从零开始搭springcloud(四) riibon和feign实现负载均衡

一、简介

    Springcloud有两种方式实现负载均衡调用服务，一种是ribbon+restTemplate，另一种是feign，首先是使用前者。

二、ribbon+restTemplate

   首先配置pom：

  <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-eureka</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-ribbon</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

   接着在yml文件中指定服务注册中心，以及程序名，ip地址，如果是从配置中心读取配置，还需要配置注册中心地址。

eureka:
  client:
    serviceUrl:
      defaultZone: http://username:pass@ip/eureka/
  instance:
    ip-address: ip
    prefer-ip-address: true
server:
  port: 8764
spring:
  application:
    name: service-ribbon
  sleuth:
    sampler:
      percentage: 1.0
  cloud:
    config:
      discovery:
        enabled: true
        service-id: CONFIG-SERVER
      label: master
      profile: dev
      name: hfz-ribbon
      username: usename
      password: pass

   在Application.java中通过@EnableDiscoveryClient向服务中心注册；并且注入一股bean–restTemplate;并通过@LoadBalanced注解表明这个restRemplate开启负载均衡的功能。

@EnableHystrix
@EnableHystrixDashboard
@SpringBootApplication
@EnableDiscoveryClient
@RefreshScope
public class HfzribbonApplication {

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

    @Bean
    @LoadBalanced
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

   写一个类HelloService，通过restTemplate来消费服务的“/hi”接口，在这里可以直接用在注册中心配置的程序名替代来具体的url地址，ribbon会根据服务名来选择具体的服务实例，根据服务实例在请求的时候会用具体的url替换掉服务名

@Service
public class HelloService {
    @Autowired
    RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "hiError")
    public String hiService(String name) {
        return restTemplate.getForObject("http://SERVER-HI/hi?name="+name,String.class);
    }
    public String hiError(String name) {
        return "hi,"+name+",sorry,error!";
    }

}

   然后可以在Controller中调用服务就行

@RestController
public class HelloControler {

    @Autowired
    HelloService helloService;
    @RequestMapping(value="/hi")

    public String hi(@RequestParam String name){
        return helloService.hiService(name);
    }

三、Feign

   Feign是一个声明式的伪Http客户端，这使得用来写Http客户端变得更简单。要使用Feign，只需要创建一个接口并注解。它具有可插拔的注解特性，可使用Feign 注解和JAX-RS注解。Feign支持可插拔的编码器和解码器。Feign默认集成了Ribbon，可以Eureka结合，默认实现了负载均衡的效果。以下是搭建过程

   首先是pom文件：

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

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

    yml文件如下：

    eureka:
      client:
        serviceUrl:
          defaultZone: http://localhost:8761/eureka/
    server:
      port: 8765
    spring:
      application:
        name: service-feign

   在程序的启动类Application上加上@EnableFeignClients注解开启Feign的功能

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
@EnableHystrixDashboard
@EnableCircuitBreaker
public class HfzfeignApplication {

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

   定义一个feign接口，通过@ FeignClient（“服务名”），来指定调用哪个服务

    @FeignClient(value = "service-hi",fallback = SchedualServiceHiHystric.class)
    public interface SchedualServiceHi {

        @RequestMapping(value = "/hi",method = RequestMethod.GET)
        String sayHiFromClientOne(@RequestParam(value = "name") String name);
    }

   然后是controller层上对外暴露的接口

@RestController
public class HiController {

        @Autowired
        SchedualServiceHi schedualServiceHi;

        @RequestMapping(value = "/hi",method = RequestMethod.GET)
        public String sayHi(@RequestParam String name){
            return schedualServiceHi.sayHiFromClientOne(name);
        }
    }

   然后可以通过访问接口来测试