1.java nio 网络编程 Server端

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最近一段时间看了下java nio，对于它的实际用途还有待继续研究，也看了网上很多人的文章博客等，收益颇多，但是还是自己动手才能知道自己是否真的会写了，会写与是否理解nio工作机制还有一定距离。我又不是一个理论派，主要还是讲究实战的，好，废话不多说，直接准备动作写。

首先你需要了解几个nio网络编程中会用到的组件(类)：

1.ByteBuffer

2.Selector

3.ServerSocketChannel

4.SocketChannel

5.SelectionKey

说一下nio server的整体实现思路：

打开Selector--》打开ServerSocketChannel --> 配置ServerSocketChannel是否阻塞 --》绑定ServerSocketChannel到某个主机以及端口 --》给ServerSocketChannel注册一个Selector --》 ServerSocketChannel监听accept事件 --》客户端连接后获取SocketChannel --》响应SocketChannel上的read/write事件

我写的可能和网络上一些人写的稍微有点不太一样，这也没办法，网络上打开10篇nio相关文章，有好几篇都是一样的，你抄我，我抄你的。个个图文并茂，个个都是架构师，分析reactor设计模式，多路复用，高性能，讲的头头是道，不过这和我没什么关系，我体会不到，应该是我太菜了。所以还是来点简单的，基础打好，总归不会有害处。

下面是具体实现代码：把这个代码拷贝到你的ide中，然后运行，用tcp连接工具，比如putty，cmd也行，不过cmd没有那么好用。有两个例子，第一个是只能少量字符传输，第二个支持大文本传输。

demo1:

package com.govert.project;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
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.Random;
import java.util.Set;

/**
 * 少量字符传输
 */
public class NioServer {

    public static void main(String[] args) throws IOException {
        // read and write byte buffer
        ByteBuffer rb = ByteBuffer.allocate(1024);
        ByteBuffer wb = ByteBuffer.allocate(1024);

        // listen hostname and port
        String hostname = "127.0.0.1";
        int port = 9000;

        // open Selector & check
        Selector selector = Selector.open();
        if (selector.isOpen()) {
            System.err.println("selector open success.");
        }

        // open ServerSocketChannel & check
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        if (serverSocketChannel.isOpen()) {
            System.err.println("serverSocketChannel open success.");
        }

        // ServerSocketChannel config non-block & bind hostname and port
        serverSocketChannel.configureBlocking(false);
        // serverSocketChannel.socket().bind(new InetSocketAddress(hostname, port));// old way bind
        serverSocketChannel.bind(new InetSocketAddress(hostname, port));// 1.7+

        // ServerSocketChannel register selector
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        // handle event loop
        while (true) {

            selector.select();

            Set<SelectionKey> keys = selector.selectedKeys();
            Iterator<SelectionKey> kit = keys.iterator();
            while (kit.hasNext()) {
                SelectionKey key = kit.next();

                // read event
                if (key.isReadable()) {
                    SocketChannel socketChannel = (SocketChannel) key.channel();

                    rb.clear();
                    socketChannel.read(rb);
                    rb.flip();
                    System.err.println("client request data: " + new String(rb.array(), 0, rb.limit(), "utf-8"));
                    //
                    key.interestOps(SelectionKey.OP_WRITE);
                }
                // write event
                else if (key.isWritable()) {
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    String resp = "server response data: " + new Random().nextInt(1000) + 1 + "\r\n";
                    wb.clear();
                    wb.put(resp.getBytes("utf-8"));
                    wb.flip();
                    socketChannel.write(wb);

                    //
                    key.interestOps(SelectionKey.OP_READ);
                }
                // accept event
                else if (key.isAcceptable()) {
                    SocketChannel socketChannel = serverSocketChannel.accept();
                    socketChannel.configureBlocking(false);
                    socketChannel.register(selector, SelectionKey.OP_READ);
                }
            }

            // clear keys
            keys.clear();
        }
    }

}

demo2:

package com.govert.project;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.Iterator;
import java.util.Random;
import java.util.Set;

/**
 * 大文本传输
 */
public class NioServer {

    public static void main(String[] args) throws IOException {
        // read and write byte buffer
        ByteBuffer rb = ByteBuffer.allocate(1024);
        ByteBuffer wb = ByteBuffer.allocate(1024);

        // listen hostname and port
        String hostname = "127.0.0.1";
        int port = 9000;

        // open Selector & check
        Selector selector = Selector.open();
        if (selector.isOpen()) {
            System.err.println("Selector open success.");
        }

        // open ServerSocketChannel & check
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        if (serverSocketChannel.isOpen()) {
            System.err.println("ServerSocketChannel open success.");
        }

        // ServerSocketChannel config non-block & bind hostname and port
        serverSocketChannel.configureBlocking(false);
        // serverSocketChannel.socket().bind(new InetSocketAddress(hostname, port));// old way bind
        serverSocketChannel.bind(new InetSocketAddress(hostname, port));// 1.7+

        // ServerSocketChannel register selector
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        // handle event loop
        while (true) {

            selector.select();

            Set<SelectionKey> keys = selector.selectedKeys();
            Iterator<SelectionKey> kit = keys.iterator();
            while (kit.hasNext()) {
                SelectionKey key = kit.next();

                // read event
                if (key.isReadable()) {
                    SocketChannel socketChannel = (SocketChannel) key.channel();

                    // large text
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    StringBuilder sb = new StringBuilder();
                    while (true) {
                        if (socketChannel.read(rb) < 1 && rb.hasRemaining()) break;
                        rb.flip();
                        baos.write(rb.array(), 0, rb.limit());
                        rb.clear();
                    }
                    //
                    System.err.println("client request data: " + new String(baos.toByteArray(), 0, baos.size(), "utf-8"));
                    //
                    key.interestOps(SelectionKey.OP_WRITE);
                }
                // write event
                else if (key.isWritable()) {
                    SocketChannel socketChannel = (SocketChannel) key.channel();
                    // large response
                    StringBuilder sb = new StringBuilder();
                    for (int i = 1; i < 1001; i++) {
                        sb.append("server respnse data: 第" + i + "条响应结果.\r\n");
                    }
                    byte[] bytes = sb.toString().getBytes("utf-8");
                    int length = bytes.length;
                    int loop = (length + 1023) / 1024;
                    int lastLoop = loop - 1;
                    int len;
                    for (int i = 0; i < loop; i++) {
                        if (i == lastLoop) len = length - i * 1024;
                        else len = 1024;
                        wb.put(bytes, i * 1024, len);
                        wb.flip();
                        socketChannel.write(wb);
                        wb.clear();
                    }

                    //
                    key.interestOps(SelectionKey.OP_READ);
                }
                // accept event
                else if (key.isAcceptable()) {
                    SocketChannel socketChannel = serverSocketChannel.accept();
                    socketChannel.configureBlocking(false);
                    socketChannel.register(selector, SelectionKey.OP_READ);
                }
            }

            // clear keys
            keys.clear();
        }
    }

}

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