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EJB3.0开发之多对多和一对一

程序员文章站 2023-12-13 19:02:40
在前面的例子中,我们演示了一对多和多对一的例子,在本章将演示多对多和一对一的关系。   学生和老师就是多对多的关系。一个学生有多个老师,一个老师教多个学生。   学生和档案...
在前面的例子中,我们演示了一对多和多对一的例子,在本章将演示多对多和一对一的关系。

  学生和老师就是多对多的关系。一个学生有多个老师,一个老师教多个学生。

  学生和档案就是一对一的关系(不知道国外的学生有没有档案?)。

  为了实现多对多的关系,数据库中需要关联表,用以在两个实体间建立关联。jboss可以自动生成关联表,你也可以@associationtable来指定关联表的信息。

  如:

  @manytomany(cascade = {cascadetype.create, cascadetype.merge}, fetch = fetchtype.eager, isinverse = true)
  @associationtable(table = @table(name = "student_teacher"),

  joincolumns = {@joincolumn(name = "teacher_id")},inversejoincolumns = {@joincolumn(name = "student_id")})

  @ associationtable的注释声明如下:
  @target({method, field})

  public @interface associationtable {
  table table() default @table(specified=false);
  joincolumn[] joincolumns() default {};
  joincolumn[] inversejoincolumns() default {};
  }

  关联表注释指定了关联表的名称、主表的列和从表的列。

  为了实现一对一的关系,需要用@onetoone来注释。

  如:

  @onetoone(cascade = {cascadetype.all})
  @joincolumn(name = "dossier_id")

  public dossier getdossier()
  {
  return dossier;
  }

  这定义了一个单向的一对一的关系。如果在dossier也定义了相关的关联,那么它就是双向的。双向的意思就是通过一个student实体就可以查找到一个dossier,通过一个dossier就可以查找到一个student。

  @ onetoone的注释声明如下:
  @target({method, field}) @retention(runtime)

  public @interface onetoone {
  string targetentity() default "";
  cascadetype[] cascade() default {};
  fetchtype fetch() default eager;
  boolean optional() default true;
  }

  这个例子主要有以下几个文件,这个例子主要实现了学生和老师、学生和档案之间的关系。student、teacher、dossier都是实体bean。student和dossier是一个双向的onetoone之间的关系,student和teacher是manytomany的关系,也是双向的。和前面的例子一样,我们还是使用client测试。

  student.java:实体bean。

  dossier.java:实体bean所依赖的类。

  teacher.java:实体bean所依赖的类。

  entitytest.java:会话bean的业务接口

  entitytest bean.java:会话bean的实现类

  client.java:测试ejb的客户端类。

  jndi.properties:jndi属性文件,提供访问jdni的基本配置属性。

  build.xml:ant 配置文件,用以编译、发布、测试、清除ejb。

  下面针对每个文件的内容做一个介绍。

  student.java

  package com.kuaff.ejb3.relationships;
  import javax.ejb.cascadetype;
  import javax.ejb.entity;
  import javax.ejb.fetchtype;
  import javax.ejb.generatortype;
  import javax.ejb.id;
  import javax.ejb.joincolumn;
  import javax.ejb.onetoone;
  import javax.ejb.manytomany;
  import javax.ejb.table;
  import javax.ejb.associationtable;
  import java.util.arraylist;
  import java.util.set;
  import java.util.collection;
  import java.io.serializable;

  @entity

  @table(name = "student")

  public class student implements serializable

  {
  private int id;
  private string first;
  private string last;
  private dossier dossier;
  private set teachers;

  @id(generate = generatortype.auto)

  public int getid()
  {
  return id;
  }

  public void setid(int id)
  {
  this.id = id;
  }

  public void setfirst(string first)
  {
  this.first = first;
  }

  public string getfirst()
  {
  return first;
  }

  public void setlast(string last)
  {
  this.last = last;
  }

  public string getlast()
  {
  return last;
  }

  public void setdossier(dossier dossier)
  {
  this.dossier = dossier;
  }

  @onetoone(cascade = {cascadetype.all})
  @joincolumn(name = "dossier_id")

  public dossier getdossier()
  {
  return dossier;
  }

  public void setteacher(set teachers)
  {
  this.teachers = teachers;
  }

  @manytomany(cascade = {cascadetype.create, cascadetype.merge}, fetch = fetchtype.eager, isinverse = true)
  @associationtable(table = @table(name = "student_teacher"),

  joincolumns = {@joincolumn(name = "teacher_id")},inversejoincolumns = {@joincolumn(name = "student_id")})

  public set getteacher()
  {
  return teachers;
  }
  }

  dossier.java

  package com.kuaff.ejb3.relationships;

  import javax.ejb.entity;
  import javax.ejb.generatortype;
  import javax.ejb.id;

  @entity

  public class dossier implements java.io.serializable
  {
  private long id;
  private string resume;

  @id(generate = generatortype.auto)
  public long getid()
  {
  return id;
  }

  public void setid(long id)
  {
  this.id = id;
  }

  public void setresume(string resume)
  {
  this.resume = resume;
  }

  public string getresume()
  {
  return resume;
  }
  }

  teacher.java

  package com.kuaff.ejb3.relationships;

  import javax.ejb.associationtable;
  import javax.ejb.basic;
  import javax.ejb.cascadetype;
  import javax.ejb.column;
  import javax.ejb.entity;
  import javax.ejb.fetchtype;
  import javax.ejb.id;
  import javax.ejb.joincolumn;
  import javax.ejb.manytomany;
  import javax.ejb.table;
  import javax.ejb.transient;
  import javax.ejb.version;
  import java.util.set;
  import javax.ejb.generatortype;

  @entity

  public class teacher implements java.io.serializable
  {
  private long id;
  private string resume;
  private string name;
  private string info;
  private set students;

  @id(generate = generatortype.identity)

  public long getid()
  {
  return id;
  }

  public void setid(long id)
  {
  this.id = id;
  }

  public void setname(string name)
  {
  this.name = name;
  }

  public string getname()
  {
  return name;
  }

  public void setinfo(string info)
  {
  this.info = info;
  }

  public string getinfo()
  {
  return info;
  }

  public void setstudents(set students)
  {
  this.students = students;
  }

  @manytomany(cascade = {cascadetype.create, cascadetype.merge}, fetch = fetchtype.eager)
  @associationtable(table = @table(name = "student_teacher"),

  joincolumns = {@joincolumn(name = "teacher_id",referencedcolumnname="id")},
  inversejoincolumns = {@joincolumn(name = "student_id",referencedcolumnname="id")})

  public set getstudents()
  {
  return students;
  }
  }

  entitytest.java

  package com.kuaff.ejb3.relationships;

  import javax.ejb.remote;
  import java.util.list;

  @remote

  public interface entitytest
  {
  public void createdata();
  public list findbyname(string name);
  }

  entitytestbean.java
  
  package com.kuaff.ejb3.relationships;

  import javax.ejb.entitymanager;
  import javax.ejb.inject;
  import javax.ejb.stateless;
  import java.util.hashset;
  import java.util.set;
  import java.util.list;

  @stateless

  public class entitytestbean implements entitytest
  {
  private @inject entitymanager manager;
  public void createdata()
  {
  teacher teacher1 = new teacher();
  teacher teacher2 = new teacher();

  set students1 = new hashset();
  set students2 = new hashset();
  student student1 = new student();
  student student2 = new student();
  student student3 = new student();

  dossier dossier1 = new dossier();
  dossier dossier2 = new dossier();
  dossier dossier3 = new dossier();
  teacher1.setid(new long(1));
  teacher1.setname("hushisheng");
  teacher1.setinfo("胡时胜教授,博士生导师");
  manager.create(teacher1);
  teacher2.setid(new long(2));
  teacher2.setname("liyongchi");
  teacher2.setinfo("李永池教授,博士生导师");
  manager.create(teacher2);

  student1.setfirst("晁");
  student1.setlast("岳攀");
  dossier1.setresume("这是晁岳攀的档案");
  student1.setdossier(dossier1);
  students1.add(student1);

  student2.setfirst("赵");
  student2.setlast("志伟");
  dossier2.setresume("这是赵志伟的档案");
  student2.setdossier(dossier2);
  students1.add(student2);

  student3.setfirst("田");
  student3.setlast("明");

  dossier3.setresume("这是田明的档案");
  student3.setdossier(dossier3);
  students2.add(student3);

  teacher1.setstudents(students1);
  teacher2.setstudents(students2);

  }

  public list findbyname(string name)
  {
  return manager.createquery("from teacher t where t.name = :name").setparameter("name", name).listresults();
  }

  }

  在这个会话bean中提供了创建各个实体bean的方法,并提供了查找老师的方法。

  client.java

  package com.kuaff.ejb3.secondary;

  import javax.naming.initialcontext;
  import javax.naming.namingexception;
  import java.util.list;

  public class client
  {
  public static void main(string[] args) throws namingexception
  {
  initialcontext ctx = new initialcontext();
  studentdao dao = (studentdao) ctx.lookup(studentdao.class.getname());
  int id = dao.create("晁","岳攀","8","smallnest@kuaff.com","男");
  dao.create("朱","立焕","6","zhuzhu@kuaff.com","女");
  list list = dao.findall();
  for(object o:list)
  {
   student s = (student)o;
   system.out.printf("%s%s的性别:%s%n",s.getname().getfirst(),s.getname().getlast(),s.getgender());
   dao.evict(s);
  }
  }
  }

  这个客户端用来测试。

  请运行{$jboss_home}/bin目录下的run.bat: run –c all,启动jboss。

  http://localhost:8080/jmx-console/htmladaptor?action=inspectmbean&name=jboss%3aservice%3dhypersonic%2cdatabase%3dlocaldb,然后调用startdatabasemanager()方法,打开hsql管理工具管理数据库。

  在eclipse的ant视图中执行ejbjar target。或者在命令行下,进入到此工程目录下,执行ant ejbjar,将编译打包发布此ejb。

  在eclipse的ant视图中执行run target。或者在命令行下,进入到此工程目录下,执行ant run,测试这个ejb。

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