Java NIO 实现进程通讯，解决用户自定义数据的组包和拆分粘包的问题

TCP通讯过程中，由于网络原因或者其他原因，经常出现粘包和半包现象。所以在具体编程中需要考虑。

下边的 java 代码是用 NIO 实现的一个Server端，消息的通讯格式为：

4字节int类型 [包头] + 包体.

包头描述出包体的长度。

package com.sof.nio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;

import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Reactor implements Runnable
{

	private static Logger logger = LoggerFactory.getLogger(Reactor.class);

	final Selector selector;
	final ServerSocketChannel serverSocket;

	public Reactor(String ip, int port) throws IOException
	{
		selector = Selector.open();
		serverSocket = ServerSocketChannel.open();
		serverSocket.socket().bind(new InetSocketAddress(port));
		serverSocket.configureBlocking(false);
		SelectionKey sk = serverSocket.register(selector, SelectionKey.OP_ACCEPT);
		sk.attach(new Acceptor());
	}

	public void run()
	{
		try
		{
			while (!Thread.interrupted())
			{
				logger.debug("selector is waitting  event....");
				selector.select();
				Set<SelectionKey> keys = selector.selectedKeys();
				if (keys.size() == 0)
				{
					logger.debug("nothing happened");
					continue;
				}

				for (SelectionKey key : keys)
				{
					if (key.isAcceptable())
					{
						logger.debug("Acceptable event happened");
					}
					else if (key.isReadable())
					{
						logger.debug("Readable event happened");
					}
					else if (key.isWritable())
					{
						logger.debug("Writeable event happened");
					}
					else
					{
						logger.debug("others event happened");
					}
					dispatch((SelectionKey) key);
				}
				keys.clear();
			}
		}
		catch (IOException ex)
		{
			logger.error(ex.getMessage());
			ex.printStackTrace();
		}
	}

	void dispatch(SelectionKey k)
	{
		Runnable r = (Runnable) (k.attachment());
		if (r != null)
		{
			r.run();
		}
	}

	public class Acceptor implements Runnable
	{
		public synchronized void run()
		{
			try
			{
				SocketChannel c = serverSocket.accept();
				logger.info("got a new connection from:  " + c.socket().toString());
				if (c != null)
				{
					new Handler(selector, c);
				}
			}
			catch (IOException ex)
			{
				logger.error(ex.getMessage());
				ex.printStackTrace();
			}
		}
	}
}

package com.sof.nio;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.sof.bas.Bytes2util;
import com.sof.bas.Util2Bytes;

final public class Handler implements Runnable
{
	private static Logger logger = LoggerFactory.getLogger(Handler.class);
	final SocketChannel socket;
	final SelectionKey sk;

	static final int MESSAGE_LENGTH_HEAD = 4;
	byte[] head = new byte[4];
	int bodylen = -1;

	Handler(Selector selector, SocketChannel socket) throws IOException
	{
		this.socket = socket;
		socket.configureBlocking(false);
		sk = socket.register(selector, 0);
		sk.attach(this);
		sk.interestOps(SelectionKey.OP_READ);
		selector.wakeup();
	}

	public void run()
	{
		try
		{
			read();
		}
		catch (IOException ex)
		{
			try
			{
				socket.close();
			}
			catch (IOException e)
			{
				e.printStackTrace();
			}
			logger.info("got a disconnect from " + socket.socket().toString());
			sk.cancel();
		}
	}

	public synchronized void read() throws IOException
	{
		ByteBuffer input = ByteBuffer.allocate(1024);
		socket.read(input);
		input.flip();
		
		//读取数据的原则: 要么读取一个完整的包头，要么读取一个完整包体。不满足这两种情况，不对ByteBuffer进行任何的get操作
		//但是要注意可能发生上次读取了一个完整的包头，下次读才读取一个完整包体情况。
		//所以包头部分必须用类的成员变量进行暂时的存储，当完整读取包头和包体后，在给业务处理部分。
		logger.debug("1: remain=" + input.remaining() + " bodylen=" + bodylen);
		while(input.remaining() > 0)
		{
			if (bodylen < 0) //还没有生成完整的包头部分, 该变量初始值为-1，并且在拼凑一个完整的消息包以后，再将该值设置为-1
			{
				if ( input.remaining() >= MESSAGE_LENGTH_HEAD) //ByteBuffer缓冲区的字节数够拼凑一个包头
				{
					input.get(head, 0, 4);
					bodylen = Util2Bytes.bytes2bigint(head);
					logger.debug("2: remain=" + input.remaining() + " bodylen=" + bodylen);
				}
				else//ByteBuffer缓冲区的字节数不够拼凑一个包头，什么操作都不做，退出这次处理，继续等待
				{
					logger.debug("3: remain=" + input.remaining() + " bodylen=" + bodylen);
					break;
				}
			}
			else if(bodylen > 0) //包头部分已经完整生成. 
			{
				if (input.remaining() >= bodylen) //缓冲区的内容够一个包体部分
				{
					byte[] body = new byte[bodylen];
					input.get(body, 0, bodylen);
					byte[] headandbody = new byte[MESSAGE_LENGTH_HEAD + bodylen];
					System.arraycopy(head, 0, headandbody, 0, head.length);
					System.arraycopy(body,0, headandbody, head.length, body.length);			
					bodylen = -1;
					logger.debug("4: remain=" + input.remaining() + " bodylen=" + bodylen);
					Bytes2util.outputHex(headandbody, 16);
				}
				else  ///缓冲区的内容不够一个包体部分，继续等待，跳出循环等待下次再出发该函数
				{
					System.out.println("5: remain=" + input.remaining() + " bodylen=" + bodylen);
					break;
				}
			}
			else if(bodylen == 0) //没有包体部分，仅仅有包头的情况
			{
				byte[] headandbody = new byte[MESSAGE_LENGTH_HEAD + bodylen];
				System.arraycopy(head, 0, headandbody, 0, head.length);
				Bytes2util.outputHex(headandbody, 16);
				bodylen = -1;
			}
		}
		
		sk.interestOps(SelectionKey.OP_READ);
	}
}

package com.sof.bas;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Bytes2util {
	private static Logger logger = LoggerFactory.getLogger(Bytes2util.class);

	public static byte[] biginttobytes(int value) {
		byte[] stream = new byte[4];
		for (int i = 0; i < 4; i++) {
			stream[i] = (byte) ((value & (0xFF << (4 - i - 1) * 8)) >> ((4 - i - 1) * 8));
		}
		outputHex(stream, 16);
		return stream;
	}

	public static byte[] bigshorttobytes(short value) {
		byte stream[] = new byte[2];
		for (int i = 0; i < 2; i++) {
			stream[i] = (byte) ((value & (0xFF << (2 - i - 1) * 8)) >> ((2 - i - 1) * 8));
		}
		outputHex(stream, 16);
		return stream;
	}

	public static byte[] smallinttobytes(int value) {
		byte stream[] = new byte[4];
		for (int i = 0; i < 4; i++) {
			stream[4 - i - 1] = (byte) ((value & (0xFF << (4 - i - 1) * 8)) >> ((4 - i - 1) * 8));
		}
		outputHex(stream, 16);
		return stream;
	}

	public static byte[] smallshorttobytes(short value) {
		byte stream[] = new byte[2];
		for (int i = 0; i < 2; i++) {
			stream[2 - i - 1] = (byte) ((value & (0xFF << (2 - i - 1) * 8)) >> ((2 - i - 1) * 8));
		}
		outputHex(stream, 16);
		return stream;
	}

	public static void outputHex(byte[] stream, int number) {
		String content = "stream display, length=" + stream.length + "\n";
		for (int i = 0; i < stream.length; i++) {
			if (i / number != 0 && i % number == 0) {
				content += "\n";
			}
			String tempstr = Integer.toHexString(stream[i] & 0xFF)
					.toUpperCase();
			if (tempstr.length() == 1)
				tempstr = "0" + tempstr;
			content += tempstr + " ";
		}
		logger.debug(content);
	}
}

package com.sof.bas;

public class Util2Bytes
{
	public static int bytes2smallint(byte stream[])
	{
		int value = 0;
		int temp = 0;
		for (int i = 3; i >= 0; i--)
		{
			if ((stream[i]) >= 0)
			{
				temp = stream[i];
			}
			else
			{
				temp = stream[i] + 256;
			}
			temp <<= (i * 8);
			value += temp;
		}
		return value;
	}

	public static short bytes2smallshort(byte stream[])
	{
		short value = 0;
		int temp = 0;
		for (int i = 1; i >= 0; i--)
		{
			if ((stream[i]) >= 0)
			{
				temp = stream[i];
			}
			else
			{
				temp = stream[i] + 256;
			}
			temp <<= (i * 8);
			value += temp;
		}
		return value;
	}

	public static int bytes2bigint(byte stream[])
	{
		int value = 0;
		int temp = 0;
		for (int i = 0; i < 4; i++)
		{
			if ((stream[i]) >= 0)
			{
				temp = stream[i];
			}
			else
			{
				temp = stream[i] + 256;
			}
			temp <<= ((4 - i - 1) * 8);
			value += temp;
		}
		return value;
	}

	public static short bytes2bigshort(byte stream[])
	{
		short value = 0;
		int temp = 0;
		for (int i = 0; i < 2; i++)
		{
			if ((stream[i]) >= 0)
			{
				temp = stream[i];
			}
			else
			{
				temp = stream[i] + 256;
			}
			temp <<= ((2 - i - 1) * 8);
			value += temp;
		}
		return value;
	}
}