ServerSocket detecting disconnection of client

Question

I am using the below code for my Server to continue listening to Client message once it's become connected.

While listening, I wanted to detect if the Client become disconnected when read value becomes -1 and finished the WhileLoop.

private volatile boolean isConnected = true;
//....
while(isConnected){ //Whe it comes to false then Receiving Message is Done.
    try {
        socket.setSoTimeout(10000); //Timeout is 10 Seconds
        InputStream inputStream = socket.getInputStream();
        BufferedInputStream inputS = new BufferedInputStream(inputStream);
        byte[] buffer = new byte[256];
        int read = inputS.read(buffer);
        String msgData = new String(buffer,0,read);

        //Detect here when client become disconnected
        if(read == -1){ //Client become disconnected
            isConnected = false;
            Log.w(TAG,"Client is no longer Connected!");
        }else{
            isConnected = true;
            Log.w(TAG,"Client Still Connected...");
        }

        //....
    }catch (SocketException e) {
        Log.e(TAG,"Failed to Receive message from Client, SocketException occured => " + e.toString());
    }catch (IOException e) {
        Log.e(TAG,"Failed to Receive message from Client, IOException occured => " + e.toString());
    }catch (Exception e) {
        Log.e(TAG,"Failed to Receive message from Client, Exception occured => " + e.toString());
    }           
}

Log.w(TAG, "Receiving Message is Done.");

The above code works on receiving message but I'm having problem detecting when the client become disconnected.

When the client become disconnected, an Exception is occured whith the following error: java.lang.StringIndexOutOfBoundsException: length=256; regionStart=0; regionLength=-1 and the WhileLoop is not breaking as expected to be done.

I am assuming that when the client become disconnected then this condition will occured if(read == -1){....}.

I just found this post while searching and the answer of EJP give me the best solution on read() returns -1 , but I'm just starting on ServerSocket so I don't know if I'm doing it correctly.

You should not construct the string if read returns -1. I would simply move the string construction to the else branch if `if(read == -1)` . — Fildor, Oct 19 '16 at 07:22
@Fildor - WTF, LOL, is that what I'm just doing wrong? I tried it and guest what? It works!!! — lopi, Oct 19 '16 at 07:36
@Fildor - How about making it Answer instead of Comment? I am happy to mark is as a correct answer. :-) — lopi, Oct 19 '16 at 07:42

score 2 · Accepted Answer · answered Oct 19 '16 at 07:46

String msgData = new String(buffer,0,read);

If readis -1 it will throw an Exception. I'd totally expect that. Just move that line to your else branch where you check read for -1 so the string will only be constructed when there is actually data.

See: https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#String-byte:A-int-int-

Throws: IndexOutOfBoundsException - If the offset and the length arguments index characters outside the bounds of the bytes array

-1 length is outside of bounds :)

ServerSocket detecting disconnection of client

1 Answers1