RestTemplate 是 Spring Resources 中一个访问第三方 RESTful API 接口的网络请求框架,它的主要方法都与 HTTP 协议的一些方法紧密相连,比如 HEAD、GET、POST、PUT、DELETE 和 OPTIONS 等方法,这些方法在 RestTemplate 中对应的方法为 headForHeaders()、getForObject()、postForObject()、put() 和 delete() 等。
Ribbon 是 Netflix 公司开源的一个负载均衡组件,在 SpringCloud 构建的微服务系统中,Ribbon 作为服务消费者的负载均衡器,有两种使用方式,一种是与 RestTemplate 相结合,另一种是和 Feign 相结合,而 Feign 已经默认集成了 Ribbon。
本例采用 Maven 多模块结构,首先创建一个 Maven 项目 spring-cloud-resttemplate 作为父项目,其 pom 文件如下:
<?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>com.wuychn</groupId>
<artifactId>spring-cloud-resttemplate</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<modules>
<module>eureka-server</module>
<module>service-provider</module>
<module>service-consumer</module>
</modules>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.0.RELEASE</version>
</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>Finchley.RELEASE</spring.cloud.version>
</properties>
<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>
</project>
在父项目下创建一个子模块,命名为 eureka-server,作为服务注册中心,其 pom 文件如下:
<?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>
<artifactId>eureka-server</artifactId>
<parent>
<artifactId>spring-cloud-resttemplate</artifactId>
<groupId>com.wuychn</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
application.yml 配置文件内容如下:
server:
port: 9001
spring:
application:
name: eureka-server
eureka:
instance:
hostname: localhost
client:
fetch-registry: false
register-with-eureka: false
serviceUrl:
defaultZone: http://localhost:9001/eureka/
程序启动类:
package com.wuychn;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;
@SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {
public static void main(String[] args) {
SpringApplication.run(EurekaServerApplication.class, args);
}
}
在父项目下再创建一个子模块,命名为 service-provider,作为服务提供者,其 pom 文件内容如下:
<?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>
<artifactId>service-provider</artifactId>
<parent>
<artifactId>spring-cloud-resttemplate</artifactId>
<groupId>com.wuychn</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<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>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
application.yml 文件内容如下:
server:
port: 9003
spring:
application:
name: service-provider
eureka:
client:
serviceUrl:
defaultZone: http://localhost:9001/eureka/
程序启动类如下:
package com.wuychn;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
@SpringBootApplication
@EnableEurekaClient
public class ServiceProviderApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceProviderApplication.class, args);
}
}
在服务提供者模块中,有一个 HiController,它提供一个 REST API 供服务消费者消费:
package com.wuychn.controller;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class HiController {
@Value("${server.port}")
private String port;
@GetMapping("/hi")
public String hi(String name) {
return "hi " + name + ", I am from port:" + port;
}
}
最后再创建一个子模块,命名为 service-consumer,作为服务消费者,其 pom 文件内容如下:
<?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>
<artifactId>service-consumer</artifactId>
<parent>
<artifactId>spring-cloud-resttemplate</artifactId>
<groupId>com.wuychn</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<dependencies>
<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-netflix-ribbon</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
application.yml 文件内容如下:
server:
port: 9004
spring:
application:
name: service-consumer
eureka:
client:
serviceUrl:
defaultZone: http://localhost:9001/eureka/
程序启动类:
package com.wuychn;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
@SpringBootApplication
@EnableEurekaClient
public class ServiceConsumerApplication {
public static void main(String[] args) {
SpringApplication.run(ServiceConsumerApplication.class, args);
}
}
在服务消费者中,也有一个 HiController,它调用 HiService,而 HiService 中会使用 RestTemplate 去调用服务提供者的接口,HiController 如下:
package com.wuychn.controller;
import com.wuychn.service.HiService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class HiController {
@Autowired
private HiService hiService;
@GetMapping("/hi")
public String hi(@RequestParam(required = false, defaultValue = "wuychn") String name) {
return hiService.hi(name);
}
}
HiService 如下:
package com.wuychn.service;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
@Service
public class HiService {
@Autowired
private RestTemplate restTemplate;
public String hi(String name) {
return restTemplate.getForObject("http://service-provider/hi?name=" + name, String.class);
}
}
RestTemplate 的配置:
package com.wuychn.config;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;
@Configuration
public class RestTemplateConfig {
@Bean
@LoadBalanced
public RestTemplate restTemplate() {
return new RestTemplate();
}
}
在声明 RestTemplate Bean 的方法上使用 @LoadBalanced 注解,此时 RestTemplate 就结合了 Ribbon 开启了负载均衡功能。
到这里,代码写完了,代码结构如图:
依次启动 eureka-server、service-provider、service-consumer,其中,service-provider 在 9002 和 9003 两个端口分别启动两个实例,在浏览器中访问 http://localhost:9001/ ,可以看到所有服务都已经注册成功:
在浏览器中多次访问 http://localhost:9004/hi,浏览器会轮流显示如下内容:
hi wuychn, I am from port:9002
hi wuychn, I am from port:9003
可见 service-consumer 使用了 RestTemplate 调用 service-provider 的接口成功,并且负载均衡起了作用。