Hibernate学习11——配置Hibernate二级缓存

package com.cy.model;

public class Class {
    private int id;
    private String name;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    
    
}

package com.cy.model;

import com.cy.model.Class;

public class Student {
    private int id;
    private String name;
    private Class c;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Class getC() {
        return c;
    }
    public void setC(Class c) {
        this.c = c;
    }
    
    
}

<hibernate-mapping package="com.cy.model">

    <class name="Class" table="t_class">
        <id name="id" column="classId">
            <generator class="native"></generator>
        </id>
        <property name="name" column="className"></property>
    </class>

</hibernate-mapping>

<hibernate-mapping package="com.cy.model">

    <class name="Student" table="t_student">
        <id name="id" column="stuId">
            <generator class="native"></generator>
        </id>
        <property name="name" column="stuName"></property>
        
        <many-to-one name="c" class="com.cy.model.Class" column="classId" cascade="save-update"></many-to-one>
    </class>

</hibernate-mapping>

package com.cy.service;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.cy.model.Class;
import com.cy.util.HibernateUtil;

public class StudentTest {

    private SessionFactory sessionFactory=HibernateUtil.getSessionFactory();
    private Session session;
    
    @Before
    public void setUp() throws Exception {
        session=sessionFactory.openSession(); 
        session.beginTransaction();
    }

    @After
    public void tearDown() throws Exception {
         session.getTransaction().commit();
         session.close();
    }
    
    /**
     * 同一个session中，同一个事务是有一级缓存的；
     */
    @Test
    public void testCache1(){
        Class c = (Class) session.get(Class.class, 1);
        System.out.println(c.getName());
        
        Class c2 = (Class) session.get(Class.class, 1);
        System.out.println(c2.getName());
        System.out.println(c == c2);
        
        /*
         *  Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=?
            08计算机本科
            08计算机本科
            true
            
            第一次取c1的时候，已经将取出来的数据c1放到缓存中。
            第二次取c2的时候，是有session缓存的。首选从缓存中找，找到，直接从缓存中拿，而不到数据库中去取了。
            两个是同一个OID对象；
         */
    }
    
    /**
     * 在不同的事务中，是否有缓存？
     */
    @Test
    public void testCache2(){
        Session session1 = sessionFactory.openSession();
        session1.beginTransaction();
        Class c = (Class) session1.get(Class.class, 1);
        System.out.println(c.getName());
        session1.getTransaction().commit();
        session1.close();
        
        
        Session session2 = sessionFactory.openSession();
        session2.beginTransaction();
        Class c2 = (Class) session2.get(Class.class, 1);
        System.out.println(c2.getName());
        session2.getTransaction().commit();
        session2.close();
        
        System.out.println(c == c2);
        /*
         *  Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=?
            08计算机本科
            Hibernate: select class0_.classId as classId1_0_0_, class0_.className as classNam2_0_0_ from t_class class0_ where class0_.classId=?
            08计算机本科
            false
            
            虽然在同一个session中有缓存，但是这里新开辟了一个事务，发出两个sql
            不同的事务是不能共用一级缓存的。
            一级缓存只适用于同一个session，同一个事务；
         */
    }
}