netty 传输

简介

传统的oio（old I/O）编程，与nio异步编程在Api级别差别比较大，但是netty在公共API做了很好的封装，这比在传统的使用JDK编程要更简单。

使用传统的jdk来实现blocking与non-blocking

实现blocking

public class PlainOioServer {
    public void serve(int port) throws IOException {
        final ServerSocket socket = new ServerSocket(port);
        try {
            for(;;) {
                final Socket clientSocket = socket.accept();
                System.out.println(
                        "Accepted connection from " + clientSocket);
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        OutputStream out;
                        try {
                            out = clientSocket.getOutputStream();
                            out.write("Hi!\r\n".getBytes(
                                    Charset.forName("UTF-8")));
                            out.flush();
                            clientSocket.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        } finally {
                            try {
                                clientSocket.close();
                            } catch (IOException ex) {
                                // ignore on close
                            }
                        }
                    }
                }).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

使用OIO只能支持中等级别的并发，并不能支持上万的连接

实现NIO

public class PlainNioServer {
    public void serve(int port) throws IOException {
        ServerSocketChannel serverChannel = ServerSocketChannel.open();
        serverChannel.configureBlocking(false);
        ServerSocket ss = serverChannel.socket();
        InetSocketAddress address = new InetSocketAddress(port);
        ss.bind(address);
        Selector selector = Selector.open();
        serverChannel.register(selector, SelectionKey.OP_ACCEPT);
        final ByteBuffer msg = ByteBuffer.wrap("Hi!\r\n".getBytes());
        for (;;){
            try {
                selector.select();
            } catch (IOException ex) {
                ex.printStackTrace();
                //handle exception
                break;
            }
            Set<SelectionKey> readyKeys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = readyKeys.iterator();
            while (iterator.hasNext()) {
                SelectionKey key = iterator.next();
                iterator.remove();
                try {
                    if (key.isAcceptable()) {
                        ServerSocketChannel server =
                                (ServerSocketChannel) key.channel();
                        SocketChannel client = server.accept();
                        client.configureBlocking(false);
                        client.register(selector, SelectionKey.OP_WRITE |
                                SelectionKey.OP_READ, msg.duplicate());
                        System.out.println(
                                "Accepted connection from " + client);
                    }
                    if (key.isWritable()) {
                        SocketChannel client =
                                (SocketChannel) key.channel();
                        ByteBuffer buffer =
                                (ByteBuffer) key.attachment();
                        while (buffer.hasRemaining()) {
                            if (client.write(buffer) == 0) {
                                break;
                            }
                        }
                        client.close();
                    }
                } catch (IOException ex) {
                    key.cancel();
                    try {
                        key.channel().close();
                    } catch (IOException cex) {
                        // ignore on close
                    }
                }
            }
        }
    }
}

比较

可以看出传统的OIO与NIO相比来说差距很大，所以对于编程来说，是需要重写的。

使用netty来实现

同步

public class NettyOioServer {
    public void server(int port)
            throws Exception {
        final ByteBuf buf =
                Unpooled.unreleasableBuffer(Unpooled.copiedBuffer("Hi!\r\n", Charset.forName("UTF-8")));
        EventLoopGroup group = new OioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(group)
                    .channel(OioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress(port))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch)
                                throws Exception {
                                ch.pipeline().addLast(
                                    new ChannelInboundHandlerAdapter() {
                                        @Override
                                        public void channelActive(
                                                ChannelHandlerContext ctx)
                                                throws Exception {
                                            ctx.writeAndFlush(buf.duplicate())
                                                    .addListener(
                                                            ChannelFutureListener.CLOSE);
                                        }
                                    });
                        }
                    });
            ChannelFuture f = b.bind().sync();
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }
}

异步

public class NettyNioServer {
    public void server(int port) throws Exception {
        final ByteBuf buf =
                Unpooled.unreleasableBuffer(Unpooled.copiedBuffer("Hi!\r\n",
                        Charset.forName("UTF-8")));
        NioEventLoopGroup group = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(group).channel(NioServerSocketChannel.class)
                    .localAddress(new InetSocketAddress(port))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                                      @Override
                                      public void initChannel(SocketChannel ch)
                                              throws Exception {
                                              ch.pipeline().addLast(
                                                  new ChannelInboundHandlerAdapter() {
                                                      @Override
                                                      public void channelActive(
                                                              ChannelHandlerContext ctx) throws Exception {
                                                                ctx.writeAndFlush(buf.duplicate())
                                                                  .addListener(
                                                                          ChannelFutureListener.CLOSE);
                                                      }
                                                  });
                                      }
                                  }
                    );
            ChannelFuture f = b.bind().sync();
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully().sync();
        }
    }
}