netty基础01_netty是什么

netty是一个网络编程框架；

如果java应用程序需要与其它程序或设备通信时，需要用到网络编程；

比如：通过java程序远程控制设备开关、接收并处理传感器传递的数据等；

 

1.利用阻塞流的socket

服务端：

public class BioSocket_server {
 
    public static void main(String[] args) throws Exception{
 
        ServerSocket serverSocket = new ServerSocket(8090);    //创建服务端socket
        new Thread(() -> {
            while(true){
                try {
                   Socket socket = serverSocket.accept();    //接收请求
                   new Thread(()->{
                       try {
                            byte[] buf = new byte[1024];
                           InputStream is = socket.getInputStream();    //获取字节流
                           while (true){
                               int len;
                               while((len = is.read(buf)) != -1){
                                   System.out.println(new String(buf, 0, len));    //输出客户端通过字节流传过来的数据
                               }
                           }
                       } catch (Exception e) {
                           e.printStackTrace();
                       }
                   }).start();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
}

服务端每接收到一个请求，将给该请求创建一个线程；

该线程用字节流读取客户端发送过来的数据，并在控制台输出；

 

客户端：

public class BioSocket_client {
 
    public static void main(String[] args) {
        new Thread(()->{
            try {
                Socket socket = new Socket("127.0.0.1", 8090);    //请求服务端
                while(true){
                    socket.getOutputStream().write((new Date() + " hello ").getBytes());    //发送数据
                    socket.getOutputStream().flush();
                    Thread.sleep(2000);    
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }).start();
    }
}

客户端每2秒给服务端发送一个字符串；

 

结果：

Tue Apr 28 16:20:35 CST 2020hello
Tue Apr 28 16:20:37 CST 2020hello
Tue Apr 28 16:20:39 CST 2020hello
Tue Apr 28 16:20:41 CST 2020hello
Tue Apr 28 16:20:43 CST 2020hello
Tue Apr 28 16:20:45 CST 2020hello
Tue Apr 28 16:20:47 CST 2020hello
Tue Apr 28 16:20:49 CST 2020hello
Tue Apr 28 16:20:51 CST 2020hello

 

这种IO编程模型在客户端较少的情况下运行良好；

但是对于客户端比较多的业务来说，IO模型可能就不太合适了；

比如在上面的例子中：

    每个连接创建成功之后都需要一个线程来维护，

    每个线程包含一个while死循环，

    那么1w个连接对应1w个线程，继而1w个while死循环

 

bio的缺点：

    线程资源受限：线程是操作系统中非常宝贵的资源，同一时刻有大量的线程处于阻塞状态是非常严重的资源浪费，操作系统耗不起

    线程切换效率低下：单机cpu核数固定，线程爆炸之后操作系统频繁进行线程切换，应用性能急剧下降。

    除了以上两个问题，IO编程中，我们看到数据读写是以字节流为单位，效率不高。    

 

2.NIO编程

java1.4引入了非阻塞式流NIO；

与传统的bio（ Blocking I/O）相比，nio（ Nonblocking I/O）可以一个线程处理多个请求；

优点：更少的内存和上下文切换开销；

 

nio服务端：

public class NIOServer {
    public static void main(String[] args) throws IOException {
        Selector serverSelector = Selector.open();
        Selector clientSelector = Selector.open();
 
        new Thread(() -> {
            try {
                // 对应IO编程中服务端启动
                ServerSocketChannel listenerChannel = ServerSocketChannel.open();
                listenerChannel.socket().bind(new InetSocketAddress(8000));
                listenerChannel.configureBlocking(false);
                listenerChannel.register(serverSelector, SelectionKey.OP_ACCEPT);
 
                while (true) {
                    // 监测是否有新的连接，这里的1指的是阻塞的时间为1ms
                    if (serverSelector.select(1) > 0) {
                        Set<SelectionKey> set = serverSelector.selectedKeys();
                        Iterator<SelectionKey> keyIterator = set.iterator();
 
                        while (keyIterator.hasNext()) {
                            SelectionKey key = keyIterator.next();
 
                            if (key.isAcceptable()) {
                                try {
                                    // (1) 每来一个新连接，不需要创建一个线程，而是直接注册到clientSelector
                                    SocketChannel clientChannel = ((ServerSocketChannel) key.channel()).accept();
                                    clientChannel.configureBlocking(false);
                                    clientChannel.register(clientSelector, SelectionKey.OP_READ);
                                } finally {
                                    keyIterator.remove();
                                }
                            }
                        }
                    }
                }
            } catch (IOException ignored) {
            }
        }).start();
 
        new Thread(() -> {
            try {
                while (true) {
                    // (2) 批量轮询是否有哪些连接有数据可读，这里的1指的是阻塞的时间为1ms
                    if (clientSelector.select(1) > 0) {
                        Set<SelectionKey> set = clientSelector.selectedKeys();
                        Iterator<SelectionKey> keyIterator = set.iterator();
 
                        while (keyIterator.hasNext()) {
                            SelectionKey key = keyIterator.next();
 
                            if (key.isReadable()) {
                                try {
                                    SocketChannel clientChannel = (SocketChannel) key.channel();
                                    ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
                                    // (3) 读取数据以块为单位批量读取
                                    clientChannel.read(byteBuffer);
                                    byteBuffer.flip();
                                    System.out.println(Charset.defaultCharset().newDecoder().decode(byteBuffer)
                                            .toString());
                                } finally {
                                    keyIterator.remove();
                                    key.interestOps(SelectionKey.OP_READ);
                                }
                            }
 
                        }
                    }
                }
            } catch (IOException ignored) {
            }
        }).start();
 
    }}

 

nio的api太过复杂，并且使用不当可能有安全问题；

为了方便使用，需要将其进行封装；

netty就是基于nio开发的网络通信框架；

 

3.netty

需要引入jar包

    <dependency>
        <groupId>io.netty</groupId>
        <artifactId>netty-all</artifactId>
        <version>4.1.6.Final</version>
    </dependency>

 

服务端：

public class NettyServer {
    public static void main(String[] args) {
        ServerBootstrap serverBootstrap = new ServerBootstrap();
 
        NioEventLoopGroup boss = new NioEventLoopGroup();
        NioEventLoopGroup worker = new NioEventLoopGroup();
        serverBootstrap
            .group(boss, worker)
            .channel(NioServerSocketChannel.class)
            .childHandler(new ChannelInitializer<NioSocketChannel>() {
                protected void initChannel(NioSocketChannel ch) {
                    ch.pipeline().addLast(new StringDecoder());
                    ch.pipeline().addLast(new SimpleChannelInboundHandler<String>() {
                        @Override
                        protected void channelRead0(ChannelHandlerContext ctx, String msg) {
                            System.out.println(msg);
                        }
                    });
                }
            })
            .bind(8000);
    }
}

服务端需要2个消息循环组：boss和worker；

boss用来创建新连接；worker用来读取发送过来的信息，并在控制台输出；

 

客户端：

public class NettyClient {
    public static void main(String[] args) throws InterruptedException {
        Bootstrap bootstrap = new Bootstrap();
        NioEventLoopGroup group = new NioEventLoopGroup();
 
        bootstrap.group(group)
                .channel(NioSocketChannel.class)
                .handler(new ChannelInitializer<Channel>() {
                    @Override
                    protected void initChannel(Channel ch) {
                        ch.pipeline().addLast(new StringEncoder());
                    }
                });
 
        Channel channel = bootstrap.connect("127.0.0.1", 8000).channel();
 
        while (true) {
            channel.writeAndFlush(new Date() + ": hello world!");
            Thread.sleep(2000);
        }
    }
}

客户端只需要一个消息循环组

每隔2秒给服务端发送字符串

 

结果：

Tue Apr 28 17:03:38 CST 2020: hello world!
Tue Apr 28 17:03:40 CST 2020: hello world!
Tue Apr 28 17:03:42 CST 2020: hello world!
Tue Apr 28 17:03:44 CST 2020: hello world!
Tue Apr 28 17:03:46 CST 2020: hello world!
Tue Apr 28 17:03:48 CST 2020: hello world!
Tue Apr 28 17:03:50 CST 2020: hello world!
Tue Apr 28 17:03:52 CST 2020: hello world!
Tue Apr 28 17:03:54 CST 2020: hello world!
Tue Apr 28 17:03:56 CST 2020: hello world!