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Java/JavaWeb 连接数据库完成增删改查

在这里插入图片描述
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连接数据库无非就是和数据库建立连接，和前面的python连接数据库差不多。

**首先在连接Java数据库的时候需要数据库的

jar

包，这点不同于python连接数据库**
mysql的jar包

下面让我们来看看数据库是如何让连接的，是如何完成数据库的一系列操作，增删改查等…

💖Java连接数据库。

🎶1、注册驱动

Class.forName("com.mysql.jdbc.Driver");

🎶2、获取连接

  conn =DriverManager.getConnection("jdbc:mysql://localhost:3306/shop","root","123456");

注意：获取连接很重要，数据的一点点错误都会导致你连接不上数据库。
😃1、

localhost

代表本机不用变
😃2、

3306

是端口号，即port,一般默认都是3306。
😃3、

root

一般指管理员，不用变，直接用即可。
😃4、

"123456"

指的是密码，一般大家常用的密码就123、111111、root或者123456几种。

🎶3、获取数据库操作对象

stmt = conn.createStatement();

🎶4、//执行sql

String sql ="select id,name,num,price from testmodel_car";
            rs = stmt.executeQuery(sql);while(rs.next()){String id = rs.getString("id");String name = rs.getString("name");String num = rs.getString("num");String price = rs.getString("price");System.out.println(id +","+ name +","+ num +","+ price);}}catch(Exception e){
            e.printStackTrace();}finally{

**

注意：

**
😃1、

java"select id,name,num,price from testmodel_car";

，从表 testmodel_car中查询 id,name,num,price四列数据
😃2、

rs = stmt.executeQuery(sql);

，获取的对象编译一下sql语句
😃3、

String id = rs.getString("id");

，取出id那一列的值赋值给id(String id 中的id可以随便换，只要不和其他变量冲突都是可以的)

🎶5、释放资源

if(rs !=null){try{
                    rs.close();}catch(Exception e){
                    e.printStackTrace();}}if(stmt !=null){try{
                    stmt.close();}catch(Exception e){
                    e.printStackTrace();}}if(conn !=null){try{
                    conn.close();}catch(Exception e){
                    e.printStackTrace();}}

不释放资源也行，在上面抛出异常也可以解决

🎶6、完整代码

importcom.mysql.jdbc.Driver;importjava.sql.Connection;importjava.sql.DriverManager;importjava.sql.ResultSet;importjava.sql.Statement;publicclassTest2{publicstaticvoidmain(String[] args){Connection conn =null;Statement stmt =null;ResultSet rs =null;try{//注册驱动Class.forName("com.mysql.jdbc.Driver");//获取连接
            conn =DriverManager.getConnection("jdbc:mysql://localhost:3306/shop","root","123456");//获取数据库操作对象
            stmt = conn.createStatement();//执行sqlString sql ="select id,name,num,price from testmodel_car";
            rs = stmt.executeQuery(sql);while(rs.next()){String id = rs.getString("id");String name = rs.getString("name");String num = rs.getString("num");String price = rs.getString("price");System.out.println(id +","+ name +","+ num +","+ price);}}catch(Exception e){
            e.printStackTrace();}finally{//释放资源if(rs !=null){try{
                    rs.close();}catch(Exception e){
                    e.printStackTrace();}}if(stmt !=null){try{
                    stmt.close();}catch(Exception e){
                    e.printStackTrace();}}if(conn !=null){try{
                    conn.close();}catch(Exception e){
                    e.printStackTrace();}}}}}

💖连接数据库------增加操作

**

add.jsp

**

<%--
  Created by IntelliJ IDEA.
  User: 17331
  Date: 2022/3/5
  Time: 15:40
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<htmllang="en"><head><metacharset="UTF-8"><linkhref="h/favicon2.ico"rel="icon"type="image/x-icon"/><title>添加信息</title><style>body{background-color:#FDF5E6;}</style><style>body{width: 100%;height: 100%;background:url('./img/olypic.jpg');background-repeat: no-repeat;background-size: 100% 100%;background-attachment: fixed;}</style><style>input{width: 20%;padding: 12px 20px;margin: 8px 0;box-sizing: border-box;border: 1px solid #555;outline: none;}input:focus{background-color: lightblue;}</style><style>#boxshadow{position: relative;-moz-box-shadow: 1px 2px 4px rgba(0, 0, 0,0.5);-webkit-box-shadow: 1px 2px 4px rgba(0, 0, 0, .5);box-shadow: 1px 2px 4px rgba(0, 0, 0, .5);padding: 10px;background:#F0F8FF;border-radius:8px;}/* Make the image fit the box */#boxshadow img{width: 50%;border: 0px solid #8a4419;border-style: inset;}#boxshadow::after{content:'';position: absolute;z-index: -1;/* hide shadow behind image */-webkit-box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);-moz-box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);width: 70%;left: 15%;/* one half of the remaining 30% */height: 100px;bottom: 0;}</style><style>.button{background-color:#337AB7;/* Green */border: none;color: white;padding: 16px 32px;text-align: center;text-decoration: none;display: inline-block;font-size: 16px;margin: 4px 2px;-webkit-transition-duration: 0.4s;/* Safari */transition-duration: 0.4s;cursor: pointer;}.button1{background-color: white;color: black;border: 2px solid #337AB7;}.button1:hover{background-color: #337AB7;color: white;box-shadow: 0 12px 16px 0 rgba(0,0,0,0.24),0 17px 50px 0 rgba(0,0,0,0.19);}</style></head><body><divstyle="padding:2px;width:1080px;height:470px;margin-top:10%;margin-left:20%;opacity: 0.8"id="boxshadow"><div><imgsrc="img/olypic.jpg"style="float:left;margin-top:5%;"></div><divstyle="float:right;"><formaction="add"method="post"><pstyle="margin-right:200px;">
                国家名称&nbsp&nbsp&nbsp<inputtype="text"name="Country"style="border-radius:8px;width:150px;height:30px;"></p><p>
                &nbsp&nbsp金牌数&nbsp&nbsp&nbsp&nbsp&nbsp<inputtype="text"name="Glod_num"style="border-radius:8px;width:150px;height:30px;margin-top:1%"></p><p>
                &nbsp&nbsp银牌数&nbsp&nbsp&nbsp&nbsp&nbsp<inputtype="text"name="Silver_num"style="border-radius:8px;width:150px;height:30px;margin-top:1%"></p><p>
                &nbsp&nbsp铜牌数&nbsp&nbsp&nbsp&nbsp&nbsp<inputtype="text"name="Copper_num"style="border-radius:8px;width:150px;height:30px;margin-top:1%"></p><p>
                &nbsp&nbsp&nbsp&nbsp&nbspid&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp<inputtype="text"name="id"style="border-radius:8px;width:150px;height:30px;margin-top:1%"></p><inputtype="submit"value="保存"/><br/></form></form></div></div></body></html>

**

Add.java

**

packagecom.bjpowernode.javaweb.servlet;importcom.bjpowernode.javaweb.utils.DButil;importjavax.servlet.ServletException;importjavax.servlet.annotation.WebServlet;importjavax.servlet.http.HttpServlet;importjavax.servlet.http.HttpServletRequest;importjavax.servlet.http.HttpServletResponse;importjava.io.IOException;importjava.sql.*;@WebServlet(name ="add", value ="/add")publicclassAddextendsHttpServlet{@OverrideprotectedvoiddoPost(HttpServletRequest request,HttpServletResponse response)throwsServletException,IOException{
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");//获取信息，前端页面注册的信息String country=request.getParameter("Country");//        String logo=request.getParameter("logo");StringGlod_num=request.getParameter("Glod_num");StringSilver_num=request.getParameter("Silver_num");StringCopper_num=request.getParameter("Copper_num");String id =request.getParameter("id");//        String Sum=request.getParameter("Sum");//连接数据库，执行insert插入语句Connection conn =null;PreparedStatement ps =null;int count=0;try{//注册驱动try{Class.forName("com.mysql.jdbc.Driver");}catch(ClassNotFoundException e){
                e.printStackTrace();}//获取连接
            conn =DriverManager.getConnection("jdbc:mysql://localhost:3306/mofa","root","123456");// TODO 2、开启事务   默认开启  我们将它关闭（）自动提交机制关闭String sql ="insert ignore into medals_table(Country,Glod_num,Silver_num,Copper_num,id) values (?,?,?,?,?);";
            ps = conn.prepareStatement(sql);
            ps.setString(1, country);//            ps.setString(2, logo);
            ps.setString(2,Glod_num);
            ps.setString(3,Silver_num);
            ps.setString(4,Copper_num);
            ps.setString(5, id);//            ps.setString(7, Sum);//返回一个值，指的是  影响了数据库中多少条记录  主要是判断是否大于0  就是是否印象数据库
            count = ps.executeUpdate();}catch(SQLException e){
            e.printStackTrace();}finally{DButil.close(conn,ps,null);}if(count==1){//增加成功   任然跳到列表页面
            request.getRequestDispatcher("Take_01").forward(request,response);}else{//删除失败
            request.getRequestDispatcher("error.jsp").forward(request,response);}}}

在这里插入图片描述
增加功能就是通过前端jsp文件text填写数据，然后通过submit提交数据，传递给后端servlet，也就是上面的Add，注意Java文件不要小写，我就没少挨骂

**

步骤：

**
😘1、前端jsp文件text写入通过submit提交
😘2、

<form action="add" method="post">

通过form表单提交给后端的servel(Add)
😘3、**

String country=request.getParameter("Country");

通过getParameter取到前端的值然后赋值给country，为后面刷数据做准备
😘4、后端servlet访问数据库，步骤访问上面第一个标题《Java连接数据库》**
😘5、成功将前端传来的数据刷如数据库

💖连接数据库------删除操作

packagecom.bjpowernode.javaweb.servlet;importcom.bjpowernode.javaweb.utils.DButil;importjavax.servlet.ServletException;importjavax.servlet.annotation.WebServlet;importjavax.servlet.http.HttpServlet;importjavax.servlet.http.HttpServletRequest;importjavax.servlet.http.HttpServletResponse;importjava.io.IOException;importjava.io.PrintWriter;importjava.sql.*;@WebServlet(name ="delete", value ="/delete")publicclassDeleteextendsHttpServlet{@OverrideprotectedvoiddoGet(HttpServletRequest request,HttpServletResponse response)throwsServletException,IOException{//根据部门编号删除部门//获取部门编号String country = request.getParameter("name");//连接数据库Connection conn =null;PreparedStatement ps =null;ResultSet rs =null;int count=0;try{//注册驱动Class.forName("com.mysql.jdbc.Driver");//获取连接
            conn =DriverManager.getConnection("jdbc:mysql://localhost:3306/mofa","root","123456");// TODO 2、开启事务   默认开启  我们将它关闭（）自动提交机制关闭
            conn.setAutoCommit(false);String sql ="delete from medals_table where Country=?";
            ps = conn.prepareStatement(sql);
            ps.setString(1,country);//返回一个值，指的是  影响了数据库中多少条记录  主要是判断是否大于0  就是是否印象数据库
            count= ps.executeUpdate();//事务提交
            conn.commit();}catch(SQLException e){if(conn!=null){try{
                    conn.rollback();}catch(SQLException ex){
                    ex.printStackTrace();}}
            e.printStackTrace();}catch(ClassNotFoundException e){
            e.printStackTrace();}finally{DButil.close(conn,ps,null);}if(count==1){PrintWriter out = response.getWriter();
            out.println("<script>");
            out.println("alert('Dear, the deletion is unrecoverable. Are you sure you deleted it？');");
            out.println("location.href='Take_01'");//跳转到用户列表页面
            out.println("</script>");//            //删除成功   任然跳到列表页面//            request.getRequestDispatcher("Take_01").forward(request,response);}else{//删除失败
            request.getRequestDispatcher("error.jsp").forward(request,response);}}}

**

String country = request.getParameter("name");

，老规矩，前端取值进行操作**

💖连接数据库------修改操作

**

edit.jsp

**

<%--
  Created by IntelliJ IDEA.
  User: 17331
  Date: 2022/3/6
  Time: 17:39
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html><head><title><%@ page contentType="text/html;charset=UTF-8" language="java" %>
        <html><head><title>新增</title></head><body><h1>新增国家奖牌信息</h1><hrcolor="red"width="100%"><formaction="edit"method="post">
    国家名称 :<inputtype='text'name='Country'value='"+country+"'/><br/>
<%--    logo :<inputtype='text'name='logo'value='"+logo+"'/><br/>--%>
    金牌数 :<inputtype='text'name='Glod_num'value='"+Glod+"'/><br/>
    银牌数 :<inputtype='text'name='Silver_num'value='"+Silver+"'/><br/>
    铜牌数 :<inputtype='text'name='Copper_num'value='"+Copper+"'/><br/>
    id  : <inputtype='text'name='Sum'value='"+sum+"'/><br/>
    总数 : <inputtype='text'name='id'value='"+id+"'/><br/><inputtype="submit"value="保存"/><br/></form></body></html>

**

Edit.java

**

packagecom.bjpowernode.javaweb.servlet;importcom.bjpowernode.javaweb.utils.DButil;importjavax.servlet.ServletException;importjavax.servlet.annotation.WebServlet;importjavax.servlet.http.HttpServlet;importjavax.servlet.http.HttpServletRequest;importjavax.servlet.http.HttpServletResponse;importjava.io.IOException;importjava.io.PrintWriter;importjava.sql.*;@WebServlet(name ="edit",value ="/edit")publicclassEditextendsHttpServlet{@OverrideprotectedvoiddoGet(HttpServletRequest request,HttpServletResponse response)throwsServletException,IOException{String contextPath = request.getContextPath();
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");PrintWriter out =response.getWriter();//jsp文档
        out.println("<html lang='en'>");
        out.println("<head>");
        out.println("    <meta charset='UTF-8'>");
        out.println("    <link href='h/favicon2.ico' rel='icon' type='image/x-icon'/>");
        out.println("    <title>添加信息</title>");
        out.println("    <style>");
        out.println("                body {");
        out.println("            background-color:#FDF5E6;");
        out.println("        }");
        out.println("    </style>");
        out.println("    <style>");
        out.println("                body {");
        out.println("            width: 100%;");
        out.println("            height: 100%;");
        out.println("            background: url('./img/olypic.jpg');");
        out.println("            background-repeat: no-repeat;");
        out.println("            background-size: 100% 100%;");
        out.println("            background-attachment: fixed;");
        out.println("        }");
        out.println("    </style>");
        out.println("    <style>");
        out.println("                input{");
        out.println("            width: 20%;");
        out.println("            padding: 12px 20px;");
        out.println("            margin: 8px 0;");
        out.println("            box-sizing: border-box;");
        out.println("            border: 1px solid #555;");
        out.println("            outline: none;");
        out.println("        }");
        out.println("");
        out.println("        input:focus {");
        out.println("            background-color: lightblue;");
        out.println("        }");
        out.println("    </style>");
        out.println("    <style>");
        out.println("        #boxshadow {");
        out.println("            position: relative;");
        out.println("            -moz-box-shadow: 1px 2px 4px rgba(0, 0, 0,0.5);");
        out.println("            -webkit-box-shadow: 1px 2px 4px rgba(0, 0, 0, .5);");
        out.println("            box-shadow: 1px 2px 4px rgba(0, 0, 0, .5);");
        out.println("            padding: 10px;");
        out.println("            background:#F0F8FF;");
        out.println("            border-radius:8px;");
        out.println("        }");
        out.println("");
        out.println("        /* Make the image fit the box */");
        out.println("        #boxshadow img {");
        out.println("            width: 50%;");
        out.println("            border: 0px solid #8a4419;");
        out.println("            border-style: inset;");
        out.println("        }");
        out.println("");
        out.println("        #boxshadow::after {");
        out.println("            content: '';");
        out.println("            position: absolute;");
        out.println("            z-index: -1; /* hide shadow behind image */");
        out.println("            -webkit-box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);");
        out.println("            -moz-box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);");
        out.println("            box-shadow: 0 15px 20px rgba(0, 0, 0, 0.3);");
        out.println("            width: 70%;");
        out.println("            left: 15%; /* one half of the remaining 30% */");
        out.println("            height: 100px;");
        out.println("            bottom: 0;");
        out.println("        }");
        out.println("    </style>");
        out.println("    <style>");
        out.println("       .button {");
        out.println("            background-color:#337AB7; /* Green */");
        out.println("            border: none;");
        out.println("            color: white;");
        out.println("            padding: 16px 32px;");
        out.println("            text-align: center;");
        out.println("            text-decoration: none;");
        out.println("            display: inline-block;");
        out.println("            font-size: 16px;");
        out.println("            margin: 4px 2px;");
        out.println("            -webkit-transition-duration: 0.4s; /* Safari */");
        out.println("            transition-duration: 0.4s;");
        out.println("            cursor: pointer;");
        out.println("        }");
        out.println("");
        out.println("       .button1 {");
        out.println("            background-color: white;");
        out.println("            color: black;");
        out.println("            border: 2px solid #337AB7;");
        out.println("        }");
        out.println("       .button1:hover {");
        out.println("            background-color: #337AB7;");
        out.println("            color: white;");
        out.println("            box-shadow: 0 12px 16px 0 rgba(0,0,0,0.24),0 17px 50px 0 rgba(0,0,0,0.19);");
        out.println("        }");
        out.println("    </style>");
        out.println("");
        out.println("</head>");
        out.println("<body>");
        out.println("");
        out.println("<div style='padding:2px;width:1080px;height:470px;margin-top:10%;margin-left:20%;opacity: 0.8' id='boxshadow'>");
        out.println("    <div>");
        out.println("        <img src='img/olypic.jpg'   style='float:left;margin-top:5%;'>");
        out.println("    </div>");
        out.println("    <div style='float:right;'>");
        out.println("        <form action='"+contextPath+"/update' method='post'>");//获取国家名称String country=request.getParameter("name");//连接数据库Connection conn=null;PreparedStatement ps=null;ResultSet rs=null;try{try{Class.forName("com.mysql.jdbc.Driver");}catch(ClassNotFoundException e){
                e.printStackTrace();}//获取连接
            conn =DriverManager.getConnection("jdbc:mysql://localhost:3306/mofa","root","123456");String sql ="select * from medals_table where Country=?";//编译sql语句
            ps = conn.prepareStatement(sql);//赋值    第一个问好赋值 country   国家名称
            ps.setString(1, country);//查询返回结果集    这个结果集只有一条记录  ，国家名称是主键  ，  故只有一条数据
            rs = ps.executeQuery();if(rs.next()){String logo=rs.getString("logo");StringGlod= rs.getString("Glod_num");StringSilver= rs.getString("Silver_num");StringCopper= rs.getString("Copper_num");String sum=rs.getString("Sum");String id=rs.getString("id");System.out.println("你好，你好，你好，齐天大圣！！！");//输出动态网页
                out.println("<p style='margin-right:200px;'>");
                out.println("                        国家名称&nbsp&nbsp&nbsp<input type='text'  name='Country'  value='"+country+"' style='border-radius:8px;width:150px;height:30px;'>");
                out.println("            </p>");//                out.println("            <p>");//                out.println("                        &nbsp&nbsp&nbsplogo&nbsp&nbsp&nbsp&nbsp&nbsp <input type='text' name='logo' value='"+logo+"' style='border-radius:8px;width:150px;height:30px;margin-top:1%'>");//                out.println("            </p>");
                out.println("            <p>");
                out.println("                        &nbsp&nbsp金牌数&nbsp&nbsp&nbsp&nbsp&nbsp<input type='text' name='Glod_num' value='"+Glod+"' style='border-radius:8px;width:150px;height:30px;margin-top:1%'>");
                out.println("            </p>");
                out.println("");
                out.println("            <p>");
                out.println("                        &nbsp&nbsp银牌数&nbsp&nbsp&nbsp&nbsp&nbsp<input type='text' name='Silver_num' value='"+Silver+"' style='border-radius:8px;width:150px;height:30px;margin-top:1%'>");
                out.println("            </p>");
                out.println("            <p>");
                out.println("                        &nbsp&nbsp铜牌数&nbsp&nbsp&nbsp&nbsp&nbsp<input type='text' name='Copper_num' value='"+Copper+"' style='border-radius:8px;width:150px;height:30px;margin-top:1%'>");
                out.println("            </p>");
                out.println("            <p>");
                out.println("                        &nbsp&nbsp&nbsp&nbsp&nbspid&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp<input type='text' name='id' value='"+id+"' style='border-radius:8px;width:150px;height:30px;margin-top:1%'>");
                out.println("            </p>");}}catch(SQLException e){
            e.printStackTrace();}finally{DButil.close(conn,ps,rs);}
        out.println("            <input type='submit' value='保存'/><br/>");
out.println("      </form>");
out.println("     </form>");
out.println("  </div>");
out.println("</div>");
out.println("</body>");
out.println("</html>");}}

**

Update.java

**

packagecom.bjpowernode.javaweb.servlet;importcom.bjpowernode.javaweb.utils.DButil;importjavax.servlet.ServletException;importjavax.servlet.annotation.WebServlet;importjavax.servlet.http.HttpServlet;importjavax.servlet.http.HttpServletRequest;importjavax.servlet.http.HttpServletResponse;importjava.io.IOException;importjava.sql.*;@WebServlet(name ="update",value ="/update")publicclassUpdateextendsHttpServlet{@OverrideprotectedvoiddoPost(HttpServletRequest request,HttpServletResponse response)throwsServletException,IOException{
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");//解决中文乱码问题String country=request.getParameter("Country");String logo=request.getParameter("logo");StringGlod_num=request.getParameter("Glod_num");StringSilver_num=request.getParameter("Silver_num");StringCopper_num=request.getParameter("Copper_num");String id=request.getParameter("id");//连接数据库执行更新操作Connection conn =null;PreparedStatement ps =null;ResultSet rs =null;int count=0;try{try{Class.forName("com.mysql.jdbc.Driver");}catch(ClassNotFoundException e){
                e.printStackTrace();}//获取连接
            conn =DriverManager.getConnection("jdbc:mysql://localhost:3306/mofa","root","123456");String sql ="update medals_table set Glod_num=?,Silver_num=?,Copper_num=?,id=? where Country=?";//编译sql语句
            ps = conn.prepareStatement(sql);//            ps.setString(1, logo);
            ps.setString(1,Glod_num);
            ps.setString(2,Silver_num);
            ps.setString(3,Copper_num);
            ps.setString(4, id);
            ps.setString(5, country);//            System.out.println(logo);
            count=ps.executeUpdate();System.out.println(count);}catch(SQLException e){
            e.printStackTrace();}finally{DButil.close(conn, ps, rs);}if(count==1){//更新成功
            request.getRequestDispatcher("Take_01").forward(request,response);}else{//更新失败
            request.getRequestDispatcher("error.jsp").forward(request,response);}}}

💋1、前端传输数据给后端edit,edit通过getParameter取到前端值完成后面的操作。
💋2、为了让修改的时候可以显示修改前的值，我们在Edit.java中写入前端代码。
💋3、Edit.jav中代码通过form表单把数据传输给Update.java。
💋4、Update.java通过getParameter取到由Edit.java中传来的值。
💋5、把取到的值存进数据库，完成刷入操作。

**

注意：我这里有个bug，就是不能修改国家名称，因为手贱的我为了让数据库看着好看就把国家名设置为主键了，，，，，，，

**

💖连接数据库------查询操作

**

Select.java

**

packagecom.bjpowernode.javaweb.servlet;importcom.bipowernode.pojo.Olypic;importcom.bjpowernode.javaweb.utils.DButil;importjavax.servlet.ServletException;importjavax.servlet.annotation.WebServlet;importjavax.servlet.http.HttpServlet;importjavax.servlet.http.HttpServletRequest;importjavax.servlet.http.HttpServletResponse;importjava.io.IOException;importjava.io.PrintWriter;importjava.sql.*;importjava.util.ArrayList;importjava.util.List;@WebServlet(name ="select",value ="/select")publicclassSelectextendsHttpServlet{@OverrideprotectedvoiddoPost(HttpServletRequest request,HttpServletResponse response)throwsServletException,IOException{
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");String name = request.getParameter("select_name");System.out.println(name);//连接数据库Connection conn =null;PreparedStatement ps =null;ResultSet rs =null;List<Olypic> olypicList=newArrayList<>();try{Class.forName("com.mysql.jdbc.Driver");//获取连接
            conn =DriverManager.getConnection("jdbc:mysql://localhost:3306/mofa","root","123456");String sql ="select * from medals_table where Country=?";//编译sql语句
            ps = conn.prepareStatement(sql);//赋值    第一个问好赋值 country   国家名称
            ps.setString(1, name);//查询返回结果集    这个结果集只有一条记录  ，国家名称是主键  ，  故只有一条数据
            rs = ps.executeQuery();if(rs.next()){String country = rs.getString("Country");StringGlod= rs.getString("Glod_num");StringSilver= rs.getString("Silver_num");StringCopper= rs.getString("Copper_num");String id=rs.getString("id");String logo=rs.getString("logo");System.out.println("这是数据");System.out.println(country);System.out.println("Glod");//                   String Sum=rs.getString("Sum");intG=Integer.valueOf(Glod).intValue();intS=Integer.valueOf(Silver).intValue();intC=Integer.valueOf(Copper).intValue();intA=G+S+C;StringSum=String.valueOf(A);//将数据封装程Java对象Olypic olpic=newOlypic();
                olpic.setCountry(country);
                olpic.setGlod_num(Glod);
                olpic.setSilver_num(Silver);
                olpic.setCopper_num(Copper);
                olpic.setId(id);
                olpic.setSum(Sum);
                olpic.setLogo(logo);// TODO 将数据放入上面定义好的容器
                olypicList.add(olpic);}}catch(SQLException e){
            e.printStackTrace();}catch(ClassNotFoundException e){
            e.printStackTrace();}finally{DButil.close(conn, ps, rs);}
        request.setAttribute("olypicList",olypicList);
        request.getRequestDispatcher("./take_03.jsp").forward(request,response);}}

可以从前端或者后端传值，完成搜索操作。但是一般是要通过前端搜索框输入值，通过form表单传走，后端通过getParameter取值完成一些列操作。

现在的项目都是通过框架，但是 了解传输和运行机制还是十分重要的。

最后介绍一下牛客。Leetcode有的刷题牛客都有，除此之外牛客里面还有招聘（社招和校招）、一些上岸大厂的大佬的面试经验。**

牛客是可以伴随一生的编程软件（完全免费），从学校到社会工作，时时刻刻你都可以用到

，感兴趣的可以去注册试试**可以伴随一生的刷题app

完整的JavaWeb项目

觉得有用的可以给个三连，关注一波！！！带你了解更多的Java小知识

标签： database mysql JavaWeb
本文转载自: https://blog.csdn.net/qq_46906413/article/details/123707839
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