Dubbo编解码系列文章目录

Dubbo编解码(一)-原理
Dubbo编解码(二)-Codec2和AbstractCodec
Dubbo编解码(三)-TransportCodec
Dubbo编解码(五)-Dubbo协议编码器
Dubbo编解码(六)-Dubbo协议解码器

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Codec2

在Dubbo-SPI(六)-各层扩展点中已经有相关介绍，根据URL中的codec参数决定使用哪一种编解码实现方式，扩展点实现如下：

传输层编解码实现
transport=org.apache.dubbo.remoting.transport.codec.TransportCodec
telnet=org.apache.dubbo.remoting.telnet.codec.TelnetCodec
交换层编解码实现
exchange=org.apache.dubbo.remoting.exchange.codec.ExchangeCodec

AbstractEndpoint#getChannelCodec

protected static Codec2 getChannelCodec(URL url) {
    
	// 编解码器扩展名 必须与 协议名 保持相同
	String codecName = url.getProtocol(); // codec extension name must stay the same with protocol name
	if (ExtensionLoader.getExtensionLoader(Codec2.class).hasExtension(codecName)) {
    
		return ExtensionLoader.getExtensionLoader(Codec2.class).getExtension(codecName);
	} else {
    
		return new CodecAdapter(ExtensionLoader.getExtensionLoader(Codec.class)
				.getExtension(codecName));
	}
}

AbstractCodec

实现了Codec2接口，但是没有去具体实现Codec2#encode和Codec2#decode方法
主要提供了检验报文长度 和 获取 具体编解码器的方法

校验报文长度

protected static void checkPayload(Channel channel, long size) throws IOException {
    
	// 获取报文长度
	int payload = getPayload(channel);
	// 判断报文长度是否超限
	boolean overPayload = isOverPayload(payload, size);
	if (overPayload) {
    
		ExceedPayloadLimitException e = new ExceedPayloadLimitException(
				"Data length too large: " + size + ", max payload: " + payload + ", channel: " + channel);
		logger.error(e);
		throw e;
	}
}

int DEFAULT_PAYLOAD = 8 * 1024 * 1024;

protected static int getPayload(Channel channel) {
    
	// payload=8M
	int payload = Constants.DEFAULT_PAYLOAD;
	if (channel != null && channel.getUrl() != null) {
    
		// 获取url中的payload参数值
		payload = channel.getUrl().getParameter(Constants.PAYLOAD_KEY, Constants.DEFAULT_PAYLOAD);
	}
	return payload;
}

protected static boolean isOverPayload(int payload, long size) {
    
	if (payload > 0 && size > payload) {
    
		return true;
	}
	return false;
}

获取具体编解码器

protected Serialization getSerialization(Channel channel, Request req) {
    
	return CodecSupport.getSerialization(channel.getUrl());
}

protected Serialization getSerialization(Channel channel, Response res) {
    
	return CodecSupport.getSerialization(channel.getUrl());
}

protected Serialization getSerialization(Channel channel) {
    
	return CodecSupport.getSerialization(channel.getUrl());
}

String SERIALIZATION_KEY = "serialization";
String DEFAULT_REMOTING_SERIALIZATION = "hessian2";

// CodecSupport#getSerialization
public static Serialization getSerialization(URL url) {
    
	// 获取扩展接口(Serialization)的扩展实例，根据url的serialization参数获取，默认是hessian2
	return ExtensionLoader.getExtensionLoader(Serialization.class).getExtension(
		url.getParameter(Constants.SERIALIZATION_KEY, Constants.DEFAULT_REMOTING_SERIALIZATION));
}

判断是客户端还是服务端

String SIDE_KEY = "side";

protected boolean isClientSide(Channel channel) {
    
	String side = (String) channel.getAttribute(SIDE_KEY);
	if (CLIENT_SIDE.equals(side)) {
    
		return true;
	} else if (SERVER_SIDE.equals(side)) {
    
		return false;
	} else {
    
		// side属性值既不是client也不是server
		InetSocketAddress address = channel.getRemoteAddress();
		URL url = channel.getUrl();
		// 使用InetSocketAddress 和 URL 进行判断
		boolean isClient = url.getPort() == address.getPort()
			&& NetUtils.filterLocalHost(url.getIp()).equals(
			NetUtils.filterLocalHost(address.getAddress()
				.getHostAddress()));
		channel.setAttribute(SIDE_KEY, isClient ? CLIENT_SIDE
			: SERVER_SIDE);
		return isClient;
	}
}

protected boolean isServerSide(Channel channel) {
    
	return !isClientSide(channel);
}