功能：利用HttpServlet完成MySql数据库my_user表的登录校验

step1:在porm.xml文件中导jdbc的依赖

mysql数据库输入

SELECT VERSION()

查询当前的数据库版本

 maven官网网址;https://mvnrepository.com/

maven官网中搜索：mySQL

并复制依赖粘贴到pom文件中

main函数下java包的class类

package com.iweb.demo03;  import org.apache.commons.codec.digest.DigestUtils;  import javax.servlet.RequestDispatcher; 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.SQLException; import java.util.List; import java.util.Map;  @WebServlet(value = "/login") public class Login extends HttpServlet {     @Override     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {      }      @Override     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {          req.setCharacterEncoding("utf-8");         resp.setCharacterEncoding("utf-8");         resp.setContentType("text/html");          PrintWriter pw = resp.getWriter();         String username = req.getParameter("username");         String password = req.getParameter("password");         password = DigestUtils.md5Hex(password);         String sql = "select count(*) cou from my_user m " +                 "where m.username=? and m.password=?";         List> list = null;         try {             list = JDBCUtill.jdbcBySelect(sql, username, password);         } catch (SQLException e) {             throw new RuntimeException(e);         } catch (ClassNotFoundException e) {             throw new RuntimeException(e);         }         Map map = list.get(0);         long cou = (long) map.get("cou");         String path="";         if (cou > 0) {             /* pw.print("欢迎您"+username);//页面跳转*/             /* resp.sendRedirect("/demo03/test5.html");*/         path=req.getContextPath() + "/test5.html";              System.out.println("登录成功");         } else {           path=req.getContextPath()+"/login.html?islogin=0";         }         resp.sendRedirect(path);     } } 

html文件 ：

                    
用户登陆
 
      账号     
     
     密码     
     
          
 
 
   

附录：

JDBC文件： 

package com.iweb.demo03;// // Source code recreated from a .class file by IntelliJ IDEA // (powered by FernFlower decompiler) //  import java.sql.*; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map;  public class JDBCUtill {     static Connection conn;     static PreparedStatement pstat;     static ResultSet rest;      public JDBCUtill() {     }      private static void getSource() throws SQLException, ClassNotFoundException {         Class.forName("com.mysql.cj.jdbc.Driver");         conn = DriverManager.getConnection("jdbc:mysql://192.168.77.100:3306/mysql?characterEncoding=utf-8", "root", "123456");     }      private static void closeSource() throws SQLException {         if (rest != null) {             rest.close();         }          if (pstat != null) {             pstat.close();         }          if (conn != null) {             conn.close();         }      }      public static List> jdbcBySelect(String sql) throws SQLException, ClassNotFoundException {         List> list = new ArrayList();         getSource();         pstat = conn.prepareStatement(sql);         rest = pstat.executeQuery();         ResultSetMetaData rsmd = rest.getMetaData();         int columnCount = rsmd.getColumnCount();          while(rest.next()) {             Map map = new HashMap();              for(int i = 1; i <= columnCount; ++i) {                 String columnName = rsmd.getColumnName(i);                 Object columnValue = rest.getObject(i);                 map.put(columnName, columnValue);             }              list.add(map);         }          closeSource();         return list;     }      public static List> jdbcBySelect(String sql, String username, String password) throws SQLException, ClassNotFoundException {         List> list = new ArrayList();         getSource();         pstat = conn.prepareStatement(sql);         pstat.setString(1, username);         pstat.setString(2, password);         rest = pstat.executeQuery();         ResultSetMetaData rsmd = rest.getMetaData();         int columnCount = rsmd.getColumnCount();          while(rest.next()) {             Map map = new HashMap();              for(int i = 1; i <= columnCount; ++i) {                 String columnName = rsmd.getColumnName(i);                 Object columnValue = rest.getObject(i);                 map.put(columnName, columnValue);             }              list.add(map);         }          closeSource();         return list;     }      public static  int updateBySql(String sql, E... e) throws SQLException, ClassNotFoundException {         getSource();         int res=0 ;         pstat = conn.prepareStatement(sql);          for(int i = 0; i < e.length; ++i) {             pstat.setObject(i + 1, e[i]);         }          res = pstat.executeUpdate();         closeSource();         return res;     } }