《深入浅出Hibernate》书中的一个错误，误导了我好久。

后来想了想，有可能是因为hibernate的版本不一样吧，忘了在这说了。谢谢xujunJ2EE同学提醒。暂时没有时间去测试3.0的版本了。下面的内容是在hibernate3.2下测试的


3.load方法可以充分利用内部缓存和二级缓存的现有数据，而get方法则仅仅在内部缓存中进行数据查找，如没有发现对应数据，将越过二级缓存，直接调用SQL完成数据读取。
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以上是深入浅出Hibernate一书第245页中的一部分。
以前因为读过这本书，所以没有使用过get()方法，一直用load()。这两天认真的重新读了一遍，并且做了试验，发现这一句有误。我写了代码测试了，两个不同session中对同一条记录的查询动作，不论是get还是load，都只输出一句sql，也就是说get和load都利用到了二级缓存。

附上测试代码：
TestCase(JUnit4)

package test.hibernate;

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

import test.hibernate.entity.Member;

/**
 * @(#)HibernateTest.java 2008-6-21 下午04:43:55
 * 
 * @author Yuan
 * 类说明
 */
public class HibernateTest {

	private static SessionFactory sessionFactory;
	
	private static Session session;
	
	@Before
	public void setUp(){
		sessionFactory = new Configuration().configure().buildSessionFactory();
	}
	
	@After
	public void tearDown(){
		sessionFactory.close();
	}
	/**
	 * 测试Session.load()
	 */
	@Test
	public void testLoad(){
		System.out.println("**********************Load**********************");
		
		openSessionAndBeginTransaction();
		((Member)session.load(Member.class, "402880b31aab576f011aab5771bc0005")).getMemberName();
		commitTransactionAndCloseSession();
		
		openSessionAndBeginTransaction();
		((Member)session.load(Member.class, "402880b31aab576f011aab5771bc0005")).getMemberName();
		commitTransactionAndCloseSession();
	}
	
	/**
	 * 测试Session.get()
	 */
	@Test
	public void testGet(){
		System.out.println("**********************Get**********************");
		
		openSessionAndBeginTransaction();
		session.get(Member.class, "402880b31aab576f011aab5771bc0005");
		commitTransactionAndCloseSession();
		
		openSessionAndBeginTransaction();
		session.get(Member.class, "402880b31aab576f011aab5771bc0005");
		commitTransactionAndCloseSession();
	}
	
	private void openSessionAndBeginTransaction(){
		session = sessionFactory.openSession();
		session.beginTransaction();
	}
	
	private void commitTransactionAndCloseSession(){
		session.getTransaction().commit();
		session.flush();
		session.close();
	}
}

Entity

package test.hibernate.entity;

import java.io.Serializable;

/**
 * @(#)Member.java 2008-6-21 下午04:47:26
 * 
 * @author Yuan
 * Member Entity
 */
public class Member implements Serializable {

	private static final long serialVersionUID = 3667540833969806410L;

	private String memberID;
	
	private String memberName;
	
	private String password;
	
	private String realName;

	public String getMemberID() {
		return memberID;
	}

	public void setMemberID(String memberID) {
		this.memberID = memberID;
	}

	public String getMemberName() {
		return memberName;
	}

	public void setMemberName(String memberName) {
		this.memberName = memberName;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

	public String getRealName() {
		return realName;
	}

	public void setRealName(String realName) {
		this.realName = realName;
	}
}

Member.hbm.xml

<?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">
<hibernate-mapping>
	<class name="test.hibernate.entity.Member" table="t_member">
		<cache usage="read-write"/>
		<id name="memberID" type="string" length="32">
			<generator class="uuid"/>
		</id>
		<property name="memberName" type="string" length="32" not-null="true"/>
		<property name="password" type="string" length="32" not-null="true"/>
		<property name="realName" type="string" length="32"/>
	</class>
</hibernate-mapping>

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">
<hibernate-configuration>
	<session-factory>
		<property name="hibernate.connection.url">
			jdbc:mysql://127.0.0.1:3306/test
		</property>
		
		<property name="hibernate.connection.driver_class">
			com.mysql.jdbc.Driver
		</property>
		
		<property name="hibernate.dialect">
			org.hibernate.dialect.MySQL5InnoDBDialect
		</property>
		
		<property name="hibernate.connection.username">root</property>
		
		<property name="hibernate.connection.password">******</property>
		
		<property name="hibernate.show_sql">true</property>
		
		<property name="hibernate.cache.provider_class">
			net.sf.ehcache.hibernate.EhCacheProvider
		</property>
		
		<!--property name="hibernate.hbm2ddl.auto">
			create
		</property-->
		
		<mapping resource="test/hibernate/entity/Member.hbm.xml"/>
	</session-factory>
</hibernate-configuration>

ehcache.xml

<?xml version="1.0" encoding="utf-8"?>
<ehcache>
	<diskStore path = "java.io.tmpdir"/>
	<defaultCache
		maxElementsInMemory="10000"
		eternal="false"
		timeToIdleSeconds="120"
		timeToLiveSeconds="120"
		overflowToDisk="true"/>
</ehcache>

评论

2 楼 yuan 2009-08-21  

嗯，这个我后来有想到，忘了补上了。

1 楼 xujunJ2EE 2009-08-21  

hibernate版本不一样而已，夏昕使用的hibernate的时候，get还没有利用缓存，所以你能说他错了吗