java查询模块如何实现? java实现查询数据库

　　首先我们在在File中选择new在选择java project在任意取一个名字，如图：

　　选择才创建的项目userManager,在src下分别创建dao包，DBHelper包（可直接在其他项目中把它复制过来），entity包和servlet包，如图：

　　打开entity，在它下面new一个class，命名为User,然后定义三个变量代码如下:

package entity;

public class User {
	private String userID;
	private String username;
	private String userword;
	
	public String getUserID() {
		return userID;
	}
	public void setUserID(String userID) {
		this.userID = userID;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getUserword() {
		return userword;
	}
	public void setUserword(String userword) {
		this.userword = userword;
	}

	}

　　打开DAO，在它下面new一个class,命名为Userdao,代码如下：

package dao;

import java.util.*;
import java.sql.*;

import entity.*;
import DBHelper.*;

public class Userdao {
	public List getAllUser() {
		String SQL = "SELECT * FROM user";
		ResultSet rs = DBHelper.getResultSet(SQL);
		return tools.ResultSettoList(rs, User.class);

		// try{
		// String SQL="SELECT*FROM user";
		// ResultSet rs= DBHelper.getResultSet(SQL);
		// List users=new ArrayList();
		// while(rs.next())
		// {
		// User u=new User();
		// u.setUserID(rs.getString("userID"));
		// u.setUsername(rs.getString("userName"));
		// u.setUserword(rs.getString("password"));
		// users.add(u);
		// }
		// return users;
		// }catch(Exception ex){return null;
		// }
		//
	}
	
	public boolean insert(User u){
		String SQL="INSERT INTO user(userID,username,userword) VALUES(?,?,?)";
		Object[] params=new Object[]{u.getUserID(),u.getUsername(),u.getUserword()};
		int n=DBHelper.ExecSql(SQL,params);
		if(n>0) return true;
		else return false;
		
	}
	public boolean update(User u){
		   String sql="update  user set username=?,userword=? where userID=?";
		   Object[] obj=new Object[]{u.getUsername(),u.getUserword(),u.getUserID()};
		   int rs=DBHelper.ExecSql(sql,obj);
		   if(rs==1)
		    return true;
		   else
		   return false;
		   
	   }
	public boolean delete(User u){
		   String sql="delete from user where userID=?";
		   Object[] obj=new Object[]{u.getUserID()};
		   int rs=DBHelper.ExecSql(sql,obj);
		   if(rs==1)
	      return true;
		   else
		  return true;
	   }

}

　　接着还需要在DAO下创建一个类，命名为testdao，用于测试Userdaobao的代码，代码如下：

package dao;

import java.sql.SQLException;
import java.util.List;

import entity.User;

public class testDAO {
	public static void main(String[] args) throws SQLException {
//		 TODO Auto-generated method stub
//		测试查询
//     Userdao dao= new Userdao();
//     List list =dao.getAllUser();
//     System.out.println(list.size());
//		测试添加：
		   Userdao dao=new Userdao();
		   User u= new User();
//		   u.setUserID("d");
//		   u.setUsername("d");
//		   u.setUserword("d");
//		    dao.insert(u);
//		   
//		   测试删除：
//		   u.setUserID("d");
//		   dao.delete(u);
//		   System.out.println("u");
//		   测试修改
		   u.setUserID("c");
		   u.setUserword("q");
		   u.setUsername("q");
		   dao.update(u);
		   System.out.println("u");
	}

}

　　打开servlet,在它下面new一个servlet，命名为UserServlet,把 pageEncoding改成UTF0-8;删除doGet和doPost里的内容，doGet和doPost里的代码如下：

package servlet;

import java.io.*;
import java.util.*;

import javax.servlet.*;
import javax.servlet.http.*;

import dao.*;
import entity.*;
import DBHelper.*;
public class Userservlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public Userservlet() {
		super();
	}

	/**
	 * 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 {
			doPost(request, response);
	}

	/**
	 * 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 {
		Userdao dao=new Userdao();
		List users=dao.getAllUser();
		request.getSession().setAttribute("users", users);
		response.sendRedirect("show.jsp");
		

	}
	

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

}

　　在WebRoot下创建一个user命名的目录,然后在user下new一个show.jsp。先导入entity包，在把 pageEncoding改成UTF0-8；然后再body里写输出的样式，代码如下：

<%@ page language="java" import="java.util.*,dao.*,DBHelper.*,entity.*"  pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

    <title>User.jsp</title>

  </head>
  
  <body>
  <%
  List<User>users = (List<User>)session.getAttribute("users");
//String uid=request.getParameter("userID");

//String uname=request.getParameter("username");
//String password=request.getParameter("password");
//out.print("用户ID:"+uid+"<hr/>");
//out.print("姓名:"+uname+"<hr/>");
//out.print("密码:"+password+"<hr/>");

out.print("<table border=1 cellspacing=1>");
  out.print("<tr><td>id</td><td>用户名</td><td>密码</td></tr>");
    for(User u:users)
   {
    out.print("<tr>");
    out.print("<td>"+u.getUserID()+"</td>");
    out.print("<td>"+u.getUsername()+"</td>");
    out.print("<td>"+u.getUserword()+"</td>");
   out.print("</tr>");
    
   }
 out.print("</table>");
   %>
  </body>
</html>

　　记得一定要将链接sql的驱动文件复制在WebRoot下的WEB-INF里的lib下面。

　　打开WebRoot下的WEB-INF，打开web.xml，复制其路径，开启服务，输入网址（网址如http://localhost:8080/userManager/servlet/UserServlet）即可查看。路径如图：