JDBC实践-实现数据查询功能

2017-12-06 18:15:21

　数据库查询操作实现

上一文已经实现了从数据库中把数据取到并且展示出来,接下来我们需要完成查询的操作,也就是输入用户名,查询到相应的用户

  • 改造ListServlet.java文件,具体内容为
package com.ungly.servlet;

import com.ungly.bean.User;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * 页面初始化控制
 */
@WebServlet(name = "ListServlet",urlPatterns = "/List")
public class ListServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/lession1", "root", "123456");
            String username = request.getParameter("username");
            StringBuilder sql = new StringBuilder("select id,username from user where 1=1");
            List<String> paramList = new ArrayList<>();
            if(username != null && !"".equals(username.trim()))
            {
                request.setAttribute("username",username);
                sql.append(" and username=?");
                paramList.add(username);
            }
            PreparedStatement preparedStatement = conn.prepareStatement(sql.toString());
            for (int i = 0; i < paramList.size(); i++) {
                preparedStatement.setString(i+1,paramList.get(i));
            }
            ResultSet resultSet = preparedStatement.executeQuery();
            List<User> userList = new ArrayList<>();
            while (resultSet.next())
            {
                User user = new User();
                userList.add(user);
                user.setId(resultSet.getString("id"));
                user.setUsername(resultSet.getString("username"));
            }
            request.setAttribute("userList",userList);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        request.getRequestDispatcher("/WEB-INF/jsp/front/list.jsp").forward(request,response);
    }
}
  • 改造list.jsp文件,具体内容为
<%--
  Created by IntelliJ IDEA.
  User: nosay
  Date: 17-12-5
  Time: 下午3:31
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

<html>
<head>
    <title>Title</title>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <link href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>

<div class="container">
    <div class="row clearfix">
        <div class="col-md-12 column">
            <form role="form" method="get" action="">
                <div class="form-group">
                    <label for="username">用户名</label><input class="form-control" name="username" value="${requestScope.username}" id="username" type="username" />
                </div>
                <button type="submit" class="btn btn-default">Submit</button>
            </form>
            <table class="table">
                <thead>
                <tr>
                    <th>编号</th>
                    <th>用户名</th>
                    <th>操作</th>
                </tr>
                </thead>
                <tbody>
                <c:forEach items="${userList}" var="user" varStatus="status">

                    <tr>
                        <td>${status.index +1}</td>
                        <td>${user.username}</td>
                        <td>编辑|删除</td>
                    </tr>

                </c:forEach>

                </tbody>
            </table>
        </div>
    </div>
</div>

</body>
</html>

运行结果如图

此是,就完成了查询的操作.
但是我发现,代码写到这里,已经开始比较乱了
比如说,数据库连接,查询以及操作统统放到了servlet层,数据库连接和对应的一系统操作结束后,并没有调用close方法
接下来我会相应的优化一下