Java持久性API（JPA）第1讲——简单实例

目标：使用Java持久性API把数据库中的数据显示出来。

基本过程包括：

u 加载驱动程序

u 创建数据库以及表

u 在NetBeans中加载驱动程序

u 在NetBeans中创建连接

u 创建持久单元以及实体类

u 创建访问持久单元的会话Bean

u 创建Servlet客户端程序，访问会话Bean，并显示结果

1、放JDBC驱动程序到下面的目录

根据自己的安装目录进行修改。如果采用默认安装，应该放在下面的目录下。

C:\Sun\AppServer\domains\domain1\lib\ext

2、在MySQL数据库中添加数据库entity

create database entity

3、创建表userinfo

在entity数据库中创建表，表结构与书上25章的一样，插入几条测试数据。

create table userinfo

(

userid varchar(10) primary key not null,

username varchar(10) not null,

userpass varchar(10) not null,

usertype char(1) not null

)

插入如下测试数据：

insert into userinfo values('user001','zhangsan','zhangsan','0');

insert into userinfo values('user002','lisi','lisi','0');

insert into userinfo values('admin001','mishu','mishu','0');

4、在NetBeans中添加驱动程序

在Drivers上面点击右键，选择New Driver。选择JDBC驱动程序所在的jar压缩包。

5、添加连接

在上图的Databases上点击右键选择New Connection，在弹出的界面上选择前面添加的驱动程序，然后修改URL，修改后：jdbc:mysql://localhost:3306/entity。

其中：localhost表示主机，3306表示端口，entity表示数据库。

6、创建EJB Module

选择FileàNew Project，选择中间的Enterprise，然后选择右边的EJB Module。工程的名字是UserSession。

7、创建持久单元

在工程上面点击右键，选择NewàFile/Folder，选择中间的Persistence，右边选择Persistence Unit。在弹出的界面中，选择数据源：选择New DataSource。在弹出的界面中输入一个JNDI名字entity2，然后选择前面第5步创建好的连接。

生成的文件如下：

<?xml version="1.0" encoding="UTF-8"?>

<persistence version="1.0"

xmlns="http://java.sun.com/xml/ns/persistence"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/persistence

http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">

<persistence-unit name="UserPU" transaction-type="JTA">

<provider>

oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider

</provider>

<jta-data-source>entity2</jta-data-source>

<properties>

<property name="toplink.ddl-generation" value="create-tables"/>

</properties>

</persistence-unit>

</persistence>

8、创建持久类

在工程上面点击右键，选择New，然后选择Entity Class from DataBase。在DataSource中选择刚才配置好的数据源entity2。然后在左下方会出现表，选择中间的Add，添加到右边。选择下一步，然后完成即可。生成的文件如下：

/*

* Userinfo.java

*

* Created on 2007年5月21日, 上午6:17

*

* To change this template, choose Tools | Template Manager

* and open the template in the editor.

*/

package jpa;

import java.io.Serializable;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.NamedQueries;

import javax.persistence.NamedQuery;

import javax.persistence.Table;

/**

* Entity class Userinfo

*

* @author Administrator

*/

@Entity

@Table(name = "userinfo")

@NamedQueries( {

@NamedQuery(name = "Userinfo.findByUserid",

query = "SELECT u FROM Userinfo u WHERE u.userid = :userid"),

@NamedQuery(name = "Userinfo.findByUsername",

query = "SELECT u FROM Userinfo u WHERE u.username = :username"),

@NamedQuery(name = "Userinfo.findByUserpass",

query = "SELECT u FROM Userinfo u WHERE u.userpass = :userpass"),

@NamedQuery(name = "Userinfo.findByUsertype",

query = "SELECT u FROM Userinfo u WHERE u.usertype = :usertype")

})

public class Userinfo implements Serializable {

@Id

@Column(name = "userid", nullable = false)

private String userid;

@Column(name = "username", nullable = false)

private String username;

@Column(name = "userpass", nullable = false)

private String userpass;

@Column(name = "usertype", nullable = false)

private char usertype;

/** Creates a new instance of Userinfo */

public Userinfo() {

}

/**

* Creates a new instance of Userinfo with the specified values.

* @param userid the userid of the Userinfo

*/

public Userinfo(String userid) {

this.userid = userid;

}

/**

* Creates a new instance of Userinfo with the specified values.

* @param userid the userid of the Userinfo

* @param username the username of the Userinfo

* @param userpass the userpass of the Userinfo

* @param usertype the usertype of the Userinfo

*/

public Userinfo(String userid, String username, String userpass, char usertype) {

this.userid = userid;

this.username = username;

this.userpass = userpass;

this.usertype = usertype;

}

/**

* Gets the userid of this Userinfo.

* @return the userid

*/

public String getUserid() {

return this.userid;

}

/**

* Sets the userid of this Userinfo to the specified value.

* @param userid the new userid

*/

public void setUserid(String userid) {

this.userid = userid;

}

/**

* Gets the username of this Userinfo.

* @return the username

*/

public String getUsername() {

return this.username;

}

/**

* Sets the username of this Userinfo to the specified value.

* @param username the new username

*/

public void setUsername(String username) {

this.username = username;

}

/**

* Gets the userpass of this Userinfo.

* @return the userpass

*/

public String getUserpass() {

return this.userpass;

}

/**

* Sets the userpass of this Userinfo to the specified value.

* @param userpass the new userpass

*/

public void setUserpass(String userpass) {

this.userpass = userpass;

}

/**

* Gets the usertype of this Userinfo.

* @return the usertype

*/

public char getUsertype() {

return this.usertype;

}

/**

* Sets the usertype of this Userinfo to the specified value.

* @param usertype the new usertype

*/

public void setUsertype(char usertype) {

this.usertype = usertype;

}

/**

* Returns a hash code value for the object.This implementation computes

* a hash code value based on the id fields in this object.

* @return a hash code value for this object.

*/

@Override

public int hashCode() {

int hash = 0;

hash += (this.userid != null ? this.userid.hashCode() : 0);

return hash;

}

/**

* Determines whether another object is equal to this Userinfo.The result is

* <code>true</code> if and only if the argument is not null and is a Userinfo object

that

* has the same id field values as this object.

* @param object the reference object with which to compare

* @return <code>true</code> if this object is the same as the argument;

* <code>false</code> otherwise.

*/

@Override

public boolean equals(Object object) {

// TODO: Warning - this method won't work in the case the id fields are not set

if (!(object instanceof Userinfo)) {

return false;

}

Userinfo other = (Userinfo)object;

if (this.userid != other.userid &&

(this.userid == null || !this.userid.equals(other.userid)))

return false;

return true;

}

/**

* Returns a string representation of the object.This implementation constructs

* that representation based on the id fields.

* @return a string representation of the object.

*/

@Override

public String toString() {

return "jpa.Userinfo[userid=" + userid + "]";

}

}

然后在Persistence.xml文件的设计界面的下面有 Add Class 按钮，点击该按钮，然后把刚创建好的实体类添加到持久单元中。

9、编写会话Bean访问该实体

在该工程中添加一个会话Bean，添加过程参考会话Bean的编写，Bean的名字是UserManager，提供Remote接口。

在该会话Bean中添加一个业务方法，下面是修改后的文件，红色部分是添加的。

9.1 接口文件

package jpa;

import javax.ejb.Remote;

import java.util.List;

/**

* This is the business interface for UserManager enterprise bean.

*/

@Remote

public interface UserManagerRemote {

public List<Userinfo> findAllUser();

}

9.2 Bean类

/*

* UserManagerBean.java

*

* Created on 2007年5月21日, 上午6:18

*

* To change this template, choose Tools | Template Manager

* and open the template in the editor.

*/

package jpa;

import javax.ejb.Stateless;

import javax.persistence.PersistenceContext;

import javax.persistence.EntityManager;

import java.util.List;

/**

*

* @author Administrator

*/

@Stateless

public class UserManagerBean implements jpa.UserManagerRemote {

@PersistenceContext

EntityManager em;

/** Creates a new instance of UserManagerBean */

public UserManagerBean() {

}

public List<Userinfo> findAllUser(){

return em.createQuery("select u from Userinfo u").getResultList();

}

}

10、编写Servlet客户端访问会话Bean

需要引入会话Bean的客户端程序，可以在Web应用的Liberaries上点击右键，选择Add Project，如下面的界面，选择前面创建的EJB模块，选择添加即可（这样就不用拷贝会话Bean的接口文件了）。

然后在工程里面添加一个Servlet，名字为FindAllUserServlet，修改后的代码如下（红色部分是添加的）：

/*

* FindAllUserServlet.java

*

* Created on 2007年5月21日, 上午6:27

*/

package jpa.web;

import java.io.*;

import java.net.*;

import javax.servlet.*;

import javax.servlet.http.*;

import javax.ejb.EJB;

import jpa.UserManagerRemote;

import jpa.Userinfo;

import java.util.List;

import java.util.Iterator;

/**

*

* @author Administrator

* @version

*/

public class FindAllUserServlet extends HttpServlet {

@EJB

UserManagerRemote user;

/** Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.

* @param request servlet request

* @param response servlet response

*/

protected void processRequest(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html;charset=UTF-8");

PrintWriter out = response.getWriter();

List<Userinfo> list=user.findAllUser();

Iterator<Userinfo> i = list.iterator();

while(i.hasNext()){

Userinfo tmpUser = i.next();

out.print(tmpUser.getUserid()+"-"+tmpUser.getUsername()+"<br>");

}

out.close();

}

// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">

/** Handles the HTTP <code>GET</code> method.

* @param request servlet request

* @param response servlet response

*/

protected void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

processRequest(request, response);

}

/** Handles the HTTP <code>POST</code> method.

* @param request servlet request

* @param response servlet response

*/

protected void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

processRequest(request, response);

}

/** Returns a short description of the servlet.

*/

public String getServletInfo() {

return "Short description";

}

// </editor-fold>

}

11、运行测试

分别部署EJB模块和Web模块，访问Servlet可以得到用户列表。

更多内容可以参考本人的书《Java EE 5实用教程——基于WebLogic和Eclipse》