概述
在前面的文章中，我们讲了使用Eureka作为服务注册中心，在服务启动后，各个微服务会将自己注册到Eureka server。那么服务之间是如何调用？又是如何进行负载均衡的呢？本文讲讲服务之间调用及负载均衡Ribbon。
目前，在Spring cloud 中服务之间通过restful方式调用有两种方式
restTemplate+Ribbon
feign
从实践上看，采用feign的方式更优雅（feign内部也使用了ribbon做负载均衡）。
本文使用如下的项目实例来分别演示这两种写法。
hello服务，读取数据库，返回信息world服务，返回信息helloworld服务，调用了hello服务和world服务（restTemplate+Ribbon方式）helloworldfeign服务，调用了hello服务和world服务（feign方式）
项目之间关系.png
本文项目代码：springcloud-demo
如何理解客户端Ribbon
zuul也有负载均衡的功能，它是针对外部请求做负载，那客户端ribbon的负载均衡又是怎么一回事？
客户端ribbon的负载均衡，解决的是服务发起方（在Eureka注册的服务）对被调用的服务的负载，比如我们查询商品服务要调用显示库存和商品明细服务，通过商品服务的接口将两个服务组合，可以减少外部应用的请求，比如手机App发起一次请求即可，可以节省网络带宽，也更省电。
ribbon是对服务之间调用做负载，是服务之间的负载均衡，zuul是可以对外部请求做负载均衡。
Ribbon负载均衡.png
hello服务与world服务
hello服务
Git项目代码：hello
pom.xml
<dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-eureka</artifactId> </dependency> <!--connect the db--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> <version>1.5.4.RELEASE</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.31</version> <scope>runtime</scope> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> <version>1.5.6.RELEASE</version> </dependency> </dependencies> <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>Dalston.SR2</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement>
启动类HelloApplication：
package com.example.hello;import com.example.hello.model.Info;import com.example.hello.repository.InfoRepository;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.boot.CommandLineRunner;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;import org.springframework.context.annotation.Bean;@EnableDiscoveryClient@SpringBootApplicationpublic class HelloApplication { private static final Logger log= LoggerFactory.getLogger(HelloApplication.class); public static final String KEY="Database"; public static final String VALUE="MYSQL FROM BILLJIANG"; public static void main(String[] args) {
SpringApplication.run(HelloApplication.class, args);
} @Bean
public CommandLineRunner initDatabase(InfoRepository repository){ return (args) -> {
repository.save(new Info(KEY,VALUE));
};
}
}入口类HelloController：
package com.example.hello.controller;import com.example.hello.HelloApplication;import com.example.hello.model.HelloMessage;import com.example.hello.model.Info;import com.example.hello.repository.InfoRepository;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.RestController;import java.util.List;@RestControllerpublic class HelloController { @Autowired
private DiscoveryClient discoveryClient; @Autowired
private InfoRepository infoRepository; @GetMapping("/") public String home(){ return "hello";
} @GetMapping("/message") public HelloMessage getMessage() {
HelloMessage helloMessage = new HelloMessage();
helloMessage.setName(getLocalInstanceInfo());
helloMessage.setMessage(getInfoFromDatabase()); return helloMessage;
} private String getLocalInstanceInfo() {
ServiceInstance serviceInstance = discoveryClient.getLocalServiceInstance(); return serviceInstance.getServiceId() + ":" + serviceInstance.getHost() + ":" + serviceInstance.getPort();
} private String getInfoFromDatabase() {
List<Info> infoList = infoRepository.findByName(HelloApplication.KEY); for (Info info : infoList) { return info.toString();
} return "(no database info)";
}
}配置文件application.yml:
#随机端口server:
port: 0#服务注册中心eureka:
client:
service-url:
default-zone: http://localhost:8761/eureka
instance:
instance-id: ${spring.application.name}:${spring.application.instance_id:${random.value}}#数据源spring:
application:
name: hello
datasource:
url: jdbc:mysql://127.0.0.1:3306/${{MYSQL_DATABASE}:foodb}
username: ${{MYSQL_USERNAME}:root}
password: ${{MYSQL_PASSWORD}:billjiang}
testWhileIdle: true
validationQuery: SELECT 1
jpa:
show-sql: true
hibernate:
ddl-auto: update
naming-strategy: org.hibernate.cfg.ImprovedNamingStrategy
properties:
hibernate:
dialect: org.hibernate.dialect.MySQL5Dialect
zipkin:
base-url: http://127.0.0.1:9411其他类略，请参照源码：
world
world服务与hello服务类似，不过没有连接数据库
项目代码：world
helloworld调用hello服务和world服务
采用restTemplate+Ribbon调用服务。
项目代码：helloworld
启动类HelloworldApplication：
配置restTemplate的Bean
package com.example.helloworld;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;@SpringBootApplication@EnableDiscoveryClientpublic class HelloworldApplication { public static void main(String[] args) {
SpringApplication.run(HelloworldApplication.class, args);
} @Bean
@LoadBalanced
RestTemplate restTemplate() { return new RestTemplate();
}
}入口类HelloworldController：
package com.example.helloworld.controller;import com.example.helloworld.model.HelloMessage;import com.example.helloworld.model.HelloworldMessage;import com.example.helloworld.model.WorldMessage;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.cloud.client.loadbalancer.LoadBalanced;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RestController;import org.springframework.web.client.RestTemplate;/**
* @author billjiang 475572229@qq.com
* @create 17-8-22
*/@RestControllerpublic class HelloworldController { private static final Logger log = LoggerFactory.getLogger(HelloworldController.class); private static final String HELLO_SERVICE_NAME = "hello"; private static final String WORLD_SERVICE_NAME = "world"; @Autowired
private RestTemplate restTemplate; @GetMapping("/") public String home() { return "hello world";
} @GetMapping("/message") public HelloworldMessage getMessage() {
HelloMessage hello = getMessageFromHelloService();
WorldMessage world = getMessageFromWorldService();
HelloworldMessage helloworld = new HelloworldMessage();
helloworld.setHello(hello);
helloworld.setWord(world);
log.debug("Result helloworld message:{}", helloworld); return helloworld;
} private HelloMessage getMessageFromHelloService() {
HelloMessage hello = restTemplate.getForObject("http://hello/message", HelloMessage.class);
log.debug("From hello service : {}.", hello); return hello;
} private WorldMessage getMessageFromWorldService() {
WorldMessage world = restTemplate.getForObject("http://world/message", WorldMessage.class);
log.debug("From world service : {}.", world); return world;
}
}测试：
helloworldfeign调用hello服务和world服务
feign方式调用服务，项目代码参考：helloworldfeign
pom.xml引入feignx
<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-feign</artifactId> </dependency>
配置启动类注解：
package com.example.helloworldfeign;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;@SpringBootApplication@EnableDiscoveryClient@EnableFeignClientspublic class HelloworldFeignApplication { public static void main(String[] args) {
SpringApplication.run(HelloworldFeignApplication.class, args);
}
}被调用接口HelloService
package com.example.helloworldfeign.service;import com.example.helloworldfeign.model.HelloMessage;import org.springframework.cloud.netflix.feign.FeignClient;import org.springframework.web.bind.annotation.GetMapping;/**
* @author billjiang 475572229@qq.com
* @create 17-8-23
*/@FeignClient(value="hello")public interface HelloService { @GetMapping("/message") HelloMessage hello();
}被调用接口WorldService
package com.example.helloworldfeign.service;import com.example.helloworldfeign.model.WorldMessage;import org.springframework.cloud.netflix.feign.FeignClient;import org.springframework.web.bind.annotation.GetMapping;/**
* @author billjiang 475572229@qq.com
* @create 17-8-23
*/@FeignClient(value="world")public interface WorldService { @GetMapping("/message") WorldMessage world();
}入口类HelloworldController：
package com.example.helloworldfeign.controller;import com.example.helloworldfeign.model.HelloMessage;import com.example.helloworldfeign.model.HelloworldMessage;import com.example.helloworldfeign.model.WorldMessage;import com.example.helloworldfeign.service.HelloService;import com.example.helloworldfeign.service.WorldService;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RestController;/**
* @author billjiang 475572229@qq.com
* @create 17-8-23
*/@RestControllerpublic class HelloworldController { private static final Logger log = LoggerFactory.getLogger(HelloworldController.class); private static final String HELLO_SERVICE_NAME = "hello"; private static final String WORLD_SERVICE_NAME = "world"; @Autowired
private HelloService helloService; @Autowired
private WorldService worldService; @GetMapping("/") public String home() { return "hello world";
} @GetMapping("/message") public HelloworldMessage getMessage() {
HelloMessage hello = helloService.hello();
WorldMessage world = worldService.world();
HelloworldMessage helloworld = new HelloworldMessage();
helloworld.setHello(hello);
helloworld.setWord(world);
log.debug("Result helloworld message:{}", helloworld); return helloworld;
}
}为了更好的地查看效果，hello服务和world服务可以启动多个实例，并把调用实例的ip和端口输出来。
作者：billJiang
链接：https://www.jianshu.com/p/7ca91139dca5
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