Feign是从Netflix中分离出来的轻量级项目，能够在类接口上添加注释，成为一个REST API 客户端，Feign默认集成了Ribbon。
Feign中对 Hystrix 有依赖关系。Feign只是一个便利的rest框架，简化调用，最后还是通过ribbon在注册服务器中找到服务实例，然后对请求进行分配
Feign是一种声明式、模板化的HTTP客户端。在Spring Cloud中使用Feign, 我们可以做到使用HTTP请求远程服务时能与调用本地方法一样的编码体验，开发者完全感知不到这是远程方法，更感知不到这是个HTTP请求。
一、使用方式
1、首先写好需要注册进注册中心的服务接口UserServiceController，该接口相当于service层，只是以RestFULL接口的形式供远程调用
@RestController @RequestMapping("userService") public class UserServiceController {@GetMapping("getUser/{userId}")public User getUser(@PathVariable("userId") String userId){System.out.println("获取User,更具UserId，查询User-->" + userId);User user = new User();user.setUserName("Tom");user.setPassword("123");return user;}@PostMapping("saveUser")public String saveUser(@RequestBody User user){System.out.println("保存User--->" + JSON.toJSONString(user));return "userId:010100100101";}@GetMapping("deleteUser/{userId}")public Boolean deleteUser(@PathVariable("userId") String userId){System.out.println("删除用户--->" + userId);return true;}@RequestMapping(value = "findUserByUserNameAndPassword")public User findUserByUserNameAndPassword(String userName, String password){System.out.println("userService--->" + userName + " password--->" + password);User user = new User();user.setUserName("Tomcat");user.setPassword("123");return user;}
2、在请求远程服务的项目的POM.XML文件中引入对Feign依赖
<dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-feign</artifactId> </dependency>
3、创建FeignClient
@FeignClient(value="springcloud-userservcie") public interface UserClient {@RequestMapping(value = "userService/getUser/{userId}", method = RequestMethod.GET)public User getUser(@PathVariable("userId") String userId);@RequestMapping(value = "userService/saveUser", method = RequestMethod.POST)public String saveUser(User user);@RequestMapping(value = "userService/deleteUser/{userId}", method = RequestMethod.GET)public Boolean deleteUser(@PathVariable("userId") String userId);@RequestMapping(value = "userService/findUserByUserNameAndPassword", method = RequestMethod.GET)public User findUserByUserNameAndPassword(@RequestParam("userName") String userName, @RequestParam("password") String password); }
- @FeignClient(value="springcloud-userservcie")：用于通知Feign组件对该接口进行代理(不需要编写接口实现)，value属性指定我们要调用注册中心的服务ID。使用者可直接通过@Autowired注入。
- @RequestMapping表示在调用该方法时需要向/group/{groupId}发送请求。
- @PathVariable与SpringMVC中对应注解含义相同。
原理：Spring Cloud应用在启动时，Feign会扫描标有@FeignClient注解的接口，生成代理，并注册到Spring容器中。生成代理时Feign会为每个接口方法创建一个RequetTemplate对象，该对象封装了HTTP请求需要的全部信息，请求参数名、请求方法等信息都是在这个过程中确定的，Feign的模板化就体现在这里
4、在Controller调用
@RestController @RequestMapping("userClient") public class UserController {@Autowiredprivate UserClient userClient;@RequestMapping(value = "getUser/{userId}", method = RequestMethod.GET)public User getUser(@PathVariable("userId") String userId){return userClient.getUser(userId);}@RequestMapping(value = "saveUser", method = RequestMethod.POST)public String saveUser(User user){return userClient.saveUser(user);}@RequestMapping(value = "deleteUser/{userId}", method = RequestMethod.GET)public Boolean deleteUser(@PathVariable("userId") String userId){return userClient.deleteUser(userId);}@RequestMapping(value = "findUserByUserNameAndPassword")public User findUserByUserNameAndPassword(String userName, String password){System.out.println("userClient--->" + userName + " password--->" + password);return userClient.findUserByUserNameAndPassword(userName, password);}}
5、启动类上添加Feign注解
@Configuration @ComponentScan @EnableAutoConfiguration @EnableEurekaClient @EnableFeignClients public class Application {public static void main(String[] args) {SpringApplication.run(Application.class, args);} }
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