SpringCloud学习笔记二：服务间调用

微服务中，很多服务系统都在独立的进程中运行，通过各个服务系统之间的协作来实现一个大项目的所有业务功能。服务系统间使用多种跨进程的方式进行通信协作，而RESTful风格的网络请求是最为常见的交互方式之一。

spring cloud提供的方式：

1.RestTemplate

2.Feign

一、服务提供者创建

在上一篇文章中我们介绍了服务的注册与发现，在此基础上我们将之前创建的eureka-client作为服务消费方创建一个服务提供方。

1.按照上篇文章中创建eureka-client的方式创建eureka-provider

其中application的配置如下

#指定启动端口号
server.port=5202#设置服务注册中心的URL，用于client和server端交流
eureka.client.service-url.defaultZone=http://localhost:5200/eureka/#指定服务名称
spring.application.name=eureka-provide

2.创建服务提供方的ProviderController

1.在包下创建controller.ProviderController,如下图：

2.写入被调用的提供方法

package shadowcoder.controller;import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class ProviderController {@GetMapping("/hello")public String hello() {return "Hello from Eureka Provider!";}
}

二、RestTemplate方式调用

RestTemplate是Spring框架提供的一个工具类，主要用于简化访问RESTful服务的过程。它是从Spring3.0开始支持的一个HTTP请求工具，它封装了底层的HTTP请求细节，让我们可以以更加优雅和简洁的方式调用RESTful API。

1.启动类配置一个R`estTemplate`的Bean，并标记为`@LoadBalanced`，以便Spring Cloud能够为其添加负载均衡支持

package com.shadowcoder;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;@SpringBootApplication
@EnableEurekaClient
public class EurekaClientApplication {public static void main(String[] args) {SpringApplication.run(EurekaClientApplication.class, args);}@Bean@LoadBalanced // 使得RestTemplate具有负载均衡的能力public RestTemplate restTemplate() {return new RestTemplate();}}

2.在eureka-client包下创建controller.ConsumerController，结构如图

3.在ConsumerController写入调用服务提供者的API：/call-hello1

package com.shadowcoder.controller;import com.netflix.appinfo.InstanceInfo;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
import com.netflix.discovery.EurekaClient;import java.util.List;@RestController
public class ConsumerController {@AutowiredEurekaClient client;private final RestTemplate restTemplate;@Autowiredpublic ConsumerController(RestTemplateBuilder restTemplateBuilder) {this.restTemplate = restTemplateBuilder.build();}@GetMapping("/call-hello")public String callHello() {//获取服务名为eureka-provide的服务实例List<InstanceInfo> instances = client.getInstancesByVipAddress("eureka-provide", false);InstanceInfo instanceInfo = instances.get(0);//打印调用的接口System.out.println("http://" + instanceInfo.getHostName() +":"+ instanceInfo.getPort() + "/hello");String url = "http://" + instanceInfo.getHostName() +":"+ instanceInfo.getPort() + "/hello";//服务提供者的APIString response = restTemplate.getForObject(url, String.class);return "Response from Service Provider: " + response;}}

（备注）：通过打印的调用接口发现实际调用的是eureka的主机名而不是spring.application.name的eureka-provider

4.测试调用接口：/call-hello1

访问localhost:5201/call-hello可以发现出现成功调用了eureka-provide的/hello方法

三、Feign方式调用

Feign是一个声明式的Web服务客户端，它使得编写HTTP客户端变得更简单。在Spring Cloud中，Feign可以很容易地与Eureka等服务发现机制集成，从而实现对微服务的调用。

1.在eureka-client中添加Feign依赖

<?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.shadowcoder</groupId><artifactId>SpringCloudTest</artifactId><version>1.0-SNAPSHOT</version></parent><artifactId>eureka-client</artifactId><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><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-web</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency></dependencies></project>

2.启动类上添加`@EnableFeignClients`注解来启用Feign客户端，代码如下

package com.shadowcoder;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class EurekaClientApplication {public static void main(String[] args) {SpringApplication.run(EurekaClientApplication.class, args);}@Bean@LoadBalanced // 使得RestTemplate具有负载均衡的能力public RestTemplate restTemplate() {return new RestTemplate();}}

3.包下新增一个接口service.ConsumerService

代码如下：

package com.shadowcoder.service;import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;@FeignClient(value = "eureka-provide")//value填写提供方的spring.application.name=eureka-provide
public interface ConsumerService {//提供方的调用API@GetMapping("/hello")String hello();
}

4.在ConsumerController注入ConsumerService以及写入调用服务提供者的API：/call-hello2

package com.shadowcoder.controller;import com.netflix.appinfo.InstanceInfo;
import com.shadowcoder.service.ConsumerService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
import com.netflix.discovery.EurekaClient;import java.util.List;@RestController
public class ConsumerController {@AutowiredEurekaClient client;@Autowiredprivate ConsumerService consumerService;private final RestTemplate restTemplate;@Autowiredpublic ConsumerController(RestTemplateBuilder restTemplateBuilder) {this.restTemplate = restTemplateBuilder.build();}@GetMapping("/call-hello")public String callHello() {//获取服务名为eureka-provide的服务实例List<InstanceInfo> instances = client.getInstancesByVipAddress("eureka-provide", false);InstanceInfo instanceInfo = instances.get(0);//打印调用的接口System.out.println("http://" + instanceInfo.getHostName() + ":" + instanceInfo.getPort() + "/hello");String url = "http://" + instanceInfo.getHostName() + ":" + instanceInfo.getPort() + "/hello";//服务提供者的APIString response = restTemplate.getForObject(url, String.class);return "Response from Service Provider: " + response;}@GetMapping("/call-hello2")public String callHello2() {return "Response from Service Provider2: " + consumerService.hello();}}