Hibernate学习之二级缓存

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二级缓存

　　- 二级缓存又称“全局缓存”、“应用级缓存”

　　- 二级缓存中的数据可适用范围是当前应用的所有会话

　　- 二级缓存是可插拔式缓存，默认是EHCache

配置二级缓存步骤

　　- 添加二级缓存所需jar包

　　- 在hibernate.cfg.xml中开启二级缓存并配置二级缓存的提供类

　　- 添加二级缓存的属性配置文件

　　- 在需要被缓存的表所对应的映射文件中添加<cache/>标签

二级缓存数据

　　- 很少被修改的数据

　　- 不是很重要的数据，允许偶尔出现并发的数据

　　- 不会被高并发访问的数据

　　- 参考数据（eg.字典表等）

一二级缓存的对比

实例

1.项目结构

2.pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  
  	<modelVersion>4.0.0</modelVersion>

	<groupId>org.proxy</groupId>
	<artifactId>Hibernate-Ehcache</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<hibernate.version>5.1.7.Final</hibernate.version>
	</properties>

	<dependencies>
		<!-- Junit -->
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
		</dependency>
		<!-- Hibernate -->
		<dependency>
		    <groupId>org.hibernate</groupId>
		    <artifactId>hibernate-core</artifactId>
		    <version>${hibernate.version}</version>
		</dependency>
		<dependency>
		    <groupId>org.hibernate</groupId>
		    <artifactId>hibernate-ehcache</artifactId>
		    <version>${hibernate.version}</version>
		</dependency>
		<!-- MySQL -->
		<dependency>
		    <groupId>mysql</groupId>
		    <artifactId>mysql-connector-java</artifactId>
		    <version>5.1.42</version>
		</dependency>
		<!-- ehcache -->
		<!-- <dependency>
		    <groupId>net.sf.ehcache</groupId>
		    <artifactId>ehcache</artifactId>
		    <version>2.10.4</version>
		</dependency> -->
	</dependencies>
</project>

3.Student.java

package org.hibernate.model;

import java.util.Date;

public class Student {
	
	private long id;// 学号
	private String name;// 姓名
	private Date birthday;// 生日
	private String sex;// 性别
	
	public Student() {
	}

	public Student(long id, String name, Date birthday, String sex) {
		this.id = id;
		this.name = name;
		this.birthday = birthday;
		this.sex = sex;
	}
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Date getBirthday() {
		return birthday;
	}
	public void setBirthday(Date birthday) {
		this.birthday = birthday;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public long getId() {
		return id;
	}
	public void setId(long id) {
		this.id = id;
	}
	
}

4.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>

	<class name="org.hibernate.model.Student" table="STUDENT">
		<cache usage="read-only"/><!-- 该表加入二级缓存 -->
		<id name="id" type="java.lang.Long">
			<column name="ID"/>
			<generator class="assigned"/>
		</id>
		<property name="name" type="java.lang.String">
			<column name="NAME"/>
		</property>
		<property name="birthday" type="date">
			<column name="BIRTHDAY"/>
		</property>
		<property name="sex" type="java.lang.String">
			<column name="SEX"/>
		</property>
	</class>

</hibernate-mapping>

5.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>

	<!-- 配置SessionFactory -->
	<session-factory>
		<!-- 配置数据库连接信息 -->
		<property name="connection.username">root</property>
		<property name="connection.password">***</property>
		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
		<property name="connection.url">
			jdbc:mysql:///hibernate?useSSL=true&amp;characterEncoding=UTF-8
		</property>
		
		<!-- 配置常用属性 -->
		<property name="hbm2ddl.auto">update</property><!-- 自动检查并创建表结构 -->
		<property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property><!-- 方言 -->
		<property name="show_sql">true</property><!-- 显示SQL语句 -->
		
		<!-- 开启二级缓存 -->
		<property name="hibernate.cache.use_second_level_cache">true</property>
		<!-- 指定二级缓存的提供类 -->
		<property name="hibernate.cache.region.factory_class">
			org.hibernate.cache.ehcache.EhCacheRegionFactory
		</property>
		
		<!-- 引入映射文件 -->
		<mapping resource="hbm/Student.hbm.xml"/>
	</session-factory>

</hibernate-configuration>

6.ehcache.xml

<ehcache>

    <diskStore path="java.io.tmpdir"/><!-- 缓存文件保存路径 -->

	<!-- 默认缓存设置
		maxElementsInMemory：缓存的最大数量
		eternal：设置元素是否是永久的。如果设置为true，则timeout失效
		timeToIdleSeconds：设置元素过期前的空闲时间
		timeToLiveSeconds：设置元素过期前的活动时间
		overflowToDisk：当缓存中的数量达到限制后，是否保存到disk
	 -->
    <defaultCache
        maxElementsInMemory="10000"
        eternal="false"
        timeToIdleSeconds="120"
        timeToLiveSeconds="120"
        overflowToDisk="true"/>

   
    <cache name="Student"
        maxElementsInMemory="10000"
        eternal="false"
        timeToIdleSeconds="300"
        timeToLiveSeconds="600"
        overflowToDisk="true"/>

</ehcache>

7.TestChcache.java

package org.hibernate.test;

import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.model.Student;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

public class TestChcache {

	private SessionFactory sessionFactory;
	private Session session;
	private Transaction transaction;
	
	@Before
	public void before() {
		
		sessionFactory = new Configuration().configure().buildSessionFactory();// 创建SessionFactory对象
		session = sessionFactory.openSession();// 获取Session对象
		transaction = session.beginTransaction();// 开启事务
		
	}
	
	@After
	public void after() {
		
		transaction.commit();// 提交事务
		session.close();// 关闭Session
		sessionFactory.close();// 关闭SessionFactory
		
	}
	
	@Test
	public void init() {
		
		Student student = new Student(1L, "张三", new Date(), "男");
		session.save(student);
		
		student = new Student(2L, "李四", new Date(), "男");
		session.save(student);
		
	}
	
	@Test
	public void testChcache() {
		
		Student student = session.get(Student.class, 1L);
		System.out.println(student.getName());
		
		session = sessionFactory.openSession();
		student = session.get(Student.class, 1L);
		System.out.println(student.getName());
		
	}
	
}

8.效果预览

　　8.1 首先执行init()方法，初始化表数据

　　8.2 屏蔽Student.hbm.xml中的<cache usage="read-only"/>，执行testChcache()方法

　　8.3 不屏蔽Student.hbm.xml中的<cache usage="read-only"/>，执行testChcache()方法

参考：http://www.imooc.com/video/9017