緩存是介于應(yīng)用程序和永久必?cái)?shù)據(jù)存儲(chǔ)源之間，目的是為了降低應(yīng)用程序直接讀寫永久必?cái)?shù)據(jù)存儲(chǔ)源的頻率，從而提高運(yùn)行性能

緩存通常是在內(nèi)存中的如：

Office中的Word、Excel

Hibernater中的session以及SessionFactory

• new 語句創(chuàng)建java對(duì)象時(shí),JVM會(huì)為當(dāng)前對(duì)象分配一個(gè)內(nèi)存
• 只要當(dāng)前對(duì)象被其它資源引用，就會(huì)一直存在內(nèi)存中
• 如果當(dāng)前對(duì)象不被其它資源引用，就結(jié)結(jié)束生命周期
• 一個(gè)對(duì)象被其它生命周期未結(jié)束的對(duì)象引用，則這個(gè)對(duì)象的生命周期也不會(huì)結(jié)束

ehcache.xml

<?xml version='1.0' encoding='UTF-8'?><ehcache>    <diskStore path="java.io.tempdir"/>        <!--        maxElementsInMemory:允許緩存可以存儲(chǔ)的總記錄數(shù)        eternal：當(dāng)前緩存是否永遠(yuǎn)不過期        overflowToDisk：當(dāng)前緩存中的數(shù)據(jù)達(dá)到最大值時(shí)，是否把緩存數(shù)據(jù)寫入本地硬盤        timeToIdleSeconds：當(dāng)前緩存最大閑置時(shí)間，超過該時(shí)間則銷毀緩存        timeToLiveSeconds:設(shè)置緩存超時(shí)時(shí)間，當(dāng)緩存創(chuàng)建后，達(dá)到該時(shí)間就自動(dòng)銷毀    -->        <defaultCache        maxElementsInMemory = "5"        eternal = "false"        overflowToDisk = "true"        timeToIdleSeconds = "15"        timeToLiveSeconds = "120"    /></ehcache>

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE hibernate-configuration PUBLIC          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"><!-- Generated by MyEclipse Hibernate Tools.                   --><hibernate-configuration>    <session-factory>        <PRoperty name="hbm2ddl.auto">update</property>        <property name="dialect">            org.hibernate.dialect.Oracle9Dialect        </property>        <property name="connection.url">            jdbc:oracle:thin:@10.0.0.11:1521:ORCL        </property>        <property name="connection.username">demo</property>        <property name="connection.password">demo</property>        <property name="connection.driver_class">            oracle.jdbc.driver.OracleDriver        </property>        <!-- 在Hibernate配置文件中激活ehcache二級(jí)緩存 -->        <property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>        <property name="hibernate.cache.use_query_cache">true</property>                <mapping resource="demo/entity/Bird.hbm.xml" />        <!-- 添加使用Hibernate注解的實(shí)體Bean，而不是映射文件 -->        <mapping class="demo.annotations.entity.Weapon" />                </session-factory></hibernate-configuration>

實(shí)體類配置

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"><!--     Mapping file autogenerated by MyEclipse Persistence Tools--><hibernate-mapping>    <class name="demo.entity.Bird" table="BIRD">        <!-- <cache usage="read-write"/> -->        <id name="birdId" type="long">            <column name="id" precision="22" scale="0" />            <generator class="native" />        </id>        <property name="name" type="string">            <column name="NAME" length="50" />        </property>    </class></hibernate-mapping>