Java 服务器将只接受来 self 的客户端的一个条目

Question

我制作了一个连接到 MySQL 数据库并接受来自客户端的请求的多线程服务器。服务器应该始终监听客户端命令，但这并没有发生。它只接受一个命令将其发送到数据库并获取我需要的任何东西，然后就完成了。它不再接受任何命令。我为您提供客户端和服务器。

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.rmi.ConnectException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;


public class Airlines {
	public static void main(String[] args) {
		ServerSocket serverSocket = null;
		Socket connection = null;
		int port = 1234;
		try{
			serverSocket = new ServerSocket(port);
			while ((connection = serverSocket.accept())!=null){
			System.out.println("Client connected!");
			Thread client = new Thread (new AirlinesThread(connection));
			client.start();
			}
		}catch (IOException e){
			System.out.println("Binding unsuccesful...");
		}
	}

}
class AirlinesThread implements Runnable{
Socket connection = null;
public AirlinesThread (Socket connection){
	this.connection = connection;
}
private static Connection connect(String url, String user, String password){
    Connection result = null;
    try{
      result = DriverManager.getConnection(url, user, password);
      System.out.println("Database connection successful!");
    }
    catch(SQLException e){
      System.out.println("Could not connect to the database!");
    }
    return result;
  }
	String url = "jdbc:mysql://localhost:3306/Airlines";
	String user = "root";
	String pass = "123456";
	Connection link = AirlinesThread.connect(url, user, pass);
	Statement stmt = null;
	ResultSet resultSet = null;
	public void run() {
		PrintWriter socketOut = null;
		DataInputStream socketIn = null;
		try{
		socketOut = new PrintWriter(this.connection.getOutputStream(),true);
		socketIn = new DataInputStream(this.connection.getInputStream());
		int command;
		boolean exists = false;
		socketOut.flush();
		loop:do{
			socketOut.flush();
			command = socketIn.readInt();
			switch (command){
			case 1:
				 try{
				      stmt = link.createStatement();
				      resultSet = stmt.executeQuery("select Flight.id, Flight.Date, Flight.Time, Flight.Total_Flight_Time, Airports.Departure, Airports.Arrivals FROM Flight, Airports WHERE Flight.id = Airports.Flight");
				      socketOut.flush();
				      socketOut.println("FlightID\tDate\t\tTime\t\tTotal Time\tDeparture\tArrivals");
				      while (resultSet.next()) {
				    	  socketOut.println(resultSet.getString("Flight.id")+"\t\t"+resultSet.getDate("Flight.Date")+"\t"+resultSet.getString("Flight.Time")+"\t"+resultSet.getString("Flight.Total_Flight_Time")+"\t\t"+resultSet.getString("Airports.Departure")+"\t"+resultSet.getString("Airports.Arrivals"));
				       
				      }
				    }
				    catch(SQLException e){
				    	System.out.println("Something went wrong at 1");
				    }
				break;
			case 2:
				try{
				      stmt = link.createStatement();
				      resultSet = stmt.executeQuery("select Flight.id, Flight.Date, Flight.Time, Pilots.First_Name, Pilots.Last_Name from Flight RIGHT JOIN Pilots ON Flight.id = Pilots.FlightID;");
				      socketOut.flush();
			    	  socketOut.println("FlightID\tDate\t\tTime\t\tFirst Name\tLast Name");
			    	  exists = resultSet.next();
				      if(exists == false){
				    	  socketOut.flush();
				    	  socketOut.println("Wrong request!");
				    	  System.out.println("Wrong query at 2");
				      }
				      while (resultSet.next()) { 
				     socketOut.flush();
				       socketOut.println(resultSet.getString("Flight.id")+"\t\t"+resultSet.getDate("Flight.Date")+"\t"+resultSet.getString("Flight.Time")+"\t"+resultSet.getString("Pilots.First_Name")+"\t\t"+resultSet.getString("Pilots.Last_Name"));
				      }
				    }
				    catch(SQLException e){
				    	System.out.println("Something went wrong at 2");
				    }
				break;
			case 3: 
				try{
				      stmt = link.createStatement();
				      resultSet = stmt.executeQuery("select Food.Breakfast, Airplanes.Plane_Model FROM Food, Airplanes Where Food.FlightID=Airplanes.Plane_Model;");
				      exists = resultSet.next();
				      if(exists == false){
				    	  socketOut.flush();
				    	  socketOut.println("Wrong request!");
				    	  System.out.println("Wrong query at 3");
				      }
				      while (resultSet.next()) { 
				       socketOut.flush();
				       socketOut.println(resultSet.getString("Food.Breakfast")+"\t\t"+resultSet.getString("Airplanes.Plane_Model"));
				       
				      }
				    }
				    catch(SQLException e){
				    	System.out.println("Something went wrong at 3");
				    }
				break;
			case 0 :
				socketOut.flush();
				socketOut.println("Exitting...");
				break loop;
			default:
				System.out.println("Unknown command!");
				socketOut.println("Unknown command!");
				break;
			}
		}while(command!=0);
		System.out.println("Closing connection to the client!");
		}catch (IOException e){
			e.printStackTrace();
		}finally{
		        try{
		          if (socketIn!=null) socketIn.close();
		          if (socketOut!=null) socketOut.close();
		          if (connection!=null) connection.close();
		          System.out.println("Connection to server closed!");
		        }
		        catch(IOException e){
		          System.err.println("Could not close connection!");
		        }
	}
		try{
			if(stmt != null) stmt.close();
			if(resultSet != null) resultSet.close();
	        if(link != null) link.close();
	        System.out.println("Database connection closed successfully!");
		}catch(SQLException ex){
			System.out.println("Could not close connection to the database!");
		}  
  }
}

客户端:

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ConnectException;
import java.net.Socket;
import java.util.Scanner;


public class AirlinesClient {

	public static void main(String[] args) {
		Socket connection = null;
		Scanner socketIn = null;
		DataOutputStream socketOut = null;
		int port = 1234;
		String host = "localhost";
		Scanner keyIn = new Scanner(System.in);
		try{
			try{
			connection = new Socket(host,port);
			socketIn = new Scanner(new BufferedReader(new InputStreamReader(connection.getInputStream())));
			socketOut = new DataOutputStream(connection.getOutputStream());
		}catch(ConnectException e){
			System.out.println("Could not connect to the host!");
			return;
		}
		System.out.println("Successfully connected to the server!");
		System.out.println("Select from the options below:\n1: Check schedules\n2: Check pilots shifts\n3: Check corresponding airplanes and food offered\n4: Possible pilot shift changes");
		loop:do{
			int command;
			socketOut.flush();
			command = keyIn.nextInt();
			socketOut.flush();
			socketOut.writeInt(command);
			while (socketIn.hasNext()){
				System.out.println(socketIn.nextLine());
			}
			
		}while(keyIn.nextInt()!=0);
		System.out.println("Closing connection to server!");
	}catch(IOException e){
		e.printStackTrace();
	} finally{
	       try{
	           if(socketIn!=null) socketIn.close();
	           if(socketOut!=null) socketOut.close();
	           if(connection!=null) connection.close();
	         }
	         catch(IOException e){
	           System.err.println("Socket could not be closed!");
	         }
	       }
		
	}
	
	
}

Answer 1

问题是您在客户端中使用了 Scanner。执行在 socketIn.hasNext() 上挂起，因为

public boolean hasNext()

Returns true if this scanner has another token in its input. This method may block while waiting for input to scan. The scanner does not advance past any input.

如果有新输入或底层流关闭(我们不希望这样)，代码将继续执行。您必须有一种在不关闭流的情况下知道传输结束的方法。请在下面查看非常简单的一个。

在服务器中每个 try-catch block 的末尾放置

socketOut.println("$$$");

在客户端声明socketIn为BufferedReader并实例化为

socketIn = new BufferedReader(new InputStreamReader(connection.getInputStream()));

在客户端也改变你的loop循环到

int command = keyIn.nextInt();
do {
    socketOut.flush();
    socketOut.writeInt(command);
    String line;
    while (!(line = socketIn.readLine()).equals("$$$"))
        System.out.println(line);
} while ((command = keyIn.nextInt()) != 0);

这也将修复您对 keyIn.nextInt() 的双重检查。在您的代码中，每个循环调用它两次(第一次迭代除外)。