验证Hibernate二级缓存的存在[通俗易懂]

大家好，又见面了，我是你们的朋友全栈君。

一、环境的搭建

请参考EHcache环境的配置

二、实体类（Student.java）

package com.hibernate.beans;

public class Student { 
   

    private Integer id;
    private String name;
    private int age;
    private double score;
    public Student() {
        super();
    }

    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    public Integer getId() {
        return id;
    }
    public Student(String name, int age, double score) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age
                + ", score=" + score + "]";
    }

    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public double getScore() {
        return score;
    }
    public void setScore(double score) {
        this.score = score;
    }
}

三、映射文件（Student.hbm.xml）

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 <hibernate-mapping package="com.hibernate.beans">
     <class name="Student" table="t_student">
        <id name="id" column="t_id">
            <!-- 主键生成策略 -->
            <generator class="native"></generator>
        </id>
        <property name="name" column="t_name"></property>
        <property name="age" column="t_age"></property>
        <property name="score" column="t_score"></property>
     </class>
 </hibernate-mapping>

四、主配置文件（hibernate.cfg.xml）

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
    <!--DB连接四要素 Ctrl shift C -->
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=UTF8</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password">123456</property>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <!-- 数据源：数据库连接池 -->
    <property name="hibernate.connection.provider_class">org.hibernate.c3p0.internal.C3P0ConnectionProvider</property>
    <!-- 当前session的上下文 保证在同一线程中获取到的是同一个session-->
    <property name="hibernate.current_session_context_class">thread</property>
    <!-- 自动建表-->
    <property name="hibernate.hbm2ddl.auto">update</property>
    <!-- 显示SQL -->
    <property name="hibernate.show_sql">true</property>
    <!-- 格式化SQL -->
    <property name="hibernate.format_sql">true</property>


    <!-- 开启二级缓存 -->
    <property name="hibernate.cache.use_second_level_cache">true</property>
    <!-- 注册二级缓存区域工厂 -->
    <property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>
    <!-- 加载映射文件 -->
    <mapping resource="com/hibernate/beans/Student.hbm.xml"/>
    <!-- 配置缓存类 -->
    <class-cache usage="read-only" class="com.hibernate.beans.Student"/>
    <!-- 配置缓存集合 <collection-cache usage="read-only" collection="com.hibernate.beans.Student.name"/> -->
    </session-factory>
</hibernate-configuration>

五、测试代码
------

public void testEHcache(){
        //获取session
        Session session = HbnUtils.getSession();
        try {
            //开启事务
            session.beginTransaction();
            //第一次执行get操作
            Student student = session.get(Student.class, 1);
            System.out.println(student);
            //第二次执行get操作
            Student student1 = session.get(Student.class, 1);
            System.out.println(student1);
            //清除session缓存
            session.clear();

            //第三次执行get操作
            Student student2 = session.get(Student.class, 1);
            System.out.println(student2);
            //提交事务
            session.getTransaction().commit();
        } catch (Exception e) {
            //回滚事务
            session.getTransaction().rollback();
        }
    }

结果

 select
        student0_.t_id as t_id1_0_0_,
        student0_.t_name as t_name2_0_0_,
        student0_.t_age as t_age3_0_0_,
        student0_.t_score as t_score4_0_0_ 
    from
        t_student student0_ 
    where
        student0_.t_id=?
Student [id=1, name=李四, age=20, score=90.0]
Student [id=1, name=李四, age=20, score=90.0]
Student [id=1, name=李四, age=20, score=90.0]

分析

日志上的sql语句是第一次查询出现了，

第一次输出的详情是从数据库中加载来的，

第二次输出的详情是从session缓存中读取的，

然后session缓存被清空，

第三次输出的详情就只能是从二级缓存中读取的了