爲了區別 load 與 get的 方法的差異 ，特作了以下測試：
實體類： Address.java
package one2one;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name="ssss")
public class Address {
private int id; String name;
public String getName() {
return name;
} public void setName(String name) { this.name = name; } public Address() { } @Id @GeneratedValue(strategy=GenerationType.AUTO) public int getId() { return id; } public void setId(int id) { this.id = id; } 
}
hibernate.cfg.xml 的內容：
<!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="connection.username">sa</property> <property name="connection.password"></property> <property name="connection.url"> jdbc:mysql://localhost:3306/db </property> <property name="dialect"> org.hibernate.dialect.MySQLDialect </property> <property name="connection.driver_class"> com.mysql.jdbc.Driver </property><!-- <property name="hbm2ddl.auto">create</property> --><!-- <property name="connection.provider_class"> org.hibernate.connection.C3P0ConnectionProvider </property> <property name="c3p0.max_size">100</property> <property name="c3p0.max_statements">100</property> --> <mapping class="one2one.Address" /> <!-- <mapping class="org.hibernate.test.annotations.join.Cat" /> <mapping class="org.hibernate.test.annotations.join.Death" /> --><!-- --> <!--<mapping class="annotations.one2one.Ticket" /> <mapping class="annotations.one2one.Discount" /> --><!-- <mapping class="annotations.Inheritance.CreditCardPayment" /> <mapping class="annotations.Inheritance.Payment" /> --><!-- <event type="load"> <listener class="org.hibernate.event.def.DefaultLoadEventListener" /> <listener class="event.Load" /> </event>--></session-factory></hibernate-configuration>
log4j.properties 的內容爲：
### direct log messages to stdout ###log4j.appender.stdout=org.apache.log4j.ConsoleAppenderlog4j.appender.stdout.Target=System.outlog4j.appender.stdout.layout=org.apache.log4j.PatternLayoutlog4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n### direct messages to file hibernate.log ####log4j.appender.file=org.apache.log4j.FileAppender#log4j.appender.file.File=hibernate.log#log4j.appender.file.layout=org.apache.log4j.PatternLayout#log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n### set log levels - for more verbose logging change 'info' to 'debug' ###log4j.rootLogger=debug, stdoutlog4j.logger.org.hibernate.event.def.DefaultLoadEventListener=debuglog4j.logger.org.hibernate=error#log4j.logger.org.hibernate=debug### log HQL query parser activity#log4j.logger.org.hibernate.hql.ast.AST=debug### log just the SQLlog4j.logger.org.hibernate.SQL=debug### log JDBC bind parameters ###log4j.logger.org.hibernate.type=info#log4j.logger.org.hibernate.type=debug### log schema export/update ###log4j.logger.org.hibernate.tool.hbm2ddl=debug### log HQL parse trees#log4j.logger.org.hibernate.hql=debug### log cache activity ####log4j.logger.org.hibernate.cache=debug### log transaction activity#log4j.logger.org.hibernate.transaction=debug### log JDBC resource acquisition#log4j.logger.org.hibernate.jdbc=debug### enable the following line if you want to track down connection ###### leakages when using DriverManagerConnectionProvider ####log4j.logger.org.hibernate.connection.DriverManagerConnectionProvider=trace
HibernateUtil ： 一個幫助類：
/* ************************************************************ *本文件歸屬於軟件有限公司，未經許可，不得擅自使用、拷貝和修改 *項目組:ESB小組 *版 本: SychroESB1.0 *日 期：2007-11-20 *時 間：上午08:31:43 *作 者：Administrator *********************************************************** */package annotations;import org.hibernate.*;import org.hibernate.cfg.*;public class HibernateUtil { private static final SessionFactory sessionFactory; static { try { sessionFactory = new AnnotationConfiguration().configure( "hibernate.cfg.xml").buildSessionFactory(); } catch (Throwable ex) { // Log exception! throw new ExceptionInInitializerError(ex); } } public static Session getSession() throws HibernateException { return sessionFactory.openSession(); }}
首先確保數據庫表中已經有了一條id爲1的紀錄。
可執行以下程序：
package annotations;import one2one.Address;import org.hibernate.Session;import org.hibernate.SessionFactory;public class Main { private static SessionFactory sessionFactory; public static void main(String[] args) throws Exception { long st = System.currentTimeMillis(); Session s = HibernateUtil.getSession(); s.beginTransaction(); // Address a=new Address(); a.setName("sss"); s.save(a); /* Address a=(Address) s.load(Address.class.getName(), 1); System.out.println(); s.load(Address.class.getName(), 1);*/ s.flush(); s.getTransaction().commit(); s.close(); long end = System.currentTimeMillis(); System.out.println("用時： "); System.out.print(end - st); }}
以下是測試過程：
1 首先我們 load 一個 隨後在 load一個
如下所示：
package annotations;import one2one.Address;import org.hibernate.Session;import org.hibernate.SessionFactory;public class Main { private static SessionFactory sessionFactory; public static void main(String[] args) throws Exception { long st = System.currentTimeMillis(); Session s = HibernateUtil.getSession(); s.beginTransaction(); // /* Address a=new Address(); a.setName("sss"); s.save(a); */ Address a=(Address) s.load(Address.class.getName(), 1); System.out.println(); s.load(Address.class.getName(), 1); s.flush(); s.getTransaction().commit(); s.close(); long end = System.currentTimeMillis(); System.out.println("用時： "); System.out.print(end - st); }}
執行後控制檯輸出：
09:48:31,991 DEBUG DefaultLoadEventListener:171 - loading entity: [one2one.Address#1]
09:48:31,991 DEBUG DefaultLoadEventListener:255 - creating new proxy for entity
09:48:32,007 DEBUG DefaultLoadEventListener:171 - loading entity: [one2one.Address#1]
09:48:32,007 DEBUG DefaultLoadEventListener:214 - entity proxy found in session cache
用時：
3343
可以看出在第二次load時是在cache中找到 id爲1的紀錄的。
2 我們首先load一個再get同樣的紀錄，如下：
package annotations;import one2one.Address;import org.hibernate.Session;import org.hibernate.SessionFactory;public class Main { private static SessionFactory sessionFactory; public static void main(String[] args) throws Exception { long st = System.currentTimeMillis(); Session s = HibernateUtil.getSession(); s.beginTransaction(); // /* Address a=new Address(); a.setName("sss"); s.save(a); */ Address a=(Address) s.load(Address.class.getName(), 1); System.out.println(); s.get(Address.class.getName(), 1); s.flush(); s.getTransaction().commit(); s.close(); long end = System.currentTimeMillis(); System.out.println("用時： "); System.out.print(end - st); }}
執行後輸出：
09:52:24,741 DEBUG DefaultLoadEventListener:171 - loading entity: [one2one.Address#1]
09:52:24,741 DEBUG DefaultLoadEventListener:255 - creating new proxy for entity
09:52:24,757 DEBUG DefaultLoadEventListener:171 - loading entity: [one2one.Address#1]
09:52:24,757 DEBUG DefaultLoadEventListener:214 - entity proxy found in session cache
09:52:24,757 DEBUG DefaultLoadEventListener:332 - attempting to resolve: [one2one.Address#1]
09:52:24,757 DEBUG DefaultLoadEventListener:369 - object not resolved in any cache: [one2one.Address#1]
09:52:24,772 DEBUG SQL:401 - select address0_.id as id0_0_, address0_.name as name0_0_ from ssss address0_ where address0_.id=?
用時：
3438
可知在 執行 s.get(Address.class.getName(), 1) 時雖然在cache中找到了一個代理，但是不能被j解析，只好再次查詢數據庫。
3 我們首先get一個再load一個 看是什麼結果：
package annotations;import one2one.Address;import org.hibernate.Session;import org.hibernate.SessionFactory;public class Main { private static SessionFactory sessionFactory; public static void main(String[] args) throws Exception { long st = System.currentTimeMillis(); Session s = HibernateUtil.getSession(); s.beginTransaction(); // /* Address a=new Address(); a.setName("sss"); s.save(a); */ Address a=(Address) s.get(Address.class.getName(), 1); System.out.println(); s.load(Address.class.getName(), 1); s.flush(); s.getTransaction().commit(); s.close(); long end = System.currentTimeMillis(); System.out.println("用時： "); System.out.print(end - st); }}輸出：
09:55:59,679 DEBUG DefaultLoadEventListener:171 - loading entity: [one2one.Address#1]
09:55:59,679 DEBUG DefaultLoadEventListener:332 - attempting to resolve: [one2one.Address#1]
09:55:59,679 DEBUG DefaultLoadEventListener:369 - object not resolved in any cache: [one2one.Address#1]
09:55:59,679 DEBUG SQL:401 - select address0_.id as id0_0_, address0_.name as name0_0_ from ssss address0_ where address0_.id=?
09:55:59,757 DEBUG DefaultLoadEventListener:171 - loading entity: [one2one.Address#1]
09:55:59,757 DEBUG DefaultLoadEventListener:244 - entity found in session cache
用時：
3437
可知在load時得到的實體是在cache中找到的。
Load在數據庫中不存在記錄時拋出異常，但get只是返回空指針。
