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简帛阁>技术文章>No fallback instance of type class UserClientFallback found for feign client service-provider

No fallback instance of type class UserClientFallback found for feign client service-provider

坑5、  无法扫描到引入包的服务降级实现,大多数情况 我们要对feignClient接口  显式声明一个fallback 以便进行服务降级   但是如果你的feignclient 接口 不在 springboot 的启动类的子类  会无法启动 显示

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean 
with name 'com.xxx.feign.api.UserService': 
FactoryBean threw exception on object creation; 
nested exception is java.lang.IllegalStateException:
 No fallback instance of type class com.xxx.feign.api.UserServiceHystrix found for feign client MEMBER-SERVICE

也就是你feign 接口的实现类  无法被注入

 

先看一下 源码:

/*
 * Copyright 2013-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.netflix.feign;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;

/**

  • Annotation for interfaces declaring that a REST client with that interface should be

  • created (e.g. for autowiring into another component). If ribbon is available it will be

  • used to load balance the backend requests, and the load balancer can be configured

  • using a @RibbonClient with the same name (i.e. value) as the feign client.

  • @author Spencer Gibb

  • @author Venil Noronha
    */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface FeignClient {

    /**

    • The name of the service with optional protocol prefix. Synonym for {@link #name()
    • name}. A name must be specified for all clients, whether or not a url is provided.
    • Can be specified as property key, eg: ${propertyKey}.
      */
      @AliasFor(“name”)
      String value() default “”;

    /**

    • The service id with optional protocol prefix. Synonym for {@link #value() value}.
    • @deprecated use {@link #name() name} instead
      */
      @Deprecated
      String serviceId() default “”;

    /**

    • The service id with optional protocol prefix. Synonym for {@link #value() value}.
      */
      @AliasFor(“value”)
      String name() default “”;

    /**

    • Sets the @Qualifier value for the feign client.
      */
      String qualifier() default “”;

    /**

    • An absolute URL or resolvable hostname (the protocol is optional).
      */
      String url() default “”;

    /**

    • Whether 404s should be decoded instead of throwing FeignExceptions
      */
      boolean decode404() default false;

    /**

    • A custom @Configuration for the feign client. Can contain override
    • @Bean definition for the pieces that make up the client, for instance
    • {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
    • @see FeignClientsConfiguration for the defaults
      */
      Class[] configuration() default {};

    /**

    • Fallback class for the specified Feign client interface. The fallback class must
    • implement the interface annotated by this annotation and be a valid spring bean.
      */
      Class fallback() default void.class;

    /**

    • Define a fallback factory for the specified Feign client interface. The fallback
    • factory must produce instances of fallback classes that implement the interface
    • annotated by {@link FeignClient}. The fallback factory must be a valid spring
    • bean.
    • @see feign.hystrix.FallbackFactory for details.
      */
      Class fallbackFactory() default void.class;

    /**

    • Path prefix to be used by all method-level mappings. Can be used with or without
    • @RibbonClient.
      */
      String path() default “”;

    /**

    • Whether to mark the feign proxy as a primary bean. Defaults to true.
      */
      boolean primary() default true;

}

  * Fallback class for the specified Feign client interface. The fallback class must
     implement the interface annotated by this annotation and be a valid spring bean. *

fallback 上会有这样的注释    说的是  声明feign客户端接口 的降级类  而且 这个降级类必须实现 该feign 接口   并且必须是一个可用的spring bean

 如果你仅仅在这个实现类上加入spring bean 声明注解 比如 @Component   你会发现依然 无法注入 来大致猜想一下流程     熟悉springboot 的 应该清楚   springboot  启动的时候  会扫描其main类 所在包的子包进行 bean 实例化     如果不在子包 默认是扫描不到的   那么如何扫描到呢  声明扫描的路径 也就是需要在main类上使用注解@ComponentScan 注解  但是 如果 我们仅仅声明了 feign 降级实现的路径 你会发现 main类的子包无法扫描到了  所以 此处应该 

@ComponentScan(basePackages = {<!-- -->"main 所在的包","降级类所在的包"})

配置好后  我们写一个降级类:

@Component
public class UserServiceHystrix implements UserService {
    @Override
    public User get(User user) {
        System.out.println("<><><><><><><><><><> MEMBER-SERVICE 挂了<><><><><><><><><><> ");
         user.setAge(20017);
         user.setGender("male");
         user.setName("服务挂了");
        return user;
    }
}

 

然后我们测试一下 启动消费方  不启动 提供方MEMBER-SERVICE  发现熔断可用:

 

 

                

送 Doris 限量T恤,快来围观!>>>

                    <p><strong>本文采用的springcloud 版本 Dalston.SR4&nbsp; &nbsp;所有例子以Dalston.SR4 版本为准</strong></p> 

spring cloud Dalston.SR4 feign 实际开发中踩坑(一)

https://my.oschina.net/u/2948566/blog/1591028

坑4、       无法扫描到引用包的feign接口

在实际的生产中 我们服务模块是有很多的, 如果 A的接口 B要调用 我们声明一次feigin客户端 api    然后C也要调A的接口  我们还要声明一次feigin客户端api   如果还有更多  就会有很多重复代码  为了提高代码复用,我们往往单独声明一个包来引入feigin 的api  其他包如果调用的化引入到工程中就行了   但是 问题来了 引用包无法被直接扫描到  我们知道 一个微服务模块 如果需要开启feign调用功能 需要加上

@EnableFeignClients 

源码:

/*
 * Copyright 2013-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.netflix.feign;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.annotation.Import;

/**

  • Scans for interfaces that declare they are feign clients (via {@link FeignClient

  • @FeignClient}). Configures component scanning directives for use with

  • {@link org.springframework.context.annotation.Configuration

  • @Configuration} classes.

  • @author Spencer Gibb

  • @author Dave Syer

  • @since 1.0
    */
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Documented
    @Import(FeignClientsRegistrar.class)
    public @interface EnableFeignClients {

    /**

    • Alias for the {@link #basePackages()} attribute. Allows for more concise annotation
    • declarations e.g.: {@code @ComponentScan(“org.my.pkg”)} instead of
    • {@code @ComponentScan(basePackages=“org.my.pkg”)}.
    • @return the array of ‘basePackages’.
      */
      String[] value() default {};

    /**

    • Base packages to scan for annotated components.
    • {@link #value()} is an alias for (and mutually exclusive with) this attribute.
    • Use {@link #basePackageClasses()} for a type-safe alternative to String-based
    • package names.
    • @return the array of ‘basePackages’.
      */
      String[] basePackages() default {};

    /**

    • Type-safe alternative to {@link #basePackages()} for specifying the packages to
    • scan for annotated components. The package of each class specified will be scanned.
    • Consider creating a special no-op marker class or interface in each package that
    • serves no purpose other than being referenced by this attribute.
    • @return the array of ‘basePackageClasses’.
      */
      Class[] basePackageClasses() default {};

    /**

    • A custom @Configuration for all feign clients. Can contain override
    • @Bean definition for the pieces that make up the client, for instance
    • {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
    • @see FeignClientsConfiguration for the defaults
      */
      Class[] defaultConfiguration() default {};

    /**

    • List of classes annotated with @FeignClient. If not empty, disables classpath scanning.
    • @return
      */
      Class[] clients() default {};
      }

     其

中basePackages  声明 扫描  feignclie

nt 注解所在的包的包路径  声明后就能扫描到你在该包下@FeignClient 标记的 feign接口

坑5、无法扫描到引入包的服务降级实现,大多数情况我们要对feignClient接口显式声明一个fallback以便进行服务降级但是如果你的feignclient接口不在springboot的启动类的子
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