关于HIBERNATE

如果不想偶合度过高，不写D表的实体映射也可以的，如果要写的话就写成3个一对多的关系！

给你一个一对多的例子给你参考参考！
Teachers.hbm.xml代码：
<?xml version="1.0"?>
<!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 - Hibernate Tools
-->
<hibernate-mapping>
<class name="manytomany.Teachers" table="teachers" catalog="test">
<id name="teacherid" type="java.lang.Integer">
<column name="teacherid" />
<generator class="assigned" />
</id>
<property name="teachername" type="java.lang.String">
<column name="teachername" length="45" not-null="true" />
</property>
<set name="students" inverse="true" table="tea_stu">
<key>
<column name="teacherid" not-null="true" />
</key>
<many-to-many class="manytomany.Students" column="studentid"></many-to-many>

</set>
</class>
</hibernate-mapping>

Students.hbm.xml代码：
<?xml version="1.0"?>
<!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 - Hibernate Tools
-->
<hibernate-mapping>
<class name="manytomany.Students" table="students" catalog="test">
<id name="studentid" type="java.lang.Integer">
<column name="studentid" />
<generator class="assigned" />
</id>
<property name="studentname" type="java.lang.String">
<column name="studentname" length="45" not-null="true" />
</property>
<set name="teachers" inverse="false" table="tea_stu" cascade="save-update">
<key>
<column name="studentid" not-null="true" />
</key>
<many-to-many class="manytomany.Teachers" column="teacherid"></many-to-many>

</set>
</class>
</hibernate-mapping>

DAO类代码：
package manytomany;

import org.hibernate.Session;
import org.hibernate.Transaction;

public class DAO {

public void save(Students students)
{
Session session = HibernateSessionFactory.getSession();
Transaction tx = session.beginTransaction();
session.save(students);
tx.commit();
session.close();
}

}

session工厂类代码：
package manytomany;

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

/**
* 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 HibernateSessionFactory {

/**
* 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 = "/hibernate.cfg.xml";
private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
private static Configuration configuration = new Configuration();
private static org.hibernate.SessionFactory sessionFactory;
private static String configFile = CONFIG_FILE_LOCATION;

private HibernateSessionFactory() {
}

/**
* 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) {
HibernateSessionFactory.configFile = configFile;
sessionFactory = null;
}

/**
* return hibernate configuration
*
*/
public static Configuration getConfiguration() {
return configuration;
}

}

操作类代码：
package manytomany;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class InfoOperate extends HttpServlet {

/**
* Destruction of the servlet. <br>
*/
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}

/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request
* the request send by the client to the server
* @param response
* the response send by the server to the client
* @throws ServletException
* if an error occurred
* @throws IOException
* if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
Students student1 = new Students();
student1.setStudentid(1);
student1.setStudentname("张三");

Students student2 = new Students();
student2.setStudentid(2);
student2.setStudentname("李四");

Teachers teacher1 = new Teachers();
teacher1.setTeacherid(1);
teacher1.setTeachername("中岛");

Teachers teacher2 = new Teachers();
teacher2.setTeacherid(2);
teacher2.setTeachername("田中");

student1.getTeachers().add(teacher1);
student1.getTeachers().add(teacher2);
student2.getTeachers().add(teacher1);
student2.getTeachers().add(teacher2);

DAO dao = new DAO();
dao.save(student1);
dao.save(student2);
}

/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to
* post.
*
* @param request
* the request send by the client to the server
* @param response
* the response send by the server to the client
* @throws ServletException
* if an error occurred
* @throws IOException
* if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}

/**
* Initialization of the servlet. <br>
*
* @throws ServletException
* if an error occure
*/
public void init() throws ServletException {
// Put your code here
}

}