Hibernate学习之二级缓存

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());}}