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.FeignClient;
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 {@Beanpublic Logger.Level feignLoggerLevel() {return Logger.Level.FULL;}@Beanpublic 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 {@Overridepublic void apply(RequestTemplate template) {System.out.println("old: " + template.url()); // /findOrderByUserId?userId=1template.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常：
java.lang.RuntimeException: Load balancer does not contain an instance for the service localhostat 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 unwrapclient = ((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 {@Beanpublic Logger.Level feignLoggerLevel() {return Logger.Level.FULL;}@Beanpublic 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;}@Overridepublic Response execute(Request request, Request.Options options) throws IOException {final URI originalUri = URI.create(request.url());// 修改urlURI 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.factory.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 {@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {if(!(beanFactory instanceof DefaultListableBeanFactory)) {return;}DefaultListableBeanFactory defaultListableBeanFactory = (DefaultListableBeanFactory) beanFactory;String[] bdNames = defaultListableBeanFactory.getBeanDefinitionNames();for (String bdName : bdNames) {BeanDefinition beanDefinition = defaultListableBeanFactory.getBeanDefinition(bdName);if (!Objects.equals("org.springframework.cloud.openfeign.FeignClientFactoryBean", beanDefinition.getBeanClassName())) {continue;}if(!bdName.equals("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");}}
}
