Hibernate一级二级缓存

花了一天时间把hibernate二级缓存研究了下，突然搞出一些门道，为了防止我的小容量的脑袋忘记，于是在这里准备把我了解到的一些东西讲一下。

第一、一级缓存二级缓存的概念解释（参考文章Hibernate中一级缓存和二级缓存使用详解）

（1）一级缓存就是Session级别的缓存，一个Session做了一个查询操作，它会把这个操作的结果放在一级缓存中，如果短时间内这个

session（一定要同一个session）又做了同一个操作，那么hibernate直接从一级缓存中拿，而不会再去连数据库，取数据；

（2）二级缓存就是SessionFactory级别的缓存，顾名思义，就是查询的时候会把查询结果缓存到二级缓存中，如果同一个sessionFactory创建的某个session执行了相同的操作，hibernate就会从二级缓存中拿结果，而不会再去连接数据库，注意只需进行了相同数据库操作，可以不是同一个session；

（3）Hibernate中提供了两级Cache，第一级别的缓存是Session级别的缓存，它是属于事务范围的缓存。这一级别的缓存由hibernate管理的，一般情况下无需进行干预；第二级别的缓存是SessionFactory级别的缓存，它是属于进程范围或群集范围的缓存。这一级别的缓存可以进行配置和更改，并且可以动态加载和卸载。 Hibernate还为查询结果提供了一个查询缓存，它依赖于第二级缓存；

第二、hibernate3和hibernate4中的EhCache的配置

（1）话说我用的hibernate3.6.10 final，发现其lib/optional/下根本就没有ehcache目录的jar包，很是奇怪，于是我下了hibernate4.2.1，发现其相同路径下是有的，所以我把它路径下的所有包加到了自己自定义了一个User Libraries,同时去网上搜索下载添加了commons-logging和backport-util-concurrent两个jar包。到此所有包添加完毕。

（2）如果是hibernate3的hibernate.cfg.xml配置：

<!-- 开启二级缓存 -->
<property name="hibernate.cache.use_second_level_cache">true</property>
<!-- 设置缓存提供者 -->
<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property>

如果是hibernate4的配置：

<!-- 开启二级缓存 -->
<property name="hibernate.cache.use_second_level_cache">true</property>

<property name="hibernate.cache.region.factory_class">org.hibernate.cache.EhCacheRegionFactory </property>

第三、程序的实现

（1）创建一个java项目，创建一个News类（MyHibernateSecondCache/src/shamrock/model/News.java）：

package shamrock.model;

public class News {
private Integer id;
private String title;
private String content;

public News(){

}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getTitle() {
return title;
}

public void setTitle(String title) {
this.title = title;
}

public String getContent() {
return content;
}

public void setContent(String content) {
this.content = content;
}

}

创建一个News相应的配置文件（MyHibernateSecondCache/src/shamrock/model/News.hbm.xml）：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2015-5-11 11:22:43 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="shamrock.model">
<class name="News" table="news_table">
<span style="color:#FF0000;">  <cache usage="read-only"/></span>
<id name="id" type="java.lang.Integer">
<column name="ID" />
<generator class="identity" />
</id>
<property name="title" type="java.lang.String">
<column name="TITLE" />
</property>
<property name="content" type="java.lang.String">
<column name="CONTENT" />
</property>
</class>
</hibernate-mapping>

（2）创建运行程序Manager（MyHibernateSecondCache/src/shamrock/run/Manager.java）:

package shamrock.run;

import java.util.List;
import java.util.Map;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import shamrock.model.News;

public class Manager {
static Configuration conf = new Configuration().configure();
static SessionFactory sf = conf.buildSessionFactory();

public static void main(String[] args){
Manager mgr = new Manager();
mgr.secondCacheTest();
mgr.stat();
}

public void secondCacheTest(){
<span style="color:#FF0000;">Session sess = sf.getCurrentSession();</span>
sess.beginTransaction();
<span style="color:#FF0000;">List names = sess.createQuery("from News news").list();</span>
sess.getTransaction().commit();
System.out.println("-------------------");
<span style="color:#FF0000;">Session sess2 = sf.getCurrentSession();</span>
sess2.beginTransaction();
<span style="color:#FF0000;">News news = (News) sess2.load(News.class, 2);</span>
System.out.println(news.getTitle());
<span style="color:#FF0000;">Session sess3 = sf.getCurrentSession();</span>
sess3.beginTransaction();
<span style="color:#FF0000;">News newss = (News) sess3.load(News.class, 3);</span>
System.out.println(newss.getTitle());
sess2.getTransaction().commit();
}
private void stat(){
Map cacheEntries = sf.getStatistics().getSecondLevelCacheStatistics("shamrock.model.News").getEntries();
System.out.println(cacheEntries);

}
}

(3)ehcahce.xml（MyHibernateSecondCache/src/ehcache.xml）的配置,该文件在hibernate官方包中的project\etc可以找到，直接复制内容。这里就不贴内容了。

(4)hibernate.cfg.xml（MyHibernateSecondCache/src/hibernate.cfg.xml）的配置

<?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">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.password">123456</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/myjava</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.c3p0.min_size">1</property>
<property name="hibernate.c3p0.timeout">5000</property>
<property name="hibernate.c3p0.acquire_increment">2</property>
<property name="hibernate.c3p0.idle_test_period">3000</property>
<property name="hibernate.c3p0.max_size">20</property>
<property name="hibernate.c3p0.max_statements">100</property>
<span style="color:#FF0000;">  <property name="hibernate.cache.use_second_level_cache">true</property>

<property name="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</property></span>
<!--
<property name="hibernate.cache.region.factory_class">org.hibernate.cache.EhCacheRegionFactory </property>
-->
<property name="hibernate.cache.use_structured_entries">true</property>
<property name="hibernate.generate_statistics">true</property>
<property name="hibernate.current_session_context_class">thread</property>
<property name="hibernate.format_sql">true</property>
<property name="hibernate.show_sql">true</property>
<property name="hibernate.hbm2ddl.auto">update</property>
<mapping resource="shamrock/model/News.hbm.xml"/>
</session-factory>
</hibernate-configuration>

第四、数据库表内容

<span style="font-size:14px;">ID     TITLE    CONTENT
1       11        111
2       22        222
3       33        333
4       44        444</span>

第五、缓存结果比较

（1）上面的程序是开启了二级缓存，运行结果如下：

五月 11, 2015 8:57:19 下午 com.mchange.v2.log.MLog <clinit>
INFO: MLog clients using java 1.4+ standard logging.
五月 11, 2015 8:57:19 下午 com.mchange.v2.c3p0.C3P0Registry banner
INFO: Initializing c3p0-0.9.1 [built 16-January-2007 14:46:42; debug? true; trace: 10]
五月 11, 2015 8:57:19 下午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
INFO: Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@963f5a0d [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@abf33e4b [ acquireIncrement -> 2, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1bqpdea99ilr5cck4icj5|101b9cf, idleConnectionTestPeriod -> 3000, initialPoolSize -> 1, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 5000, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 100, maxStatementsPerConnection -> 0, minPoolSize -> 1, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@96b69ade [ description -> null, driverClass -> null, factoryClassLocation -> null, identityToken -> 1bqpdea99ilr5cck4icj5|317bdd, jdbcUrl -> jdbc:mysql://localhost:3306/myjava, properties -> {user=******, password=******} ], preferredTestQuery -> null, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, factoryClassLocation -> null, identityToken -> 1bqpdea99ilr5cck4icj5|38f07b, numHelperThreads -> 3 ]
Hibernate:
select
news0_.ID as ID0_,
news0_.TITLE as TITLE0_,
news0_.CONTENT as CONTENT0_
from
news_table news0_
-------------------
22
33
{1={content=111, title=11, _version=null, _lazyPropertiesUnfetched=true, _subclass=shamrock.model.News}, 2={content=222, title=22, _version=null, _lazyPropertiesUnfetch

可以看出设置了二级缓存，不管操作是不是完全一样，只要打开的session是同一个操作，即查询操作，那就只进行第一次查询操作的[b]数据库连接，后面两次直接去二级缓存里面去取，因为SessionFactory存在含有查询内容的Session实体的内容值。[/b]

（2）MyHibernateSecondCache/src/shamrock/model/News.hbm.xml中 <cache usage="read-only"/>去掉，运行结果如下：

五月 11, 2015 9:05:36 下午 com.mchange.v2.c3p0.C3P0Registry banner
INFO: Initializing c3p0-0.9.1 [built 16-January-2007 14:46:42; debug? true; trace: 10]
五月 11, 2015 9:05:36 下午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
INFO: Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@30c6cffd [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@dc46c428 [ acquireIncrement -> 2, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1bqpdea99im1t6p9a9bry|1cd6a5b, idleConnectionTestPeriod -> 3000, initialPoolSize -> 1, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 5000, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 100, maxStatementsPerConnection -> 0, minPoolSize -> 1, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@1750a1c [ description -> null, driverClass -> null, factoryClassLocation -> null, identityToken -> 1bqpdea99im1t6p9a9bry|157ace, jdbcUrl -> jdbc:mysql://localhost:3306/myjava, properties -> {user=******, password=******} ], preferredTestQuery -> null, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, factoryClassLocation -> null, identityToken -> 1bqpdea99im1t6p9a9bry|1355469, numHelperThreads -> 3 ]
Hibernate:
select
news0_.ID as ID0_,
news0_.TITLE as TITLE0_,
news0_.CONTENT as CONTENT0_
from
news_table news0_
-------------------
Hibernate:
select
news0_.ID as ID0_0_,
news0_.TITLE as TITLE0_0_,
news0_.CONTENT as CONTENT0_0_
from
news_table news0_
where
news0_.ID=?
22
Hibernate:
select
news0_.ID as ID0_0_,
news0_.TITLE as TITLE0_0_,
news0_.CONTENT as CONTENT0_0_
from
news_table news0_
where
news0_.ID=?
33
Exception in thread "main" java.lang.NullPointerException
at shamrock.run.Manager.start(Manager.java:39)
at shamrock.run.Manager.main(Manager.java:19)

这里没有设置二级缓存，所有操作都不同，也不是在一个session中，所以，这里每一次查询都要进行数据库操作，不存在二级缓存故也不存在相应实体key-value所以mgr.stat();报错为null。

（3）在（2）的基础上，修改manager.java中News newss = (News) sess3.load(News.class, 3);修改为News newss = (News) sess3.load(News.class, 2);运行结果：

五月 11, 2015 9:11:16 下午 com.mchange.v2.log.MLog <clinit>
INFO: MLog clients using java 1.4+ standard logging.
五月 11, 2015 9:11:16 下午 com.mchange.v2.c3p0.C3P0Registry banner
INFO: Initializing c3p0-0.9.1 [built 16-January-2007 14:46:42; debug? true; trace: 10]
五月 11, 2015 9:11:17 下午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
INFO: Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@2eeaac69 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@da6aa094 [ acquireIncrement -> 2, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1bqpdea99im93nne6to47|1cd6a5b, idleConnectionTestPeriod -> 3000, initialPoolSize -> 1, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 5000, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 100, maxStatementsPerConnection -> 0, minPoolSize -> 1, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@226df030 [ description -> null, driverClass -> null, factoryClassLocation -> null, identityToken -> 1bqpdea99im93nne6to47|157ace, jdbcUrl -> jdbc:mysql://localhost:3306/myjava, properties -> {user=******, password=******} ], preferredTestQuery -> null, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, factoryClassLocation -> null, identityToken -> 1bqpdea99im93nne6to47|1355469, numHelperThreads -> 3 ]
Hibernate:
select
news0_.ID as ID0_,
news0_.TITLE as TITLE0_,
news0_.CONTENT as CONTENT0_
from
news_table news0_
-------------------
Hibernate:
select
news0_.ID as ID0_0_,
news0_.TITLE as TITLE0_0_,
news0_.CONTENT as CONTENT0_0_
from
news_table news0_
where
news0_.ID=?
22
22
Exception in thread "main" java.lang.NullPointerException
at shamrock.run.Manager.start(Manager.java:39)
at shamrock.run.Manager.main(Manager.java:19)

这里虽然没有设置二级缓存，但是因为是同一个session下进行完全相同的操作即查询id=2的记录获取其title，所以这里hibernate默认是开启了一级缓存，所以直接去一级缓存里面取，二级缓存不存在，故stat()报错。

第五、综合阐述

综合上面，我们做的比较，可以看出，要是开启了二级缓存，只要是对同一个sessionFactory创建的session执行了同一个数据库对象的操作，注意这里并不是完全相同，只要是查询，不一定是查询同一记录，因为实体类news对应的数据库记录类都缓存在了session中，只要通过key-value去取相应实体就可以了。

如果是同一个session下，执行完全相同操作，即使操作同一数据表都是查询但是id不一样也是不同的，也要进行多次数据库的连接查找，只要找的记录是同一条，才会去session中完全相同的记录。

以上是我菜鸟的一点点自己想法，如果哪位大神无意看到，请勿喷。