How to close ServerSocket connection when catching IOException?

Question

Sorry for question, but I'm totally noob in Java. What is the best practice to execute ServerSocket.close() when caught IOException from ServerSocket? According to docs, ServerSocket.close() throws IOException and compiler asks us to catch it. What is the proper way to close connection on IOException?

try {
    server = new ServerSocket(this.getServerPort());
    while(true) {
        socket = server.accept();
        new Handler( socket );
    }
} catch (IOException e) {
    if (server != null && !server.isClosed()) {
        server.close(); //compiler do not allow me to do because I should catch IOExceoption from this method also...
    }
}

Thank you!

score 8 · Accepted Answer · answered Nov 03 '11 at 20:17

8

That's ugly in Java. I hate it, but this is the way you should do it: Wrapping it into another try-catch:

try {
    server = new ServerSocket(this.getServerPort());
    while(true) {
        socket = server.accept();
        new Handler( socket );
    }
} catch (IOException e) {
    if (server != null && !server.isClosed()) {
        try {
            server.close();
        } catch (IOException e)
        {
            e.printStackTrace(System.err);
        }
    }
}

answered Nov 03 '11 at 20:17

Martijn Courteaux

67,591
47
198
287

This *really* sucks!. Thanks for answer, its very useful! – wrzasa Apr 01 '14 at 11:23
2

Note, the new try with resources in Java 7. – Martijn Courteaux Apr 01 '14 at 16:05
2

Thanks, I've [seen](http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html) it. Looks awful. – wrzasa Apr 02 '14 at 15:31

score 8 · Answer 2 · answered Nov 03 '11 at 20:19

If you are going to close the ServerSocket outside of the try{}catch{} anyways, you may as well put it in a finally{}

try {
    server = new ServerSocket(this.getServerPort());
    while(true) {
        socket = server.accept();
        new Handler( socket );
    }
} catch (IOException e) {
    // Do whatever you need to do here, like maybe deal with "socket"?
}
finally {
    try {  
        server.close();
    } catch(Exception e) {
        // If you really want to know why you can't close the ServerSocket, like whether it's null or not
    }
}

score 7 · Answer 3 · answered Nov 11 '15 at 04:59

In Java SE 7 or later you can use try-with-resources statement, ServerSocket implements java.io.Closeable, so you don't need to explicitly #close() the socket when used in this way.

try (ServerSocket server = new ServerSocket(this.getServerPort())) {
    while(true) {
        socket = server.accept();
        new Handler( socket );
    }
} catch (IOException e) {
    // It's already closed, just print the exception
    System.out.println(e);
}

score 2 · Answer 4 · answered Nov 03 '11 at 20:18

2

You can close the resources in the finally block,

http://download.oracle.com/javase/tutorial/essential/exceptions/finally.html

 } finally {
      try {
        socket.close();
      } catch(IOException e) {
         e.printStackTrace(); 
      }
}

answered Nov 03 '11 at 20:18

r0ast3d

2,639
1
14
18

Yes, that's true. But it still won't compile because of it might throw an IOException. – Martijn Courteaux Nov 03 '11 at 20:19
1

It doesn't make a sense. Compiler will also ask to catch `IOException` from `ServerSocket.close()`. – Kirzilla Nov 03 '11 at 20:20
true, you should still wrap it with a try catch. – r0ast3d Nov 03 '11 at 20:23

How to close ServerSocket connection when catching IOException?

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