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(二)Eureka，注冊中心，服務者，消費者（Ribbon，Feign）

Eureka

按照官方介紹：

Eureka is a REST (Representational State Transfer) based service that is primarily used in the AWS cloud for locating services for the purpose of load balancing and failover of middle-tier servers.

Eureka 是一個基于 REST 的服務，主要在 AWS 雲中使用, 定位服務來進行中間層伺服器的負載均衡和故障轉移。

Spring Cloud 封裝了 Netflix 公司開發的 Eureka 子產品來實作服務注冊和發現。Eureka 采用了 C-S 的設計架構。Eureka Server 作為服務注冊功能的伺服器，它是服務注冊中心。而系統中的其他微服務，使用 Eureka 的用戶端連接配接到 Eureka Server，并維持心跳連接配接。這樣系統的維護人員就可以通過 Eureka Server 來監控系統中各個微服務是否正常運作。Spring Cloud 的一些其他子產品（比如Zuul）就可以通過 Eureka Server 來發現系統中的其他微服務，并執行相關的邏輯。

Eureka由兩個元件組成：Eureka伺服器和Eureka用戶端。Eureka伺服器用作服務注冊伺服器。Eureka用戶端是一個java用戶端，用來簡化與伺服器的互動、作為輪詢負載均衡器，并提供服務的故障切換支援。Netflix在其生産環境中使用的是另外的用戶端，它提供基于流量、資源使用率以及出錯狀态的權重負載均衡。

用一張圖來認識以下：

(二)Eureka，注冊中心，服務者，消費者（Ribbon，Feign）

上圖簡要描述了Eureka的基本架構，由3個角色組成：

1、Eureka Server

  • 提供服務注冊和發現

2、Service Provider

  • 服務提供方
  • 将自身服務注冊到Eureka，進而使服務消費方能夠找到

3、Service Consumer

  • 服務消費方
  • 從Eureka擷取注冊服務清單，進而能夠消費服務

案例實踐

Eureka Server

1. 服務注冊中心

在IDEA中建立一個Spring Cloud工程，引入Eureka-Server包，pom檔案整體如下：

<?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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>service-register</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <!-- eureka-server -->
        <dependency>
          <groupId>org.springframework.cloud</groupId>
          <artifactId>spring-cloud-starter-eureka-server</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>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>                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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>service-register</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <!-- eureka-server -->
        <dependency>
          <groupId>org.springframework.cloud</groupId>
          <artifactId>spring-cloud-starter-eureka-server</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>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

在src/main/java包下建立一個名為hello的包，然後建立 

EurekaServiceRegisterApplication

 類                                                    @SpringBootApplication                                                                                                                                         @EnableEurekaServer觸發Spring Boot的自動配置機制，spring boot會在容器中建立對應的bean。EurekaServiceRegisterApplication的代碼如下：

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@EnableEurekaServer 
@SpringBootApplication
public class EurekaServiceRegisterApplication {

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

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@EnableEurekaServer 
@SpringBootApplication
public class EurekaServiceRegisterApplication {

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

application.properties配置。

#是否需要注冊到注冊中心
eureka.client.register-with-eureka=false
#是否需要從注冊中心擷取服務清單
eureka.client.fetch-registry=false
#注冊伺服器的位址
eureka.client.service-url.defaultZone=http://localhost:8761/eureka

logging.level.com.netflix.eureka=OFF
logging.level.com.netflix.discovery=OFF                
eureka.client.register-with-eureka=false
#是否需要從注冊中心擷取服務清單
eureka.client.fetch-registry=false
#注冊伺服器的位址
eureka.client.service-url.defaultZone=http://localhost:8761/eureka

logging.level.com.netflix.eureka=OFF
logging.level.com.netflix.discovery=OFF

啟動注冊服務，通路： 

http://localhost:8761

 ，就可以看到如下界面。

(二)Eureka，注冊中心，服務者，消費者（Ribbon，Feign）

服務注冊中心背景

2. 服務提供者

建立一個Spring Boot工程，代表服務提供者。

工程的pom檔案内容如下：

<?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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>service-client</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
        <relativePath/> 
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

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

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
          <groupId>org.springframework.cloud</groupId>
          <artifactId>spring-cloud-starter-eureka-server</artifactId>
          <scope>test</scope>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>                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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>service-client</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
        <relativePath/> 
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

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

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
          <groupId>org.springframework.cloud</groupId>
          <artifactId>spring-cloud-starter-eureka-server</artifactId>
          <scope>test</scope>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

添加spring-cloud-starter-eureka這個Jar包，其中包含了eureka的用戶端實作。

在src/main/java/hello下建立工程的主類EurekaServerProducerApplication。                                                   @EnableDiscoveryClient在服務啟動的時，觸發服務注冊的過程，向配置檔案中指定的服務注冊中心（Eureka-Server）的位址注冊自己提供的服務。EurekaServerProducerApplication：

package hello;

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


@EnableDiscoveryClient
@SpringBootApplication
public class EurekaServerProducerApplication {

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

}                 hello;

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


@EnableDiscoveryClient
@SpringBootApplication
public class EurekaServerProducerApplication {

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

}

配置檔案的内容如下：

#服務提供者的名字
spring.application.name=compute-service

#服務提供者的端口号
server.port=8888

#服務注冊中心的位址
eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/                
spring.application.name=compute-service

#服務提供者的端口号
server.port=8888

#服務注冊中心的位址
eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/

服務提供者的基本架構搭好後，需要實作服務的具體内容，在ServiceInstanceRestController類中實作，它的具體代碼如下：

package hello;


import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;


@RestController
public class ServiceInstanceRestController {

    private static final Logger logger = LoggerFactory.getLogger(ServiceInstanceRestController.class);

    @Autowired
    private DiscoveryClient discoveryClient; //服務發現用戶端

    @GetMapping(value = "/add")
    public Integer add(@RequestParam Integer a, @RequestParam Integer b) {
        ServiceInstance instance = discoveryClient.getLocalServiceInstance();
        Integer r = a + b;
        logger.info("/add, host:" + instance.getHost() + ", service_id:" + instance.getServiceId() + ", result:" + r);
        return r;
    }
}                 hello;


import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;


@RestController
public class ServiceInstanceRestController {

    private static final Logger logger = LoggerFactory.getLogger(ServiceInstanceRestController.class);

    @Autowired
    private DiscoveryClient discoveryClient; //服務發現用戶端

    @GetMapping(value = "/add")
    public Integer add(@RequestParam Integer a, @RequestParam Integer b) {
        ServiceInstance instance = discoveryClient.getLocalServiceInstance();
        Integer r = a + b;
        logger.info("/add, host:" + instance.getHost() + ", service_id:" + instance.getServiceId() + ", result:" + r);
        return r;
    }
}

啟動服務注冊中心的工程，然後啟動服務提供者， 

localhost:8761

，如下圖所示，服務提供者已經注冊到服務注冊中心啦。

(二)Eureka，注冊中心，服務者，消費者（Ribbon，Feign）

服務提供者注冊到服務注冊中心

在Spring Cloud Netflix中，使用Ribbon實作用戶端負載均衡，使用Feign實作聲明式HTTP用戶端調用——即寫得像本地函數調用一樣。

3. 服務消費者-Ribbon

建立一個Spring boot工程，引入ribbon和eureka，pom檔案内容如下：

<?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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>serviceconsumer</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

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

    <dependencies>
        <!-- 用戶端負載均衡 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-ribbon</artifactId>
        </dependency>

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

        <!-- spring boot實作Java Web服務-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>                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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>serviceconsumer</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

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

    <dependencies>
        <!-- 用戶端負載均衡 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-ribbon</artifactId>
        </dependency>

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

        <!-- spring boot實作Java Web服務-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

建立EurekaConsumerApplication類，定義REST用戶端執行個體，代碼如下：

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@EnableDiscoveryClient //開啟服務發現的能力
@SpringBootApplication
public class EurekaConsumerApplication {

    @Bean //定義REST用戶端，RestTemplate執行個體
    @LoadBalanced //開啟負債均衡的能力
    RestTemplate restTemplate() {
        return new RestTemplate();
    }

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

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@EnableDiscoveryClient //開啟服務發現的能力
@SpringBootApplication
public class EurekaConsumerApplication {

    @Bean //定義REST用戶端，RestTemplate執行個體
    @LoadBalanced //開啟負債均衡的能力
    RestTemplate restTemplate() {
        return new RestTemplate();
    }

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

application.properties中定義了服務注冊中心的位址、消費者服務的端口号、消費者服務的名稱這些内容：

#應用名稱
spring.application.name=ribbon-consumer

#端口号
server.port=9000

#注冊中心的位址
eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/                
spring.application.name=ribbon-consumer

#端口号
server.port=9000

#注冊中心的位址
eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/

消費者服務的入口為：ConsumerController，我們通過這個執行個體進行測試。消費者服務啟動過程中，會從服務注冊中心中拉最新的服務清單，當浏覽器觸發對應的請求，就會根據COMPUTE-SERVICE查找服務提供者的IP和端口号，然後發起調用。

package hello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;


@RestController
public class ConsumerController {

    @Autowired
    private RestTemplate restTemplate;

    @GetMapping(value = "/add")
    public String add() {
        return restTemplate.getForEntity("http://COMPUTE-SERVICE/add?a=10&b=20", String.class).getBody();
    }
}                 hello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;


@RestController
public class ConsumerController {

    @Autowired
    private RestTemplate restTemplate;

    @GetMapping(value = "/add")
    public String add() {
        return restTemplate.getForEntity("http://COMPUTE-SERVICE/add?a=10&b=20", String.class).getBody();
    }
}

首先啟動服務注冊中心，第二分别啟動兩個服務提供者（IP相同、端口不同即可），然後啟動服務消費者。

(二)Eureka，注冊中心，服務者，消費者（Ribbon，Feign）

兩個服務提供者

在浏覽器裡通路 

localhost:9000/add

 兩次，可以看到請求有時候會在8888端口的服務，有時候會到8889的服務。具體背後選擇的原理，還有待後續研究。

4. 服務消費者-Feign

上一節中，使用類似 

restTemplate.getForEntity("http://COMPUTE-SERVICE/add?a=10&b=20", String.class).getBody()

 這樣的語句進行服務間調用并非不可以，隻是我們在服務化的過程中，希望跨服務調用能夠看起來像本地調用，這也是我了解的Feign的使用場景。

建立一個spring boot工程，該工程的pom檔案與上一節的類似，隻是把ribbon的依賴換為feign的即可，代碼如下：

<?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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>serviceconsumer</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

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

    <dependencies>
        <!-- Feign實作聲明式HTTP用戶端 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>

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

        <!-- spring boot實作Java Web服務-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>                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>

    <groupId>org.example.springcloud</groupId>
    <artifactId>serviceconsumer</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.1.RELEASE</version>
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
    </properties>

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

    <dependencies>
        <!-- Feign實作聲明式HTTP用戶端 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>

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

        <!-- spring boot實作Java Web服務-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>Camden.SR5</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

首先建立應用程式啟動類：EurekaConsumerApplication，代碼如下：

package hello;

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


@EnableDiscoveryClient //用于啟動服務發現功能
@EnableFeignClients //用于啟動Fegin功能
@SpringBootApplication
public class EurekaConsumerApplication {

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

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


@EnableDiscoveryClient //用于啟動服務發現功能
@EnableFeignClients //用于啟動Fegin功能
@SpringBootApplication
public class EurekaConsumerApplication {

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

然後定義遠端調用的接口，在hello包下建立depend包，然後建立ComputeClient接口，使用@FeignClient("COMPUTE-SERVICE")注解修飾，COMPUTE-SERVICE就是服務提供者的名稱，然後定義要使用的服務，代碼如下：

package hello.depend;

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

@FeignClient("COMPUTE-SERVICE")
public interface ComputeClient {

    @RequestMapping(method = RequestMethod.GET, value = "/add")
    Integer add(@RequestParam(value = "a") Integer a, @RequestParam(value = "b") Integer b);
}                 hello.depend;

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

@FeignClient("COMPUTE-SERVICE")
public interface ComputeClient {

    @RequestMapping(method = RequestMethod.GET, value = "/add")
    Integer add(@RequestParam(value = "a") Integer a, @RequestParam(value = "b") Integer b);
}

在ConsumerController中，像引入普通的spring bean一樣引入ComputeClient對象，其他的和Ribbon的類似。

package hello;

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;

import hello.depend.ComputeClient;

@RestController
public class ConsumerController {

    @Autowired
    private ComputeClient computeClient;

    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public Integer add() {
        return computeClient.add(10, 20);
    }
}                 hello;

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;

import hello.depend.ComputeClient;

@RestController
public class ConsumerController {

    @Autowired
    private ComputeClient computeClient;

    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public Integer add() {
        return computeClient.add(10, 20);
    }
}

application.properties的内容如下：

#應用名稱
spring.application.name=fegin-consumer

#端口号
server.port=9000

#注冊中心的位址
eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/                
spring.application.name=fegin-consumer

#端口号
server.port=9000

#注冊中心的位址
eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/

啟動fegin消費者，通路 

localhost:9000/add

 ，也可以看到服務提供者已經收到了消費者發來的請求。

(二)Eureka，注冊中心，服務者，消費者（Ribbon，Feign）

請求到達服務提供者1

(二)Eureka，注冊中心，服務者，消費者（Ribbon，Feign）

請求到達服務提供者2

spring-cloud
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