使用JDBC实现对数据的增删改查

为员工管理添加增加、删除和修改的功能，即在查询结果页面中提供删除、修改的操作链接，并实现在删除或修改后回到查询页面的效果。如下图所示：

步骤
step1: 添加ListEmpServlet，添加删除链接、修改链接和添加链接
代码如下：

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ListEmpServlet extends HttpServlet{
    protected void service(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException,IOException{
        //保证正确读取Post提交来的中文
        request.setCharacterEncoding("utf-8");
        //保证正确输出中文
        response.setContentType("text/html;charset=utf-8");
        //获取输出流对象，并输出信息
        PrintWriter out=response.getWriter();
        //获取表单提交的数据
        //String name= request.getParameter("name");
        //double salary = Double.valueOf(request.getParameter("salary"));
        //int age = Integer.valueOf(request.getParameter("age"));
        //将数据插入到数据库t_emp表中
        Connection conn = null;
        PreparedStatement stat=null;
        try {
            //1、加载MySQL的JDBC的驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2、取得连接的URL，能访问MySQL数据库的用户名和密码
            String url="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8";
            String username = "root";
            String password = "123456"; 
            //3、创建与MySQL数据库的连接类的实例
            conn=DriverManager.getConnection(url,username,password);
            stat=conn.prepareStatement("select * from t_emp");
            ResultSet rs = stat.executeQuery();
            //4、输出表格之前的页面标记
            out.println("");
            out.println("");
            out.println("");
            out.println("+
                         "cellspacing='0' width='600px'");out.println("");  //定义表格标题out.println(""+
                           "");
            //3、遍历结果集，以表格形式输出数据
            while(rs.next()){
                int id=rs.getInt("id");
                String name=rs.getString("name");
                double salary=rs.getDouble("salary");
                int age=rs.getInt("age");out.println("");out.println("");out.println("");out.println("");out.println("");out.println("");out.println("");
            }
            out.println("

            
员工信息列表
            
编号
姓名
薪水
年龄
  操作
                

                
"+id+"
                
"+name+"
                
"+salary+"
                
"+age+"
                
+
                        "οnclick=\"return confirm('是否确定删除"+name+"');\">删除");
                out.println("修改
                
");
            out.println(">>添加员工信息");
            out.println("");
        } catch (Exception e) {
            e.printStackTrace();
            out.print("系统繁忙，稍后重试");
        }finally{
            if(stat!=null){
                try {
                    stat.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }

            }
        }
    }
}

Step2： 新建DeleteEmpServlet类，处理删除动作
获取请求参数值id，构建删除语句并执行
代码如下：

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class DeleteEmpServlet extends HttpServlet{
    private static final long serialVersionUID = 1L;

    protected void service(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException,IOException{
        //保证正确读取Post提交来的中文
        request.setCharacterEncoding("utf-8");
        //保证正确输出中文
        response.setContentType("text/html;charset=utf-8");
        //获取输出流对象，并输出信息
        PrintWriter out=response.getWriter();
        //获取删除的编号
        int id =Integer.parseInt(request.getParameter("id"));
        //连接数据库，执行删除操作
        Connection conn = null;
        PreparedStatement stmt=null;
        try {
            //1、加载MySQL的JDBC的驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2、取得连接的URL，能访问MySQL数据库的用户名和密码
            String url="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8";
            String username = "root";
            String password = "123456"; 
            //3、创建与MySQL数据库的连接类的实例
            conn=DriverManager.getConnection(url,username,password);
            stmt=conn.prepareStatement("delete from t_emp where id=?");//删除的sql语句
            stmt.setInt(1, id);
            stmt.executeUpdate();// 用于执行 INSERT、UPDATE 或 DELETE 语句以及 SQL DDL（数据定义语言）语句，例如 CREATE TABLE 和 DROP TABLE
            response.sendRedirect("list");  //重定向到查询页面
        } catch (Exception e) {
            e.printStackTrace();
            out.print("系统繁忙，稍后重试");
        }finally{
            if(stmt!=null){
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }

            }
        }

    }
}

Step3 : 新建LoadEmpServlet.java文件
获取请求参数值id，查询数据并构建表单显示数据
代码如下：

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class LoadEmpServlet extends HttpServlet{
    protected void service(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException,IOException{
        //保证正确读取Post提交来的中文
        request.setCharacterEncoding("utf-8");
        //保证正确输出中文
        response.setContentType("text/html;charset=utf-8");
        //获取输出流对象，并输出信息
        PrintWriter out=response.getWriter();
        //获取请求参数值id
        int id = Integer.parseInt(request.getParameter("id"));
        //根据ID查询数据库获取员工信息
        Connection conn = null;
        PreparedStatement stmt=null;
        ResultSet rs=null;
        try {
            //1、加载MySQL的JDBC的驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2、取得连接的URL，能访问MySQL数据库的用户名和密码
            String url="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8";
            String username = "root";
            String password = "123456"; 
            //3、创建与MySQL数据库的连接类的实例
            conn=DriverManager.getConnection(url,username,password);
            stmt=conn.prepareStatement("select * from t_emp where id=?");
            stmt.setInt(1, id);
            rs=stmt.executeQuery();
            out.println("");
            if(rs.next()){
                String name=rs.getString("name");
                double salary=rs.getDouble("salary");
                int age=rs.getInt("age");
                out.println("
");//输出表单
                out.println("编号："+ id + "
");
                out.println("
");
                out.println("姓名：
");
                out.println("薪水：
");
                out.println("年龄：
");
                out.println("");
                out.println(""
);
                out.println("");
                }
        } catch (Exception e) {
            e.printStackTrace();
            out.print("系统繁忙，稍后重试");
        }finally{
            if(stmt!=null){
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }

            }
        }

    }
}

Step4: 新建ModifyEmpServlet.java文件
修改数据表中的数据
代码如下：

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class ModifyEmpServlet extends HttpServlet{
    protected void service(HttpServletRequest request,
            HttpServletResponse response)
            throws ServletException,IOException{
        //保证正确读取Post提交来的中文
        request.setCharacterEncoding("utf-8");
        //保证正确输出中文
        response.setContentType("text/html;charset=utf-8");
        //获取输出流对象，并输出信息
        PrintWriter out=response.getWriter();
        //1、获取请求参数值
        int id=Integer.parseInt(request.getParameter("id"));
        String name= request.getParameter("name");
        double salary = Double.valueOf(request.getParameter("salary"));
        int age = Integer.valueOf(request.getParameter("age"));
        //2、数据库数据更新
        Connection conn = null;
        PreparedStatement stmt=null;
        try {
            //1、加载MySQL的JDBC的驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2、取得连接的URL，能访问MySQL数据库的用户名和密码
            String url="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8";
            String username = "root";
            String password = "123456"; 
            //3、创建与MySQL数据库的连接类的实例
            conn=DriverManager.getConnection(url,username,password);
            stmt=conn.prepareStatement("update t_emp set name=?,"+
                    "salary=?,age=? where id=?"); //数据更新SQL
            stmt.setString(1, name);
            stmt.setDouble(2, salary);
            stmt.setInt(3, age);
            stmt.setInt(4, id);
            stmt.executeUpdate();
            response.sendRedirect("list");//从定向到查询界面
        } catch (Exception e) {
            e.printStackTrace();
            out.print("系统繁忙，稍后重试");
        }finally{
            if(stmt!=null){
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }

            }
        }

    }
}

Step5: 新建AddEmpServlet.java文件
添加数据：
代码如下：

package web;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class AddEmpServlet extends HttpServlet
{
    protected void service(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException
    {
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();

        //读取请求参数值
        String name = request.getParameter("name");
        double salary = Double.parseDouble(request.getParameter("salary"));
        int age = Integer.parseInt(request.getParameter("age"));

        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");

        //JDBC
        Connection conn = null;
        PreparedStatement stat = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            //2、取得连接的URL，能访问MySQL数据库的用户名和密码
            String url="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8";
            String username = "root";
            String password = "123456"; 
            //3、创建与MySQL数据库的连接类的实例
            conn=DriverManager.getConnection(url,username,password);

            stat = conn.prepareStatement("INSERT INTO t_emp(name,salary,age) VALUES(?,?,?)");
            stat.setString(1, name);
            stat.setDouble(2, salary);
            stat.setInt(3, age);
            stat.executeUpdate();
//          out.println("添加员工成功");
//          out.println("查看所有员工");
            //重定向到员工列表
            response.sendRedirect("list");
            System.out.println("重定向之后的代码");
        } catch (Exception e) {
            e.printStackTrace();
            /*
             * 判断异常是否能够恢复，如果不能够恢复
             * (比如,数据库服务暂停,网络中断等等,一般称之为系统异常),提示用户稍后重试即可。
             * 如果能够恢复(应用异常)，要立即恢复。
             */
            out.println("系统繁忙,稍后重试");
        }finally{
            if(stat!=null){
                try{
                    stat.close();
                }catch(SQLException e){
                    e.printStackTrace();
                }
            }
            if(conn!=null){
                try{
                    conn.close();
                }catch(SQLException e){
                    e.printStackTrace();
                }
            }
        }
    }
}

Step6： 新建一个addEmp.jsp文件，实现添加员工信息操作
代码如下：

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


<html>
  <head>
    <base href="<%=basePath%>">

    <title>Servlet programtitle>
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <meta http-equiv="content-type" content="text/html;charset=utf-8">
    
  head>

  <body>
    <form action="add" method="post"> 
        <fieldset>
            <legend>添加员工legend>
            姓名：<input name="name"/><br>
            薪水：<input name="salary"/><br>
            年龄：<input name="age"/><br>
            <input type="submit" value="添加">
        fieldset>
    form>
  body>
html>

Step6： 修改web.xml文件实现配置

<web-app version="3.0" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <display-name>display-name> 
  <welcome-file-list>
    <welcome-file>addEmp.jspwelcome-file>
  welcome-file-list>
 
  <servlet>
    <servlet-name>addEmpServletservlet-name>
    <servlet-class>web.AddEmpServletservlet-class>
  servlet>
  
  <servlet>
    <servlet-name>deleteEmpServletservlet-name>
    <servlet-class>web.DeleteEmpServletservlet-class>
  servlet>
  
  <servlet>
    <servlet-name>loadEmpServletservlet-name>
    <servlet-class>web.LoadEmpServletservlet-class>
  servlet>
   
  <servlet>
    <servlet-name>modifyEmpServletservlet-name>
    <servlet-class>web.ModifyEmpServletservlet-class>
  servlet>
  
  <servlet>
    <servlet-name>listEmpServletservlet-name>
    <servlet-class>web.ListEmpServletservlet-class>
  servlet>
  <servlet-mapping>
    <servlet-name>addEmpServletservlet-name>
    <url-pattern>/addurl-pattern>  
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>deleteEmpServletservlet-name>
    <url-pattern>/deleteurl-pattern>  
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>loadEmpServletservlet-name>
    <url-pattern>/loadurl-pattern>  
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>modifyEmpServletservlet-name>
    <url-pattern>/modifyurl-pattern>  
  servlet-mapping>
  <servlet-mapping>
    <servlet-name>listEmpServletservlet-name>
    <url-pattern>/listurl-pattern>  
  servlet-mapping>
web-app>

Step7 :加载到Tomcat服务器中，在浏览器运行
页面见第一个图。

附上表结构sql:

-- ----------------------------
-- Table structure for t_emp
-- ----------------------------
DROP TABLE IF EXISTS `t_emp`;
CREATE TABLE `t_emp` (
  `id` int(4) NOT NULL AUTO_INCREMENT,
  `name` varchar(8) NOT NULL,
  `salary` float(8,2) DEFAULT NULL,
  `age` int(2) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

感谢 u014586688 指出问题，现已更改，程序测试成功。
AddEmpServlet.java已在上面添加。
另外，对web.xml文件做一个修改，修改位置如下：

file-list>
    file>addEmp.jspfile>
  file-list>

注意：运行此例子需要加载mysql的jar包，
我使用的是：mysql-connector-java-5.1.7-bin.jar

这样，一个简单的增删改查操作就完成了。
如果发现不妥或疑问之处，麻烦提出。这段时间正在学习这方面的知识，欢迎交流。