基于Java控制台的客户端-服务器登录应用程序-数据库身份验证错误

Question

从早上开始，我一直在努力解决这个问题。我有客户端和服务器应用程序，客户端发送用户名和密码，服务器接收它，检查数据库，向正确的用户发送消息成功
但是，我无法处理客户端的请求
问题出在哪里？等待专家解决方案。。。

这是服务器：

import java.io.*;
import java.net.*;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.io.File;
import java.sql.*;
class TCPServer
{
    public static void main(String argv[]) throws Exception
       {
          String clientSentence,clientpassword;
          String capitalizedSentence;
          ServerSocket welcomeSocket = new ServerSocket(4003);
          Connection con = null;
          String url = "jdbc:mysql://localhost:3306/";
          String db = "database";
          String driver = "com.mysql.jdbc.Driver";
          String user = "root";
          String pass = "root";
          while(true)
          {
             Socket connectionSocket = welcomeSocket.accept();
             BufferedReader inFromClient =
             new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
             BufferedReader inFromClient1 =
             new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
             DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
             clientSentence = inFromClient.readLine(); 
             clientpassword = inFromClient.readLine();
             System.out.println("Received User Name: " + clientSentence);
             System.out.println("Received Password: " + clientpassword);
             Class.forName(driver).newInstance();
             con = DriverManager.getConnection(url+db, user, pass);
             Statement st = con.createStatement();
             ResultSet res = st.executeQuery("SELECT * FROM  table WHERE user='clientSentence' AND password='clientpassword'");
             while (res.next()) { 
             String u = res.getString("user");
             String p = res.getString("password");
             if (clientSentence.equals(u) && clientpassword.equals(p)){
             capitalizedSentence = "Welcome "+clientSentence+" n";
             outToClient.writeBytes(capitalizedSentence); 
            }else{  
             capitalizedSentence = "Sorry, not authorized n";
             outToClient.writeBytes(capitalizedSentence); 
            }    
          }
        }con.close();
       }
}

客户：

import java.io.*;
import java.net.*;
import java.io.File;
import java.io.FileInputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.util.Arrays;
import java.lang.*;
import java.util.Scanner;
class TCPClient
{
  public static void main(String argv[]) throws Exception
  {
   String sentence,sentence1;
   String modifiedSentence;
   BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
   BufferedReader inFromUser1 = new BufferedReader( new InputStreamReader(System.in));
   Socket clientSocket = new Socket("localhost", 4003);
   DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
   DataOutputStream outToServer1 = new DataOutputStream(clientSocket.getOutputStream());
   BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
   Console console = System.console();
   String username = console.readLine("Enter your Username :");
   char pswd[] = console.readPassword("Enter your Password :");
   String upwd=new String(pswd);
   outToServer.writeBytes(username + 'n');
   outToServer1.writeBytes(upwd + 'n');
   modifiedSentence = inFromServer.readLine();
   System.out.println("FROM SERVER: " + modifiedSentence);
}
   clientSocket.close();
  }
}

Answer 1

如果没有与JVM关联的Console，则代码将在TCPClient中生成NullPointerException。

---

ResultSet res=st.executeQuery（"SELECT*FROM table WHERE user='ClientContent'AND password='clientpassword'"）；

除非你真的想一直使用用户名"clientSentence"和密码"clientpassword"，否则这肯定行不通。

您应该传递在该行上方设置的相应java变量的实际值。此外，正确的方法是使用PreparedStatement并将用户输入作为参数传递，以便驱动程序负责清除输入，以避免SQL注入或类似ImbecilUserException的错误。：）

Answer 2

如果在同一台机器上运行客户端和服务器，则客户端和服务器套接字不应该使用相同的端口。。使用不同的端口。。