spring cloud Dalston.SR4 feign 實際開發中踩坑(二)

本文采用的springcloud 版本 Dalston.SR4   全部例子以Dalston.SR4 版本爲準

spring cloud Dalston.SR4 feign 實際開發中踩坑(一)

http://www.javashuo.com/article/p-dxecfgvv-kv.html

坑四、       沒法掃描到引用包的feign接口

在實際的生產中 咱們服務模塊是有不少的, 若是 A的接口 B要調用 咱們聲明一次feigin客戶端 api    而後C也要調A的接口  咱們還要聲明一次feigin客戶端api   若是還有更多  就會有不少重複代碼  爲了提升代碼複用，咱們每每單獨聲明一個包來引入feigin 的api  其餘包若是調用的化引入到工程中就好了   可是 問題來了 引用包沒法被直接掃描到  咱們知道 一個微服務模塊 若是須要開啓feign調用功能 須要加上

@EnableFeignClients

源碼：

/*
 * 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
 * <code>@FeignClient</code>}). Configures component scanning directives for use with
 * {@link org.springframework.context.annotation.Configuration
 * <code>@Configuration</code>} 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.
	 * <p>
	 * {@link #value()} is an alias for (and mutually exclusive with) this attribute.
	 * <p>
	 * 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.
	 * <p>
	 * 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 <code>@Configuration</code> for all feign clients. Can contain override
	 * <code>@Bean</code> 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  聲明 掃描  feignclient 註解所在的包的包路徑  聲明後就能掃描到你在該包下@FeignClient 標記的 feign接口

坑五、  沒法掃描到引入包的服務降級實現，大多數狀況 咱們要對feignClient接口  顯式聲明一個fallback 以便進行服務降級   可是若是你的feignclient 接口 不在 springboot 的啓動類的子類  會沒法啓動 顯示

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 接口的實現類  沒法被注入

 

先看一下 源碼：

/*
 * 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 <code>@RibbonClient</code> 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 <code>@Qualifier</code> 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 <code>@Configuration</code> for the feign client. Can contain override
	 * <code>@Bean</code> 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
	 * <code>@RibbonClient</code>.
	 */
	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 上會有這樣的註釋    說的是  聲明feign客戶端接口 的降級類  並且 這個降級類必須實現 該feign 接口   而且必須是一個可用的spring bean

 若是你僅僅在這個實現類上加入spring bean 聲明註解 好比 @Component   你會發現依然 沒法注入 來大體猜測一下流程     熟悉springboot 的 應該清楚   springboot  啓動的時候  會掃描其main類 所在包的子包進行 bean 實例化     若是不在子包 默認是掃描不到的   那麼如何掃描到呢  聲明掃描的路徑 也就是須要在main類上使用註解@ComponentScan 註解  可是 若是 咱們僅僅聲明瞭 feign 降級實現的路徑 你會發現 main類的子包沒法掃描到了  因此 此處應該 

@ComponentScan(basePackages = {"main 所在的包","降級類所在的包"})

配置好後  咱們寫一個降級類：

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

 

而後咱們測試一下 啓動消費方  不啓動 提供方MEMBER-SERVICE  發現熔斷可用：