前言

Spring Cloud Feign基於Netflix Feign實現，整合了Spring Cloud Ribbon與Spring Cloud Hystrix，除了提供這兩者的強大功能外，還提供了一種宣告式的Web服務客戶端定義方式，我們可以做到使用HTTP請求遠端服務時能與呼叫本地方法一樣的編碼體驗，讓開發者在開發過程中感知不到這是個HTTP請求

快速入門

在pom.xml檔案中匯入如下依賴

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
 

         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <artifactId>spring-cloud-parent</artifactId>
        <groupId
 
>com.roberto.springcloud</groupId>
        <version>1.0.0-SNAPSHOT</version>
    </parent>

    <artifactId>spring-cloud-movie-service</artifactId>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
 

            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>
    </dependencies>
</project>

在啟動類新增@EnableFeignClients開啟Spring Cloud Feign的支援

package com.roberto.springcloud;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

@EnableEurekaClient
@EnableFeignClients
@SpringBootApplication
public class SpringCloudMovieService {
    public static void main(String args[]) {
        SpringApplication.run(SpringCloudMovieService.class, args);
    }
}

定義Service介面，通過@FeignClient註解指定服務名來繫結服務，然後使用SpringMVC的註解來繫結具體服務提供的REST介面

package com.roberto.springcloud.feign;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@FeignClient(name = "USER-SERVICE")
public interface UserFeignClient {
    @RequestMapping(value = "/hello", method = RequestMethod.GET)
    String index();
}

此處USER-SERVICE為服務名 且/hello介面返回Hello World

在Controller層注入Feign介面進行呼叫

package com.roberto.springcloud.controller;

import com.roberto.springcloud.feign.UserFeignClient;
import com.roberto.springcloud.feign.UserFeignClient2;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MovieController {
    @Autowired
    private UserFeignClient userFeignClient;

    @RequestMapping(value = "/index", method = RequestMethod.GET)
    public String index() {
        return userFeignClient.index();
    }
}

application.yml檔案配置如下

spring:
  application:
    name: movie-service
server:
  port: 9092
eureka:
  client:
    healthcheck:
      enabled: true
    serviceUrl:
      defaultZone: http://roberto:[email protected]:8761/eureka
  instance:
    prefer-ip-address: true

呼叫/index介面檢視結果

Feign引數繫結

新建User實體類

package com.roberto.springcloud.entity;

public class User {
    private String username;
    private String password;

    public User() {

    }

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

修改USER-SERVICE服務的介面

package com.roberto.springcloud.controller;

import com.roberto.springcloud.entity.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.web.bind.annotation.*;

import javax.annotation.Resource;

@RestController
public class UserController {
    @RequestMapping(value = "hello", method = RequestMethod.GET)
    public String hello(@RequestParam String username) {
        return "Hello " + username;
    }

    @RequestMapping(value = "hello2", method = RequestMethod.GET)
    public User hello(@RequestHeader String username, @RequestHeader String password) {
        return new User(username, password);
    }

    @RequestMapping(value = "hello3", method = RequestMethod.POST)
    public User hello(@RequestBody User user) {
        return user;
    }
}

修改UserFeignClient介面

package com.roberto.springcloud.feign;

import com.roberto.springcloud.entity.User;
import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.*;

@FeignClient(name = "USER-SERVICE")
public interface UserFeignClient {
    @RequestMapping(value = "/hello", method = RequestMethod.GET)
    String hello(@RequestParam("username") String username);

    @RequestMapping(value = "/hello2", method = RequestMethod.GET)
    User hello(@RequestHeader("username") String username, @RequestHeader("password") String password);

    @RequestMapping(value = "/hello3", method = RequestMethod.POST)
    User hello(@RequestBody User user);
}

注:在定義各引數繫結時，@RequestParam和@RequestHeader等可以指定引數名稱的註解，他們的value千萬不能省略，在SpringMVC中這些註解會根據引數名作為預設值但在Feign中必須顯示指定，否則會丟擲異常

在Controller中新增測試介面進行測試

package com.roberto.springcloud.controller;

import com.roberto.springcloud.entity.User;
import com.roberto.springcloud.feign.UserFeignClient;
import com.roberto.springcloud.feign.UserFeignClient2;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MovieController {
    @Autowired
    private UserFeignClient userFeignClient;

    @RequestMapping(value = "helloTest", method = RequestMethod.GET)
    public String helloTest() {
        StringBuffer stringBuffer = new StringBuffer();
        stringBuffer.append(userFeignClient.hello("RobertoHuang")).append("\n");
        stringBuffer.append(userFeignClient.hello("RobertoHuang","123456")).append("\n");
        stringBuffer.append(userFeignClient.hello(new User("RobertoHuang","123456"))).append("\n");
        return stringBuffer.toString();
    }
}

訪問/helloTest介面檢視輸出結果

Feign繼承特性

在使用SpringMVC的註解來繫結服務介面時，我們幾乎完全可以從服務提供方的Controller中依靠複製操作，構建出相應的服務客戶端繫結介面，既然存在這麼多複製操作，我們可以把相同的部分進行抽象以減少編碼量，下面我們對上面工程進行改造

新建USER-API工程，在pom.xml檔案中匯入如下依賴

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <artifactId>spring-cloud-parent</artifactId>
        <groupId>com.roberto.springcloud</groupId>
        <version>1.0.0-SNAPSHOT</version>
    </parent>

    <artifactId>spring-cloud-user-api</artifactId>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
</project>

在USER-API工程中新建User類

package com.roberto.springcloud.entity;

public class User {
    private String usernamne;
    private String password;

    public User() {
    }

    public User(String usernamne, String password) {
        this.usernamne = usernamne;
        this.password = password;
    }

    public String getUsernamne() {
        return usernamne;
    }

    public void setUsernamne(String usernamne) {
        this.usernamne = usernamne;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "usernamne='" + usernamne + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

在USER-API工程中新建UserServiceApi類

package com.roberto.springcloud.api;

import com.roberto.springcloud.entity.User;
import org.springframework.web.bind.annotation.*;

public interface UserServiceApi {
    @RequestMapping(value = "hello", method = RequestMethod.GET)
    String hello(@RequestParam("username") String username);

    @RequestMapping(value = "hello2", method = RequestMethod.GET)
    User hello(@RequestHeader("username") String username, @RequestHeader("password") String password);

    @RequestMapping(value = "hello3", method = RequestMethod.POST)
    User hello(@RequestBody User user);
}

在USER-SERVICE的pom檔案新增USER-API的依賴

 <dependency>
    <groupId>com.roberto.springcloud</groupId>
    <artifactId>spring-cloud-user-api</artifactId>
    <version>1.0.0-SNAPSHOT</version>
</dependency>

修改USER-SERVICE的UserController

package com.roberto.springcloud.controller;

import com.roberto.springcloud.api.UserServiceApi;
import com.roberto.springcloud.entity.User;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestHeader;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController implements UserServiceApi {
    @Override
    public String hello(@RequestParam String username) {
        return "Hello " + username;
    }

    @Override
    public User hello(@RequestHeader String username, @RequestHeader String password) {
        return new User(username, password);
    }

    @Override
    public User hello(@RequestBody User user) {
        return user;
    }
}

在服務呼叫方的pom檔案新增USER-API的依賴

 <dependency>
    <groupId>com.roberto.springcloud</groupId>
    <artifactId>spring-cloud-user-api</artifactId>
    <version>1.0.0-SNAPSHOT</version>
</dependency>

修改服務呼叫者的UserFeignClient

package com.roberto.springcloud.feign;

import com.roberto.springcloud.api.UserServiceApi;
import org.springframework.cloud.netflix.feign.FeignClient;

@FeignClient(name = "USER-SERVICE")
public interface UserFeignClient extends UserServiceApi{

}

訪問/helloTest介面檢視輸出結果

Feign日誌配置

Spring Cloud Feign在構建被@FeignClient註解修飾的服務客戶端時，會為每一個客戶端建立一個feign.Logger例項，我們可以配置修改日誌列印級別，在application.yml檔案中新增如下配置

logging:
  level:
    com.roberto.springcloud.feign: debug

如果只配置瞭如上內容是無法打印出Feign的日誌的，因為Feign客戶端預設的Logger.Level物件定義為NONE級別，該級別不會記錄任何Feign呼叫過程中的資訊，所以我們需要調整它的級別，針對全域性日誌級別，在主類或配置類中直接加入Logger.Level的Bean建立，具體如下:

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

測試結果如下

Feign的Logger級別主要提供了下面4類，可根據實際情況調整使用

NONE：不記錄任何資訊
BASIC：僅記錄請求方法、URL以及響應狀態和時間
HEADERS：除了記錄BASIC級別的資訊外，還會記錄請求和響應的頭資訊
FULL：記錄所有請求與響應的明細，包括頭資訊、請求體、元資料等

Feign請求壓縮

Spring Cloud Feign支援對請求與響應進行GZIP壓縮，以減少通訊過程中的效能損耗，我們只需要通過如下兩個引數進行設定，就能開啟請求與響應壓縮的功能

feign.compression.request.enabled=true
feign.compression.response.enabled=true

同時我們還能對請求壓縮做一些更細緻的設定，比如下面的配置內容指定了壓縮的請求資料型別，並設定了請求壓縮的大小下限，只有超過這個大小的請求才會對其進行壓縮

feign.compression.request.enabled=true
feign.compression.request.mime-types=text/xml,application/xml,application/json
feign.compression.request.min-request-size=2048

上述配置的mime-types與min-request-size均為預設值