场景： 前端传来了一个大的字符串 发现请求不通 一番调试发现SpringGateway 默认内存缓冲区262144字节
网上查了很多种常见的解决方案无效之后 直接重写底层

网友的解决方案

方案1（无效）

直接修改缓冲区大小

spring:
  codec:
    max-in-memory-size: 1048576

方案2（无效）

方案3 无效

gateway-2.2.3以上版本修复了该bug，在GatewayAutoConfiguration中加入了配置写入，但只限ReadBodyPredicateFactory类，如自定义类型需要使用方案二。

package org.springframework.cloud.gateway.handler.predicate;
...
public class ReadBodyPredicateFactory
		extends AbstractRoutePredicateFactory<ReadBodyPredicateFactory.Config> {
...
	private final List<HttpMessageReader<?>> messageReaders;
 
	public ReadBodyPredicateFactory() {
		super(Config.class);
		this.messageReaders = HandlerStrategies.withDefaults().messageReaders();
	}
    /**
     * GatewayAutoConfiguration初始化配置写入相关配置
     */
	public ReadBodyPredicateFactory(List<HttpMessageReader<?>> messageReaders) {
		super(Config.class);
		this.messageReaders = messageReaders;
	}
...
 
}

方案4（无效）

重写ReadBodyPredicateFactory，注入ServerCodecConfigurer，使用ServerCodecConfigurer.getReaders()获取相关配置。

...
/**
 * @description: 自定义ReadBodyPredicateFactory，copy之ReadBodyPredicateFactory
 * @author: lizz
 * @date: 2020/6/8 14:22
 */
@Component
public class GwReadBodyPredicateFactory extends AbstractRoutePredicateFactory<GwReadBodyPredicateFactory.Config> {
    /**
     * 获取Spring配置，解决最大body问题
     */
    @Autowired
    ServerCodecConfigurer codecConfigurer;
 
    @Override
    @SuppressWarnings("unchecked")
    public AsyncPredicate<ServerWebExchange> applyAsync(GwReadBodyPredicateFactory.Config config) {
...
        return new AsyncPredicate<ServerWebExchange>() {
            @Override
            public Publisher<Boolean> apply(ServerWebExchange exchange) {
                    return ServerWebExchangeUtils.cacheRequestBodyAndRequest(exchange,
                            (serverHttpRequest) -> ServerRequest
                                    .create(exchange.mutate().request(serverHttpRequest)
                                            .build(), codecConfigurer.getReaders())
                                    .bodyToMono(inClass)
									.doOnNext(objectValue -> exchange.getAttributes().put(
											CACHE_REQUEST_BODY_OBJECT_KEY, objectValue))
									.map(objectValue -> config.getPredicate()
											.test(objectValue)));
...
}

方案5 有效

直接重写SpringGateway底层处理请求请求的 

org.springframework.core.codec.AbstractDataBufferDecoder类

/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.codec;

import java.util.Map;

import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.ResolvableType;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.MimeType;

/**
 * 重写SpringWebFex底层 为了解决GateWay报错：Exceeded limit on max bytes to buffer : 262144 错误
 * Abstract base class for {@code Decoder} implementations that can decode
 * a {@code DataBuffer} directly to the target element type.
 *
 * <p>Sub-classes must implement {@link #decodeDataBuffer} to provide a way to
 * transform a {@code DataBuffer} to the target data type. The default
 * {@link #decode} implementation transforms each individual data buffer while
 * {@link #decodeToMono} applies "reduce" and transforms the aggregated buffer.
 *
 * <p>Sub-classes can override {@link #decode} in order to split the input stream
 * along different boundaries (e.g. on new line characters for {@code String})
 * or always reduce to a single data buffer (e.g. {@code Resource}).
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 * @param <T> the element type
 */
@SuppressWarnings("deprecation")
public abstract class AbstractDataBufferDecoder<T> extends AbstractDecoder<T> {

	private int maxInMemorySize = 256 * 1024*10;


	protected AbstractDataBufferDecoder(MimeType... supportedMimeTypes) {
		super(supportedMimeTypes);
	}


	/**
	 * Configure a limit on the number of bytes that can be buffered whenever
	 * the input stream needs to be aggregated. This can be a result of
	 * decoding to a single {@code DataBuffer},
	 * {@link java.nio.ByteBuffer ByteBuffer}, {@code byte[]},
	 * {@link org.springframework.core.io.Resource Resource}, {@code String}, etc.
	 * It can also occur when splitting the input stream, e.g. delimited text,
	 * in which case the limit applies to data buffered between delimiters.
	 * <p>By default this is set to 256K.
	 * @param byteCount the max number of bytes to buffer, or -1 for unlimited
	 * @since 5.1.11
	 */
	public void setMaxInMemorySize(int byteCount) {
		this.maxInMemorySize = byteCount;
	}

	/**
	 * Return the {@link #setMaxInMemorySize configured} byte count limit.
	 * @since 5.1.11
	 */
	public int getMaxInMemorySize() {
		return this.maxInMemorySize;
	}


	@Override
	public Flux<T> decode(Publisher<DataBuffer> input, ResolvableType elementType,
			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

		return Flux.from(input).map(buffer -> decodeDataBuffer(buffer, elementType, mimeType, hints));
	}

	@Override
	public Mono<T> decodeToMono(Publisher<DataBuffer> input, ResolvableType elementType,
			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

		return DataBufferUtils.join(input, this.maxInMemorySize)
				.map(buffer -> decodeDataBuffer(buffer, elementType, mimeType, hints));
	}

	/**
	 * How to decode a {@code DataBuffer} to the target element type.
	 * @deprecated as of 5.2, please implement
	 * {@link #decode(DataBuffer, ResolvableType, MimeType, Map)} instead
	 */
	@Deprecated
	@Nullable
	protected T decodeDataBuffer(DataBuffer buffer, ResolvableType elementType,
			@Nullable MimeType mimeType, @Nullable Map<String, Object> hints) {

		return decode(buffer, elementType, mimeType, hints);
	}

}