Spring Cloud Gateway 自定义 ReadBodyPredicateFactory 实现动态路由

梦里梦外; 2022-11-30 15:50 420阅读 0赞

在互网企业当中网关的重要性我就不再赘述了，相信大家都比较清楚。我们公司网关采用的是 Spring Cloud Gateway。并且是通过自定义 RouteLocator 来实现动态路由的。路由规则是请求参数里面的 `bizType`，比如接收 JSON 格式体的请求对象并且业务方请求的是创建支付订单接口，下面就是业务方需要传递的参数：

{
    	"bizType" : "createOrder",
    	.... 其它业务参数 
    }

下面就是读取 requestBody 里面的主动参数，然后解析请求对象里面的 `bizType`，来决定它的路由地址：  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTI0MTA3MzM_size_16_color_FFFFFF_t_70_pic_center][]

由于历史原因，网关不仅需要 `application/json` 这种 Json 格式 MediaType 的请求对象，还需要支持 MediaType 为`application/x-www-form-urlencoded` 这种请求。而网关之前的处理方式比较粗暴，当有请求来临的时候因为有可能是 `application/x-www-form-urlencoded`所以直接 URLDecoder ：

> 将请求中特殊字符转义

public static String requestDecode(String requestBody){
           try {
               return URLDecoder.decode(convertStringForAdd(requestBody), "UTF-8");
           } catch (UnsupportedEncodingException e) {
               log.error("requestBody decode error: {}", e);
           }
           return requestBody;
       }

这种处理方式导致的问题就是如果 JSON 请求参数里面带有 % 就会报以下错误：

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTI0MTA3MzM_size_16_color_FFFFFF_t_70_pic_center 1]  
针对这种问题其实有两种处理方式：

*  把对象进行转换成 JSON，如果转换成功就OK，否则就先 UrlEncode，然后再用 & 分离 Key/value。
 *  还有一种方式就是在进行读取 requestBody 之前获取到它的 MediaType

上面两种方式当然就第二种方式更加优雅。下面我们来想一想如何在读取 requestBody 之前获取到 Http 请求的 MediaType 的。

当我们在路由调用 readBody 的时候其实就是调用下面的方法：

> org.springframework.cloud.gateway.route.builder.PredicateSpec\#readBody

public <T> BooleanSpec readBody(Class<T> inClass, Predicate<T> predicate) {
    	return asyncPredicate(getBean(ReadBodyPredicateFactory.class)
    			.applyAsync(c -> c.setPredicate(inClass, predicate)));
    }

Spring Cloud 中 ReadBodyPredicateFactory 的实现方式如下：

public class ReadBodyPredicateFactory
    		extends AbstractRoutePredicateFactory<ReadBodyPredicateFactory.Config> {
    	...
    	
    	@Override
    	@SuppressWarnings("unchecked")
    	public AsyncPredicate<ServerWebExchange> applyAsync(Config config) {
    		return exchange -> {
    			Class inClass = config.getInClass();
    
    			Object cachedBody = exchange.getAttribute(CACHE_REQUEST_BODY_OBJECT_KEY);
    			Mono<?> modifiedBody;
    			// We can only read the body from the request once, once that happens if we
    			// try to read the body again an exception will be thrown. The below if/else
    			// caches the body object as a request attribute in the ServerWebExchange
    			// so if this filter is run more than once (due to more than one route
    			// using it) we do not try to read the request body multiple times
    			if (cachedBody != null) {
    				try {
    					boolean test = config.predicate.test(cachedBody);
    					exchange.getAttributes().put(TEST_ATTRIBUTE, test);
    					return Mono.just(test);
    				}
    				catch (ClassCastException e) {
    					if (log.isDebugEnabled()) {
    						log.debug("Predicate test failed because class in predicate "
    								+ "does not match the cached body object", e);
    					}
    				}
    				return Mono.just(false);
    			}
    			else {
    				return ServerWebExchangeUtils.cacheRequestBodyAndRequest(exchange,
    						(serverHttpRequest) -> ServerRequest
    								.create(exchange.mutate().request(serverHttpRequest)
    										.build(), messageReaders)
    								.bodyToMono(inClass)
    								.doOnNext(objectValue -> exchange.getAttributes()
    										.put(CACHE_REQUEST_BODY_OBJECT_KEY, objectValue))
    								.map(objectValue -> config.getPredicate()
    										.test(objectValue)));
    			}
    		};
    	}
    	...
    }

我们可以看到这里使用了对象 `ServerWebExchange`，而这个对象就是 Spring webflux 定义的 Http 请求对象。上面的代码逻辑是判断 `exchange` 中的属性中是否包含属性为 `cachedRequestBodyObject` 的 `requestBody` 对象，如果不包含就解析并添加`cachedRequestBodyObject` 到 `exchange`。在这里可以看到我们对 `ReadBodyPredicateFactory` 对象并不可以扩展，所以唯一的方式就是继承这个类，因为在读取 MediaType 的时候参数只有 `requestBody:String`，所以我们只有通过 ThreadLocal 来进行参数传递。在真正 `PredicateSpec#readBody`获取到 MediaType，就可以很好的解析 `requestBody`。下面就是具体的代码实现：

## 1、GatewayContext.java ##

GatewayContext 定义网关上下文，保存 MediaType 用于 readBody 时解析。

> GatewayContext.java

@Getter
    @Setter
    public class GatewayContext {
    
    	private MediaType mediaType;
    
    }

## 2、GatewayContextHolder.java ##

GatewayContextHolder 通过 ThreadLocal 传递 GatewayContext ，在请求对象解析时使用。

> GatewayContextHolder.java

public class GatewayContextHolder { 
    
        private static Logger logger = LoggerFactory.getLogger(GatewayContextHolder.class);
    
        private static ThreadLocal<GatewayContext> tl = new ThreadLocal<>();
    
        public static GatewayContext get() { 
            if (tl.get() == null) { 
                logger.error("gateway context not exist");
                throw new RuntimeException("gateway context is null");
            }
            return tl.get();
        }
    
        public static void set(GatewayContext sc) { 
            if (tl.get() != null) { 
                logger.error("gateway context not null");
                tl.remove();
            }
            tl.set(sc);
        }
    
        public static void cleanUp() { 
            try { 
                if (tl.get() != null) { 
                    tl.remove();
                }
            } catch (Exception e) { 
                logger.error(e.getMessage(), e);
            }
        }
    
    }

## 3、CustomReadBodyPredicateFactory.java ##

CustomReadBodyPredicateFactory 继承 ReadBodyPredicateFactory ，在原有解析 requestBody 的情况下，添加获取 MediaType 的逻辑。

> CustomReadBodyPredicateFactory.java

public class CustomReadBodyPredicateFactory extends ReadBodyPredicateFactory { 
    
        protected static final Log log = LogFactory.getLog(CustomReadBodyPredicateFactory.class);
    
        private static final String TEST_ATTRIBUTE = "read_body_predicate_test_attribute";
    
        private static final String CACHE_REQUEST_BODY_OBJECT_KEY = "cachedRequestBodyObject";
    
        private static final List<HttpMessageReader<?>> messageReaders = HandlerStrategies
                .withDefaults().messageReaders();
    
        public CustomReadBodyPredicateFactory() { 
            super();
        }
    
        @Override
        public AsyncPredicate<ServerWebExchange> applyAsync(ReadBodyPredicateFactory.Config config) { 
            return exchange -> { 
                Class inClass = config.getInClass();
    
                Object cachedBody = exchange.getAttribute(CACHE_REQUEST_BODY_OBJECT_KEY);
                
                // 获取 MediaType
                MediaType mediaType = exchange.getRequest().getHeaders().getContentType();
                GatewayContext context = new GatewayContext();
                context.setMediaType(mediaType);
                GatewayContextHolder.set(context);
                // We can only read the body from the request once, once that happens if we
                // try to read the body again an exception will be thrown. The below if/else
                // caches the body object as a request attribute in the ServerWebExchange
                // so if this filter is run more than once (due to more than one route
                // using it) we do not try to read the request body multiple times
                if (cachedBody != null) { 
                    try { 
                        boolean test = config.getPredicate().test(cachedBody);
                        exchange.getAttributes().put(TEST_ATTRIBUTE, test);
                        return Mono.just(test);
                    }
                    catch (ClassCastException e) { 
                        if (log.isDebugEnabled()) { 
                            log.debug("Predicate test failed because class in predicate "
                                    + "does not match the cached body object", e);
                        }
                    }
                    return Mono.just(false);
                }
                else { 
                    return ServerWebExchangeUtils.cacheRequestBodyAndRequest(exchange,
                            (serverHttpRequest) -> ServerRequest
                                    .create(exchange.mutate().request(serverHttpRequest)
                                            .build(), messageReaders)
                                    .bodyToMono(inClass)
                                    .doOnNext(objectValue -> exchange.getAttributes()
                                            .put(CACHE_REQUEST_BODY_OBJECT_KEY, objectValue))
                                    .map(objectValue -> config.getPredicate()
                                            .test(objectValue)));
                }
            };
        }
    
    }

## 4、GatewayBeanFactoryPostProcessor.java ##

通过 Spring framework 的 BeanDefinitionRegistryPostProcessor 扩展在实例化对象之前，把 readBody 的原有操作类`ReadBodyPredicateFactory` 删除，替换成我们自定义类 `CustomReadBodyPredicateFactory`。

> GatewayBeanFactoryPostProcessor.java

@Component
    public class GatewayBeanFactoryPostProcessor implements BeanDefinitionRegistryPostProcessor { 
    
        @Override
        public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { 
            // do nothing
        }
    
        @Override
        public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { 
            registry.removeBeanDefinition("readBodyPredicateFactory");
            BeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(CustomReadBodyPredicateFactory.class)
                    .setScope(BeanDefinition.SCOPE_SINGLETON)
                    .setRole(BeanDefinition.ROLE_SUPPORT)
                    .getBeanDefinition();
            registry.registerBeanDefinition("readBodyPredicateFactory", beanDefinition);
        }
    
    }

下面就是修改后的自定义路由规则。

public RouteLocatorBuilder.Builder route(RouteLocatorBuilder.Builder builder) {
        return builder.route(r -> r.readBody(String.class, requestBody -> {
            MediaType mediaType = GatewayContextHolder.get().getMediaType();
            // 通过 mediaType 解析 requestBody 然后从解析后的对象获取路由规则
            ...
        );
    }

后面就不会报之前的异常了。

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