高性能NIO框架Netty-对象传输

http://cxytiandi.com/blog/detail/17403

上篇文章高性能NIO框架Netty入门篇我们对Netty做了一个简单的介绍，并且写了一个入门的Demo,客户端往服务端发送一个字符串的消息，服务端回复一个字符串的消息，今天我们来学习下在Netty中怎么使用对象来传输数据。

上篇文章中传输字符串我们用的是框架自带的StringEncoder，StringDecoder编解码器，现在想要通过对象来传输数据，该怎么弄呢？

既然StringEncoder和StringDecoder可以传输字符串，我们来看看这2个类的源码不就知道它们到底做了一些什么工作。

StringEncoder

public class StringEncoder extends MessageToMessageEncoder<CharSequence> {
// TODO Use CharsetEncoder instead.
private final Charset charset;
/**
* Creates a new instance with the current system character set.
*/
public StringEncoder() {
this(Charset.defaultCharset());
}
/**
* Creates a new instance with the specified character set.
*/
public StringEncoder(Charset charset) {
if (charset == null) {
throw new NullPointerException("charset");
}
this.charset = charset;
}
@Override
protected void encode(ChannelHandlerContext ctx, CharSequence msg, List<Object> out) throws Exception {
if (msg.length() == 0) {
return;
}
out.add(ByteBufUtil.encodeString(ctx.alloc(), CharBuffer.wrap(msg), charset));
}
}

通过继承MessageToMessageEncoder，重写encode方法来进行编码操作，就是将字符串进行输出即可。

StringDecoder

public class StringDecoder extends MessageToMessageDecoder<ByteBuf> {
// TODO Use CharsetDecoder instead.
private final Charset charset;
/**
* Creates a new instance with the current system character set.
*/
public StringDecoder() {
this(Charset.defaultCharset());
}
/**
* Creates a new instance with the specified character set.
*/
public StringDecoder(Charset charset) {
if (charset == null) {
throw new NullPointerException("charset");
}
this.charset = charset;
}
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf msg, List<Object> out) throws Exception {
out.add(msg.toString(charset));
}
}

继承MessageToMessageDecoder，重写decode方法，将ByteBuf数据直接转成字符串进行输出，解码完成。

通过上面的源码分析，我们发现编解码的原理无非就是在数据传输前进行一次处理，接收后进行一次处理，在网络中传输的数据都是字节，我们现在想要传PO对象，那么必然需要进行编码和解码2个步骤，我们可以自定义编解码器来对对象进行序列化，然后通过ByteBuf的形式进行传输, 传输对象需要实现java.io.Serializable接口。

首先我们定义一个传输对象，实现序列化接口，暂时先定义2个字段，一个ID,用来标识客户端，一个内容字段，代码如下：

public class Message implements Serializable {
private static final long serialVersionUID = -7543514952950971498L;
private String id;
private String content;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
}

传输对象定好后，定义对象的编解码器。

对象编码器

将对象序列化成字节，通过ByteBuf形式进行传输，ByteBuf是一个byte存放的缓冲区，提供了读写操作。

public class MessageEncoder extends MessageToByteEncoder<Message> {
@Override
protected void encode(ChannelHandlerContext ctx, Message message, ByteBuf out) throws Exception {
byte[] datas = ByteUtils.objectToByte(message);
out.writeBytes(datas);
ctx.flush();
}
}

对象解码器

接收ByteBuf数据，将ByteBuf反序列化成对象

public class MessageDecoder extends ByteToMessageDecoder {
@Override
protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
Object obj = ByteUtils.byteToObject(ByteUtils.read(in));
out.add(obj);
}
}

将上篇文章中服务端的编解码器改成对象编解码器：

public class ImServer {
public void run(int port) {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
//实体类传输数据，jdk序列化
ch.pipeline().addLast("decoder", new MessageDecoder());
ch.pipeline().addLast("encoder", new MessageEncoder());
ch.pipeline().addLast(new ServerPoHandler());
//字符串传输数据
/*ch.pipeline().addLast("decoder", new StringDecoder());
ch.pipeline().addLast("encoder", new StringEncoder());
ch.pipeline().addLast(new ServerStringHandler());*/
}
})
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);
try {
ChannelFuture f = bootstrap.bind(port).sync();
f.channel().closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();
}
}
}

接下来编写服务端的消息处理类：

public class ServerPoHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
Message message = (Message) msg;
System.err.println("server:" + message.getId());
ctx.writeAndFlush(message);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}

服务端改造好了之后，就要改造客户端了，同样的道理，客户端和服务端的编解码器都要一致才行。

客户端连接时指定对象编解码器和对象消息处理类，代码如下：

public class ImConnection {
private Channel channel;
public Channel connect(String host, int port) {
doConnect(host, port);
return this.channel;
}
private void doConnect(String host, int port) {
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(workerGroup);
b.channel(NioSocketChannel.class);
b.option(ChannelOption.SO_KEEPALIVE, true);
b.handler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
//实体类传输数据，jdk序列化
ch.pipeline().addLast("decoder", new MessageDecoder());
ch.pipeline().addLast("encoder", new MessageEncoder());
ch.pipeline().addLast(new ClientPoHandler());
//字符串传输数据
/*ch.pipeline().addLast("decoder", new StringDecoder());
ch.pipeline().addLast("encoder", new StringEncoder());
ch.pipeline().addLast(new ClientStringHandler());*/
}
});
ChannelFuture f = b.connect(host, port).sync();
channel = f.channel();
} catch(Exception e) {
e.printStackTrace();
}
}
}

客户端消息处理类：

/**
* 当编解码器为实体对象时时用来接收数据
* @author yinjihuan
*
*/
public class ClientPoHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
Message message = (Message) msg;
System.out.println("client:" + message.getContent());
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}

客户端启动类也需要改造，将发送字符串的消息变成对象消息

public class ImClientApp {
public static void main(String[] args) {
String host = "127.0.0.1";
int port = 2222;
Channel channel = new ImConnection().connect(host, port);
//对象传输数据
Message message = new Message();
message.setId(UUID.randomUUID().toString().replaceAll("-", ""));
message.setContent("hello yinjihuan");
channel.writeAndFlush(message);
//字符串传输数据
//channel.writeAndFlush("yinjihuan");
}
}

源码参考：https://github.com/yinjihuan/netty-im