OpenFeign指定url方式调用的方式详解

目录

• 引言
• FeignClient注解配置URL
• 实现RequestInterceptor接口？
• 自定义FeignblockingLoadBalancerClient
• BeanFactoryPostProcessor修改bean的url属性

引言

OpenFeign一般是结合注册中心一起使用的，也就是可以通过提供服务的名称而不是url来完成对目标服务的访问。但是出于本地调试的需要，或者考虑到一些简单的服务可能并不需要依赖注册中心，所以本篇我们就讲解一下OpenFeign直接通过目标服务的url进行调用的方式。

FeignClient注解配置URL

在@FeignClient注解的url属性中写一个固定的调用地址：

package com.morris.user.client;

import com.morris.user.entity.Order;
import org.springframework.cloud.openfeign.Feihttp://www.devze.comgnClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;

import Java.util.List;

/**
 * 指定url属性
 */
@FeignClient(value = "order-service", url = "http://localhost:8020", path = "/order", contextId = "orderUrl")
public interface OrderUrlClient {

    @GetMapping("findOrderByUserId")
    List<Order> findOrderByUserId(@RequestParam("userId") Long userId);

}

或者写一个可配置的地址，这样可以在配置文件里指定，可以根据不同的环境配置不同的URL，这种方式在创建feign客户端的时候就需要规划好：

@FeignClient(value = "order-service", url = "${customer.url}", path = "/order", contextId = "orderUrl")
public interface OrderUrlClient {

    @GetMapping("findOrderByUserId")
    List<Order> findOrderByUserId(@RequestParam("userId") Long userId);

}

实现RequestInterceptor接口？

实现RequestInterceptor接口在发起HTTP请求之前将注册中心调用方式修改为url方式调用。

在@FeignClient注解中指定configuration属性，这里并没有指定url属性：

package com.morris.user.client;

import com.morris.user.config.FeignUrlConfig;
import com.morris.user.entity.Order;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;

import java.util.List;

@FeignClient(value = "order-service", path = "/order", contextId = "orderUrl2", configuration = FeignUrlConfig.class)
public interface OrderUrlClient2 {

    @GetMapping("findOrderByUserId")
    List<Order> findOrderByUserId(@RequestParam("userId") Long userId);

}

FeignUrlConfig类中注入了一个RequestInterceptor类来拦截OrderUrlClient2中的请求，这里只会拦截OrderUrlClient2类中的请求：

package com.morris.user.config;

import feign.Logger;
import feign.Request;
import org.springframework.context.annotation.Bean;

public class FeignUrlConfig {

    @Bean
    public Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }

    @Bean
    public FeignUrlRequestInterceptor feignTraceRequestInterceptor() {
        return new FeignUrlRequestInterceptor();
    }
}

FeignUrlRequestInterceptor类中将请求的地址修改为具体的url，而不是之前的serviceId。

package com.morris.user.config;

import feign.RequestInterceptor;
import feign.RequestTemplate;

public class FeignUrlRequestInterceptor implements RequestInterceptor {
    @Override
    public void apply(RequestTemplate template) {
        System.out.println("old: " + template.url()); // /findOrderByUserId?userId=1
        template.target("http://localhost:8020/order");
        System.out.println("new: " + template.url()); // http://localhost:8020/order/findOrderByUserId?userId=1
    }
}

发起请求后抛出如下异XmnrqIzQ常：

java.lang.RuntimeException: Load balancer does not contain an instance for the service localhost
	at com.morris.user.config.FeignErrorDecoder.decode(FeignErrorDecoder.java:24) ~[classes/:na]

可以发现Feign还是会去注册中心寻找服务，这是为什么呢？

通过阅读FeignClientFactoryBean源码发现：

<T> T getTarget() {
  FeignContext context = applicationContext.getBean(FeignContext.class);
  Feign.Builder builder = feign(context);

  if (!StringUtils.hasText(url)) {
    if (!name.startsWith("http")) {
      url = "http://" + name;
    }
    else {
      url = name;
    }
    url += cleanPath();
    // url不存在
    return (T) loadBalance(builder, context,
        new HardCodedTarget<>(type, name, url));
  }
  if (StringUtils.hasText(url) && !url.startsWith("http")) {
    url = "http://" + url;
  }
  String url = this.url + cleanPath();
  Client client = getOptional(context, Client.class);
  if (client != null) {
    if (client instanceof LoadBalancerFeignClient) {
      // not load balancing because we have a url,
      // but ribbon is on the classpath, so unwrap
      client = ((LoadBalancerFeignClient) client).getDelegate();
    }
    if (client instanceof FeignBlockingLoadBalancerClient) {
      // not load balancing because we have a url,
      // but Spring Cloud LoadBalancer is on the classpath, so unwrap
      // url不存在
      client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
    }
    builder.client(client);
  }
  Targeter targeter = get(context, Targeter.class);
  return (T) targeter.target(this, builder, context,
      new HardCodedTarget<>(type, name, url));
}

当@FeignClient中的url属性不存在时，底层的Client使用的是FeignBlockingLoadBalancerClient，这个Client会根据serviceId去注册中心查询服务，并进行负载均衡，虽然FeignUrlRequestInterceptor修改了url地址，但是Client会根据修改后的serviceId，也就是FeignUrlRequestInterceptor只能修改serviceId，不能改变调用方式。

当@FeignClient中的url属性存在时，底层的Client使用的是FeignBlockingLoadBalancerClient.getDelegate()，也就是ApacheHttpClient，这个client就不会去注册中心查询服务了，直接发起接口的调用。

自定义FeignBlockingLoadBalancerClient

自定义一个FeignBlockingLoadBalancerClient来改写url：

@FeignClient注解中指定configuration属性：

package com.morris.user.client;

import com.morris.user.config.OrderUrlClient3Config;
import com.morris.user.entity.Order;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;

import java.util.List;

@FeignClient(value = "order-service", path = "/order", contextId = "orderUrl3", configuration = OrderUrlClient3Config.class)
public interface OrderUrlClient3 {

    @GetMapping("findOrderByUserId")
    List<Order> findOrderByUserId(@RequestParam("userId") Long userId);

}

OrderUrlClient3Config类中注入了一个OrderUrlClient3Client类来拦截OrderUrlClient3中的请求，这里只会拦截OrderUrlClient3类中的请求，如果要实现全局的拦截，可以在OrderUrlClient3Config类上加@Configuration注解：

package com.morris.user.config;

import feign.Client;
import feign.Logger;
import org.springframework.context.annotation.Bean;

public class OrderUrlClient3Config {

    @Bean
    public Logger.Level feignLoggerLevel() {
        return Logger.Level.FULL;
    }

    @Bean
    public OrderUrlClient3Client orderUrlClient3Client() {
        return new OrderUrlClient3Client(new Client.Default(null, null), null);
    }
}

OrderUrlClient3Client类继承了FeignBlockingLoadBalancerClient，重写了execute()方法：

package com.morris.user.config;

import feign.Client;
import feign.Request;
import feign.Response;
import org.springframework.cloud.loadbalancer.blocking.client.BlockingLoadBalancerClient;
import org.springframework.cloud.openfeign.loadbalancer.FeignBlockingLoadBalancerClient;
import org.springframework.web.util.UriComponentsBuilder;

import java.io.IOException;
import java.net.URI;

public class OrderUrlClient3Client extends FeignBlockingLoadBalancerClient {

    private final Client delegate;

    public OrderUrlClient3Client(Client delegate, BlockingLoadBalancerClient loadBalancerClient) {
        super(delegate, loadBalancerClient);
        this.delegate = delegate;
    }

    @Override
    public Response execute(Request request, Request.Options options) throws IOException {
        final URI originalUri = URI.create(request.url());
        // 修改url
        URI newUri = UriComponentsBuilder.fromUri(originalUri).host("localhost").port(8020)
                .build().toUri();
        Request newRequest = Request.create(request.httpMethod(), newUri.toString(),
                request.headers(), request.body(), request.charset(),
                request.requestTemplate());
        return delegate.execute(newRequest, options);
    }
}

BeanFactoryPostProcessor修改bean的url属性

这里可以使用Spring的扩展，给@FeignClient对应的Bean对象FeignClientFactoryBean加上url属性，这样在容器启动过程中就加上了url属性，feign创建的client为ApacheHttpClient，而不是FeignBlockingLoadBalancerClient

package com.morris.user.config;

import org.apache.commons.lang.StringUtils;
import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValue;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.fact编程客栈ory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.stereotype.Component;

import java.util.Objects;

@Component
public class OrderUrl4BeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        if(!(beanFactory instanceof DefaultListableBeanFactory)) {
            return;
        }

        DefaultListableBeanFactory defaultListableBeanFactory = (DefaultListableBeanFactory) beanFactory;

        String[] bdNames = defaultListableBeanFactory.getBeanDefinitionNames();
       javascript for (String bdName : bdNames) {
            BeanDefinition beanDefinition = defaultListableBeanFactory.getBeanDefinition(bdName);

            if (!Objects.equals("org.springframework.cloud.openfeign.FeignClientFactoryBean", beanDefinition.getBeanClassName())) {
                continue;
            }

            if(!bdName.eqjavascriptuals("com.morris.user.client.OrderUrlClient4")) {
                // 这里只拦截OrderUrlClient4，放开就是全局
                continue;
            }

            PropertyValue urlPv = beanDefinition.getPropertyValues().getPropertyValue("url");
            if (Objects.nonNull(urlPv)) {
                Object value = urlPv.getValue();
                if (value instanceof String) {
                    String url = (String) value;
                    if (StringUtils.isNotBlank(url)) {
                        // 已指定url跳过
                        continue;
                    }
                }
            }

            // 相当于给@FeignClinet注解加上url属性
            beanDefinition.getPropertyValues().addPropertyValue("url", "http://localhost:8020");
        }
    }
}

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