sc-gateway-10-修改请求响应体

10.sc-gateway-10-修改请求响应体

1 修改请求响应体的几种做法

1. 可以自己写一个全局过滤器，获取请求体，修改请求体。但对scg所使用的非servlet技术会比较陌生。
2. ReadBodyPredicateFactory里面缓存了request body的信息，于是在自定义router中配置了ReadBodyPredicateFactory，然后在filter中通过cachedRequestBodyObject缓存字段获取request body信息。
3. 官方推荐的做法是 ModifyRequestBody ，ModifyResponseBody

• 官方推荐的3是1的简化版本，在06中我们也知道了

25. ModifyResponseBody
26. ModifyRequestBody
    可以修改响应体和请求体，那具体该怎么做呢？

2 修改请求体步骤

1. 在代码配置路由的时候，调用filters方法，该方法的入参是个lambda表达式
2. 此lambda表达式固定调用modifyResponseBody方法，咱们只要定义好modifyResponseBody方法的三个入参即可
3. modifyRequestBody方法的第一个入参是输入类型,第二个入参是返回类型
4. 第三个是RewriteFunction接口的实现

我们要写的就是RewriteFunction接口的实现

1. 接口实现

   package com.bolingcavalry.changebody.function;
   
   import com.fasterxml.jackson.databind.ObjectMapper;
   import lombok.extern.slf4j.Slf4j;
   import org.reactivestreams.Publisher;
   import org.springframework.cloud.gateway.filter.factory.rewrite.RewriteFunction;
   import org.springframework.web.server.ServerWebExchange;
   import reactor.core.publisher.Mono;
   import java.util.Map;
   
   
   @Slf4j
   public class RequestBodyRewrite implements RewriteFunction<String, String> {
   
       private ObjectMapper objectMapper;
   
       public RequestBodyRewrite(ObjectMapper objectMapper) {
           this.objectMapper = objectMapper;
       }
   
       /**
        * 根据用户ID获取用户名称的方法，可以按实际情况来内部实现，例如查库或缓存，或者远程调用
        * @param userId
        * @return
        */
       private  String mockUserName(int userId) {
           return "user-" + userId;
       }
   
       @Override
       public Publisher<String> apply(ServerWebExchange exchange, String body) {
           try {
               Map<String, Object> map = objectMapper.readValue(body, Map.class);
   
               // 取得id
               int userId = (Integer)map.get("user-id");
   
               // 得到nanme后写入map
               map.put("user-name", mockUserName(userId));
   
               // 添加一个key/value
               map.put("gateway-request-tag", userId + "-" + System.currentTimeMillis());
   
               return Mono.just(objectMapper.writeValueAsString(map));
           } catch (Exception ex) {
               log.error("1. json process fail", ex);
               // json操作出现异常时的处理
               return Mono.error(new Exception("1. json process fail", ex));
           }
       }
   }

2. 配置类

   package com.bolingcavalry.changebody.config;
   
   import com.bolingcavalry.changebody.function.RequestBodyRewrite;
   import com.bolingcavalry.changebody.function.ResponseBodyRewrite;
   import com.fasterxml.jackson.databind.ObjectMapper;
   import org.springframework.cloud.gateway.route.RouteLocator;
   import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
   import org.springframework.context.annotation.Bean;
   import org.springframework.context.annotation.Configuration;
   import org.springframework.http.MediaType;
   import reactor.core.publisher.Mono;
   
   @Configuration
   public class FilterConfig {
       @Bean
       public RouteLocator routes(RouteLocatorBuilder builder, ObjectMapper objectMapper) {
           return builder
                   .routes()
                   .route("path_route_change",
                           r -> r.path("/change")
                                   .filters(f -> f
                                           .modifyRequestBody(String.class,String.class,new RequestBodyRewrite(objectMapper))
                                           )
                           .uri("http://127.0.0.1:8082"))
                   .build();
       }
   }
   

3.修改响应体也是同样的套路

接口

package com.bolingcavalry.changebody.function;

import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.extern.slf4j.Slf4j;
import org.reactivestreams.Publisher;
import org.springframework.cloud.gateway.filter.factory.rewrite.RewriteFunction;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;
import java.util.Map;

@Slf4j
public class ResponseBodyRewrite implements RewriteFunction<String, String> {

    private ObjectMapper objectMapper;

    public ResponseBodyRewrite(ObjectMapper objectMapper) {
        this.objectMapper = objectMapper;
    }

    @Override
    public Publisher<String> apply(ServerWebExchange exchange, String body) {
        try {
            Map<String, Object> map = objectMapper.readValue(body, Map.class);

            // 取得id
            int userId = (Integer)map.get("user-id");

            // 添加一个key/value
            map.put("gateway-response-tag", userId + "-" + System.currentTimeMillis());

            return Mono.just(objectMapper.writeValueAsString(map));
        } catch (Exception ex) {
            log.error("2. json process fail", ex);
            return Mono.error(new Exception("2. json process fail", ex));
        }
    }
}

2. 配置类

   package com.bolingcavalry.changebody.config;
   
   import com.bolingcavalry.changebody.function.RequestBodyRewrite;
   import com.bolingcavalry.changebody.function.ResponseBodyRewrite;
   import com.fasterxml.jackson.databind.ObjectMapper;
   import org.springframework.cloud.gateway.route.RouteLocator;
   import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
   import org.springframework.context.annotation.Bean;
   import org.springframework.context.annotation.Configuration;
   import org.springframework.http.MediaType;
   import reactor.core.publisher.Mono;
   
   @Configuration
   public class FilterConfig {
   
       @Bean
       public RouteLocator routes(RouteLocatorBuilder builder, ObjectMapper objectMapper) {
           return builder
                   .routes()
                   .route("path_route_change",
                           r -> r.path("/change")
                                   .filters(f -> f
                                           .modifyRequestBody(String.class,String.class,new RequestBodyRewrite(objectMapper))
                                           .modifyResponseBody(String.class, String.class, new ResponseBodyRewrite(objectMapper))
                                           )
                           .uri("http://127.0.0.1:8082"))
                   .build();
       }
   }

4. 异常处理初探

1. 修改请求或者响应body的过程中，如果发现问题需要提前返回错误（例如必要的字段不存在），代码该怎么写？

2. 我们修改请求body的代码集中在RequestBodyRewrite.java，增加下图内容
   

3. 想告诉客户端具体的错误，但实际上客户端收到的是被Gateway框架处理后的内容

对于异常的探究接下来一篇文章会接着写