Java 用 try 语句关闭 Connection 和 InputStream

Question

Should I close HttpUrlConnection and InputStream in this case? Only closing the connection will close the stream also? I feel that it's a bad practice but don't know exactly why.

Closing both:

HttpURLConnection con = (HttpURLConnection) obj.openConnection();
try (AutoCloseable ac = con::disconnect) {
    int responseCode = con.getResponseCode();
    try (InputStream ins = responseCode >= 400 ? con.getErrorStream() : con.getInputStream();
        BufferedReader in = new BufferedReader(new InputStreamReader(ins))) {
        // receive response
    }
}

Closing Connection only:

HttpURLConnection con = (HttpURLConnection) obj.openConnection();
try (AutoCloseable ac = con::disconnect) {
    int responseCode = con.getResponseCode();
    BufferedReader in = new BufferedReader(new InputStreamReader(ins)))
    // ins will close automatically when con closes?
    // receive response
}

Answer 1

When you disconnect the HttpURLConnection object, it MAY also close any InputStream or OutputStream that it has opened.

HttpURLConnection.disconnect() method description:

Calling the disconnect() method may close the underlying socket if a persistent connection is otherwise idle at that time.

You can read more here .

In turn, Socket.close() method description:

Closing this socket will also close the socket's InputStream and OutputStream. If this socket has an associated channel then the channel is closed as well.

You can read more here .

But pay attention that "disconnecting" HttpURLConnection doesn't mandatory close the Socket . It have been already discussed quite well in that thread :

(When keepAlive == true ) If client called HttpURLConnection.getInputSteam().close() , the later call to HttpURLConnection.disconnect() will NOT close the Socket . ie The Socket is reused (cached) If client does not call close() , call disconnect() will close the InputStream and close the Socket . So in order to reuse the Socket , just call InputStream.close() . Do not call HttpURLConnection.disconnect() .

On the other hand, in the official oracle tutorials they suggest to close InputStream explicitly in order to be sure that resources don't leak.