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一起来学SpringCloud之-服务消费者（Feign-上）

上一篇文章，讲述了Ribbon去做负载请求的服务消费者，本章讲述声明性REST客户端：Feign的简单使用方式

- Feign简介

Feign是一个声明式的Web服务客户端。这使得Web服务客户端的写入更加方便。它具有可插拔注释支持，包括Feign注释和JAX-RS注释。Feign还支持可插拔编码器和解码器。Spring Cloud增加了对Spring MVC注释的支持，并HttpMessageConverters在Spring Web中使用了默认使用的相同方式。Spring Cloud集成了Ribbon和Eureka，在使用Feign时提供负载平衡的http客户端。

官方文档： http://cloud.spring.io/spring-cloud-static/Dalston.SR2/#spring-cloud-feign

- 准备工作

1.启动Consul，所有文章都将以Consul作为服务注册中心

2.创建 battcn-feign-hello ， battcn-feign-hi

battcn-feign-hello

- 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>

    <groupId>com.battcn</groupId>
    <artifactId>battcn-feign-hello</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>battcn-feign-hello</name>
    <description>Feign请求</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Dalston.SR2</spring-cloud.version>
    </properties>

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

- BattcnFeignHelloApplication.java

package com.battcn;

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

@SpringBootApplication
@EnableDiscoveryClient
public class BattcnFeignHelloApplication {

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

创建一个打招呼的的Controller

- HelloController.java

package com.battcn.controller;

import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/hello")
public class HelloController {

    @ResponseStatus(HttpStatus.OK)
    @GetMapping
    public String findStudentByName(@RequestParam("name") String name) {
        // TODO：不做具体代码实现，只打印Log
        return "挽歌- My Name's" + name;
    }

}

- bootstrap.yml

server:
  port: 8765

spring:
  application:
    name: battcn-feign-hello
  cloud:
    consul:
      host: localhost
      port: 8500
      enabled: true
      discovery:
        enabled: true
        prefer-ip-address: true

访问： http://localhost:8765/hello?name=Levin

结果： 挽歌- My Name's Levin 表示我们第一个服务运行一切正常

battcn-feign-hi

- 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>

    <groupId>com.battcn</groupId>
    <artifactId>battcn-feign-hi</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>battcn-feign-hi</name>
    <description>Feign请求</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Dalston.SR2</spring-cloud.version>
    </properties>

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

- BattcnFeignHiApplication.java

package com.battcn;

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
@EnableFeignClients(basePackages = {"com.battcn.client"})
@SpringBootApplication
public class BattcnFeignHiApplication {

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

- HelloClient.java

创建一个声明式 FeignClient 的接口 HelloClient

package com.battcn.client;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseStatus;

/**
 * @author Levin
 * @date 2017-07-28.
 */
@FeignClient(name = "battcn-feign-hello")
public interface HelloClient {

    /** 
     * 在新版本中，Feign 已经可以解析 RestFul 标准的接口API，比如GET POST DELETE PATCH PUT 
     * 旧版中
     * @RequestMapping(method = RequestMethod.GET, value = "/hello")
     * 或者是
     * @RequestMapping(method = RequestMethod.POST, value = "/hello")
     * 
     * 早期文章：http://blog.battcn.com/2017/07/07/springcloud-feign-analysis/
     * /
    @ResponseStatus(HttpStatus.OK)
    @GetMapping("/hello")
    String findStudentByName(@RequestParam("name") String name);
}

- HiController.java

package com.battcn.controller;

import com.battcn.client.HelloClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/hi")
public class HiController {

    @Autowired
    HelloClient helloClient;

    @ResponseStatus(HttpStatus.OK)
    @GetMapping
    public String find(@RequestParam("name") String name) {
        // TODO：只是演示Feign调用的方法
        return "Hi," + helloClient.findStudentByName(name);
    }

}

- bootstrap.yml

server:
  port: 8766

spring:
  application:
    name: battcn-feign-hi
  cloud:
    consul:
      host: localhost
      port: 8500
      enabled: true
      discovery:
        enabled: true
        prefer-ip-address: true

访问： http://localhost:8766/hi?name=Levin

结果： Hi,挽歌- My Name'sLevin 表示第二个服务(hi)通过FeignClient调用服务（hello）一切正常