详解SpringCloud Finchley Gateway 统一异常处理

SpringCloud Finchley Gateway 统一异常处理

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1 . 问题：使用SpringCloud Gateway时，会出现各种系统级异常，默认返回HTML.

2 . Finchley版本的Gateway，使用WebFlux形式作为底层框架，而不是Servlet容器，所以常规的异常处理无法使用

翻阅源码，默认是使用DefaultErrorWebExceptionHandler这个类实现结构如下：

可以实现参考DefaultErrorWebExceptionHandler和AbstractErrorWebExceptionHandler自定义实现ErrorWebExceptionHandler，然后，注册为Bean到Spring容器中即可（Bean Name:"errorWebExceptionHandler"）

具体实现代码如下：

package pro.chenggang.example.spring.cloud.gateway.support;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.web.reactive.error.ErrorWebExceptionHandler;
import org.springframework.cloud.gateway.support.NotFoundException;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.codec.HttpMessageReader;
import org.springframework.http.codec.HttpMessageWriter;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.util.Assert;
import org.springframework.web.reactive.function.BodyInserters;
import org.springframework.web.reactive.function.server.RequestPredicates;
import org.springframework.web.reactive.function.server.RouterFunctions;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.reactive.function.server.ServerResponse;
import org.springframework.web.reactive.result.view.ViewResolver;
import org.springframework.web.server.ResponseStatusException;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;

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

/**
 * @classDesc: 统一异常处理,参考{@link org.springframework.web.server.AbstractErrorWebExceptionHandler}修改
 * @author: chenggang
 * @createTime: 2018/10/30
 */
public class JsonExceptionHandler implements ErrorWebExceptionHandler {

 private static final Logger log = LoggerFactory.getLogger(JsonExceptionHandler.class);

 /**
  * MessageReader
  */
 private List<HttpMessageReader<?>> messageReaders = Collections.emptyList();

 /**
  * MessageWriter
  */
 private List<HttpMessageWriter<?>> messageWriters = Collections.emptyList();

 /**
  * ViewResolvers
  */
 private List<ViewResolver> viewResolvers = Collections.emptyList();

 /**
  * 存储处理异常后的信息
  */
 private ThreadLocal<Map<String,Object>> exceptionHandlerResult = new ThreadLocal<>();

 /**
  * 参考AbstractErrorWebExceptionHandler
  * @param messageReaders
  */
 public void setMessageReaders(List<HttpMessageReader<?>> messageReaders) {
  Assert.notNull(messageReaders, "'messageReaders' must not be null");
  this.messageReaders = messageReaders;
 }

 /**
  * 参考AbstractErrorWebExceptionHandler
  * @param viewResolvers
  */
 public void setViewResolvers(List<ViewResolver> viewResolvers) {
  this.viewResolvers = viewResolvers;
 }

 /**
  * 参考AbstractErrorWebExceptionHandler
  * @param messageWriters
  */
 public void setMessageWriters(List<HttpMessageWriter<?>> messageWriters) {
  Assert.notNull(messageWriters, "'messageWriters' must not be null");
  this.messageWriters = messageWriters;
 }

 @Override
 public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
  /**
   * 按照异常类型进行处理
   */
  HttpStatus httpStatus;
  String body;
  if (ex instanceof NotFoundException) {
   httpStatus = HttpStatus.NOT_FOUND;
   body = "Service Not Found";
  }else if(ex instanceof ResponseStatusException) {
   ResponseStatusException responseStatusException = (ResponseStatusException) ex;
   httpStatus = responseStatusException.getStatus();
   body = responseStatusException.getMessage();
  }else{
   httpStatus = HttpStatus.INTERNAL_SERVER_ERROR;
   body ="Internal Server Error";
  }
  /**
   * 封装响应体,此body可修改为自己的jsonBody
   */
  Map<String,Object> result = new HashMap<>(2,1);
  result.put("httpStatus",httpStatus);
  result.put("body",body);
  /**
   * 错误记录
   */
  ServerHttpRequest request = exchange.getRequest();
  log.error("[全局异常处理]异常请求路径:{},记录异常信息:{}",request.getPath(),ex.getMessage());
  /**
   * 参考AbstractErrorWebExceptionHandler
   */
  if (exchange.getResponse().isCommitted()) {
   return Mono.error(ex);
  }
  exceptionHandlerResult.set(result);
  ServerRequest newRequest = ServerRequest.create(exchange, this.messageReaders);
  return RouterFunctions.route(RequestPredicates.all(), this::renderErrorResponse).route(newRequest)
    .switchIfEmpty(Mono.error(ex))
    .flatMap((handler) -> handler.handle(newRequest))
    .flatMap((response) -> write(exchange, response));

 }

 /**
  * 参考DefaultErrorWebExceptionHandler
  * @param request
  * @return
  */
 protected Mono<ServerResponse> renderErrorResponse(ServerRequest request) {
  Map<String,Object> result = exceptionHandlerResult.get();
  return ServerResponse.status((HttpStatus) result.get("httpStatus"))
    .contentType(MediaType.APPLICATION_JSON_UTF8)
    .body(BodyInserters.fromObject(result.get("body")));
 }

 /**
  * 参考AbstractErrorWebExceptionHandler
  * @param exchange
  * @param response
  * @return
  */
 private Mono<? extends Void> write(ServerWebExchange exchange,
          ServerResponse response) {
  exchange.getResponse().getHeaders()
    .setContentType(response.headers().getContentType());
  return response.writeTo(exchange, new ResponseContext());
 }

 /**
  * 参考AbstractErrorWebExceptionHandler
  */
 private class ResponseContext implements ServerResponse.Context {

  @Override
  public List<HttpMessageWriter<?>> messageWriters() {
   return JsonExceptionHandler.this.messageWriters;
  }

  @Override
  public List<ViewResolver> viewResolvers() {
   return JsonExceptionHandler.this.viewResolvers;
  }

 }
}

注册Bean

 /**
  * 自定义异常处理[@@]注册Bean时依赖的Bean，会从容器中直接获取，所以直接注入即可
  * @param viewResolversProvider
  * @param serverCodecConfigurer
  * @return
  */
 @Primary
 @Bean
 @Order(Ordered.HIGHEST_PRECEDENCE)
 public ErrorWebExceptionHandler errorWebExceptionHandler(ObjectProvider<List<ViewResolver>> viewResolversProvider,
                ServerCodecConfigurer serverCodecConfigurer) {

  JsonExceptionHandler jsonExceptionHandler = new JsonExceptionHandler();
  jsonExceptionHandler.setViewResolvers(viewResolversProvider.getIfAvailable(Collections::emptyList));
  jsonExceptionHandler.setMessageWriters(serverCodecConfigurer.getWriters());
  jsonExceptionHandler.setMessageReaders(serverCodecConfigurer.getReaders());
  log.debug("Init Json Exception Handler Instead Default ErrorWebExceptionHandler Success");
  return jsonExceptionHandler;
 }

[@@]注意事项：

1 .上面为示例代码，其中牵扯到策略工厂和响应封装的类，可以自定义实现

2 .注册Bean时依赖的Bean，都会从Spring容器中获取到

3 .参考此方法思路，可实现统一异常处理，统一封装错误信息。

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