Feign 的使用

Feign 简介

Feign 是对 Hystrix 和 Ribbon 的封装，简便了代码的编写，代价是对服务的性能有一定的影响，在并发量非常高的场景下不建议使用。（用 Hystrix 的场景并发量能不高么？所以基本上就是不建议使用）

配置与使用

服务发现方

依赖配置

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

启动类配置

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

配置文件配置

#feign开启熔断器
feign.hystrix.enabled=true
#开启feign的压缩功能
feign.compression.request.enabled=true
#feign.compression.request.mime-types=text/xml,application/xml,application/json
#feign.compression.request.min-request-size=2048
feign.compression.response.enabled=true

#另外还可以配置关于hystrix的配置，如
#hystrix.command.default.execution.isolation.strategy=SEMAPHORE

接口配置

/*
* fallback = StudentServiceFallback.class
* 不能获取具体异常
*
* */
@FeignClient(name = "MICRO-ORDER",path = "/feign"
        /*fallback = StudentServiceFallback.class,*/
        ,fallbackFactory = StudentServiceFallbackFactory.class)
public interface StudentService {

    //相当于每一个方法上都加上了@Hystrix
    @GetMapping("/student/getAllStudent")
    String getAllStudent();

	//入参为pojo，@RequestBody 不能丢
    @PostMapping("/student/saveStudent")
    String saveStudent(@RequestBody Student student);

	//入参为基本数据类型/String，@RequestParam 不能丢
    @GetMapping("/student/getStudentById")
    String getStudentById(@RequestParam("id") Integer id);

}

服务降级

@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;
            }
        };
    }
}

异常信息过滤器

@Configuration
public class FeignErrMessageFilter {

    @Bean
    public ErrorDecoder errorDecoder() {
        return new FeignErrorDecoder();
    }

    /*
    * 当调用服务时，如果服务返回的状态码不是200，就会进入到Feign的ErrorDecoder中
    * 只有这种方式才能获取所有的被feign包装过的异常信息
    *
    * 这里如果创建的Exception是HystrixBadRequestException
    * 则不会走熔断逻辑，不记入熔断统计
    * */
    class FeignErrorDecoder implements ErrorDecoder {

        private Logger logger = LoggerFactory.getLogger(FeignErrorDecoder.class);

        @Override
        public Exception decode(String s, Response response) {

            RuntimeException runtimeException = null;

            try {
                String retMsg = Util.toString(response.body().asReader());
                logger.info(retMsg);

                runtimeException = new RuntimeException(retMsg);

            } catch (IOException e) {
                e.printStackTrace();
            }
            return runtimeException;
        }
    }
}

服务提供方

服务接口与实现类

• 接口：有返回值的方法只能返回String类型。
  远程调用会传输序列化的Json格式的字符串。

• 实现类：注意返回值转换成Json格式的字符串。
  可以考虑用 alibaba 的 fastjson，用 JSONObject.toJSONString() 包裹 pojo。

Controller

@RestController
public class StudentController implements StudentService {

    @Autowired
    private StudentService studentService;

    @RequestMapping("/feign/student/getAllStudent")
    @Override
    public String getAllStudent() {
        return studentService.getAllStudent();
    }

    @RequestMapping("/feign/student/getStudentById")
    @Override
    public String queryStudentById(@RequestParam("id") Integer id) {
        return studentService.queryStudentById(id);
    }

    @RequestMapping("/feign/student/saveStudent")
    @Override
    public String saveStudent(@RequestBody Student student) {
        return studentService.saveStudent(student);
    }
}