Java Tutorial/Network/SocketChannel

Channel selector

   <source lang="java">

import java.io.IOException; import java.net.InetSocketAddress; import java.nio.ByteBuffer; import java.nio.channels.SelectionKey; import java.nio.channels.Selector; import java.nio.channels.ServerSocketChannel; import java.nio.channels.SocketChannel; import java.util.Iterator; import java.util.Set; public class MainClass {

 private static byte[] data = new byte[255];
 public static void main(String[] args) throws IOException {
   for (int i = 0; i < data.length; i++)
     data[i] = (byte) i;
   ServerSocketChannel server = ServerSocketChannel.open();
   server.configureBlocking(false);
   server.socket().bind(new InetSocketAddress(9000));
   Selector selector = Selector.open();
   server.register(selector, SelectionKey.OP_ACCEPT);
   while (true) {
     selector.select();
     Set readyKeys = selector.selectedKeys();
     Iterator iterator = readyKeys.iterator();
     while (iterator.hasNext()) {
       SelectionKey key = (SelectionKey) iterator.next();
       iterator.remove();
       if (key.isAcceptable()) {
         SocketChannel client = server.accept();
         System.out.println("Accepted connection from " + client);
         client.configureBlocking(false);
         ByteBuffer source = ByteBuffer.wrap(data);
         SelectionKey key2 = client.register(selector, SelectionKey.OP_WRITE);
         key2.attach(source);
       } else if (key.isWritable()) {
         SocketChannel client = (SocketChannel) key.channel();
         ByteBuffer output = (ByteBuffer) key.attachment();
         if (!output.hasRemaining()) {
           output.rewind();
         }
         client.write(output);
       }
       key.channel().close();
     }
   }
 }

}</source>

Create SocketChannel from IP address

   <source lang="java">

import java.net.InetSocketAddress; import java.net.SocketAddress; import java.nio.ByteBuffer; import java.nio.IntBuffer; import java.nio.channels.SocketChannel; public class MainClass {

 public static void main(String[] args) throws Exception {
   int port = 1919;
   SocketAddress address = new InetSocketAddress("127.0.0.1", port);
   SocketChannel client = SocketChannel.open(address);
   ByteBuffer buffer = ByteBuffer.allocate(4);
   IntBuffer view = buffer.asIntBuffer();
   for (int expected = 0;; expected++) {
     client.read(buffer);
     int actual = view.get();
     buffer.clear();
     view.rewind();
     if (actual != expected) {
       System.err.println("Expected " + expected + "; was " + actual);
       break;
     }
     System.out.println(actual);
   }
 }

}</source>

Creating a Non-Blocking Socket: requires a socket channel.

   <source lang="java">

import java.net.InetSocketAddress; import java.nio.channels.SocketChannel; public class Main {

 public static void main(String[] argv) throws Exception {
   SocketChannel sChannel = SocketChannel.open();
   sChannel.configureBlocking(false);
   sChannel.connect(new InetSocketAddress("hostName", 12345));
   while (!sChannel.finishConnect()) {
     // Do something else
   }
 }

}</source>

Demonstrate asynchronous connection of a SocketChannel

   <source lang="java">

import java.net.InetSocketAddress; import java.nio.channels.SocketChannel;

public class MainClass {

 public static void main(String[] argv) throws Exception {
   String host = "localhost";
   int port = 80;
   InetSocketAddress addr = new InetSocketAddress(host, port);
   SocketChannel sc = SocketChannel.open();
   sc.configureBlocking(false);
   System.out.println("initiating connection");
   sc.connect(addr);
   while (!sc.finishConnect()) {
     System.out.println("doing something useless");
   }
   System.out.println("connection established");
   sc.close();
 }

}</source>

Reading from a SocketChannel

   <source lang="java">

import java.nio.ByteBuffer; import java.nio.channels.SocketChannel; public class Main {

 public static void main(String[] argv) throws Exception {
   ByteBuffer buf = ByteBuffer.allocateDirect(1024);
   SocketChannel sChannel = SocketChannel.open();
   sChannel.configureBlocking(false);
   sChannel.connect(new InetSocketAddress("hostName", 12345));
   int numBytesRead = sChannel.read(buf);
   if (numBytesRead == -1) {
     sChannel.close();
   } else {
     buf.flip();
   }
 }

}</source>

Use SocketChannel to get Web page

   <source lang="java">

import java.io.FileOutputStream; import java.io.IOException; import java.net.InetSocketAddress; import java.net.SocketAddress; import java.net.URL; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; import java.nio.channels.SocketChannel; public class MainClass {

 public static void main(String[] args) throws IOException {
   URL u = new URL("http://www.jexp.ru");
   String host = u.getHost();
   int port = 80;
   String file = "/";
   SocketAddress remote = new InetSocketAddress(host, port);
   SocketChannel channel = SocketChannel.open(remote);
   FileOutputStream out = new FileOutputStream("yourfile.htm");
   FileChannel localFile = out.getChannel();
   String request = "GET " + file + " HTTP/1.1\r\n" + "User-Agent: HTTPGrab\r\n"
       + "Accept: text/*\r\n" + "Connection: close\r\n" + "Host: " + host + "\r\n" + "\r\n";
   ByteBuffer header = ByteBuffer.wrap(request.getBytes("US-ASCII"));
   channel.write(header);
   ByteBuffer buffer = ByteBuffer.allocate(8192);
   while (channel.read(buffer) != -1) {
     buffer.flip();
     localFile.write(buffer);
     buffer.clear();
   }
   localFile.close();
   channel.close();
 }

}</source>

Writing to a SocketChannel

   <source lang="java">

import java.net.InetSocketAddress; import java.nio.ByteBuffer; import java.nio.channels.SocketChannel; public class Main {

 public static void main(String[] argv) throws Exception {
   SocketChannel sChannel = SocketChannel.open();
   sChannel.configureBlocking(false);
   sChannel.connect(new InetSocketAddress("hostName", 12345));
   ByteBuffer buf = ByteBuffer.allocateDirect(1024);
   buf.put((byte) 0xFF);
   buf.flip();
   int numBytesWritten = sChannel.write(buf);
 }

}</source>