概述
这里介绍两种解决办法：1、利用LengthFieldBasedFrameDecoder解码器 2、设置自定义编解码。
一般出现数据粘包问题很难复现，因为在开发中，我们都是模拟发数据，真正上线了，我们的数据发送就没有什么规律，可能很快，也可能慢，频率不同，难以捕捉问题，但是肯定会出现一些粘包问题。
所谓粘包，就是接收的数据，无法分开，一个包的数据可能是两个或者多个报文记录，我们需要严格按照报文格式将这些合在一起的包拆开。思路就是要么报文有严格的分隔符，要么定长，再就是自定义解码器或者利用netty自带的LengthFieldBasedFrameDecoder解码器。
前面说过，粘包问题在实际中很难复现，这对于我们查找问题不是很方便，但是我这里通过自己编写的client发送报文，几乎可以100%的复现。
这个客户端，就是前面两篇博客中提到的c语言自定义tcp协议实现socket通信的客户端。
netty实现的tcp server代码如下所示：
package com.xxx.huali.hualitest.nettyio;
import java.nio.ByteOrder;
import com.xxx.huali.hualitest.nettyio.decode.MyDecoder;
import com.xxx.huali.hualitest.nettyio.decode.MyHandler;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
public class ServerApp {
private final static int port = 6666;
public static void main(String[] args) {
EventLoopGroup boss = new NioEventLoopGroup();
EventLoopGroup work = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(boss, work)
.channel(NioServerSocketChannel.class)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
//ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(ByteOrder.LITTLE_ENDIAN, 65535, 8 , 4, 1, 0, true));
//ch.pipeline().addLast("decoder",new MyDecoder());
ch.pipeline().addLast(new ServerHandler());
//ch.pipeline().addLast("handler", new MyHandler());
}
})
.option(ChannelOption.SO_BACKLOG, 1024)
.childOption(ChannelOption.SO_KEEPALIVE, true);
ChannelFuture future = bootstrap.bind(port).sync();
future.channel().closeFuture().sync();
} catch (Exception e) {
e.printStackTrace();
}finally {
boss.shutdownGracefully();
work.shutdownGracefully();
}
}
}
class ServerHandler extends SimpleChannelInboundHandler<ByteBuf>{
int count = 1;
@Override
protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception {
// TODO Auto-generated method stub
// flag version type reserved length payload checksum
// 2 2 2 2 4 length 1
byte dst[] = new byte[8];
msg.readBytes(dst,0,2);
System.out.println("flag->"+(dst[0]&0xff)+","+(dst[1]&0xff));
msg.readBytes(dst, 0, 2);
System.out.println("version->"+(dst[0]&0xff)+","+(dst[1]&0xff));
msg.readBytes(dst, 0, 2);
System.out.println("type->"+(dst[0]&0xff)+","+(dst[1]&0xff));
msg.readBytes(dst, 0, 2);
System.out.println("reserved->"+(dst[0]&0xff)+","+(dst[1]&0xff));
msg.readBytes(dst, 0, 4);
System.out.println("length->"+(dst[0]&0xff)+","+(dst[1]&0xff)+","+(dst[2]&0xff)+","+(dst[3]&0xff));
byte[] dst2 = new byte[4];
System.arraycopy(dst, 0, dst2, 0, 4);
int len = bytes2Int(dst2);
byte[] payload = new byte[len];
msg.readBytes(payload,0,len);
System.out.println("payload->"+new String(payload));
msg.readBytes(dst,0,1);
System.out.println("checksum->"+(dst[0]&0xff));
System.out.println("***********************************"+(count++));
//ctx.fireChannelRead(payload);
System.out.println(msg.readableBytes());
}
private int bytes2Int(byte[] data) {
int res = 0;
if(4!=data.length)
throw new RuntimeException("invalid bytes,please check data");
for(int i=3;i>=0;i--) {
res <<= 8;
res |= (data[i]&0xff);
}
return res;
}
}
默认情况下，我启动这个服务，然后启动client发送10条报文数据。服务端第一次打印的记录总是少于10条，一般是8条或者9条。
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->27,0,0,0
payload->{"name":"xxx6799","age":18}
checksum->0
***********************************1
41
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->27,0,0,0
payload->{"name":"xxx4068","age":18}
checksum->0
***********************************2
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->27,0,0,0
payload->{"name":"xxx9232","age":18}
checksum->0
***********************************3
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx20097","age":18}
checksum->0
***********************************4
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx10497","age":18}
checksum->0
***********************************5
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->27,0,0,0
payload->{"name":"xxx8182","age":18}
checksum->0
***********************************6
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx11246","age":18}
checksum->0
***********************************7
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx26867","age":18}
checksum->0
***********************************8
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx13514","age":18}
checksum->0
***********************************9
0我刚开始以为是网络传输丢掉了，最后加了一个打印，发现每次在第一包数据里面解析完成，会多余一些数据，后续的解析就都是正常的，即使多次运行client发送数据，也都是正常的，所以说这个粘包的问题很难复现。
我首先在childHandler这里通过pipeline增加了一个解码器：
再次运行这个server，然后client第一次发送数据，第一包解析不会出现多余一些报文数据，服务端会打印10条报文记录：
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->27,0,0,0
payload->{"name":"xxx8418","age":18}
checksum->0
***********************************1
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx20121","age":18}
checksum->0
***********************************2
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx17337","age":18}
checksum->0
***********************************3
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx17083","age":18}
checksum->0
***********************************4
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx24318","age":18}
checksum->0
***********************************5
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx24843","age":18}
checksum->0
***********************************6
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx11861","age":18}
checksum->0
***********************************7
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->27,0,0,0
payload->{"name":"xxx1109","age":18}
checksum->0
***********************************8
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx24616","age":18}
checksum->0
***********************************9
0
flag->165,90
version->1,0
type->1,0
reserved->255,255
length->28,0,0,0
payload->{"name":"xxx11497","age":18}
checksum->0
***********************************10
0这个解码器LengthFieldBasedFrameDecoder，需要设置几个参数：
1、byteOrder端序，这个必须要注意，netty其实支持小端序，所以这里就直接选择小端序ByteOrder.LITTLE_ENDIAN。
2、lengthFieldOffset 表示报文中length这个字段的起始位置，这个根据协议来指定。
3、lengthFieldLength表示length字段的长度，这个会用来计算报文体也就是payload的长度，他跟小端序大端序也有很大的关系。
4、lengthAdjustment，这个是length字段可以调整的位数，一般是1-2位，其实也就是校验位的长度。
从这些参数可以看出，有了这些东西其实就能根据协议各个字段的类型，以及长度来分割一包数据了。
还有一种办法，就是前面提到的，自定义解码器：
自定义解码，解码之后就不再是原始的byte数组了，就是我们的报文实体类，所以也需要新的handler来处理解析之后的数据。
这里会新增三个类：协议类，协议解码器，消息处理器。
协议类：
package com.xxx.huali.hualitest.nettyio.decode;
public class MyProtocol {
private String flag;
private short version;
private short type;
private short reserved;
private int length;
private byte[] payload;
private byte checksum;
public MyProtocol() {
}
public MyProtocol(String flag,short version,short type,short reserved,int length,
byte[] payload,byte checksum) {
this.flag = flag;
this.version = version;
this.type = type;
this.reserved = reserved;
this.length = length;
this.payload = payload;
this.checksum = checksum;
}
public String getFlag() {
return flag;
}
public void setFlag(String flag) {
this.flag = flag;
}
public short getVersion() {
return version;
}
public void setVersion(short version) {
this.version = version;
}
public short getType() {
return type;
}
public void setType(short type) {
this.type = type;
}
public short getReserved() {
return reserved;
}
public void setReserved(short reserved) {
this.reserved = reserved;
}
public int getLength() {
return length;
}
public void setLength(int length) {
this.length = length;
}
public byte[] getPayload() {
return payload;
}
public void setPayload(byte[] payload) {
this.payload = payload;
}
public byte getChecksum() {
return checksum;
}
public void setChecksum(byte checksum) {
this.checksum = checksum;
}
@Override
public String toString() {
return this.flag+":"+this.version+":"+this.type+":"+this.reserved+":"+this.length+":"+new String(this.payload)+":"+this.checksum;
}
}
协议解码器：
package com.xxx.huali.hualitest.nettyio.decode;
import java.util.List;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;
public class MyDecoder extends ByteToMessageDecoder{
private final String PACKET_FLAG = "A55A";
private final int BASE_LENGTH = 2+2+2+2+4+1;
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
// TODO Auto-generated method stub
System.out.println("decode bytes length -> "+in.readableBytes());
if(in.readableBytes()>=BASE_LENGTH) {
//skip
if(in.readableBytes()>2048) {
in.skipBytes(in.readableBytes());
}
int index;
String flag;
while(true) {
index = in.readerIndex();
in.markReaderIndex();
byte[] dst = new byte[2];
in.readBytes(dst, 0, 2);
flag = Utils.byte2Hex(dst);
if(PACKET_FLAG.equals(flag))
break;
in.resetReaderIndex();
in.readByte();
if(in.readableBytes()<BASE_LENGTH)
return;
}
System.out.println("start to resolve.");
short version = in.readShortLE();
short type = in.readShortLE();
short reserved = in.readShortLE();
int length = in.readIntLE();
if(in.readableBytes()<length) {
in.readerIndex(index);
return;
}
byte[] payload = new byte[length];
in.readBytes(payload);
byte checksum = in.readByte();
MyProtocol protocol = new MyProtocol(flag,version,type,reserved,length,payload,checksum);
out.add(protocol);
}
}
}
消息处理器：
package com.xxx.huali.hualitest.nettyio.decode;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
public class MyHandler extends SimpleChannelInboundHandler<MyProtocol>{
@Override
protected void channelRead0(ChannelHandlerContext ctx, MyProtocol msg) throws Exception {
// TODO Auto-generated method stub
System.out.println(msg);
}
}
因为有了解码器，我们的handler就不再需要解析原始的ByteBuf了。
childHandler中的配置如下所示：
同样的，启动server,然后利用client发送10条报文，服务端也会打印10次消息，不会出现粘包问题。这里严格来说，还需要增加一个编码器，因为服务端会向客户端回复消息也需要编码，这里没有编写，主要服务端这里只做数据接收，不涉及向client发送数据。
服务端打印信息：
decode bytes length -> 41
start to resolve.
A55A:1:1:-1:28:{"name":"xxx12964","age":18}:0
decode bytes length -> 40
start to resolve.
A55A:1:1:-1:27:{"name":"xxx6927","age":18}:0
decode bytes length -> 41
start to resolve.
A55A:1:1:-1:28:{"name":"xxx13352","age":18}:0
decode bytes length -> 41
start to resolve.
A55A:1:1:-1:28:{"name":"xxx24320","age":18}:0
decode bytes length -> 41
start to resolve.
A55A:1:1:-1:28:{"name":"xxx29822","age":18}:0
decode bytes length -> 41
start to resolve.
A55A:1:1:-1:28:{"name":"xxx18595","age":18}:0
decode bytes length -> 41
start to resolve.
A55A:1:1:-1:28:{"name":"xxx19017","age":18}:0
decode bytes length -> 41
start to resolve.
A55A:1:1:-1:28:{"name":"xxx22343","age":18}:0
decode bytes length -> 40
start to resolve.
A55A:1:1:-1:27:{"name":"xxx5613","age":18}:0
decode bytes length -> 40
start to resolve.
A55A:1:1:-1:27:{"name":"xxx5834","age":18}:0正确打印了10条报文，说明利用自定义解码器解决了粘包问题。
个人推荐使用自定义编解码器，使用netty自带的LengthFieldBasedFrameDecoder，之后，还需要解码，而且如果需要向客户端传输数据，还需要编码器，不如编解码一起做了。
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