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Spring Cloud Feign 之Fallback

Spring Cloud Feign 之Fallback

作者: 孙平平 | 来源:发表于2018-08-18 15:13 被阅读0次
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    Spring Cloud Feign 之Fallback

    环境信息: java 1.8、Spring boot 1.5.10.RELEASE、spring cloud-Edgware.SR3、maven 3.3+

    在网络请求时,可能会出现异常请求,如果还想再异常情况下使系统可用,那么就需要容错处理,比如:网络请求超时时给用户提示“稍后重试”或使用本地快照数据等等。

    Spring Cloud Feign就是通过Fallback实现的,有两种方式:

    1、@FeignClient.fallback = UserFeignFallback.class指定一个实现Feign接口的实现类。

    2、@FeignClient.fallbackFactory = UserFeignFactory.class指定一个实现FallbackFactory<T>工厂接口类

    因为Fallback是通过Hystrix实现的, 所以需要开启Hystrix,spring boot application.properties文件配置feign.hystrix.enabled=true,这样就开启了Fallback

    Fallback-实现Feign接口

    UserFeignFallback回调实现,由spring创建使用@Component(其他的注册也可以)注解

    HystrixTargeter.targetWithFallback方法实现了@FeignClient.fallback处理逻辑,通过源码可以知道UserFeignFallback回调类是从Spring容器中获取的,所以UserFeignFallback由spring创建。

    UserFeign配置:

    package com.example.feign;
    
    import org.springframework.cloud.netflix.feign.FeignClient;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.PathVariable;
    import org.springframework.web.bind.annotation.PostMapping;
    
    import java.util.List;
    
    @FeignClient(name = "user",url = "${user.url}",fallback = UserFeignFallback.class
            /*fallbackFactory = UserFeignFactory.class*/)
    public interface UserFeign {
    
        @PostMapping
        void save(User user);
    
        @GetMapping("/{id}")
        User getUserByID(@PathVariable("id") String id);
    
        @GetMapping
        List<User> findAll();
    }
    

    UserFeignFallback类:

    package com.example.feign;
    
    import org.springframework.stereotype.Component;
    
    import java.util.List;
    
    @Component
    public class UserFeignFallback implements UserFeign {
    
        @Override
        public void save(User user) {
    
        }
    
        @Override
        public User getUserByID(String id) {
            User user = new User();
            user.setId("100");
            user.setName("fallback 回调用户");
            return user;
        }
    
        @Override
        public List<User> findAll() {
            return null;
        }
    }
    

    为了模拟回调失败服务提供方,抛出500错误。

     @GetMapping("/{id}")
        public User getUserByID(@PathVariable("id") String id) {
    
    //        return userMap.get(id);
            throw new RuntimeException("服务端测试异常!");
        }
    

    运行单元测试UserFeignTest.getUserByID控制台输出结果:

    2018-08-18 11:47:59.800  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] ---> GET http://localhost:8080/user/1 HTTP/1.1
    2018-08-18 11:47:59.800  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] ---> END HTTP (0-byte body)
    2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] <--- HTTP/1.1 500 (27ms)
    2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] connection: close
    2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] content-type: application/json;charset=UTF-8
    2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] date: Sat, 18 Aug 2018 03:47:59 GMT
    2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] transfer-encoding: chunked
    2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] 
    2018-08-18 11:47:59.829  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] {"timestamp":1534564079825,"status":500,"error":"Internal Server Error","exception":"java.lang.RuntimeException","message":"服务端测试异常!","path":"/user/1"}
    2018-08-18 11:47:59.829  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] <--- END HTTP (167-byte body)
    User{id='100', name='fallback 回调用户'}
    

    服务提供方抛出的500错误代码,但是客户端程序还可以正常运行输出了UserFeignFallback.getUserByID方法返回的结果。

    FallbackFactory<T>工厂

    上面的实现方式简单,但是获取不到HTTP请求错误状态码和信息 ,这时就可以使用工厂模式来实现Fallback

    同样工厂实现类也要交由spring管理,同时结合UserFeignFallback使用,这里需要注意的create方法返回值类型一定要实现Feign接口,否则会报错。

    UserFeignFactory只做了打印异常处理:

    package com.example.feign;
    
    import feign.hystrix.FallbackFactory;
    import org.springframework.stereotype.Component;
    
    @Component
    public class UserFeignFactory implements FallbackFactory<UserFeign> {
    
        private final UserFeignFallback userFeignFallback;
    
        public UserFeignFactory(UserFeignFallback userFeignFallback) {
            this.userFeignFallback = userFeignFallback;
        }
    
        @Override
        public UserFeign create(Throwable cause) {
            //打印下异常
            cause.printStackTrace();
            return userFeignFallback;
        }
    }
    

    UserFeign:

    package com.example.feign;
    
    import org.springframework.cloud.netflix.feign.FeignClient;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.PathVariable;
    import org.springframework.web.bind.annotation.PostMapping;
    
    import java.util.List;
    
    @FeignClient(name = "user", url = "${user.url}",
    /*fallback = UserFeignFallback.class*/
            fallbackFactory = UserFeignFactory.class)
    public interface UserFeign {
    
        @PostMapping
        void save(User user);
    
        @GetMapping("/{id}")
        User getUserByID(@PathVariable("id") String id);
    
        @GetMapping
        List<User> findAll();
    }
    

    运行单元测试UserFeignTest.getUserByID可以看到控制台打印的异常feign.FeignException更多信息省略。

    ErrorDecoder接口处理请求错误信息,默认实现ErrorDecoder.Default抛出FeignException异常

    FeignException.status 方法返回HTTP状态码,FallbackFactory.create默认情况下可以强制转换成FeignException异常这样就可以获取到HTTP状态码了。

    自定义ErrorDecoder

    第一种:application.properties

    全局配置,通过application.properties配置文件

    feign.client.default-config=my-config
    feign.client.config.my-config.error-decoder=com.example.feign.MyErrorDecoder
    

    错误解码实现类MyErrorDecoder

    package com.example.feign;
    
    import feign.Response;
    import feign.codec.ErrorDecoder;
    
    public class MyErrorDecoder implements ErrorDecoder {
    
        @Override
        public Exception decode(String methodKey, Response response) {
            return new MyFeignException(methodKey,response);
        }
    }
    

    自定义异常MyFeignException

    package com.example.feign;
    
    import feign.Response;
    
    public class MyFeignException extends RuntimeException {
        private final String methodKey;
        private Response response;
    
    
        MyFeignException(String methodKey, Response response) {
            this.methodKey = methodKey;
            this.response = response;
        }
    
    
        public Response getResponse() {
            return response;
        }
    
        public String getMethodKey() {
            return methodKey;
        }
    }
    

    第二种:@EnableFeignClients

    全局配置,@EnableFeignClients.defaultConfiguration注解

    package com.example;
    
    import com.example.feign.FeignClientsConfig;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.cloud.netflix.feign.EnableFeignClients;
    
    /**
     * 启动类
     *
     * @author: sunshaoping
     * @date: Create by in 上午10:47 2018/8/7
     */
    @EnableFeignClients(
            defaultConfiguration = FeignClientsConfig.class
    )
    @SpringBootApplication
    public class FeignApplication {
    
        public static void main(String[] args) {
            SpringApplication.run(FeignApplication.class, args);
        }
    
    
    }
    

    第三种:@FeignClient

    作用范围是Feign接口,优先级要高于上面两种,@FeignClient.configuration 注解

    package com.example.feign;
    
    import org.springframework.cloud.netflix.feign.FeignClient;
    import org.springframework.web.bind.annotation.GetMapping;
    import org.springframework.web.bind.annotation.PathVariable;
    import org.springframework.web.bind.annotation.PostMapping;
    
    import java.util.List;
    
    @FeignClient(name = "user", url = "${user.url}",
    /*fallback = UserFeignFallback.class*/
            decode404 = true,
            fallbackFactory = UserFeignFactory.class,
            configuration = FeignClientsConfig.class
    )
    public interface UserFeign {
    
        @PostMapping
        void save(User user);
    
        @GetMapping("/{id}")
        User getUserByID(@PathVariable("id") String id);
    
        @GetMapping
        List<User> findAll();
    }
    

    总结

    本章节讲了如下内容

    Spring Cloud Feign HTTP请求异常Fallback容错机制,它是基于Hystrix实现的,所以要通过配置参数feign.hystrix.enabled=true开启该功能,及其两种实现方式。

    Fallback工厂方式引出了ErrorDecoder错误解码自定义处理,有三种方式,可根据实际请求选择,举一反三其他自定义配置也可以通过这种方式实现如:Decoder、Encoder、Logger(第二、三章有介绍)。

    如果开启的Hystrix就不要用feign的超时配置了,单位是毫秒

    feign.client.config.defalut.connect-timeout=10000
    

    defalut是默认配置名称,可以使用feign.client.default-config替换自定义名称

    feign.client.default-config=my-config
    feign.client.config.my-config.connect-timeout=10000
    

    请使用如下属性配置超时时间,单位毫秒

    hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds=20000
    

    样例地址 spring-cloud-feign 分支 Spring-Cloud-Feign-之fallback

    写在最后

    Spring Cloud Feign 系列持续更新中。。。。。欢迎关注

    如发现哪些知识点有误或是没有看懂,请在评论区提出,博主及时改正。

    欢迎转载请注明出处。

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