Spring gateway 修改Request的body内容

开发过程中我们需要修改request的body内容，比如说网关中统一解析token，并把解析内容放到reques的body中，以参数形式传给下游服务。

import org.reactivestreams.Publisher;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.filter.factory.rewrite.CachedBodyOutputMessage;
import org.springframework.cloud.gateway.filter.factory.rewrite.ModifyRequestBodyGatewayFilterFactory;
import org.springframework.cloud.gateway.filter.factory.rewrite.RewriteFunction;
import org.springframework.cloud.gateway.support.BodyInserterContext;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.http.HttpHeaders;
import org.springframework.http.codec.HttpMessageReader;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpRequestDecorator;
import org.springframework.stereotype.Component;
import org.springframework.web.reactive.function.BodyInserter;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.server.HandlerStrategies;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.util.List;
import java.util.Map;


@Component
public class InsertBodyGlobalFilter implements GlobalFilter, Ordered {
    private final List<HttpMessageReader<?>> messageReaders = HandlerStrategies.withDefaults().messageReaders();

    @SuppressWarnings({"unchecked", "rawtypes"})
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        ServerRequest serverRequest = ServerRequest.create(exchange, messageReaders);
        ModifyRequestBodyGatewayFilterFactory.Config config = new ModifyRequestBodyGatewayFilterFactory.Config();
        config.setInClass(Map.class);
        config.setOutClass(Map.class);
        Class inClass = config.getInClass();
        Class outClass = config.getOutClass();
        config.setRewriteFunction(inClass, outClass, new BodyRewrite());

        // TODO: flux or mono
        Mono<?> modifiedBody = serverRequest.bodyToMono(inClass)
                .flatMap(originalBody -> config.getRewriteFunction().apply(exchange, originalBody))
                .switchIfEmpty(Mono.defer(() -> (Mono) config.getRewriteFunction().apply(exchange, null)));
        BodyInserter bodyInserter = BodyInserters.fromPublisher(modifiedBody, config.getOutClass());
        HttpHeaders headers = new HttpHeaders();
        headers.putAll(exchange.getRequest().getHeaders());
        // the new content type will be computed by bodyInserter
        // and then set in the request decorator
        headers.remove(HttpHeaders.CONTENT_LENGTH);
        // if the body is changing content types, set it here, to the bodyInserter
        // will know about it
        if (config.getContentType() != null) {
            headers.set(HttpHeaders.CONTENT_TYPE, config.getContentType());
        }
        CachedBodyOutputMessage outputMessage = new CachedBodyOutputMessage(exchange, headers);
        return bodyInserter.insert(outputMessage, new BodyInserterContext())
                .then(Mono.defer(() -> {
                    ServerHttpRequest decorator = decorate(exchange, headers, outputMessage);
                    return chain.filter(exchange.mutate().request(decorator).build());
                }));
    }

    /**
     * 优先级，order越大，优先级越低
     *
     * @return
     */
    @Override
    public int getOrder() {
        return 0;
    }

    ServerHttpRequestDecorator decorate(ServerWebExchange exchange, HttpHeaders headers, CachedBodyOutputMessage outputMessage) {
        return new ServerHttpRequestDecorator(exchange.getRequest()) {
            @Override
            public HttpHeaders getHeaders() {
                long contentLength = headers.getContentLength();
                HttpHeaders httpHeaders = new HttpHeaders();
                httpHeaders.putAll(headers);
                if (contentLength > 0) {
                    httpHeaders.setContentLength(contentLength);
                } else {
                    // TODO: this causes a 'HTTP/1.1 411 Length Required' // on
                    // httpbin.org
                    httpHeaders.set(HttpHeaders.TRANSFER_ENCODING, "chunked");
                }
                return httpHeaders;
            }

            @Override
            public Flux<DataBuffer> getBody() {
                return outputMessage.getBody();
            }
        };
    }

    private class BodyRewrite implements RewriteFunction<Map, Map> {
        @SuppressWarnings("unchecked")
        @Override
        public Publisher<Map> apply(ServerWebExchange t, Map u) {
            //在这里添加插入的数据
            u.put("userid", 4356);
            return Mono.just(u);
        }
    }
}