
	}

	// 擷取SqlSessionFactory的靜态方法
	public static SqlSessionFactory getSqlSessionFactory() {
		return sqlSessionFactory;
	}
}
           

UserMapper.java

package com.mapper;

import java.util.List;

import com.bean.User;

public interface UserMapper {
	// 根據id查詢User
	User selectUserById(Integer id);
	
	// 查詢所有User
	List<User> selectAllUser();
		
	// 根據id删除User
	void deleteUserById(Integer id);
}
           

UserMapper.xml

<?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">
<!-- namespace指使用者自定義的命名空間。 -->
<mapper namespace="com.mapper.UserMapper">
  <!-- 根據id查詢User -->
  <select id="selectUserById" parameterType="int" resultType="com.bean.User">
       select * from tb_user3 where id = #{id}
  </select>
  
  <!-- 查詢所有User -->
  <select id="selectAllUser" resultType="com.bean.User">
  	select * from tb_user3
  </select>
  
  <!-- 根據id删除User -->
  <delete id="deleteUserById" parameterType="int" >
  	 delete from tb_user3 where id = #{id}
  </delete>
</mapper>
           

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
  <!--  XML 配置檔案包含對 MyBatis 系統的核心設定 -->
<configuration>
	<properties resource="db.properties"/>
	<!-- 指定 MyBatis 所用日志的具體實作 -->
	<settings>
		<setting name="logImpl" value="LOG4J"/>
	</settings>
	<!-- 設定别名 -->
	<typeAliases>
		<typeAlias  alias="user" type="com.bean.User"/>
	</typeAliases>
	<environments default="mysql">
	<!-- 環境配置，即連接配接的資料庫。 -->
    <environment id="mysql">
    <!--  指定事務管理類型，type="JDBC"指直接簡單使用了JDBC的送出和復原設定 -->
      <transactionManager type="JDBC"/>
      <!--  dataSource指資料源配置，POOLED是JDBC連接配接對象的資料源連接配接池的實作。 -->
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  <!-- mappers告訴了MyBatis去哪裡找持久化類的映射檔案 -->
  <mappers>
  	<mapper resource="com/mapper/UserMapper.xml"/>
  </mappers>
</configuration>
           

TestOneLevelCache.java

package com.test;

import org.apache.ibatis.session.SqlSession;

import com.bean.User;
import com.factory.FKSqlSessionFactory;
import com.mapper.UserMapper;

public class TestOneLevelCache {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
        TestOneLevelCache test = new TestOneLevelCache();
      //test.testCache1();
      //test.testCache2();
        test.testCache3();
	}

	/*
	 * 一級緩存: 也就Session級的緩存(預設開啟)
	 */
	public void testCache1 (){
		// 使用工廠類獲得SqlSession對象
		SqlSession session=FKSqlSessionFactory.getSqlSession();
		// 獲得UserMapping對象
		UserMapper um=session.getMapper(UserMapper.class);
		// 查詢id為1的User對象，會執行select語句
		User user=um.selectUserById(1);
		System.out.println(user);
		// 再次查詢id為1的User對象,因為是同一個SqlSession,是以會從之前的一級緩存中查找資料
		User user2=um.selectUserById(1);
		System.out.println(user2);
		session.close();
	}
	
	public void testCache2 (){
		// 使用工廠類獲得SqlSession對象
		SqlSession session = FKSqlSessionFactory.getSqlSession();
		// 獲得UserMapping對象
		UserMapper um = session.getMapper(UserMapper.class);
		// 查詢id為1的User對象，會執行select語句
		User user = um.selectUserById(1);
		System.out.println(user);
		// 執行delete操作
		um.deleteUserById(4);
		session.commit();
		// 再次查詢id為1的User對象,因為DML操作會清空SqlSession緩存,是以會再次執行select語句
		User user2 = um.selectUserById(1);
		System.out.println(user2);
		session.close();
	}
	
	public void testCache3 (){
		// 使用工廠類獲得SqlSession對象
		SqlSession session = FKSqlSessionFactory.getSqlSession();
		// 獲得UserMapping對象
		UserMapper um = session.getMapper(UserMapper.class);
		// 查詢id為1的User對象，會執行select語句
		User user = um.selectUserById(1);
		System.out.println(user);
		// 關閉一級緩存
		session.close();
		// 再次通路,需要再次擷取一級緩存，然後才能查找資料，否則會抛出異常
		session = FKSqlSessionFactory.getSqlSession();
		// 再次獲得UserMapping對象
		um = session.getMapper(UserMapper.class);
		// 再次通路，因為現在使用的是一個新的SqlSession對象,是以會再次執行select語句
		User user2 = um.selectUserById(1);
		System.out.println(user2);
		// 關閉SqlSession對象
		session.close();
	}
}
           

截圖：