NIO 實例demo-Server

NIO 實例demo-Server

下面是NIO編程的一個簡單的demo ，總共包括四部分，Client，ClientHandler，Server和ServerHandler首先是Server端，NIO的server端的通信序列圖如下圖：

TimeServer

Server 的兩部分代碼如下：
Server主類比簡單，設定端口號和serverHandler線程；

package MyTestNetty.Server;

/**
 * Created by User on 2017/8/4.
 */
public class TimeServer {
    public static void main(String[] args) {
        int port = 8080;
        MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);
        new Thread(timeServer,"myNIo server").start();

    }
}

MultiplexerTimeServer

第二部分是ServerHandler部分代碼如下：

package MyTestNetty.Server;

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;

/**
 * Created by User on 2017/8/4.
 */
public class MultiplexerTimeServer implements Runnable {
    private Selector selector;
    private ServerSocketChannel serverSocketChannel;
    private volatile boolean stop;
    public MultiplexerTimeServer(int port){
        try {
            selector = Selector.open();
            serverSocketChannel = ServerSocketChannel.open();
            serverSocketChannel.configureBlocking(false);
            serverSocketChannel.socket().bind(new InetSocketAddress(port),1024);
            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
            System.out.println("the time server start in port :"+ port);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public void stop(){
        this.stop =true;
    }
    @Override
    public void run() {
        while(!stop){//循環遍歷selector,休眠時間爲1S,當又處於就緒狀態的CHannel時，selector將返回該channel的集合。通過對Channel集合的迭代，可進行網絡異步讀寫操作
            try {
                selector.select(1000);
                Set<SelectionKey> selectKeys = selector.selectedKeys();
                Iterator<SelectionKey> it = selectKeys.iterator();
                SelectionKey key = null;
                while (it.hasNext()){
                    key = it.next();
                    it.remove();
                    handleInput(key);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        //多路複用器關閉後，所註冊在上面的Channel和Pipe等資源會被自動去註冊並關閉，所以不需要重複釋放資源
        if(selector!=null){
            try {
                selector.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }


    }

    private void handleInput(SelectionKey key) throws IOException {
        if(key.isValid()){
            if(key.isAcceptable()){//通過SelectionKey的操作位判斷其事件的類型
                ServerSocketChannel ssc =(ServerSocketChannel) key.channel();//
                try {
                    SocketChannel sc =ssc.accept();//創建SocketChannel實例
                    sc.configureBlocking(false);
                    sc.register(selector,SelectionKey.OP_READ);
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
            if(key.isReadable()){//讀取客戶端請求
                SocketChannel sc = (SocketChannel)key.channel();
                ByteBuffer readbuffer = ByteBuffer.allocate(1024);
                try {
                    int readBytes = sc.read(readbuffer);
                    if(readBytes>0){
                        readbuffer.flip();
                        byte[] bytes = new byte[readbuffer.remaining()];
                        readbuffer.get(bytes);
                        String body = new String(bytes,"UTF-8");
                        System.out.println("Hello，glad to see you :"+body);
                        String current = "QUERY TIME ORDER".equalsIgnoreCase(body)?new java.util.Date(System.currentTimeMillis()).toString():"BAD ORDER";
                        doWrite(sc," server");
                    }else{
                        key.cancel();
                        sc.close();
                    }
                } catch (IOException e) {//如果在catch中不添加key.cancel將會一直不停的拋出這個異常
                    key.cancel();
                    sc.socket().close();
                    sc.close();
                    System.out.println("execption handled");
                    //e.printStackTrace();
                }

            }
        }
    }

    private void doWrite(SocketChannel sc, String current) throws IOException {//
        if(current!=null&&current.toString().trim().length()>0){
            byte[] bytes = current.getBytes();
            ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
            writeBuffer.put(bytes);
            writeBuffer.flip();
            sc.write(writeBuffer);

        }
    }
}

這一部分主要是包括監聽客戶端發送過來的請求，selector循環檢查是否有channel就緒，如果有就緒的channel就將其的selectionKey選出進行IO讀寫，啓動運行後可輸出一下結果表示服務端啓動成功

注意這一部分代碼在90多行左右，這部分代碼如果去掉，運行之後會不斷的拋出異常：

catch (IOException e) {//如果在catch中不添加key.cancel將會一直不停的拋出這個異常
                    key.cancel();
                    sc.socket().close();
                    sc.close();
                    System.out.println("execption handled");
                    //e.printStackTrace();
                }

如果去掉之後會拋出一下異常：

這是因爲客戶端異常關閉後，服務器的選擇器會獲取到與客戶端套接字對應的套接字通道SelectionKey，並且這個key的興趣是OP_READ，執行從這個通道讀取數據時，客戶端已套接字已關閉，所以會出現“java.io.IOException: 遠程主機強迫關閉了一個現有的連接”的錯誤。所以在catch中要進行處理，即取消當前key並關閉通道。