在工作中用到Netty进行服务端开发，当服务端接收上位机字节数超过1000字节，服务端接收数据错误。为 什么服务端接收数据有时候没有问题，有时候会接收数据混乱。在不断的测试和对Netty知识点巩固，Netty 在项目开发中有了新的思考。
在TCP通信一定会出现粘包、拆包问题？如果不一定，什么时候出现粘包拆包问题？如果服务端单次接收字节 数超过1000字节的时候，byteBuf容量小于1000字节会出现什么问题？如何解决？
备注(Netty系列)
如果想要对网络编程和Netty是个小白，建议查看列表三篇文章。
1 七层协议和TCP/IP协议、三次握手四次挥手、BIO、NIO(Netty前置)
2 一文入门Netty（Netty一）
3 项目开发中如何选择编解码器？如何解决TCP粘包问题？(Netty二)
本文解决方案代码
GitHub代码地址
gitee代码地址
一 粘包(服务端客户端之间通信)
1.1 实例不出现粘包
1.1.1 代码实现
客户端以每500毫秒间隔向服务端发送相同字节数组，服务端将接收到字节转化为字符串，打印出来。
1. 服务端的配置类
public class TcpServer {
private final int port;
public TcpServer(int port) {
this.port = port;
}
public void init() {
NioEventLoopGroup boss = new NioEventLoopGroup();//主线程组
NioEventLoopGroup work = new NioEventLoopGroup();//工作线程组
try {
ServerBootstrap bootstrap = new ServerBootstrap();//引导对象
bootstrap.group(boss, work);//配置工作线程组
bootstrap.channel(NioServerSocketChannel.class);//配置为NIO的socket通道
bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel ch) throws Exception {//绑定通道参数
ch.pipeline().addLast("logging", new LoggingHandler("DEBUG"));//设置log监听器，并且日志级别为debug，方便观察运行流程
ch.pipeline().addLast("encode", new EncoderHandler());//编码器。发送消息时候用过
ch.pipeline().addLast("decode", new DecoderHandler());//解码器，接收消息时候用
ch.pipeline().addLast("handler", new TcpServerHandler());//业务处理类，最终的消息会在这个handler中进行业务处理
}
});
//使用了Future来启动线程，并绑定了端口
ChannelFuture future = bootstrap.bind(port).sync();
//以异步的方式关闭端口
future.channel().closeFuture().sync();
} catch (Exception e) {
} finally {
work.shutdownGracefully();
//出现异常后，关闭线程组
boss.shutdownGracefully();
}
}
}
2. 服务端解码器(decode)
public class DecoderHandler extends ByteToMessageDecoder {
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
System.out.println("byteBuf的容量为：" + in.capacity());
System.out.println("byteBuf的可读容量为：" + in.readableBytes());
System.out.println("byteBuf的可写容量为：" + in.writableBytes());
byte[] data = new byte[in.readableBytes()];
//读取核心的数据
in.readBytes(data);
out.add(data);
}
}
3. 服务端编码器(encode)
public class EncoderHandler extends MessageToByteEncoder {
protected void encode(ChannelHandlerContext ctx, Object msg, ByteBuf out) throws Exception {
out.writeBytes((byte[]) msg);
}
}
4. 服务端的ChannelHandler
public class TcpServerHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
byte[] recevierByte = (byte[]) msg;
String recevierString = ByteTransform.bytesToHexString(recevierByte);
System.out.println("-------------------长度为：" + recevierString.length());
System.out.println("---tcp服务接受设备端加密数据：" + recevierString);
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
super.channelActive(ctx);
}
/**
* 客户端断开连接触发方法
*/
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
super.channelInactive(ctx);
}
/**
* 方法中报错，触发方法
*/
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
super.exceptionCaught(ctx, cause);
}
}
5. 服务端启动类
public class StartServer {
public static void main(String[] args) {
try {
new TcpServer(5566).init();
} catch (Exception e) {
e.printStackTrace();
}
}
}
6. 工具类(知道方法是干嘛的就行)
public class ByteTransformIntUtil {
/**
* 根据byte转化为int
*/
public static int getIntFromBytes(byte high_h, byte high_l, byte low_h, byte low_l) {
return (high_h & 0xff) << 24 | (high_l & 0xff) << 16 | (low_h & 0xff) << 8 | low_l & 0xff;
}
/**
* 根据byte转化为int
*/
public static int getIntFromBytes(byte low_h, byte low_l) {
return ByteTransformIntUtil.getIntFromBytes((byte)0,(byte)0,low_h,low_l);
}
}
7. 客户端的配置类
public class MyRPCClient {
public void start(String host, int port) throws Exception {
//定义工作线程组
EventLoopGroup worker = new NioEventLoopGroup();
try {
//注意：client使用的是Bootstrap
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(worker)
.channel(NioSocketChannel.class) //注意：client使用的是NioSocketChannel
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new MyClientHandler());
}
});
//连接到远程服务
ChannelFuture future = bootstrap.connect(host, port).sync();
future.channel().closeFuture().sync();
} finally {
worker.shutdownGracefully();
}
}
}
8. 客户端启动类
public class StartClient {
public static void main(String[] args) {
new Thread() {
public void run() {
try {
new MyRPCClient().start("127.0.0.1", 5566);
} catch (Exception e) {
e.printStackTrace();
}
}
}.start();
}
}
9. 客户端ChannelHandler
public class MyClientHandler extends SimpleChannelInboundHandler<Object> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object buf) throws Exception {
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
// 向服务端发送数据
Timer timer = new Timer();
final byte[] bytes = ByteTransform.hexStringToBytes("10000000");
timer.scheduleAtFixedRate(new TimerTask() {
public void run() {
byte[] msg1 = {0x00,0x00,0x00,0x00,0x01, 0x01, 0x02,0x01};
ctx.writeAndFlush(Unpooled.copiedBuffer(msg1));
}
}, 5000, 50);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
public int getIntFromBytes(byte high_h, byte high_l, byte low_h, byte low_l) {
return (high_h & 0xff) << 24 | (high_l & 0xff) << 16 | (low_h & 0xff) << 8 | low_l & 0xff;
}
}
1.1.2 对结果进行分析
image
查看客户端的Handler,向服务端发送数据的方法，是以50毫秒为间隔发送数据。但是服务端没有出现粘包问题。
总结 客户端向服务端有间隔时间向服务端发送数据，并不会出现粘包问题。
1.2 出现粘包问题
1.2.1 代码实例
客户端不间断的向服务端发字节数组（16个字节）
- 客户端ChannelHandler（只需要将上面客户端的MyClientHandler进行替换，其他代码依旧）
public class MyClientHandler extends SimpleChannelInboundHandler<Object> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object buf) throws Exception {
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
while (true){
i = i + 1;
byte[] msg = {0x00, 0x00, 0x00, 0x0c, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109, 98};
ctx.writeAndFlush(Unpooled.copiedBuffer(msg));
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
public int getIntFromBytes(byte high_h, byte high_l, byte low_h, byte low_l) {
return (high_h & 0xff) << 24 | (high_l & 0xff) << 16 | (low_h & 0xff) << 8 | low_l & 0xff;
}
}
1.2.2 对结果进行分析
客户端不间断向服务端发送字节数组(16个字节)，服务将接收的字节打印出来。
image
现象： 每次读取的字节长度发生了改变。
总结： 如果客户端同事接收多比数据会出现粘包问题。
二 拆包
2.1 不出现拆包问题
2.1.1 代码实现
public class MyClientHandler extends SimpleChannelInboundHandler<Object> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object buf) throws Exception {
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
// 向服务端发送数据
Timer timer = new Timer();
final byte[] bytes = ByteTransform.hexStringToBytes("10000000");
timer.scheduleAtFixedRate(new TimerTask() {
public void run() {
byte[] msg1 = {0x00,0x00,0x00,0x00,0x01, 0x01, 0x02,0x01};
ctx.writeAndFlush(Unpooled.copiedBuffer(msg1));
}
}, 5000, 50);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
public int getIntFromBytes(byte high_h, byte high_l, byte low_h, byte low_l) {
return (high_h & 0xff) << 24 | (high_l & 0xff) << 16 | (low_h & 0xff) << 8 | low_l & 0xff;
}
}
2.1.2 结果分析
image
查看客户端的Handler,向服务端发送数据的方法，是以50毫秒为间隔发送数据。但是服务端没有出现粘包问题。
总结客户端向服务端发送若字节数组(十几个字节)，并不会出现拆包问题。
2.2 实例netty拆包问题(一)
public class MyClientHandler extends SimpleChannelInboundHandler<Object> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object buf) throws Exception {
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
// 向服务端发送数据
Timer timer = new Timer();
final byte[] bytes = ByteTransform.hexStringToBytes("10000000");
timer.scheduleAtFixedRate(new TimerTask() {
public void run() {
byte[] msg = {0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
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0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
0x01, 98, 49, 50, 51, 52, 53, 54, 0x12, 0x11, 0x11, 0x00, 0x00, 109, 109,
};
ctx.writeAndFlush(Unpooled.copiedBuffer(msg));
}
}, 5000, 1000);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
public int getIntFromBytes(byte high_h, byte high_l, byte low_h, byte low_l) {
return (high_h & 0xff) << 24 | (high_l & 0xff) << 16 | (low_h & 0xff) << 8 | low_l & 0xff;
}
}
image
现象 服务端接收前两次之数据之后，服务端接收客户端发过来的数据都是定长的。前两次数据长度之后为后面数据之和。
分析 ByteBuf初始容量是一个300-1024随机值,当接收到的数据长度大于ByteBuf的容量的时候,ByteBuf分两次来接收.造成拆包效果.
三 解决粘包和拆包问题
2.1 方案一
2.1.1 代码实现
思路 在传递数据前加上固定包头,存储数据的长度.每次读取规定的长度.
- 服务端decode(解码器)
public class DecoderHandler extends ByteToMessageDecoder {
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
System.out.println("byteBuf的容量为：" + in.capacity());
System.out.println("byteBuf的可读容量为：" + in.readableBytes());
System.out.println("byteBuf的可写容量为：" + in.writableBytes());
int len = ByteTransformIntUtil.getIntFromBytes(in.readByte(), in.readByte());
byte[] data = new byte[len];
//读取核心的数据
in.readBytes(data);
out.add(data);
}
}
- 客户端的Handler
2.1.2 对结果分析
image
现象 服务端发生报错.
分析 因为客户端传过来规定数据长度为1000个字节以上,从ByteBuf取出的字节长度大于ByteBuf容量.
代码分析
//规定客户端传递的数据长度
int len = ByteTransformIntUtil.getIntFromBytes(in.readByte(), in.readByte());
//规定字节数组长度
byte[] data = new byte[len];
//读取核心的数据
in.readBytes(data);
注意 chennelPipeline 里面是一个个得ChannelHandler,入站得时候从第一个ChannelHandler执行,一次执行到尾部.出战是从尾执行到头.但是出站的时候,不执行解码器.进站时候,不执行编码器.我是用代码debug调试的,这里就演示了.感兴趣可以自己写个demo试试.
2.2 方案二(解决了)
2.2.1 代码实现
思路 方案一,是因为传递数据长度大于ByteBuf长度,读取报错.那就如果接收数据长度大于BetuBuf长度,让这次读取返回.和下次一起读取.(这样解决数据读取不完整,也解决数据粘包)
- 服务端decode(解码器)
public class DecoderHandler extends ByteToMessageDecoder {
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
System.out.println("byteBuf的容量为：" + in.capacity());
System.out.println("byteBuf的可读容量为：" + in.readableBytes());
System.out.println("byteBuf的可写容量为：" + in.writableBytes());
//将当前ByteBuf的读指针,存在一个变量m中
in.markReaderIndex();
int len = ByteTransformIntUtil.getIntFromBytes(in.readByte(), in.readByte());
System.out.println("数据实际长度：" + len);
if(len > in.readableBytes()){
//将读指针恢复到刚才标记的变量值
in.resetReaderIndex();
//如果接收数据长度大于ByteBuf长度时候,将不进行此次读取和下次一起读取.
return;
}
byte[] data = new byte[len];
//读取核心的数据
in.readBytes(data);
out.add(data);
}
}
2.2.2 对结果分析
客户端不间断的向服务端发送字节数据(长度为1710),服务端将接收数据打印出来
image
现象 服务端打印字节数组长度全为1710个字节.
总结 解决了TCP使用Netty的粘包和拆包问题.
