How to use SocketChannel to connect to remote webserver - socketchannel

Question

I am trying to get the response sent by the web server through Java NIO socketChannel. The read call of SocketChannel is not returning anything when it is in non-blocking
clientSocket.configureBlocking(false);
When specified true, means blocking mode, then it is returning response. Someone saying that we should use Selector when non-blocking mode enabled. But I didn't find a way to implement this.
FYI, Following is the code snippet I am trying.
public static void main(String[] args) throws IOException, InterruptedException
{
URL u = new URL("http://www.google.com");
InetSocketAddress addr = new InetSocketAddress("www.google.com", 80);
SocketChannel clientSocket = SocketChannel.open(addr);
clientSocket.configureBlocking(false);
byte[] message = new String("GET " + u.getFile() + " HTTP/1.0\r\n").getBytes();
ByteBuffer writeBuff = ByteBuffer.wrap(message);
clientSocket.write(writeBuff);
ByteBuffer readBuff = MappedByteBuffer.allocate(1500);
clientSocket.read(readBuff);
while(clientSocket.read(readBuff) > 0)
{
System.out.println(new String(readBuff.array()).trim());
}
clientSocket.close();
}
Thanks in advance.

Answer 1

You should use loops to read() and write() till the buffer has no remaining bytes when non-blocking mode.

Answer 2

There two problems in your code:
the http request body is wrong. it needs additional "\r\n".
the readBuff need to cleared each time after reading.
below code is a working version:
static void working() throws Exception {
URL u = new URL("http://www.baidu.com");
InetSocketAddress addr = new InetSocketAddress("www.baidu.com", 80);
SocketChannel clientSocket = SocketChannel.open(addr);
clientSocket.configureBlocking(false);
byte[] message = new String("GET / HTTP/1.0\r\n\r\n").getBytes();
ByteBuffer writeBuff = ByteBuffer.wrap(message);
clientSocket.write(writeBuff);
ByteBuffer readBuff = MappedByteBuffer.allocate(1500);
while (clientSocket.read(readBuff) != -1) {
System.out.println("Entring...");
System.out.println(new String(readBuff.array()).trim());
readBuff.clear();
}
clientSocket.close();
}
}
Notice, if it's http version 1.1, it will not break too. because it has a keeplive.