1.背景介绍：学生和教师之间可以认为是多对多的关系

2.persistence.xml

3.实体bean

Student.java

package com.sinoi.bean;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;@Entitypublic class Student {	@Id @GeneratedValue	private Integer id;	@Column(length=10, nullable=false)	private String name;	@ManyToMany(cascade=CascadeType.ALL, fetch=FetchType.LAZY)	@JoinTable(name="student_teacher", inverseJoinColumns=@JoinColumn(name="tea_id"),			 joinColumns=@JoinColumn(name="stu_id"))	//inverseJoinColumn指向另外一个类对应表的id，而joinColumns指向就是所在这个类对应表的id	private Set
    
      teachers = new HashSet
     
      ();		public Student(String name) {		this.name = name;	}		public Student() {}		public Integer getId() {		return id;	}	public void setId(Integer id) {		this.id = id;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}	public Set
      
        getTeachers() {		return teachers;	}	public void setTeachers(Set
       
         teachers) {		this.teachers = teachers;	}	public void addTeacher(Teacher teacher) {		this.teachers.add(teacher);	}	public void removeTeacher(Teacher teacher) {		if (this.teachers.contains(teacher)) {			this.teachers.remove(teacher);		}	}	}
       
      
     
    

Teacher.java

package com.sinoi.bean;import java.util.HashSet;import java.util.Set;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.ManyToMany;//被维护端@Entitypublic class Teacher {	@Id @GeneratedValue	private Integer id;	@Column(length=10, nullable=false)	private String name;	@ManyToMany(mappedBy="teachers", fetch=FetchType.LAZY)	private Set
    
      students = new HashSet
     
      ();		public Teacher(String name) {		this.name = name;	}		public Teacher() {}	public Integer getId() {		return id;	}	public void setId(Integer id) {		this.id = id;	}	public String getName() {		return name;	}	public void setName(String name) {		this.name = name;	}	public Set
      
        getStudents() {		return students;	}	public void setStudents(Set
       
         students) {		this.students = students;	}	@Override	public int hashCode() {		final int prime = 31;		int result = 1;		result = prime * result + ((id == null) ? 0 : id.hashCode());		return result;	}	@Override	public boolean equals(Object obj) {		if (this == obj)			return true;		if (obj == null)			return false;		if (getClass() != obj.getClass())			return false;		Teacher other = (Teacher) obj;		if (id == null) {			if (other.id != null)				return false;		} else if (!id.equals(other.id))			return false;		return true;	}	}
       
      
     
    

4.测试

package junit.test;import javax.persistence.EntityManager;import javax.persistence.EntityManagerFactory;import javax.persistence.Persistence;import org.junit.Test;import com.sinoi.bean.Student;import com.sinoi.bean.Teacher;public class UnitTest {	//保存数据	@Test	public void save() {		EntityManagerFactory factory = Persistence.createEntityManagerFactory("unitname");		EntityManager manager = factory.createEntityManager();		manager.getTransaction().begin();				manager.persist(new Teacher("Mr li"));		manager.persist(new Student("bean"));				manager.getTransaction().commit();		manager.close();		factory.close();	}		//建立联系	@Test	public void buildST() {		EntityManagerFactory factory = Persistence.createEntityManagerFactory("unitname");		EntityManager manager = factory.createEntityManager();		manager.getTransaction().begin();				//需要无参构造函数，否则会出现错误		Teacher teacher = manager.getReference(Teacher.class, 1);		Student student = manager.getReference(Student.class, 1);		student.addTeacher(teacher);				manager.getTransaction().commit();		manager.close();		factory.close();	}		//解除教师与学生关系	@Test	public void deleteTeacher() {		EntityManagerFactory factory = Persistence.createEntityManagerFactory("unitname");		EntityManager manager = factory.createEntityManager();		manager.getTransaction().begin();				Teacher teacher = manager.getReference(Teacher.class, 1);		Student student = manager.getReference(Student.class, 1);		student.removeTeacher(teacher);				manager.getTransaction().commit();		manager.close();		factory.close();	}		//删除学生   	//注：如果要删除老师，得先将解除老师和学生之间的关系，然后再删除老师	@Test	public void deleteStudent() {		EntityManagerFactory factory = Persistence.createEntityManagerFactory("unitname");		EntityManager manager = factory.createEntityManager();		manager.getTransaction().begin();				Student student = manager.getReference(Student.class, 1);		manager.remove(student);				manager.getTransaction().commit();		manager.close();		factory.close();	}}