motan源码分析七：序列化

motan的序列化支持两种协议，一种是json，另一种是hessian2。主要涉及到的类和接口是是：FastJsonSerialization、Hessian2Serialization、Serialization、Codec、AbstractCodec、NettyDecoder、NettyEncoder、DefaultRpcCodec和CompressRpcCodec等。

1.FastJsonSerialization使用json作为数据交换协议，Hessian2Serialization使用hessian2作为数据交换协议

@SpiMeta(name = "hessian2")
public class Hessian2Serialization implements Serialization {

    @Override
    public byte[] serialize(Object data) throws IOException {//使用hessan2进行序列化
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        Hessian2Output out = new Hessian2Output(bos);
        out.writeObject(data);
        out.flush();
        return bos.toByteArray();
    }

    @SuppressWarnings("unchecked")
    @Override
    public <T> T deserialize(byte[] data, Class<T> clz) throws IOException {//使用hessan2进行反序列化
        Hessian2Input input = new Hessian2Input(new ByteArrayInputStream(data));
        return (T) input.readObject(clz);
    }
}

2.motan支持压缩和非压缩两种方式

    public byte[] encode(Channel channel, Object message) throws IOException {
        if (needEncodeV1(message)) {//判断使用哪个版本的encode,decode同样
            return v1Codec.encode(channel, message);
        } else {
            // 使用v2压缩版本
            return encodeV2(channel, message);//使用压缩版本的encode
        }

    }

    public byte[] encodeV2(Channel channel, Object message) throws IOException {
        try {
            if (message instanceof Request) {
                return encodeRequest(channel, (Request) message);//序列化并压缩request对象

            } else if (message instanceof Response) {
                return encodeResponse(channel, (Response) message);//序列化并压缩response对象

            }
        } catch (Exception e) {
            if (ExceptionUtil.isMotanException(e)) {
                throw (RuntimeException) e;
            } else {
                throw new MotanFrameworkException("encode error: isResponse=" + (message instanceof Response), e,
                        MotanErrorMsgConstant.FRAMEWORK_ENCODE_ERROR);
            }
        }

        throw new MotanFrameworkException("encode error: message type not support, " + message.getClass(),
                MotanErrorMsgConstant.FRAMEWORK_ENCODE_ERROR);
    }

    private byte[] encodeRequest(Channel channel, Request request) throws IOException {
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        ObjectOutput output = createOutput(outputStream);
        addMethodInfo(output, request);

        //拿到hessian2或fasjson处理对象
        Serialization serialization =
                ExtensionLoader.getExtensionLoader(Serialization.class).getExtension(
                        channel.getUrl().getParameter(URLParamType.serialize.getName(), URLParamType.serialize.getValue()));

        if (request.getArguments() != null && request.getArguments().length > 0) {
            for (Object obj : request.getArguments()) {
                serialize(output, obj, serialization);//序列化
            }
        }

        if (request.getAttachments() == null || request.getAttachments().isEmpty()) {
            // empty attachments
            output.writeShort(0);
        } else {
            // 需要copy一份attachment进行签名替换，这样在失败重试时原始的request信息不会变更
            Map<String, String> attachments = copyMap(request.getAttachments());
            replaceAttachmentParamsBySign(channel, attachments);

            addAttachment(output, attachments);
        }

        output.flush();
        byte[] body = outputStream.toByteArray();

        byte flag = MotanConstants.FLAG_REQUEST;

        output.close();
        Boolean usegz = channel.getUrl().getBooleanParameter(URLParamType.usegz.getName(), URLParamType.usegz.getBooleanValue());
        int minGzSize = channel.getUrl().getIntParameter(URLParamType.mingzSize.getName(), URLParamType.mingzSize.getIntValue());
        return encode(compress(body, usegz, minGzSize), flag, request.getRequestId());//压缩处理
    }

3.通过NettyDecoder和NettyEncoder与netty框架进行结合

	protected Object encode(ChannelHandlerContext ctx, Channel nettyChannel, Object message) throws Exception {
		
		long requestId = getRequestId(message);//获取requestId
		byte[] data = null;
		
		if (message instanceof Response) {
			try {
				data = codec.encode(client, message);
			} catch (Exception e) {
				LoggerUtil.error("NettyEncoder encode error, identity=" + client.getUrl().getIdentity(), e);
				Response response = buildExceptionResponse(requestId, e);
				data = codec.encode(client, response);
			}
		} else {
			data = codec.encode(client, message);//调用DefaultRpcCodec或压缩的codec来编码
		}

		byte[] transportHeader = new byte[MotanConstants.NETTY_HEADER];
		ByteUtil.short2bytes(MotanConstants.NETTY_MAGIC_TYPE, transportHeader, 0);
		transportHeader[3] = getType(message);
		ByteUtil.long2bytes(getRequestId(message), transportHeader, 4);
		ByteUtil.int2bytes(data.length, transportHeader, 12);

		return ChannelBuffers.wrappedBuffer(transportHeader, data);
	}