问题一：由于马虎，缺少配置，报错如下：

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.gemantic.springcloud.service.AdditionClient': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: Method add not annotated with HTTP method type (ex. GET, POST)


Caused by: java.lang.IllegalStateException: Method add not annotated with HTTP method type (ex. GET, POST)

解决方案，在Feign接口上没有配置请求式，在接口上增加请求方式 @GetMapping(value="/add") 或 @RequestMapping(value="/add")，完整代码如下：

@FeignClient("springcloud-addition-service")
public interface AdditionClient {

    /**
     * 加法接口
     * @param a
     * @param b
     * @return
     */
//    @RequestMapping(value = "/add")
    @GetMapping(value = "/add")
    ResponseEntity<ResultData> add(@RequestParam("a") @NotNull Integer a, @RequestParam("b") @NotNull Integer b);
}

注： value="/add" 与真正服务一致。

问题二：

Caused by: java.lang.IllegalStateException: RequestParam.value() was empty on parameter 0

暴漏Restful服务的方法如下：

@Slf4j
@RestController
@Api(description = "加法接口")
public class AdditionController {

    @Autowired
    private Addition addition;

    @GetMapping(value = "/add")
    @ApiOperation(value = "a + b = ?")
    public ResponseEntity<ResultData> add(@RequestParam @NotNull Integer a, @RequestParam @NotNull Integer b) {

        if (log.isInfoEnabled()) {
            log.info("add {} + {}", a, b);
        }
        int result = addition.add(a, b);
        ResultData resultData = ResultData.builder().message(Message.builder().code(0).message(Message.SUCCESS_MESSAGE).build()).build();
        resultData.setData(result);
        return ResponseEntity.ok(resultData);
    }
}

Feign的方式的接口如下：

@GetMapping(value = "/add")
ResponseEntity<ResultData> add(@RequestParam @NotNull Integer a, @RequestParam @NotNull Integer b);

服务启动时就会报错误：

Caused by: java.lang.IllegalStateException: RequestParam.value() was empty on parameter 0

解决方案：在 @RequestParam 增加方法名

@GetMapping(value = "/add")
ResponseEntity<ResultData> add(@RequestParam("a") @NotNull Integer a, @RequestParam("b") @NotNull Integer b);

注： @PathVariable 与 @RequestParam类似的。

问题三：

Caused by: java.lang.IllegalStateException: Method has too many Body parameters: public abstract org.springframework.http.ResponseEntity com.gemantic.springcloud.service.AdditionClient.add(java.lang.Integer,java.lang.Integer)

解决方案：当使用Feign时，如果发送的是get请求，那么需要在请求参数前加上 @RequestParam或 @PathVariable注解修饰，Controller里面可以不加该注解修饰。

@GetMapping(value = "/add")
ResponseEntity<ResultData> add(@RequestParam("a") @NotNull Integer a, @RequestParam("b") @NotNull Integer b);