Feign

自定义配置时，@Configuration和@ComponentScan包不应重叠

• 示例：
  • @FeignClient注解的放在com.mmzs.cloud.feign包下面

      @FeignClient(name = "xxxx", url = "http://localhost:8761/", configuration = Configuration2.class)
  

  • @Configuration注解的放在com.mmzs.config包下面

@FeignClient所在的接口中，不支持@GetMapping等组合注解

//value此处的值一定要和指定的应用microservice-provider-user的controller中的映射路径一致
@RequestMapping(method = RequestMethod.GET, value = "/user/{id}", consumes = "application/json")
// 此处有两个坑：
//- 1. 不支持@GetMapping等组合注解   
//- 2. @PathVariable得设置value
public User findById(@PathVariable("id") Long id);
    

使用@PathVariable时，需要指定其value

  public String findServiceName(@PathVariable("serviceName") String serviceName);

Feign暂不支持复杂对象作为一个参数

• [ ] ==错误用法==

// 该请求不会成功，只要参数是复杂对象，即使指定了是GET方法，feign依然会以POST方法进行发送请求。可能是我没找到相应的注解或使用方法错误。
@RequestMapping(method = RequestMethod.GET, value = "/feign-get-user")
public User getUser(User user);

• [x] ==正确用法==

@RequestMapping(method = RequestMethod.GET, value = "/feign-get-user")
public User getUser(@RequestParam("id") Long id, @RequestParam("username") String username, @RequestParam("age") String age);

feign对hystrix的支持

添加feign对hystrix的支持,全局配置

application.xml配置：

feign.hystrix.enabled = true

禁用单个FegionClient的Hystrix的支持

// Configuration1表示feign的自定义配置类
@FeignClient(name = "microservice-provider-user", configuration = Configuration1.class)

@Configuration
public class Configuration1 {

    //禁用当前配置的hystrix，局部禁用
    @Bean
    @Scope("prototype")
    public Feign.Builder feignBuilder() {
        return Feign.builder();
    }
    
}

fallback和fallbackFactory定义的类

• fallback定义的类
  • 只重写了一个方法

@Component
//这个类不一定要和UserFeignClient写在同一个类中，
public class HystrixClientFallback implements UserFeignClient {

    @Override
    public User findById(Long id) {
        User user = new User();
        user.setId(1L);
        user.setUsername("我是HystrixClientFallback");
        return user;
    }
}

• fallbackFactory定义的类
  • 不只重写了方法，还能捕获异常

@Component
public class HystrixClientFallbackFactory implements FallbackFactory<UserFeignClient> {
    
    private static Logger LOGGER = LoggerFactory.getLogger(HystrixClientFallbackFactory.class);
    
    @Override
    public UserFeignClient create(Throwable cause) {
        //打印日志
        HystrixClientFallbackFactory.LOGGER.info("fallback; reason was: " + cause.getMessage());
        
        return new UserFeignClient() {
            @Override
            public User findById(Long id) {
                User user = new User();
                user.setId(-1L);
                user.setUsername("我是HystrixClientFallbackFactory");
                
                return user;
            }
        };
    }
    
}

==注：== fallbackFactory相当于fallback的增强版，也就是说fallbackFactory的范围更广，到收集异常的边界处了。因此我们是可以利用fallbackFactory属性来打印fallback异常的。
-正确用法如下：

@FeignClient(name = "microservice-provider-user", /*fallback = HystrixClientFallback.class,*/ fallbackFactory = HystrixClientFallbackFactory.class)

fallback和fallbackFactory

如下这种方式的注解，fallback和fallbackFactory是会有冲突的，但不会报错，只是会让断路器执行fallback中重写的方法

@FeignClient(name = "microservice-provider-user", fallback = HystrixClientFallback.class, fallbackFactory = HystrixClientFallbackFactory.class)