How to detect a remote side socket close

Question

How do you detect if Socket close   has been called on a socket on the remote side

User · Answer

You can also check for socket output stream error while writing to client socket   out println output   if out checkError          throw new Exception  Error transmitting data

User · Answer

The isConnected method won t help  it will return true even if the remote side has closed the socket  Try this    public class MyServer       public static final int PORT   12345      public static void main String   args  throws IOException  InterruptedException           ServerSocket ss   ServerSocketFactory getDefault   createServerSocket PORT           Socket s   ss accept            Thread sleep 5000           ss close            s close             public class MyClient       public static void main String   args  throws IOException  InterruptedException           Socket s   SocketFactory getDefault   createSocket  localhost   MyServer PORT           System out println   connected      s isConnected             Thread sleep 10000           System out println   connected      s isConnected               Start the server  start the client  You ll see that it prints  connected  true  twice  even though the socket is closed the second time   The only way to really find out is by reading  you ll get -1 as return value  or writing  an IOException  broken pipe  will be thrown  on the associated Input OutputStreams

User · Answer

The method Socket Available will immediately throw a SocketException if the remote system has disconnected closed the connection

User · Answer

Since the answers deviate I decided to test this and post the result - including the test example   The server here just writes data to a client and does not expect any input   The server   ServerSocket serverSocket   new ServerSocket 4444   Socket clientSocket   serverSocket accept    PrintWriter out   new PrintWriter clientSocket getOutputStream    true   while  true      out println  output      if  out checkError    System out println  ERROR writing data to socket          System out println clientSocket isConnected       System out println clientSocket getInputStream   read                thread sleep          break condition   close sockets and the like          clientSocket isConnected   returns always true once the client connects  and even after the disconnect  weird    getInputStream   read     makes the thread wait for input as long as the client is connected and therefore makes your program not do anything - except if you get some input returns -1 if the client disconnected  out checkError   is true as soon as the client is disconnected so I recommend this

[java] How to detect a remote side socket close?

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