TCP 是面向连接的，面向流的，提供高可靠性服务。收发两端(客户端和服务器端) 都要有一一成对的 socket，因此，发送端为了将多个发给接收端的包，更有效的发给对方，使用了优化方法(Nagle 算法)，将多次间隔较小且数据量小的数据，合并成一个大的数据块，然后进行封包。这样做虽然提高了效率，但是接收端就难于分辨出完整的数据包了，因为面向流的通信是无消息保护边界的。
优于TCP无消息保护边界，需要在接收端处理消息边界问题，也就是我们所说的粘包、拆包问题。
我们从图中可以看出，客户端发送的D1和D2数据，是有可能会被拆分开进行数据传输的，Server端如果不做特殊处理的话，不知道D1和D2的数据边界，可能会少读或者多读，导致数据错乱。
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
public class MyServer {
public static void main(String[] args) throws Exception{
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).childHandler(new MyServerInitializer()); //自定义一个初始化类
ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
channelFuture.channel().closeFuture().sync();
}finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
public class MyServerInitializer extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyServerHandler());
}
}
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
import java.util.UUID;
public class MyServerHandler extends SimpleChannelInboundHandler<ByteBuf>{
private int count;
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
//cause.printStackTrace();
ctx.close();
}
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
//将buffer转成字符串
String message = new String(buffer, Charset.forName("utf-8"));
System.out.println("服务器接收到数据 " + message);
System.out.println("服务器接收到消息量=" + (++this.count));
//服务器回送数据给客户端, 回送一个随机id ,
ByteBuf responseByteBuf = Unpooled.copiedBuffer(UUID.randomUUID().toString() + " ", Charset.forName("utf-8"));
ctx.writeAndFlush(responseByteBuf);
}
}
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
public class MyClient {
public static void main(String[] args) throws Exception{
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group).channel(NioSocketChannel.class)
.handler(new MyClientInitializer()); //自定义一个初始化类
ChannelFuture channelFuture = bootstrap.connect("localhost", 7000).sync();
channelFuture.channel().closeFuture().sync();
}finally {
group.shutdownGracefully();
}
}
}
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
public class MyClientInitializer extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyClientHandler());
}
}
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
public class MyClientHandler extends SimpleChannelInboundHandler<ByteBuf> {
private int count;
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
//使用客户端发送10条数据 hello,server 编号
for(int i= 0; i< 10; ++i) {
ByteBuf buffer = Unpooled.copiedBuffer("hello,server " + i, Charset.forName("utf-8"));
ctx.writeAndFlush(buffer);
}
}
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
byte[] buffer = new byte[msg.readableBytes()];
msg.readBytes(buffer);
String message = new String(buffer, Charset.forName("utf-8"));
System.out.println("客户端接收到消息=" + message);
System.out.println("客户端接收消息数量=" + (++this.count));
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
先启动server端，再启动client端，多次启动不同client端查看结果，我们会发现server端接收的数据并没有固定的规律，这就是粘包拆包了。
服务器接收到消息量=1
服务器接收到数据 hello,server 0
服务器接收到消息量=1
服务器接收到数据 hello,server 1
服务器接收到消息量=2
服务器接收到数据 hello,server 2hello,server 3hello,server 4hello,server 5
服务器接收到消息量=3
服务器接收到数据 hello,server 6hello,server 7hello,server 8
服务器接收到消息量=4
服务器接收到数据 hello,server 9
服务器接收到消息量=5
Netty解决粘包和拆包问题的四种方案
//协议包
public class MessageProtocol {
private int len; //关键，content的长度
private byte[] content;
public int getLen() {
return len;
}
public void setLen(int len) {
this.len = len;
}
public byte[] getContent() {
return content;
}
public void setContent(byte[] content) {
this.content = content;
}
}
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ReplayingDecoder;
import java.util.List;
public class MyMessageDecoder extends ReplayingDecoder<Void> {
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
System.out.println("MyMessageDecoder decode 被调用");
//需要将得到二进制字节码-> MessageProtocol 数据包(对象)
// 通过长度，获取我们的content
int length = in.readInt();
byte[] content = new byte[length];
in.readBytes(content);
//封装成 MessageProtocol 对象，放入 out， 传递下一个handler业务处理
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(length);
messageProtocol.setContent(content);
// 消息传递给下一个handler
//out.add(messageProtocol);
// 这样也行
ctx.fireChannelRead(messageProtocol);
}
}
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;
public class MyMessageEncoder extends MessageToByteEncoder<MessageProtocol> {
@Override
protected void encode(ChannelHandlerContext ctx, MessageProtocol msg, ByteBuf out) throws Exception {
System.out.println("MyMessageEncoder encode 方法被调用");
// 编码
out.writeInt(msg.getLen());
out.writeBytes(msg.getContent());
}
}
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
public class MyServer {
public static void main(String[] args) throws Exception{
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).childHandler(new MyServerInitializer()); //自定义一个初始化类
ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
channelFuture.channel().closeFuture().sync();
}finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
public class MyServerInitializer extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyMessageDecoder());//解码器
pipeline.addLast(new MyMessageEncoder());//编码器
pipeline.addLast(new MyServerHandler());
}
}
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
import java.util.UUID;
//处理业务的handler
public class MyServerHandler extends SimpleChannelInboundHandler<MessageProtocol>{
private int count;
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
//cause.printStackTrace();
ctx.close();
}
@Override
protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {
//接收到数据，并处理
int len = msg.getLen();
byte[] content = msg.getContent();
System.out.println();
System.out.println();
System.out.println();
System.out.println("服务器接收到信息如下");
System.out.println("长度=" + len);
System.out.println("内容=" + new String(content, Charset.forName("utf-8")));
System.out.println("服务器接收到消息包数量=" + (++this.count));
//回复消息
String responseContent = UUID.randomUUID().toString();
int responseLen = responseContent.getBytes("utf-8").length;
byte[] responseContent2 = responseContent.getBytes("utf-8");
//构建一个协议包
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(responseLen);
messageProtocol.setContent(responseContent2);
ctx.writeAndFlush(messageProtocol);
}
}
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
public class MyClient {
public static void main(String[] args) throws Exception{
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group).channel(NioSocketChannel.class)
.handler(new MyClientInitializer()); //自定义一个初始化类
ChannelFuture channelFuture = bootstrap.connect("localhost", 7000).sync();
channelFuture.channel().closeFuture().sync();
}finally {
group.shutdownGracefully();
}
}
}
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
public class MyClientInitializer extends ChannelInitializer<SocketChannel> {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast(new MyMessageEncoder()); //加入编码器
pipeline.addLast(new MyMessageDecoder()); //加入解码器
pipeline.addLast(new MyClientHandler());
}
}
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import java.nio.charset.Charset;
public class MyClientHandler extends SimpleChannelInboundHandler<MessageProtocol> {
private int count;
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
//使用客户端发送10条数据 "你好啊，我的baby" 编号
for(int i = 0; i< 5; i++) {
String mes = "你好啊，我的baby";
byte[] content = mes.getBytes(Charset.forName("utf-8"));
int length = mes.getBytes(Charset.forName("utf-8")).length;
//创建协议包对象
MessageProtocol messageProtocol = new MessageProtocol();
messageProtocol.setLen(length);
messageProtocol.setContent(content);
ctx.writeAndFlush(messageProtocol);
}
}
// @Override
protected void channelRead0(ChannelHandlerContext ctx, MessageProtocol msg) throws Exception {
int len = msg.getLen();
byte[] content = msg.getContent();
System.out.println("客户端接收到消息如下");
System.out.println("长度=" + len);
System.out.println("内容=" + new String(content, Charset.forName("utf-8")));
System.out.println("客户端接收消息数量=" + (++this.count));
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
System.out.println("异常消息=" + cause.getMessage());
ctx.close();
}
}
我们发现，server端严格遵守我们的协议包进行分批次接收消息了，此时解决了粘包拆包问题。