（二）服务的提供与Feign调用

本文中有三个角色，分别是服务的提供者，服务的消费者，注册中心Eureka
整体流程：
（1）先启动注册中心Eureka
（2）启动服务的提供者，将服务注册到注册中心Eureka上对外提供服务
（3）启动服务的消费者，在注册中心中找到服务并完成消费

1、服务提供者

（1）pom.xm

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.springcloud</groupId>
    <artifactId>producer</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>producer</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR1</spring-cloud.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

（2）配置文件application.yml

server:
  port: 8090
spring:
  application:
    name: spring-cloud-producer
eureka:
  server:
    enable-self-preservation: false #关闭eureka的自我保护，防止已被关停的节点也错误的显示在线
  client:
    register-with-eureka: true #否允许客户端向Eureka 注册表获取信息，服务器为设置为false,客户端设置为true
    fetch-registry: true #是否允许向Eureka Server注册信息 如果是服务器端，应该设置为false
    service-url:
      defaultZone: http://peer1:8761/eureka/ #此eureka server的应用注册地址

（3）启动类ProducerApplication.java

@SpringBootApplication
@EnableEurekaClient //如果是其他注册中心可以使用注解@EnableDiscoveryClient来进行服务的注册
public class ProducerApplication {

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

}

（4）Controller

@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String hello(@RequestParam String name) {
        return "hello "+name+"，producer is ready";
    }
}

2、服务消费者

（1）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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.springcloud</groupId>
    <artifactId>consumers</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>consumers</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR1</spring-cloud.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

（2）application.yml

server:
  port: 8091
spring:
  application:
    name: spring-cloud-consumers
eureka:
  server:
    enable-self-preservation: false #关闭eureka的自我保护，防止已被关停的节点也错误的显示在线
  client:
    register-with-eureka: true #否允许客户端向Eureka 注册表获取信息，服务器为设置为false,客户端设置为true
    fetch-registry: true #是否允许向Eureka Server注册信息 如果是服务器端，应该设置为false
    service-url:
      defaultZone: http://peer1:8761/eureka/ #此eureka server的应用注册地址

（3）启动类ConsumersApplication.java

@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients //这个注解是通知SpringBoot在启动的时候，扫描被 @FeignClient 修饰的类
public class ConsumersApplication {

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

}

（4）Feign远程调用，创建一个remote接口

@FeignClient(name= "spring-cloud-producer")
public interface HelloRemote {
    @RequestMapping(value = "/hello")
    String hello(@RequestParam(value = "name") String name);
}

（5）Controller

@RestController
public class HelloController {

    @Autowired
    private HelloRemote helloRemote;

    @RequestMapping("/hello")
    public String hello(@RequestParam("name") String name) {
        return helloRemote.hello(name);
    }
}

依次启动eureka，producer，consumer三个项目，
在浏览器输入http://localhost:8090/hello?name=springcloud，可以看到producer启动正常。
在浏览器输入http://localhost:8091/hello?name=spring，可以看到客户端成功通过feign调用了远程服务hello。

负载均衡

复制一份producer，修改名称为producer2，同时修改相应pom文件，修改application.yml中端口号为8092，修改Controller如下：

@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String hello(@RequestParam String name) {
        return "hello "+name+"，producer2 is ready";
    }
}

启动producer2，可以看到应用名为spring-cloud-producer的有两台机器。
我们再去访问消费端的http://localhost:8091/hello?name=spring，可以看到producer和producer2轮流打印，说明注册中心提供了服务负载均衡功能。