Feign快速入门

简介：Feign是声明式（注解）web服务客户端。Feign是一个远程调用的组件（接口、注解）完成http调用，Feign集成了ribbon、ribbon里面集成了eureka。使用feign需要创建一个接口添加feign注解。

依旧沿用之前的项目，创建一个feign的空项目，再创建springboot项目，springboot版本2.3.12.RELEASE，springcloud版本Hoxton.SR12，基本依赖有eureka、spring web、Lombok

创建一个order-service项目代码：

@RestController
public class OrderController {

    @GetMapping("doOrder")
    public String doOrder(){
        return "订单接口";
    }
}

server:
  port: 8080
spring:
  application:
    name: order-service
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka

@SpringBootApplication
@EnableEurekaClient
public class OrderServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(OrderServiceApplication.class, args);
    }

}

创建user-service项目代码，这个项目增加一个feign依赖：

server:
  port: 8081
spring:
  application:
    name: user-service
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients // 开启feign的客户端功能
public class UserServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(UserServiceApplication.class, args);
    }

}

@RestController
public class UserController {

    @Autowired
    public UserOrderFeign userOrderFeign;

    
    @GetMapping("userDoOrder")
    public String userDoOrder(){
        System.out.println("用户请求");
        //发起一个远程调用 请求order-service
        String s = userOrderFeign.doOrder();
        return  s;
    }
}

feign接口：

@FeignClient(value = "order-service")
public interface UserOrderFeign {
    
    @GetMapping("doOrder")
    String doOrder();

}

把eureka-server和上面的两个新代码运行起来访问localhost:8081/userDoOrder

修改order-service控制层代码

@RestController
public class OrderController {

    @GetMapping("doOrder")
    public String doOrder(){
        try {
            //模拟操作数据库的耗时
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "订单接口";
    }
}

重启后，再次访问localhost:8081/userDoOrder 会发现报500 ，控制台报Read timed out超时，这是因为feign封装了ribbon，ribbon默认等待时间1000毫秒，所以超过1s直接报错超时

增加user-service配置

# feign只是封装了远程调用的功能，底层还是ribbon，所以修改ribbon的时间
ribbon:
  ReadTimeout: 3000   # 调用超时时间（毫秒）
  ConnectTimeout: 3000  # 连接服务的超时时间（毫秒）

重启user-service，访问localhost:8081/userDoOrder，此时正常

Feign简单实现

主要是通过动态代理，这里重写一下invoke方法。获取注解的value再拼接url，最后使用restTemplate把拼好的url放进去即可。这里的url其实还是接口名的形式，ribbon会再处理一下把接口变成ip。

@SpringBootTest
class UserServiceApplicationTests {
    @Autowired
    private RestTemplate restTemplate;

    @Test
    void contextLoads() {
        UserOrderFeign o = (UserOrderFeign) Proxy.newProxyInstance(UserController.class.getClassLoader(), new Class[]{UserOrderFeign.class}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                System.out.println("重写了invoke");
                //拿到对方的ip和端口 并且拿到这个方法上面注解的值
                String name = method.getName();
                GetMapping annotation = method.getAnnotation(GetMapping.class);
                String[] paths = annotation.value();
                String path = paths[0];
                Class declaringClass = method.getDeclaringClass();
                FeignClient annotation1 = declaringClass.getAnnotation(FeignClient.class);
                String applicationName = annotation1.value();
                String url = "http://" + applicationName + "/" + path;
                String forObject = restTemplate.getForObject(url, String.class);
                return forObject;
            }
        });
        String s = o.doOrder();
        System.out.println(s);
    }

}

Feign参数处理

order-service添加一个新的controller

@RestController
public class ParamController {

    @GetMapping("testUrl/{name}/{age}")
    public String testUrl(@PathVariable("name")String name,@PathVariable("age")Integer age){
        System.out.println(name+":"+age);
        return "ok";
    }

    @GetMapping("oneParam")
    public String oneParam(@RequestParam(required = false) String name){
        System.out.println(name);
        return "ok";
    }

    @GetMapping("twoParam")
    public String twoParam(@RequestParam(required = false) String name,@RequestParam(required = false)Integer age){
        System.out.println(name);
        System.out.println(age);
        return "ok";
    }

    @PostMapping("oneObj")
    public String oneObj(@RequestBody Order order){
        System.out.println(order);
        return "ok";
    }

    @PostMapping("oneObjOneParam")
    public String oneObjOneParam(@RequestBody Order order,@RequestParam("name") String name){
        System.out.println(order);
        System.out.println(name);
        return "ok";
    }
}

order实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class Order {
    private Integer id;
    private String name;
    private Double price;
    private Date time;

}

user-service controller添加一个方法

@GetMapping("testParam")
public String testParam(){
    String testUrl = userOrderFeign.testUrl("testUrl", 18);
    System.out.println(testUrl);
    String oneParam = userOrderFeign.oneParam("oneParam");
    System.out.println(oneParam);
    String twoParam = userOrderFeign.twoParam("twoParam", 18);
    System.out.println(twoParam);
    Order order = Order.builder().name("abc").price(100D).time(new Date()).id(1).build();
    String oneObj = userOrderFeign.oneObj(order);
    System.out.println(oneObj);
    String oneObjOneParam = userOrderFeign.oneObjOneParam(order, "oneObjOneParam");
    System.out.println(oneObjOneParam);
    return "ok";
}

实体类也要粘过来

接口添加代码

@GetMapping("testUrl/{name}/{age}")
public String testUrl(@PathVariable("name")String name, @PathVariable("age")Integer age);

@GetMapping("oneParam")
public String oneParam(@RequestParam(required = false) String name);

@GetMapping("twoParam")
public String twoParam(@RequestParam(required = false) String name,@RequestParam(required = false)Integer age);

@PostMapping("oneObj")
public String oneObj(@RequestBody Order order);

@PostMapping("oneObjOneParam")
public String oneObjOneParam(@RequestBody Order order,@RequestParam("name") String name);

测试传递时间参数

order-service controller添加一个方法
```
@GetMapping("testTime")
public String testTime(@RequestParam Date date){
    System.out.println(date);
    return "ok";
}
```
user-service controller添加方法
```
@GetMapping("time")
public String testTime(){
    Date date = new Date();
    System.out.println(date);
    String s = userOrderFeign.testTime(date);
    return s;
}
```
feign接口添加
```
@GetMapping("testTime")
public String testTime(@RequestParam Date date);
```
访问http://localhost:8081/time结果如下

user-service Mon Jul 11 17:18:57 CST 2022

order-service Tue Jul 12 07:18:57 CST 2022

会发现有14小时差距，所以最好不要单独传递时间参数

可以转成字符串或者使用LocalDate 年月日

但是使用LocalDateTime 会丢失秒
Feign日志功能

Feign的Logger类有四个日志级别
```
public enum Level {
    
    NONE,
    
    BASIC,
    
    HEADERS,
    
    FULL
  }
```
- none 无日志
- basic 记录请求方法、url、响应状态码、时间
- headers 记录请求和响应的主要信息
- full 最高的日志级别，记录请求和响应的头、体、元数据

如何开启Feign功能

修改配置文件

logging:
  level:
    com.example.userservice.feign.UserOrderFeign: debug # 打印该接口下的日志

修改启动类

@Bean
public Logger.Level level(){
    return Logger.Level.FULL;
}

aders 记录请求和响应的主要信息

full 最高的日志级别，记录请求和响应的头、体、元数据

如何开启Feign功能

修改配置文件

logging:
  level:
    com.example.userservice.feign.UserOrderFeign: debug # 打印该接口下的日志

修改启动类

@Bean
public Logger.Level level(){
    return Logger.Level.FULL;
}

Feign快速入门

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