上一篇文章中已经介绍了服务器端如何改造以支持HTTP2.0 + protobuf，并且给了一个客户端实现的例子，但这个例子并没有与SpringBoot结合。比如能否让RestTemplate或WebClient支持HTTP2.0 + protobuf，下面就给出代码：

1、RestTemplate

	public static void doWithRestTemplate(ReqtObj reqt) {
		String url = "http://127.0.0.1:8080/object/doTest";

		RestTemplate restTemplate = new RestTemplate();
		restTemplate.getMessageConverters().add(new ProtoBufHttpMessageConverter());

		HttpHeaders httpHeaders = new HttpHeaders();
//		httpHeaders.add("Content-Type", "application/json");        // #1
//		httpHeaders.add("Accept", "application/json");              // #2
		httpHeaders.add("Content-Type", "application/protobuf");    // #3
		httpHeaders.add("Accept", "application/protobuf");          // #4

		HttpEntity<ReqtObj> httpEntity = new HttpEntity<>(reqt, httpHeaders);

		ResponseEntity<RespObj> respEntity = restTemplate.exchange(url,
				HttpMethod.POST, httpEntity, RespObj.class);

		RespObj reqtObj = respEntity.getBody();

		System.out.println("++++++++++++++++++++" + reqtObj.toString());
	}

上面的代码使RestTemplate能够支持protobuf格式的报文，但由于RestTemplate先天的局限性，只能支持HTTP/1.1，不能支持HTTP/2.0。

另外，将#3#4注释掉后，上面的代码就可以直接变回采用JSON报文了。

2、WebClient

package com.cebbank;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.reactivestreams.Publisher;
import org.springframework.core.ResolvableType;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.http.MediaType;
import org.springframework.http.ReactiveHttpOutputMessage;
import org.springframework.http.codec.HttpMessageWriter;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

public class ProtoBufMessageWriter implements HttpMessageWriter<Object> {

	private static final List<MediaType> MEDIA_TYPES = Collections
			.unmodifiableList(Arrays.asList(new MediaType("application", "protobuf")));

	@Override
	public List<MediaType> getWritableMediaTypes() {
		return MEDIA_TYPES;
	}

	@Override
	public boolean canWrite(ResolvableType elementType, MediaType mediaType) {
		return true;
	}

	@Override
	public Mono<Void> write(Publisher<? extends Object> inputStream, ResolvableType elementType, MediaType mediaType,
			ReactiveHttpOutputMessage message, Map<String, Object> hints) {

		Flux<DataBuffer> dataBufferFlux = Flux.from(inputStream).map(value -> {
			byte[] data = ProtoBufTools.serialize(value);

			DataBufferFactory bufferFactory = message.bufferFactory();
			DataBuffer buffer = bufferFactory.allocateBuffer(data.length);
			buffer.write(data);

			return buffer;
		});
		return message.writeWith(dataBufferFlux);
	}
}

package com.cebbank;

import java.io.ByteArrayOutputStream;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.springframework.core.ResolvableType;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.http.MediaType;
import org.springframework.http.ReactiveHttpInputMessage;
import org.springframework.http.codec.HttpMessageReader;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

public class ProtoBufMessageReader implements HttpMessageReader<Object> {

	private static final List<MediaType> MEDIA_TYPES = Collections
			.unmodifiableList(Arrays.asList(new MediaType("application", "protobuf")));

	@Override
	public List<MediaType> getReadableMediaTypes() {
		return MEDIA_TYPES;
	}

	@Override
	public boolean canRead(ResolvableType elementType, MediaType mediaType) {
		return true;
	}

	@Override
	public Flux<Object> read(ResolvableType elementType, ReactiveHttpInputMessage message, Map<String, Object> hints) {
		Mono<Object> mono = createObject(message);

		return mono.flux();
	}

	@Override
	public Mono<Object> readMono(ResolvableType elementType, ReactiveHttpInputMessage message,
			Map<String, Object> hints) {
		Mono<Object> mono = createObject(message);

		return mono;
	}

	private Mono<Object> createObject(ReactiveHttpInputMessage message) {
		Mono<Object> mono = message.getBody().collectList().map(list -> {
			ByteArrayOutputStream bos = new ByteArrayOutputStream();

			try {
				for (DataBuffer dataBuffer : list) {
					int len = dataBuffer.readableByteCount();
					byte[] buffer = new byte[len];
					dataBuffer.read(buffer);

					bos.write(buffer);
				}

				byte[] data = bos.toByteArray();

				return ProtoBufTools.deserialize(data, RespObj.class);
			} catch (Exception e) {
				e.printStackTrace();
			}

			return null;
		});

		return mono;
	}
}

	public static void doWithWebClientUseReactor(ReqtObj reqt) {
		String url = "http://127.0.0.1:8080/object/doTest";

		try {
			HttpClient httpClient = HttpClient.create().protocol(HttpProtocol.H2C);
			ReactorClientHttpConnector reactorClientHttpConnector = new ReactorClientHttpConnector(httpClient);

			WebClient webClient = WebClient.builder()//
					.clientConnector(reactorClientHttpConnector)//
					.codecs(configurer -> {

						configurer.customCodecs().register(new ProtoBufMessageReader());
						configurer.customCodecs().register(new ProtoBufMessageWriter());
					})//
					.build();

			System.out.println("======================" + reqt.toString());
			System.out.println("reqtLen=" + data.length);

			MediaType mediaType = new MediaType("application", "protobuf");
//			MediaType mediaType = new MediaType("application", "json");

			Mono<RespObj> RespObjMono = webClient.post().uri(url).contentType(mediaType).accept(mediaType)
					.bodyValue(reqt).retrieve().bodyToMono(RespObj.class);

			RespObj resp = RespObjMono.block();
			System.out.println("======================" + resp.toString());

		} catch (Throwable e) {
			e.printStackTrace();
		}
	}

通过实现ProtoBufMessageReader和ProtoBufMessageWriter，就可以让WebClient支持HTTP2.0 + protobuf了。