背景

我们使用了springcloud gateway作为也给路由转发功能，由于历史遗留问题，不仅仅需要根据path转发，还需要根据get或者post中的参数进行转发

解决方案

这里我们使用自定义的Predicate进行转发

简介

这里简单介绍下相关术语（1）Filter（过滤器）：

和Zuul的过滤器在概念上类似，可以使用它拦截和修改请求，并且对上游的响应，进行二次处理。过滤器为org.springframework.cloud.gateway.filter.GatewayFilter类的实例。

（2）Route（路由）：

网关配置的基本组成模块，和Zuul的路由配置模块类似。一个Route模块由一个 ID，一个目标 URI，一组断言和一组过滤器定义。如果断言为真，则路由匹配，目标URI会被访问。

（3）Predicate（断言）：

这是一个 Java 8 的 Predicate，可以使用它来匹配来自 HTTP 请求的任何内容，例如 headers 或参数。断言的输入类型是一个 ServerWebExchange。

这里我们会使用自定义的断言来实现，常用的断言有如下几个：

springcloud gateway高级功能之根据参数自定义路由Predicate

详细信息可以参考下面链接：https://www.jianshu.com/p/d2c3b6851e1d?utm_source=desktop&utm_medium=timeline

GET请求转发

在常用断言中就有支持根据get参数转发，所以这里需要同时使用path以及query断言，可以根据如下配置

spring:
  cloud:
    gateway:
      routes:
        - id: blog
          uri: http://blog.yuqiyu.com
          predicates:
            - Path=/api/demo
            - Query=xxx, zzz

根据上面配置，我们限定了参数xxx必须为zzz时才会被成功转发，否则会出现404抓发失败，根据上面配置就可以根据get参数转发

POST请求转发

post参数转发，没有现成的转发断言，这里我们需要参考readbody断言来实现，下面是ReadBodyPredicateFactory 的源码

public class ReadBodyPredicateFactory extends AbstractRoutePredicateFactory<ReadBodyPredicateFactory.Config> {
    protected static final Log log = LogFactory.getLog(ReadBodyPredicateFactory.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 ReadBodyPredicateFactory() {
        super(ReadBodyPredicateFactory.Config.class);
    }

    public AsyncPredicate<ServerWebExchange> applyAsync(ReadBodyPredicateFactory.Config config) {
        return (exchange) -> {
            Class inClass = config.getInClass();
            Object cachedBody = exchange.getAttribute("cachedRequestBodyObject");
            if (cachedBody != null) {
                try {
                    boolean test = config.predicate.test(cachedBody);
                    exchange.getAttributes().put("read_body_predicate_test_attribute", test);
                    return Mono.just(test);
                } catch (ClassCastException var6) {
                    if (log.isDebugEnabled()) {
                        log.debug("Predicate test failed because class in predicate does not match the cached body object", var6);
                    }

                    return Mono.just(false);
                }
            } else {
                return ServerWebExchangeUtils.cacheRequestBodyAndRequest(exchange, (serverHttpRequest) -> {
                    return ServerRequest.create(exchange.mutate().request(serverHttpRequest).build(), messageReaders).bodyToMono(inClass).doOnNext((objectValue) -> {
                        exchange.getAttributes().put("cachedRequestBodyObject", objectValue);
                    }).map((objectValue) -> {
                        return config.getPredicate().test(objectValue);
                    });
                });
            }
        };
    }

    public Predicate<ServerWebExchange> apply(ReadBodyPredicateFactory.Config config) {
        throw new UnsupportedOperationException("ReadBodyPredicateFactory is only async.");
    }

    public static class Config {
        private Class inClass;
        private Predicate predicate;
        private Map<String, Object> hints;

        public Config() {
        }

        public Class getInClass() {
            return this.inClass;
        }

        public ReadBodyPredicateFactory.Config setInClass(Class inClass) {
            this.inClass = inClass;
            return this;
        }

        public Predicate getPredicate() {
            return this.predicate;
        }

        public ReadBodyPredicateFactory.Config setPredicate(Predicate predicate) {
            this.predicate = predicate;
            return this;
        }

        public <T> ReadBodyPredicateFactory.Config setPredicate(Class<T> inClass, Predicate<T> predicate) {
            this.setInClass(inClass);
            this.predicate = predicate;
            return this;
        }

        public Map<String, Object> getHints() {
            return this.hints;
        }

        public ReadBodyPredicateFactory.Config setHints(Map<String, Object> hints) {
            this.hints = hints;
            return this;
        }
    }
}

这个只是把post参数读入到缓存，配置如下

predicates:
        - Path=/card/api/**
        - name: ReadBodyPredicateFactory #使用ReadBodyPredicateFactory断言，将body读入缓存
          args:
            inClass: '#{T(String)}'
            predicate: '#{@bodyPredicate}' #注入实现predicate接口类

但是这个暂时不能满足要求，我们需要参考ReadBodyPredicateFactory自定义一个predicatefactory来实现我们的需求

@Component()
@Slf4j
public class MyReadBodyPredicateFactory extends AbstractRoutePredicateFactory<MyReadBodyPredicateFactory.Config> {


    private static final List<HttpMessageReader<?>> messageReaders = HandlerStrategies
            .withDefaults().messageReaders();

    public MyReadBodyPredicateFactory() {
        super(MyReadBodyPredicateFactory.Config.class);
    }

    public MyReadBodyPredicateFactory(Class<MyReadBodyPredicateFactory.Config> configClass) {
        super(configClass);
    }

    @Override
    @SuppressWarnings("unchecked")
    public AsyncPredicate<ServerWebExchange> applyAsync(MyReadBodyPredicateFactory.Config config) {
        return new AsyncPredicate<ServerWebExchange>() {
            @Override
            public Publisher<Boolean> apply(ServerWebExchange exchange) {
                Object cachedBody = exchange.getAttribute(MyFacadeConstants.CACHE_REQUEST_BODY_OBJECT_KEY);
                if (cachedBody != null) {
                    try {
                        boolean test = match(config.sceneIds, (MycRequest) cachedBody);
                        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(MycRequest.class)
                                    .doOnNext(objectValue -> exchange.getAttributes().put(MyFacadeConstants.CACHE_REQUEST_BODY_OBJECT_KEY,objectValue))
                                    .map(objectValue -> { return match(config.sceneIds, objectValue);}));
                }
            }
        };
    }

    private boolean match(String params, MycRequest mycRequest) {
        if("others".equals(params)){
            return true;
        }
        String[] paramArray = params.split(",");
        if (ArrayUtils.contains(paramArray, mycRequest.getRouteId)) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    @SuppressWarnings("unchecked")
    public Predicate<ServerWebExchange> apply(MyReadBodyPredicateFactory.Config config) {
        throw new UnsupportedOperationException(
                "MyReadBodyPredicateFactory is only async.");
    }

    public static class Config {

        private String params;

        public MyReadBodyPredicateFactory.Config setParams(params) {
            this.params = params;
            return this;
        }

        public String getParams() {
            return params;
        }
    }
}

这里我们可以根据将参数转为MyRequest，然后再进行判断是否路由，当然这里我们同样也需要使用到path断言，配置如下：

spring:
  cloud:
    gateway:
      routes:
        - id: route1
          uri: http://host1:8080
          predicates:
            - Path=/api/demo
            - name: MyReadBodyPredicateFactory 
              args:
                params: "23,22" 
        - id: route2
          uri: http://host2:8080
          predicates:
            - Path=/api/demo
            - name: RecommendReadBodyPredicateFactory 
              args:
                params: "44,56"

这样就可以根据post参数路由转发了，如下监控：

springcloud gateway高级功能之根据参数自定义路由Predicate