springcloud-Feign 的使用

Feign 的使用

Feign 是对服务端和客户端通用接口的封装，让代码可以复用做到统一管理。简化了调用方的代码

Feign相当于ribbon + Hystrix的封装集成，但是是由额外的性能开销的；

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>

开启注解

@EnableFeignClients
@EnableDiscoveryClient
//或者
//开启feign支持，clients指定哪个类开启feign
@EnableFeignClients(clients = {
          
   StudentService.class,TeacherServiceFeign.class})

客户端接口注解申明

@FeignClient(name = "MICRO-ORDER",path = "/feign"
        /*fallback = StudentServiceFallback.class,*/
        ,fallbackFactory = StudentServiceFallbackFactory.class)
public interface StudentService {
          
   

    @GetMapping("/student/getAllStudent")
    String getAllStudent();

    @PostMapping("/student/saveStudent")
    String saveStudent(@RequestBody Student student);

    @GetMapping("/student/getStudentById")
    String getStudentById(@RequestParam("id") Integer id);
	//验证异常的接口
    @GetMapping("/student/errorMessage")
    String errorMessage(@RequestParam("id") Integer id);
}

服务端提供出对应url的Controller即可

FeignClient注解的一些属性

Feign 的服务降级

从上面注解信息可以看到，服务降级方式由两种 fallback 和 fallbackFactory

fallback

如上示例的接口中，fallback 配置可以这么写

@Service
public class StudentServiceFallback implements StudentService{
          
   

    @Override
    public String getAllStudent() {
          
   
        return "获取所有学生信息失败";
    }

    @Override
    public String saveStudent(Student student) {
          
   
        return "保存学生信息失败";
    }

    @Override
    public String getStudentById(Integer id) {
          
   
        return "根据Id获取学生信息失败";
    }

    /*
    * 这种方式拿不到provider的具体异常信息
    * */
    @Override
    public String errorMessage(Integer id) {
          
   
        return "根据Id获取学生信息失败";
    }
}

这个用法的缺点是无法获取到Exception 信息

fallbackFactory

而fallbackFactory的使用例子如下

@Slf4j
@Component
public class StudentServiceFallbackFactory implements FallbackFactory<StudentService> {
          
   
    @Override
    public StudentService create(Throwable throwable) {
          
   
        if(throwable == null) {
          
   
            return null;
        }
        final String msg = throwable.getMessage();
        log.info("exception:" + msg);
        return new StudentService() {
          
   
            @Override
            public String getAllStudent() {
          
   
                log.info("exception=====getAllStudent==========" + msg);
                return msg;
            }
            @Override
            public String saveStudent(Student student) {
          
   
                log.info("exception=====saveStudent==========" + msg);
                return msg;
            }
            @Override
            public String getStudentById(Integer id) {
          
   
                log.info("exception=====getStudentById==========" + msg);
                return msg;
            }
            @Override
            public String errorMessage(Integer id) {
          
   
                log.info("exception=====errorMessage==========" + msg);
                return msg;
            }
        };
    }
}

其中的参数throwable中的message内容是被组件封装过的，并不是java原生的异常信息

Feign 的异常处理器ErrorDecoder

配合前面服务降级，Feign也有类似springMvc异常处理器，如果定义了，会在fallbackFactory处理之前处理过throwable参数

@Slf4j
class FeignErrorDecoder implements ErrorDecoder {
          
   
        @Override
        public Exception decode(String s, Response response) {
          
   
            RuntimeException runtimeException = null;
            try {
          
   
                //重新包装
                String retMsg = Util.toString(response.body().asReader());
                log.info(retMsg);
                runtimeException = new RuntimeException(retMsg);
            } catch (IOException e) {
          
   
                e.printStackTrace();
            }
            return runtimeException;
        }
    }