上个小节我们浅析了在Netty的使用的时候TCP的粘包和拆包的现象，Netty对此问题提供了相对比较丰富的解决方案
Netty提供了几个常用的解码器，帮助我们解决这些问题，其实上述的粘包和拆包的问题，归根结底的解决方案就是发送端给远程端一个标记，告诉远程端，每个信息的结束标志是什么，这样，远程端获取到数据后，根据跟发送端约束的标志，将接收的信息分切或者合并成我们需要的信息，这样我们就可以获取到正确的信息了
例如，我们刚才的例子中，我们可以在发送的信息中，加一个结束标志，例如两个远程端规定以行来切分数据，那么发送端，就需要在每个信息体的末尾加上行结束的标志，部分代码如下：
修改BaseClientHandler的req的构造：
public BaseClientHandler() {
// req = ("BazingaLyncc is learner").getBytes();
req = ("In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. His book w"
+ "ill give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the process "
+ "of configuring and connecting all of Netty’s components to bring your learned about threading models in ge"
+ "neral and Netty’s threading model in particular, whose performance and consistency advantages we discuss"
+ "ed in detail In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. Hi"
+ "s book will give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the"
+ " process of configuring and connecting all of Netty’s components to bring your learned about threading "
+ "models in general and Netty’s threading model in particular, whose performance and consistency advantag"
+ "es we discussed in detailIn this chapter you general, we recommend Java Concurrency in Practice by Bri"
+ "an Goetz. His book will give We’ve reached an exciting point—in the next chapter;the counter is: 1 2222"
+ "sdsa ddasd asdsadas dsadasdas" + System.getProperty("line.separator")).getBytes();
}
我们在我们巨长的req中末尾加了System.getProperty("line.separator")，这样相当于给req打了一个标记
打完标记，其实我们这个示例中的server中还不知道是以行为结尾的，所以我们需要修改server的handler链，在inbound链中加一个额外的处理链，判断一下，获取的信息按照行来切分，我们很庆幸，这样枯燥的代码Netty已经帮我们完美地完成了，Netty提供了一个LineBasedFrameDecoder这个类，顾名思义，这个类名字中有decoder，说明是一个解码器，我们再看看它的详细声明：
/**
* A decoder that splits the received {@link ByteBuf}s on line endings.
* <p>
* Both {@code "\n"} and {@code "\r\n"} are handled.
* For a more general delimiter-based decoder, see {@link DelimiterBasedFrameDecoder}.
*/
public class LineBasedFrameDecoder extends ByteToMessageDecoder {
/** Maximum length of a frame we're willing to decode. */
private final int maxLength;
/** Whether or not to throw an exception as soon as we exceed maxLength. */
private final boolean failFast;
private final boolean stripDelimiter;
/** True if we're discarding input because we're already over maxLength. */
private boolean discarding;
private int discardedBytes;
它是继承ByteToMessageDecoder的，是将byte类型转化成Message的，所以我们应该将这个解码器放在inbound处理器链的第一个，所以我们修改一下Server端的启动代码：
package com.lyncc.netty.stickpackage.myself;
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;
import java.net.InetSocketAddress;
public class BaseServer {
private int port;
public BaseServer(int port) {
this.port = port;
}
public void start(){
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap sbs = new ServerBootstrap().group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port))
.childHandler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new LineBasedFrameDecoder(2048));
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new BaseServerHandler());
};
}).option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);
// 绑定端口，开始接收进来的连接
ChannelFuture future = sbs.bind(port).sync();
System.out.println("Server start listen at " + port );
future.channel().closeFuture().sync();
} catch (Exception e) {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
int port;
if (args.length > 0) {
port = Integer.parseInt(args[0]);
} else {
port = 8080;
}
new BaseServer(port).start();
}
}
这样，我们只是在initChannel方法中增加了一个LineBasedFrameDecoder这个类，其中2048是规定一行数据最大的字节数
我们再次运行，我们再看看效果：
可以看到客户端发送的两次msg，被服务器端成功地两次接收了，我们要的效果达到了
我们将LineBasedFrameDecoder中的2048参数，缩小一半，变成1024，我们再看看效果：
出现了异常，这个异常时TooLongFrameException,这个异常在Netty in Action中介绍过，帧的大小太大，在我们这个场景中，就是我们发送的一行信息大小是1076，大于了我们规定的1024所以报错了
我们再解决另一个粘包的问题，我们可以看到上节中介绍的那个粘包案例中，我们发送了100次的信息“BazingaLyncc is learner”，这个案例很特殊，这个信息是一个特长的数据，字节长度是23，所以我们可以使用Netty为我们提供的FixedLengthFrameDecoder这个解码器，看到这个名字就明白了大半，定长数据帧的解码器，所以我们修改一下代码：
BaseClientHandler：
package com.lyncc.netty.stickpackage.myself;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
public class BaseClientHandler extends ChannelInboundHandlerAdapter{
private byte[] req;
public BaseClientHandler() {
req = ("BazingaLyncc is learner").getBytes();
// req = ("In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. His book w"
// + "ill give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the process "
// + "of configuring and connecting all of Netty’s components to bring your learned about threading models in ge"
// + "neral and Netty’s threading model in particular, whose performance and consistency advantages we discuss"
// + "ed in detail In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. Hi"
// + "s book will give We’ve reached an exciting point—in the next chapter we’ll discuss bootstrapping, the"
// + " process of configuring and connecting all of Netty’s components to bring your learned about threading "
// + "models in general and Netty’s threading model in particular, whose performance and consistency advantag"
// + "es we discussed in detailIn this chapter you general, we recommend Java Concurrency in Practice by Bri"
// + "an Goetz. His book will give We’ve reached an exciting point—in the next chapter;the counter is: 1 2222"
// + "sdsa ddasd asdsadas dsadasdas" + System.getProperty("line.separator")).getBytes();
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
ByteBuf message = null;
for (int i = 0; i < 100; i++) {
message = Unpooled.buffer(req.length);
message.writeBytes(req);
ctx.writeAndFlush(message);
}
// message = Unpooled.buffer(req.length);
// message.writeBytes(req);
// ctx.writeAndFlush(message);
// message = Unpooled.buffer(req.length);
// message.writeBytes(req);
// ctx.writeAndFlush(message);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
ctx.close();
}
}
BaseServer：
package com.lyncc.netty.stickpackage.myself;
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.FixedLengthFrameDecoder;
import io.netty.handler.codec.string.StringDecoder;
import java.net.InetSocketAddress;
public class BaseServer {
private int port;
public BaseServer(int port) {
this.port = port;
}
public void start(){
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap sbs = new ServerBootstrap().group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port))
.childHandler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new FixedLengthFrameDecoder(23));
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new BaseServerHandler());
};
}).option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);
// 绑定端口，开始接收进来的连接
ChannelFuture future = sbs.bind(port).sync();
System.out.println("Server start listen at " + port );
future.channel().closeFuture().sync();
} catch (Exception e) {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
int port;
if (args.length > 0) {
port = Integer.parseInt(args[0]);
} else {
port = 8080;
}
new BaseServer(port).start();
}
}
我们就是在channelhandler链中，加入了FixedLengthFrameDecoder，且参数是23，告诉Netty，获取的帧数据有23个字节就切分一次
运行结果：
可以看见，我们获取到了我们想要的效果
当然Netty还提供了一些其他的解码器，有他们自己的使用场景，例如有按照某个固定字符切分的DelimiterBasedFrameDecoder的解码器
我们再次修改代码：
BaseClientHandler.java
package com.lyncc.netty.stickpackage.myself;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
public class BaseClientHandler extends ChannelInboundHandlerAdapter{
private byte[] req;
public BaseClientHandler() {
// req = ("BazingaLyncc is learner").getBytes();
req = ("In this chapter you general, we recommend Java Concurrency in Practice by Brian Goetz. $$__ His book w"
+ "ill give We’ve reached an exciting point—in the next chapter we’ll $$__ discuss bootstrapping, the process "
+ "of configuring and connecting all of Netty’s components to bring $$__ your learned about threading models in ge"
+ "neral and Netty’s threading model in particular, whose performance $$__ and consistency advantages we discuss"
+ "ed in detail In this chapter you general, we recommend Java $$__Concurrency in Practice by Brian Goetz. Hi"
+ "s book will give We’ve reached an exciting point—in the next $$__ chapter we’ll discuss bootstrapping, the"
+ " process of configuring and connecting all of Netty’s components $$__ to bring your learned about threading "
+ "models in general and Netty’s threading model in particular, $$__ whose performance and consistency advantag"
+ "es we discussed in detailIn this chapter you general, $$__ we recommend Java Concurrency in Practice by Bri"
+ "an Goetz. His book will give We’ve reached an exciting $$__ point—in the next chapter;the counter is: 1 2222"
+ "sdsa ddasd asdsadas dsadasdas" + System.getProperty("line.separator")).getBytes();
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
ByteBuf message = null;
// for (int i = 0; i < 100; i++) {
// message = Unpooled.buffer(req.length);
// message.writeBytes(req);
// ctx.writeAndFlush(message);
// }
message = Unpooled.buffer(req.length);
message.writeBytes(req);
ctx.writeAndFlush(message);
message = Unpooled.buffer(req.length);
message.writeBytes(req);
ctx.writeAndFlush(message);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
ctx.close();
}
}
我们在req的字符串中增加了“$$__”这样的切割符，然后再Server中照例增加一个DelimiterBasedFrameDecoder，来切割字符串：
ServerBootstrap sbs = new ServerBootstrap().group(bossGroup,workerGroup).channel(NioServerSocketChannel.class).localAddress(new InetSocketAddress(port))
.childHandler(new ChannelInitializer<SocketChannel>() {
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new DelimiterBasedFrameDecoder(1024,Unpooled.copiedBuffer("$$__".getBytes())));
ch.pipeline().addLast(new StringDecoder());
ch.pipeline().addLast(new BaseServerHandler());
};
}).option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);
我们在initChannel中第一个inbound中增加了DelimiterBasedFrameDecoder，且规定切割符就是“$$__”，这样就能正常切割了，我们看看运行效果：
可以看到被分了20次读取，我们可以这样理解，客户端发送了2次req字节，每个req中有10个“$$__”，这样就是第11次切割的时候其实发送了粘包，第一个req中末尾部分和第二次的头部粘在了一起，作为第11部分的内容
而最后一部分的内容因为没有"$$__"切割，所以没有打印在控制台上~
其实这类的Handler还是相对比较简单的，真实的生产环境这些decoder只是作为比较基本的切分类，但是这些decoder还是很好用的~
希望讲的对您有所帮助~END~
时间： 2024-10-08 20:36:05