Hibernate Step By Step (2)
考虑把通过xxx.hbm.xml转换为用Annotation从而省去配置文件。首先假定已经可以在hbm.xml配置方式下运行成功 ，Step by step 1中已经描述。接下来需要在原来的方案上的改变如下：
1，首先，引入包，在保证hbm.xml方式运行的包的基础上，还需要:ejb3-persistence.jar(不要以为它是EJB的专用了)，hibernate-annotation.jar。如果你用myeclipse开发，在hibernate相关目录下都可以找到的。
这一步有一些需要特别注意的地方：版本问题。因为我因为这个问题碰到过麻烦。下面也简单的介绍一下。
hibernate-annotation.jar 用的3.2.0.CR2版本，是比较新的版本了。
开始时hibernate我是用的hibernate-3.2.5版本的。
于是我把hibernate3.2.5换作了3.1 ,又发现另外一些类比如NativeSqlQueryReurn找不到...
最后再尝试用hibernate3.2.0.cr4 ，终于看到了我想要的。所以在这一步要比较小心。
其中一步我发现会报如下错误：SqlresultsetMappings Not found 。解决方法是引入Java EE 5的库。后来发现，如果引入了Java EE 5的库以后，就不用再引入ejb3-persistence.jar了 。因为Java EE 5已经把这个部分包含了，不再是EJB独有的了。
2，要用到的库文件就这些了，接下来开始写配置文件(Hibernate.cfg.xml这个配置还是需要的)。
hibernate.cfg.xml和用hbm.xml方式的区别是，mapping字段不再用resource，而改用 class=Myclass.
内容如下：
<?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="connection.driver_class">
org.hsqldb.jdbcDriver
</property>
<property name="connection.url">
jdbc:hsqldb:hsql://localhost
</property>
<property name="connection.username">SA</property>
<property name="connection.password"></property>
<property name="dialect">
org.hibernate.dialect.HSQLDialect
</property>
<property name="connection.pool_size">3</property>
<property name="show_sql">true</property>
<property name="hbm2ddl.auto">create</property>
<property name="current_session_context_class">thread</property>
<mapping class="dian.ikeel.annotation.Picture"/>
</session-factory>
</hibernate-configuration>
3，开始写Java类了，注意要用到Annotation的：
package dian.ikeel.annotation;
import javax.persistence.*;
import org.hibernate.annotations.AccessType;
@Entity
@Table(name="Pics")
@AccessType("property")
public class Picture {
private long picid;
private String picname;
private int picsize;
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
public long getPicid() {
return picid;
}
public void setPicid(long picid) {
this.picid = picid;
}
public String getPicname() {
return picname;
}
public void setPicname(String picname) {
this.picname = picname;
}
public int getPicsize() {
return picsize;
}
public void setPicsize(int picsize) {
this.picsize = picsize;
}
}
我就不详细解释每个标注的意思了。
4，下面该关心如何或得SessionFactory了，跟以前的方式的区别只有一点点，我们用到了AnnotationConfiguration;
代码如下：
package dian.ikeel.hibernate.util.SessionFactory;
import org.hibernate.HibernateException;
import org.hibernate.Session;
//import org.hibernate.cfg.Configuration;
import org.hibernate.cfg.AnnotationConfiguration;
/**
* Configures and provides access to Hibernate sessions, tied to the
* current thread of execution.Follows the Thread Local Session
* pattern, see {@link http://hibernate.org/42.html }.
*/
public class AnnotationSessionFactory {
/**
* Location of hibernate.cfg.xml file.
* Location should be on the classpath as Hibernate uses
* #resourceAsStream style lookup for its configuration file.
* The default classpath location of the hibernate config file is
* in the default package. Use #setConfigFile() to update
* the location of the configuration file for the current session.
*/
private static String CONFIG_FILE_LOCATION = "/annotationhibernate.cfg.xml";
private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
privatestatic AnnotationConfiguration configuration = new AnnotationConfiguration();
private static org.hibernate.SessionFactory sessionFactory;
private static String configFile = CONFIG_FILE_LOCATION;
static {
try {
configuration.configure(configFile);
sessionFactory = configuration.buildSessionFactory();
}catch (Exception e) {
System.err
.println("%%%% Error Creating SessionFactory %%%%"+e.getLocalizedMessage());
e.printStackTrace();
}
}
/**
* Returns the ThreadLocal Session instance.Lazy initialize
* the <code>SessionFactory</code> if needed.
*
*@return Session
*@throws HibernateException
*/
public static Session getSession() throws HibernateException {
Session session = (Session) threadLocal.get();
if (session == null || !session.isOpen()) {
if (sessionFactory == null) {
rebuildSessionFactory();
}
session = (sessionFactory != null) ? sessionFactory.openSession()
: null;
threadLocal.set(session);
}
return session;
}
/**
*Rebuild hibernate session factory
*
*/
public static void rebuildSessionFactory() {
try {
configuration.configure(configFile);
sessionFactory = configuration.buildSessionFactory();
} catch (Exception e) {
System.err
.println("%%%% Error Creating SessionFactory %%%%");
e.printStackTrace();
}
}
/**
*Close the single hibernate session instance.
*
*@throws HibernateException
*/
public static void closeSession() throws HibernateException {
Session session = (Session) threadLocal.get();
threadLocal.set(null);
if (session != null) {
session.close();
}
}
/**
*return session factory
*
*/
public static org.hibernate.SessionFactory getSessionFactory() {
return sessionFactory;
}
/**
*return session factory
*
*session factory will be rebuilded in the next call
*/
public static void setConfigFile(String configFile) {
AnnotationSessionFactory.configFile = configFile;
sessionFactory = null;
}
/**
*return hibernate configuration
*
*/
public static AnnotationConfiguration getConfiguration() {
return configuration;
}
}
5，接下来，启动数据库，我用的是hsql。然后给一个入口点就OK了。
最简单的入口函数：
package dian.ikeel.hibernate.BLL;
import org.hibernate.Session;
import dian.ikeel.annotation.Picture;
import dian.ikeel.hibernate.util.SessionFactory.*;
import org.hibernate.cfg.AnnotationConfiguration;;
public class AnnotationEntry {
/**
* @param args
*/
public static void main(String[] args) {
Sessionsession=AnnotationSessionFactory.getSessionFactory().getCurrentSession();
session.beginTransaction();
Picturepic=new Picture();
pic.setPicname("heat3");
pic.setPicsize(123);
session.save(pic);
session.getTransaction().commit();
System.out.println("AnnotationEntry excuted");
}
}
6，这样就算是最简单的Annotation 的Demo运行通过了。再去研究一下某些步骤是不是一定得那么做。
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