@coldxiangyu 2017-07-13T10:20:27.000000Z 字数 3761 阅读 2082

关于ByteBuffer中allocate与allocateDirect的区别

源码系列

前言

在使用NIO对现有纯Socket项目进行改造的过程中，遇到了诸多问题。也正是因为NIO在实际应用中困难重重，所以大部分架构师基本上采用netty、mina这种非常成熟的框架。但是NIO本身就显得轻量多了，很多问题我们也是通过查看NIO的源码进行问题的解决的。

这篇文章是探究ByteBuffer中allocate和allocateDirector源码级别的区别。

探究

下面是我模拟单线程监听N个端口的服务端代码：

package com.sinosoft.midplat.net;
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.nio.charset.Charset;
import java.util.Iterator;
/**
 * Created by coldxiangyu on 2017/7/7.
 */
public class ChannelServer {
    private static final int BUF_SIZE=1024;
    private static int[] PORTS;
    private static final int TIMEOUT = 3000;
    public static void main(String[] args) {
        PORTS = new int[]{60970, 60950, 60940, 60930, 60840 ,60111};
        selector();
    }
    public static void handleAccept(SelectionKey key) throws IOException{
        ServerSocketChannel ssChannel = (ServerSocketChannel)key.channel();
        SocketChannel sc = ssChannel.accept();
        sc.configureBlocking(false);
        sc.register(key.selector(), SelectionKey.OP_READ, ByteBuffer.allocateDirect(BUF_SIZE));
    }
    public static void handleRead(SelectionKey key) throws IOException{
        //Charset cn = Charset.forName("GBK");
        SocketChannel sc = (SocketChannel)key.channel();
        ByteBuffer buf = (ByteBuffer)key.attachment();
        buf.clear();
        long bytesRead = sc.read(buf);
        if(bytesRead == -1){
            sc.close();
        }
        /*while(bytesRead > 0){
            buf.flip();
            while(buf.hasRemaining()){
                //System.out.print(buf.get());
                System.out.print(cn.decode(buf));
            }
            System.out.println();
            buf.clear();
            bytesRead = sc.read(buf);
        }*/
        else{
            buf.flip();
            byte[] data = buf.array();  
            String msg = new String(data).trim();  
            System.out.println("客户端：" + msg);  
            ByteBuffer outBuffer = ByteBuffer.wrap(msg.getBytes());  
            //将消息回送给客户端  
            sc.write(outBuffer);
            key.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE);
        }
    }
    public static void handleWrite(SelectionKey key) throws IOException{
        System.out.println("begin to write now!");
        ByteBuffer buf = (ByteBuffer)key.attachment();
        buf.flip();
        SocketChannel sc = (SocketChannel) key.channel();
        while(buf.hasRemaining()){
            sc.write(buf);
        }
        buf.compact();
    }
    public static void selector() {
        Selector selector = null;
        ServerSocketChannel ssc = null;
        try{
            selector = Selector.open();
            for (int i=0; i<PORTS.length; i++) {
                ssc = ServerSocketChannel.open();
                ssc.socket().bind(new InetSocketAddress(PORTS[i]));
                ssc.configureBlocking(false);
                ssc.register(selector, SelectionKey.OP_ACCEPT);
                System.out.println("开始监听端口:" + PORTS[i] + "...");
            }
            while(true){
                if(selector.select(TIMEOUT) == 0){
                    //System.out.println("==");
                    continue;
                }
                Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
                while(iter.hasNext()){
                    SelectionKey key = iter.next();
                    try{
                        if(key.isAcceptable()){
                            handleAccept(key);
                        }
                        if(key.isReadable()){
                            handleRead(key);
                        }
                        if(key.isWritable() && key.isValid()){
                            handleWrite(key);
                        }
                        if(key.isConnectable()){
                            System.out.println("isConnectable = true");
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    } finally {
                        iter.remove();
                        key.cancel();
                    }
                }
            }
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}