Netty中LineBasedFrameDecoder解碼器使用與分析：解決TCP粘包問題
阿新 • • 發佈：2018-02-11
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Netty中LineBasedFrameDecoder解碼器使用與分析：解決TCP粘包問題
上一篇文章《Netty中TCP粘包問題代碼示例與分析》演示了使用了時間服務器的例子演示了TCP的粘包問題，這裏使用LineBasedFrameDecoder就是用來解決這個問題的。
不過需要註意的是，LineBasedFrameDecoder見名知其義，可見其是與行相關的，而在前面演示TCP粘包問題時，作者是有意在發送的消息中都加入了換行符，目的也是為了在後面去講解LineBasedFrameDecoder的使用，當然也是給出一種簡單解決TCP粘包問題的方法，或者是通過一個簡單案例來讓我們這些學習者有更直觀的理解。
代碼來自於《Netty權威指南》第4章，不過我依然是做了部分的修改。
服務端代碼
TimeServer.java
package cn.xpleaf.netty02; import io.netty.bootstrap.ServerBootstrap; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelInitializer; import io.netty.channel.ChannelOption; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.NioServerSocketChannel; import io.netty.handler.codec.LineBasedFrameDecoder; import io.netty.handler.codec.string.StringDecoder; public class TimeServer { public void bind(int port) throws Exception { // 配置服務端的NIO線程組 EventLoopGroup bossGroup = new NioEventLoopGroup(); EventLoopGroup workerGroup = new NioEventLoopGroup(); try { ServerBootstrap b = new ServerBootstrap(); b.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, 1024) .childHandler(new ChildChannelHandler()); // 綁定端口，同步等待成功 ChannelFuture f = b.bind(port).sync(); // 等待服務端監聽端口關閉 f.channel().closeFuture().sync(); } finally { // 優雅退出，釋放線程池資源 bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); } } private class ChildChannelHandler extends ChannelInitializer<SocketChannel> { @Override protected void initChannel(SocketChannel ch) throws Exception { // 核心在下面兩行，加入了LineBasedFrameDecoder和StringDecoder兩個解碼器 // 所以當消息到達我們的業務處理handler即TimerServerHandler，所看到的消息 // 都是前面兩個解碼器經過處理之後的結果 ch.pipeline().addLast(new LineBasedFrameDecoder(1024)); ch.pipeline().addLast(new StringDecoder()); ch.pipeline().addLast(new TimeServerHandler()); } } public static void main(String[] args) throws Exception { int port = 8080; if(args != null && args.length > 0) { try { port = Integer.valueOf(port); } catch (NumberFormatException e) { // TODO: handle exception } } new TimeServer().bind(port); } }
TimeServerHandler.java
package cn.xpleaf.netty02; import java.sql.Date; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerAdapter; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; public class TimeServerHandler extends ChannelInboundHandlerAdapter { private int counter = 0; @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { String body = (String) msg; // counter的作用是標記這是第幾次收到客戶端的請求 System.out.println("The time server receive order : " + body + " ; the counter is : " + ++counter); String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(System.currentTimeMillis()).toString() : "BAD ORDER"; currentTime = currentTime + System.getProperty("line.separator"); ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes()); ctx.write(resp); } @Override public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { ctx.close(); } }
客戶端代碼
TimeClient.java
package cn.xpleaf.netty02;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.LineBasedFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
public class TimeClient {
public void connect(int port, String host) throws Exception {
// 配置客戶端NIO線程組
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(group).channel(NioSocketChannel.class)
.option(ChannelOption.TCP_NODELAY, true)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
// 核心在下面兩行，加入了LineBasedFrameDecoder和StringDecoder兩個解碼器
// 所以當消息到達我們的業務處理handler即TimerServerHandler，所看到的消息
// 都是前面兩個解碼器經過處理之後的結果
ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new TimeClientHandler());
}
});
// 發起異步連接操作
ChannelFuture f = b.connect(host, port).sync();
// 等待客戶端鏈路關閉
f.channel().closeFuture().sync();
} finally {
// 優雅退出，釋放NIO線程組
group.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
int port = 8080;
if(args != null && args.length > 0) {
try {
port = Integer.valueOf(port);
} catch (NumberFormatException e) {
// 采用默認值
}
}
new TimeClient().connect(port, "localhost");
}
}TimeClientHandler.java
package cn.xpleaf.netty02;
import java.util.logging.Logger;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
public class TimeClientHandler extends ChannelInboundHandlerAdapter {
private static final Logger logger = Logger.getLogger(TimeServerHandler.class.getName());
private int counter;
private byte[] req;
public TimeClientHandler() {
req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes();
}
@Override
public void channelActive(ChannelHandlerContext ctx) {
ByteBuf message = null;
for(int i = 0; i < 100; i++) {
message = Unpooled.buffer(req.length);
message.writeBytes(req);
ctx.writeAndFlush(message);
}
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
String body = (String) msg;
// counter的作用是標記這是第幾次收到客戶端的請求
System.out.println("Now is : " + body + " ; the counter is : " + ++counter);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
logger.warning("Unexpected exception from downstream : ");
ctx.close();
}
}測試
服務端運行結果：
The time server receive order : QUERY TIME ORDER ; the counter is : 1
The time server receive order : QUERY TIME ORDER ; the counter is : 2
The time server receive order : QUERY TIME ORDER ; the counter is : 3
...省略多行...
The time server receive order : QUERY TIME ORDER ; the counter is : 98
The time server receive order : QUERY TIME ORDER ; the counter is : 99
The time server receive order : QUERY TIME ORDER ; the counter is : 100客戶端運行結果：
Now is : 2018-02-11 ; the counter is : 1
Now is : 2018-02-11 ; the counter is : 2
Now is : 2018-02-11 ; the counter is : 3
...省略多行...
Now is : 2018-02-11 ; the counter is : 98
Now is : 2018-02-11 ; the counter is : 99
Now is : 2018-02-11 ; the counter is : 100從輸出結果可以看出，這確實解決了TCP的粘包問題。
原理分析
下面的分析來自於書本上，這裏也貼出來：
Netty中LineBasedFrameDecoder解碼器使用與分析：解決TCP粘包問題