SpringCloud入门(五)-服务消费者(Feign)

Feign 是一个声明式的伪 Http 客户端，它使得写 Http 客户端变得更简单。使用 Feign，只需要创建一个接口并注解。它具有可插拔的注解特性，Feign 支持可插拔的编码器和解码器。Feign 默认集成了 Ribbon，并和 Eureka 结合，默认实现了负载均衡的效果(所以说服务消费者一般使用Feign)

• Feign采用的是基于接口的注解

• Feign整合了Ribbon

Ribbon和Feign的区别

• 启动类使用的注解不同，Ribbon用的是@RibbonClient，Feign用的是@EnableFeignClients。

•  服务的指定位置不同，Ribbon是在@RibbonClient注解上声明，Feign则是在定义抽象方法的接口中使用@FeignClient声明。

• 调用方式不同，Ribbon需要自己构建http请求，模拟http请求然后使用RestTemplate发送给其他服务，步骤相当繁琐。

  Feign则是在Ribbon的基础上进行了一次改进，采用接口的方式，将需要调用的其他服务的方法定义成抽象方法即可，不需要自己构建http请求。不过要注意的是抽象方法的注解、方法签名要和提供服务的方法完全一致。

---

创建服务消费者

创建一个目录为hello-spring-cloud-web-admin-feign

创建pom.xml

<?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>
        <groupId>com.funtl</groupId>
        <artifactId>hello-spring-cloud-dependencies</artifactId>
        <version>1.0.0-SNAPSHOT</version>
        <relativePath>../hello-spring-cloud-dependencies/pom.xml</relativePath>
    </parent>
 
    <artifactId>hello-spring-cloud-web-admin-feign</artifactId>
    <packaging>jar</packaging>
 
    <name>hello-spring-cloud-web-admin-feign</name>
    <url>http://www.funtl.com</url>
    <inceptionYear>2018-Now</inceptionYear>
 
    <dependencies>
        <!-- Spring Boot Begin -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- Spring Boot End -->
 
        <!-- Spring Cloud Begin -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <!-- Spring Cloud End -->
 
        <!-- 解决 thymeleaf 模板引擎一定要执行严格的 html5 格式校验问题 -->
        <dependency>
            <groupId>net.sourceforge.nekohtml</groupId>
            <artifactId>nekohtml</artifactId>
        </dependency>
    </dependencies>
 
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <mainClass>com.einblatt.hello.spring.cloud.web.admin.feign.WebAdminFeignApplication</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

托管pom由maven管理依赖创建项目基础目录src/main/java     src/main/resources

创建启动类WebAdminFeignApplication

package com.funtl.hello.spring.cloud.web.admin.feign;


import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;


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

配置程序端口号：

spring:
  application:
    name: hello-spring-cloud-web-admin-feign
  thymeleaf:
    cache: false
    mode: LEGACYHTML5
    encoding: UTF-8
    servlet:
      content-type: text/html
server:
  port: 8765
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/   #Eureka服务注册中心地址

创建Feign接口

通过@Feign("服务名")注解来指定调用哪个服务，代码如下：

package com.funtl.hello.spring.cloud.web.admin.feign.service;


import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;


@FeignClient(value = "hello-spring-cloud-service-admin")
public interface AdminService {
    @RequestMapping(value = "hi",method = RequestMethod.GET)
    public String sayHi(@RequestParam(value = "message") String message);
}

注意：@RequestParam的value值必须与别调用接口的参数名一致。

创建测试用的Controller

package com.funtl.hello.spring.cloud.web.admin.feign.controller;


import com.funtl.hello.spring.cloud.web.admin.feign.service.AdminService;
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 AdminController {


    @Autowired
    private AdminService adminService;
    
    @RequestMapping(value = "hi",method = RequestMethod.GET)
    public String sayHi(String message){
        return adminService.sayHi(message);
    }
}

测试访问

在浏览器上多次访问http://localhost:8765/hi?message=HelloFeign

浏览器交替显示：

Hi your message is : HelloFeign port :8762
Hi your message is : HelloFeign port :8763

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