DelimiterBasedFrameDecoder解决TCP粘包拆包问题

通过对DelimiterBasedFrameDecoder的使用,我们可以自动完成分隔符为结束标识的消息的解码。

下面的例子中,将$_作为分隔符。

服务端代码:

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/**
* 使用DelimiterBasedFrameDecoder解码器解决TCP粘包/拆包问题。
*
* @author j.tommy
* @version 1.0
* @date 2017/11/17
*/
public class EchoServer {
protected final static String DELIMITER = "$_";
public static void main(String[] args) {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 1024)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel socketChannel) throws Exception {
ByteBuf delimiter = Unpooled.copiedBuffer(DELIMITER.getBytes());
socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter)); // 这里的1024标识单条消息的最大长度,如果达到长度后仍然没有读取到分隔符,就抛出TooLongFrameException,防止由于异常码流缺失导致的内存溢出,这是Netty解码器的可靠性保护;第二个参数是分隔符
socketChannel.pipeline().addLast(new StringDecoder());
socketChannel.pipeline().addLast(new EchoServerHandler());
}
});
try {
ChannelFuture f = b.bind(8899).sync();
f.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
class EchoServerHandler extends ChannelHandlerAdapter {
private int counter;
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
ctx.close();
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
String body = (String) msg;
System.out.println("接收到客户端请求:" + body + ",counter=" + ++counter);
// 响应客户端
body += EchoServer.DELIMITER;
ByteBuf resp = Unpooled.copiedBuffer(body.getBytes());
ctx.write(resp);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
ctx.flush();
}
}

客户端代码:

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/**
* @author j.tommy
* @version 1.0
* @date 2017/11/17
*/
public class EchoClient {
protected final static String DELIMITER = "$_";
public static void main(String[] args) {
EventLoopGroup group = new NioEventLoopGroup();
Bootstrap b = new Bootstrap();
b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY,true).handler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel socketChannel) throws Exception {
ByteBuf delimiter = Unpooled.copiedBuffer(DELIMITER.getBytes());
socketChannel.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,delimiter));
socketChannel.pipeline().addLast(new StringDecoder());
socketChannel.pipeline().addLast(new EchoClientHandler());
}
});
try {
ChannelFuture f = b.connect("127.0.0.1",8899).sync();
f.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
}
finally {
group.shutdownGracefully();
}
}
}

class EchoClientHandler extends ChannelHandlerAdapter {
private int counter = 0;
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
ctx.close();
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
String req = "hello,this message is from client."+EchoClient.DELIMITER;
ByteBuf sendBuf = null;
for (int i=0;i<100;i++) {
sendBuf = Unpooled.copiedBuffer(req.getBytes());
ctx.writeAndFlush(sendBuf);
}
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
String resp = (String) msg;
System.out.println("接收到服务端响应:" + resp + ",counter=" + ++counter);
}
}

参考《Netty权威指南》

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