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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
import com.mysql.jdbc.Driver;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.Statement;public class Test2 { public static void main(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 { //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" %><html lang="en"><head> <meta charset="UTF-8"> <link href="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('./https://blog.csdn.net/qq_46906413/article/details/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; } #boxshadow img { width: 50%; border: 0px solid #8a4419; border-style: inset; } #boxshadow::after { content: ''; position: absolute; z-index: -1; -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%; height: 100px; bottom: 0; } style> <style> .button { background-color:#337AB7; 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; 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><div style="padding:2px;width:1080px;height:470px;margin-top:10%;margin-left:20%;opacity: 0.8" id="boxshadow"> <div> <img src="https://blog.csdn.net/qq_46906413/article/details/img/olypic.jpg" style="float:left;margin-top:5%;"> div> <div style="float:right;"> <form action="add" method="post"> <p style="margin-right:200px;"> 国家名称 <input type="text" name="Country" style="border-radius:8px;width:150px;height:30px;"> p> <p> 金牌数 <input type="text" name="Glod_num" style="border-radius:8px;width:150px;height:30px;margin-top:1%"> p> <p> 银牌数 <input type="text" name="Silver_num" style="border-radius:8px;width:150px;height:30px;margin-top:1%"> p> <p> 铜牌数 <input type="text" name="Copper_num" style="border-radius:8px;width:150px;height:30px;margin-top:1%"> p> <p> id <input type="text" name="id" style="border-radius:8px;width:150px;height:30px;margin-top:1%"> p> <input type="submit" value="保存"/><br/> form> form> div>div>body>html>Add.java
package com.bjpowernode.javaweb.servlet;import com.bjpowernode.javaweb.utils.DButil;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.*;@WebServlet(name = "add", value = "/add")public class Add extends HttpServlet { @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, 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"); String Glod_num=request.getParameter("Glod_num"); String Silver_num=request.getParameter("Silver_num"); String Copper_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); } }}
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、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
package com.bjpowernode.javaweb.servlet;import com.bjpowernode.javaweb.utils.DButil;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.io.PrintWriter;import java.sql.*;@WebServlet(name = "delete", value = "/delete")public class Delete extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, 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("");// //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><hr color="red" width="100%"><form action="edit" method="post"> 国家名称 :<input type='text' name='Country' value='"+country+"'/><br/><%-- logo :<input type='text' name='logo' value='"+logo+"'/><br/>--%> 金牌数 :<input type='text' name='Glod_num' value='"+Glod+"'/><br/> 银牌数 :<input type='text' name='Silver_num' value='"+Silver+"'/><br/> 铜牌数 :<input type='text' name='Copper_num' value='"+Copper+"'/><br/> id : <input type='text' name='Sum' value='"+sum+"'/><br/> 总数 : <input type='text' name='id' value='"+id+"'/><br/> <input type="submit" value="保存"/><br/>form>body>html>Edit.java
package com.bjpowernode.javaweb.servlet;import com.bjpowernode.javaweb.utils.DButil;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.io.PrintWriter;import java.sql.*;@WebServlet(name = "edit",value = "/edit")public class Edit extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, 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(""); out.println(""); out.println(" "); out.println(" "); out.println(" 添加信息 "); out.println(" "); out.println(" "); out.println(" "); out.println(" "); out.println(" "); out.println(""); out.println(""); out.println(""); out.println(""); out.println(""); out.println(" "); out.println(" 
"); out.println(" "); out.println(" "); out.println("); //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"); String Glod = rs.getString("Glod_num"); String Silver = rs.getString("Silver_num"); String Copper = 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(""
); out.println(" 国家名称 "); out.println(" ");// out.println(" ");
// out.println(" logo ");// out.println(" "); out.println(" "
); out.println(" 金牌数 "); out.println(" "); out.println(""); out.println(" "
); out.println(" 银牌数 "); out.println(" "); out.println(" "
); out.println(" 铜牌数 "); out.println(" "); out.println(" "
); out.println(" id "); out.println(" "); } } catch (SQLException e) { e.printStackTrace(); }finally { DButil.close(conn,ps,rs); } out.println("
");out.println(" ");out.println(" ");out.println(" ");out.println("");out.println("");out.println(""); }}Update.java
package com.bjpowernode.javaweb.servlet;import com.bjpowernode.javaweb.utils.DButil;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.*;@WebServlet(name = "update",value = "/update")public class Update extends HttpServlet { @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, 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"); String Glod_num=request.getParameter("Glod_num"); String Silver_num=request.getParameter("Silver_num"); String Copper_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
package com.bjpowernode.javaweb.servlet;import com.bipowernode.pojo.Olypic;import com.bjpowernode.javaweb.utils.DButil;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.io.PrintWriter;import java.sql.*;import java.util.ArrayList;import java.util.List;@WebServlet(name = "select",value = "/select")public class Select extends HttpServlet { @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, 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=new ArrayList<>(); 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"); String Glod = rs.getString("Glod_num"); String Silver = rs.getString("Silver_num"); String Copper = 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"); int G = Integer.valueOf(Glod).intValue(); int S = Integer.valueOf(Silver).intValue(); int C = Integer.valueOf(Copper).intValue(); int A=G+S+C; String Sum=String.valueOf(A); //将数据封装程Java对象 Olypic olpic=new Olypic(); 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
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
来源地址：https://blog.csdn.net/qq_46906413/article/details/123707839
