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("<HTML>");
out.println("<HEAD></HEAD>");
out.println("<BODY style='font-size:30px'>");
out.println("<table border='1' cellpadding='0'"+
"cellspacing='0' width='600px'");
out.println("<tr><caption>员工信息列表</caption></tr>"); //定义表格标题
out.println("<tr><td>编号</td><td>姓名</td><td>薪水</td>"+
"<td>年龄</td><td> 操作</td></tr>");
//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("<tr>");
out.println("<td>"+id+"</td>");
out.println("<td>"+name+"</td>");
out.println("<td>"+salary+"</td>");
out.println("<td>"+age+"</td>");
out.println("<td><a href='delete?id="+id+"' "+
"onclick=\"return confirm('是否确定删除"+name+"');\">删除</a>");
out.println("<a href='load?id="+id+"'>修改</a></td>");
out.println("</tr>");
}
out.println("</table>");
out.println("<a href='addEmp.jsp' style='font-size:20px'>>>添加员工信息</a></td>");
out.println("</body></HTML>");
} 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("<html><head></head><body style='font-size:30px'>");
if(rs.next()){
String name=rs.getString("name");
double salary=rs.getDouble("salary");
int age=rs.getInt("age");
out.println("<form action='modify' method='post'>");//输出表单
out.println("编号："+ id + "<br>");
out.println("<input type='hidden' name='id' value='"+id+"'/><br>");
out.println("姓名：<input name='name' value='"+name+"'/><br>");
out.println("薪水：<input name='salary' value='"+salary+"'/><br>");
out.println("年龄：<input name='age' value='"+age+"'/><br>");
out.println("<input type='submit' value='修改'/>");
out.println("</form>");
out.println("</body></html>");
}
} 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+"/"; %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>Servlet program</title>
<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">
<!-- <link rel="stylesheet" type="text/css" href="styles.css"> -->
</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
<?xml version="1.0" encoding="UTF-8"?>
<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>index.jsp</welcome-file>
</welcome-file-list>
<!-- 添加员工信息 -->
<servlet>
<servlet-name>addEmpServlet</servlet-name>
<servlet-class>web.AddEmpServlet</servlet-class>
</servlet>
<!-- 删除员工信息 -->
<servlet>
<servlet-name>deleteEmpServlet</servlet-name>
<servlet-class>web.DeleteEmpServlet</servlet-class>
</servlet>
<!-- 加载员工信息 -->
<servlet>
<servlet-name>loadEmpServlet</servlet-name>
<servlet-class>web.LoadEmpServlet</servlet-class>
</servlet>
<!-- 更新员工信息 -->
<servlet>
<servlet-name>modifyEmpServlet</servlet-name>
<servlet-class>web.ModifyEmpServlet</servlet-class>
</servlet>
<!-- 查询员工信息 -->
<servlet>
<servlet-name>listEmpServlet</servlet-name>
<servlet-class>web.ListEmpServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>addEmpServlet</servlet-name>
<url-pattern>/add</url-pattern> <!-- 地址栏必须是addEmp.jsp，提交表单后出现在地址栏的地址 -->
</servlet-mapping>
<servlet-mapping>
<servlet-name>deleteEmpServlet</servlet-name>
<url-pattern>/delete</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>loadEmpServlet</servlet-name>
<url-pattern>/load</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>modifyEmpServlet</servlet-name>
<url-pattern>/modify</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>listEmpServlet</servlet-name>
<url-pattern>/list</url-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。
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。