最近因为上链路追踪后发现如果在服务层将异常拦截掉，在链路追踪界面上就不会显示异常链路信息，除了服务异常意外，系统的异常不会触发链路error，所以对服务层做了个变更，将所有未处理异常直接捕获后统一封装完抛出，这个时候就需要在网关层统一处理那么网关需要对响应数据进行拦截如果是 9999错误码，则封装后返回，如果是其它响应码或者其它数据直接返回。

起初写法测试后发现数据过长时被截断。

 return super.writeWith(fluxBody.map(dataBuffer -> {
	

	byte[] content = new byte[dataBuffer.readableByteCount()];
	
	dataBuffer.read(content);
	// 释放掉内存
	DataBufferUtils.release(dataBuffer);
	String str = new String(content, Charset.forName("UTF-8"));

	originalResponse.getHeaders().setContentLength(str.getBytes().length);
	log.error("gateway catch service exception error:"+ str);
	
	JsonResult result = new JsonResult();
	result.setCode(ErrorCode.SYS_EXCEPTION.getCode());
	result.setMessage(ErrorCode.SYS_EXCEPTION.getMsg());
	
	return bufferFactory.wrap(str.getBytes());
}));                   

查询api后发现存在一个DataBufferFactory可以一次性join完所有数据后拼接就不会产生截断问题。

DataBufferFactory dataBufferFactory = new DefaultDataBufferFactory();

于是修改代码如下

package com.server.gateway.filters;

import java.nio.charset.Charset;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.http.protocol.HTTP;
import org.reactivestreams.Publisher;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.core.Ordered;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.core.io.buffer.DefaultDataBufferFactory;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.http.server.reactive.ServerHttpResponseDecorator;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;

import com.framework.common.enums.ErrorCode;
import com.framework.common.web.JsonResult;

import lombok.extern.slf4j.Slf4j;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
 
@Component
@Slf4j
public class WrapperResponseGlobalFilter implements GlobalFilter, Ordered{

	@Override
	public int getOrder() {
		// -1 is response write filter, must be called before that
		return -2;
	}

	@Override
	public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
		ServerHttpResponse originalResponse = exchange.getResponse();
		DataBufferFactory bufferFactory = originalResponse.bufferFactory();
		ServerHttpResponseDecorator decoratedResponse = new ServerHttpResponseDecorator(originalResponse) {
			@Override
			public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
				AtomicReference<String> bodyRef = new AtomicReference<>();
				if (body instanceof Flux) {
					Flux<? extends DataBuffer> fluxBody = (Flux<? extends DataBuffer>) body;
					
					return super.writeWith(fluxBody.buffer().map(dataBuffers -> {
						
						DataBufferFactory dataBufferFactory = new DefaultDataBufferFactory();
						DataBuffer join = dataBufferFactory.join(dataBuffers);
						
						byte[] content = new byte[join.readableByteCount()];
						
						join.read(content);
						// 释放掉内存
						DataBufferUtils.release(join);
						String str = new String(content, Charset.forName("UTF-8"));
		
						originalResponse.getHeaders().setContentLength(str.getBytes().length);
						log.error("gateway catch service exception error:"+ str);
						
						JsonResult result = new JsonResult();
				        result.setCode(ErrorCode.SYS_EXCEPTION.getCode());
				        result.setMessage(ErrorCode.SYS_EXCEPTION.getMsg());
				        
						return bufferFactory.wrap(str.getBytes());
					}));
					
				}
				// if body is not a flux. never got there.
	                return super.writeWith(body);
	            }
	        };
	        // replace response with decorator
	        return chain.filter(exchange.mutate().response(decoratedResponse).build());
	    }

}

经过如上修改后链路追踪可以实现哪个服务出错就立马出现链路异常马上可以定位到哪个服务出现了未处理异常