Java NIO 【处理消息边界】

方案一

客户端和服务端约定好传输的最大长度（缺点：容易造成资源浪费）

方案二

约定好分隔符，例如（\n）,根据分隔符创建新的butebuffer

server

java 复制代码

package com.yys.mes.demo3;

import lombok.extern.slf4j.Slf4j;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.nio.charset.Charset;
import java.util.Iterator;

@Slf4j
public class Server {

    private static void split(ByteBuffer source) {
        source.flip();
        for (int i = 0; i < source.limit(); i++) {
            if (source.get(i) == '\n'){
                int length = i + 1 - source.position();
                ByteBuffer target = ByteBuffer.allocate(length);
                for (int j = 0; j < length; j++) {
                    target.put(source.get());
                }
                target.flip();
                String s = Charset.defaultCharset().decode(target).toString();
                log.info("target:{}", s);
            }
        }
        source.compact();
        }
    public static void main(String[] args) throws IOException {
        Selector selector = Selector.open();
        ServerSocketChannel ssc = ServerSocketChannel.open();
        ssc.configureBlocking(false);
        SelectionKey sscKey = ssc.register(selector, 0, null);
        sscKey.interestOps(SelectionKey.OP_ACCEPT);
        log.info("sscKey:{}", sscKey);
        ssc.bind(new InetSocketAddress(8080));
        while (true) {
            selector.select();
            Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
            while (iter.hasNext()) {
                SelectionKey key = iter.next();
                iter.remove();
                log.info("key: {}", key);
                if (key.isAcceptable()) {
                    ServerSocketChannel channel = (ServerSocketChannel) key.channel();
                    SocketChannel sc = channel.accept();
                    sc.configureBlocking(false);
                    ByteBuffer buffer = ByteBuffer.allocate(4);
                    //attachment作为附件关联到SelectionKey
                    SelectionKey scKey = sc.register(selector, 0, buffer);
                    scKey.interestOps(SelectionKey.OP_READ);
                    log.info("{}", sc);
                    log.info("scKey:{}", scKey);
                } else if (key.isReadable()) {
                    try {
                        SocketChannel channel = (SocketChannel) key.channel();
                        //拿到SelectionKey  关联的attachment附件
                        ByteBuffer buffer = (ByteBuffer)key.attachment();
                        int read = channel.read(buffer); // 如果是正常断开，read 的方法的返回值是 -1
                        if(read == -1) {
                            key.cancel();
                        } else {
                            split(buffer);
                            if (buffer.position() == buffer.limit()){
                                //扩容
                                ByteBuffer newBuffer = ByteBuffer.allocate(buffer.capacity() * 2);
                                buffer.flip();
                                newBuffer.put(buffer);
                                //替换附件
                                key.attach(newBuffer);
                            }
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                        key.cancel();  // 因为客户端断开了,因此需要将 key 取消（从 selector 的 keys 集合中真正删除 key）
                    }
                }
            }
        }
    }
}

client

java 复制代码

package com.yys.mes.nio;

import lombok.extern.slf4j.Slf4j;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;

@Slf4j
public class Client {
    public static void main(String[] args) throws IOException {
        SocketChannel sc = SocketChannel.open();
        sc.connect(new InetSocketAddress("127.0.0.1", 8080));
        log.info("client start");
        sc.write(Charset.defaultCharset().encode("hello123\n"));

        log.info("client end");

    }
}

方案三

根据长度分配bytebuffer

Todo: 明天写