Question

我正在尝试实现java命令行聊天服务器和客户端。我使用4个类，Server.java设置ServerSocket并接受所有连接。 Client.java可以连接到Server，然后使用SendMessages.java和ReceiveMessages.java创建客户端和服务器的2个线程。线程负责从stdin获取输入并将其发送到套接字的输出流，并将传入的输入流打印到stdout。启动服务器并连接客户端时，一切正常，聊天也有效。但是，当客户端或服务器终止时，会导致资源泄漏。我希望SendMessages类和ReceiveMessages类能够检测客户端或服务器的连接何时终止，并关闭所有资源以避免资源泄漏。这是代码：

Server.java

import java.net.*;
import java.io.*;
import java.util.*;
public class Server{
public static void main(String[] args) throws SocketException,IOException{
    ServerSocket s = new ServerSocket(8000);
    s.setSoTimeout(10000000);
    while(true){
        Socket clientSocket = s.accept();
    handle(clientSocket);

}  
}

   static void handle(Socket clientSocket) throws IOException{
    System.out.println("connection accepted from " + clientSocket.getRemoteSocketAddress());
    receiveMessages(clientSocket);
    sendMessages(clientSocket);
  }

  static void receiveMessages(Socket clientSocket) throws IOException{
    (new Thread(new ReceiveMessages(clientSocket))).start();;

  }

  static void sendMessages(Socket clientSocket)throws IOException{
    (new Thread(new SendMessages(clientSocket))).start();
  }
}

Client.java

import java.net.*;
import java.io.*;
import java.util.*;

public class Client{


public static void main(String[] args) throws IOException, UnknownHostException, ConnectException{
    String hostname = args[0];
    int port = Integer.parseInt(args[1]);
    Socket s = null;
    s = connect(hostname, port);
    handle(s);
}


public static Socket connect(String hostname, int port) throws UnknownHostException, IOException, ConnectException{
    Socket s = null;
    try{
    s = new Socket(hostname, port);
    } catch(ConnectException e){
        System.out.println("Connect Exception caught!");
    }
return s;
}

static void handle(Socket clientSocket) throws IOException, UnknownHostException{
receiveMessages(clientSocket);
sendMessages(clientSocket);
}

static void receiveMessages(Socket clientSocket) throws IOException, NullPointerException{
    (new Thread(new ReceiveMessages(clientSocket))).start();
  }

static void sendMessages(Socket clientSocket)throws IOException, NullPointerException{
  (new Thread(new SendMessages(clientSocket))).start();
}

}

SendMessages.java

import java.io.*;
import java.net.*;
import java.util.*;
public class SendMessages implements Runnable{
Socket clientSocket;

public SendMessages(Socket clientSocket){
    this.clientSocket = clientSocket;
}

public void run(){
    System.out.println("SendMessages thread has started.");
    Scanner sc = new Scanner(System.in);
    PrintWriter out = null;
    try{
    out = new PrintWriter(clientSocket.getOutputStream(), true);
    }
    catch(IOException | NullPointerException e){}

    String message;

    while(true){
        message = sc.nextLine();
        out.println(message);
        if(out.checkError()){
            out.close();
            sc.close();
            System.out.println("SendMessages closed");
        }
    }

}
}

ReceiveMessages.java

import java.io.*;
import java.net.*;
import java.util.*;
public class ReceiveMessages implements Runnable{
    Socket clientSocket;
    public ReceiveMessages(Socket clientSocket){
        this.clientSocket = clientSocket;
    }
    public void run(){
        System.out.println("ReceiveMessages thread has started.");
        BufferedReader in = null;
        try{
        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        }catch(IOException|NullPointerException e){}
        String message;
        try{
            while(true){
            while((message = in.readLine())!= null){
                System.out.println(message);
            }

    }
    } catch(IOException|NullPointerException e){
        System.out.println("ReceiveMessages resources closed.");
        try{  
        in.close();
            clientSocket.close();
            }
            catch(IOException f){}
    }
}
}

谢谢！

Answer 1

所以我最近已经解决了这个问题。

问题是，通过关闭连接的一端，仍然存在"half-open"连接（这不再是真正的连接）。

如果合作的服务/设备仍然存在，则Socket API没有检查选项。

那该怎么办？我自己更喜欢心跳的概念。每隔10秒（或任何其他时间帧，由您决定），心跳将发送到套接字的输出流。当流不再可用时，此操作将抛出IOException。因此，您可以捕获异常并处理catch块中的所有“关闭”操作。

示例：

public class Heartbeater implements Runnable { private OutputStream os; private ServerHandler servhand; private Logger logger = Logger.getLogger( Logger.GLOBAL_LOGGER_NAME ); //NOTE: ServerHandler is my class which handles the socket of the server after ServerSocket.accept(); public Heartbeater( OutputStream os, ServerHandler servhand ) { this.servhand = servhand; this.os = os; } @Override public void run() { try { Thread.currentThread().setName( "Heartbeater" ); // while the handler's connection is alive while ( servhand.isConnectionAlive() ) { Thread.sleep( 10000 ); // dummy write to trigger the exception if the client does not respond properly os.write( "_HEARTBEAT_".getBytes() ); } } catch ( InterruptedException e ) { logger.log( Level.SEVERE, "HEARTBEATER GOT INTERRUPTED", e ); Thread.currentThread().interrupt(); } catch ( IOException e ) { logger.log( Level.INFO, "The connection to the client has been lost." ); // Here you would define the resource close operation. servhand.setConnectionAlive( false ); } } }

关闭后Java客户端/服务器资源泄漏

1 个答案: