OpenFeign的Java接口定義規范如下：

1. 使用@FeignClient注解標記接口，指定服務名稱和路徑

@FeignClient(name = "service-name", path = "/api")
public interface MyFeignClient {
    // 接口方法
}

2. 定義接口方法，并使用@RequestMapping注解指定請求方法、路徑和參數

@FeignClient(name = "service-name", path = "/api")
public interface MyFeignClient {
    
    @RequestMapping(method = RequestMethod.GET, value = "/users/{userId}")
    User getUserById(@PathVariable("userId") Long userId);
}

3. 定義接口方法參數和返回值

public class User {
    private Long id;
    private String name;
    
    // getters and setters
}

4. 使用@RequestParam、@PathVariable等注解指定參數來源和值

@FeignClient(name = "service-name", path = "/api")
public interface MyFeignClient {
    
    @RequestMapping(method = RequestMethod.GET, value = "/users")
    List<User> getUsers(@RequestParam("page") int page, @RequestParam("size") int size);
}

5. 接口方法可以定義任意類型的參數和返回值，包括基本類型、對象類型、集合類型等

@FeignClient(name = "service-name", path = "/api")
public interface MyFeignClient {
    
    @RequestMapping(method = RequestMethod.POST, value = "/users")
    void createUser(User user);
}