java - 非阻塞回声服务器 - Java

Question

这是一个 Echo 服务器。我不明白为什么在第一次与客户端连接后，即使在客户端关闭连接后服务器仍在打印“Reading..”和“Writing..”。服务器不应该用 select() 方法阻塞吗？谢谢

import java.nio.*;
import java.nio.channels.*;
import java.net.*;
import java.util.*;
import java.io.IOException;

public class EchoServer
{
    public static int DEFAULT_PORT=7;

    public static void main(String [] args)
    {

        ServerSocketChannel serverChannel;
        Selector selector;
        try
        {
            serverChannel = ServerSocketChannel.open();
            ServerSocket ss = serverChannel.socket();
            InetSocketAddress address = new InetSocketAddress(DEFAULT_PORT);
            ss.bind(address);
            serverChannel.configureBlocking(false);
            selector=Selector.open();
            serverChannel.register(selector,SelectionKey.OP_ACCEPT);
        } catch(IOException ex) {ex.printStackTrace(); return;}


        while(true)
        {
            int selectednum=0;
            try{
                selectednum=selector.select();  //blocks
            }catch (IOException ex) {ex.printStackTrace(); break;}
            if (selectednum>0) {
            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();
                        System.out.println("Accepted from "+client);
                        client.configureBlocking(false);
                        SelectionKey clientKey=client.register(
                            selector, SelectionKey.OP_WRITE | SelectionKey.OP_READ);
                        ByteBuffer buffer = ByteBuffer.allocate(100);
                        clientKey.attach(buffer);
                    }
                    if (key.isReadable()){
                        SocketChannel client = (SocketChannel) key.channel();
                        ByteBuffer output = (ByteBuffer) key.attachment();
                        System.out.println("Reading..");
                        client.read(output);
                    }
                    if (key.isWritable()){
                        SocketChannel client = (SocketChannel) key.channel();
                        ByteBuffer output = (ByteBuffer) key.attachment();
                        output.flip();
                        System.out.println("Writing..");
                        client.write(output);
                        output.compact();
                    }
                } catch (IOException ex) {
                    key.cancel(); 
                    try { key.channel().close();} 
                    catch (IOException cex) {}; 
                }
            }
        }
        }
    }
}

Answer 1

从客户端读取时，您没有检测到流结束。 read() 方法返回 -1。发生这种情况时，您应该关闭 channel 。