[Java知识库]SpringCloudAlibaba生态环境搭建二：负载均衡

1、什么是Spring Cloud LoadBalancer

Spring Cloud LoadBalancer是Spring Cloud官方自己提供的客户端负载均衡器，用来替代Ribbon。（Ribbon：也进入了维护状态，停止更新了，但是Spring官方还在使用）

Spring官方提供了两种负载均衡的客户端：

????????第一种：RestTemplate:

RestTemplate默认依赖jdk的HTTP连接工具，提供了多种便捷访问远程Http服务的方法，是Spring提供的用于访问Rest服务的客户端；

????????第二种：WebClient:

从Spring WebFlux5.0开始提供的一个非阻塞的基于响应式编程的进行Http请求的客户端工具。它的响应式编程基于Reactor。WebClient中提供了标准Http请求方式对应的get、post、put、delete等方法，可以用来发起相应请求。

2、RestTemplate整合LoadBalancer

2.1引入依赖

<dependencies>
        <!--LoadBalancer-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-loadbalancer</artifactId>
        </dependency>
        <!--提供了RestTemplate支持-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!--nacos服务注册与发现，移除ribbon支持-->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.cloud</groupId>
                    <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

nacos-discovery中引入了ribbon，需要移除ribbon的包，如果不移除，也可以在yml中配置不使用ribbon

server:
  port: 10001

spring:
  application:
    name: service-consumer
  cloud:
    nacos:
      discovery:
        server-addr: http://101.132.143.77:8848
    # 不使用ribbon
    loadbalancer:
      ribbon:
        enabled: false

原理：默认情况下，如果同时拥有RibbonLoadBalancerClient和BlockingLoadBalancerClient，为了保持向后兼容性，将使用RibbonLoadBalancerClient。要覆盖它，可以设置spring.cloud.loadbalancer.ribbon.enabled属性等于false;

?

?2.2使用@LaodBalanced注解配置RestTemplate

@Configuration
public class CommonConfig {

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

?2.3使用

@RestController
@RequestMapping("/provide/")
public class ProvideController {

    @Autowired
    private RestTemplate restTemplate;

    @GetMapping("hello")
    public String test(){
        return "hello,provider";
    }

    @GetMapping("consume")
    public String consume(){
        String url = "http://service-consumer/consume/hello";
        return restTemplate.getForObject(url,String.class);
    }
}

3、WebClient整合LoadBalancer

3.1引入依赖

<!--LoadBalancer-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-loadbalancer</artifactId>
        </dependency>
        <!--webflux-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <!--nacos服务注册与发现，移除ribbon支持-->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.cloud</groupId>
                    <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

3.2配置WebClient作为负载均衡器client

@Configuration
public class CommonConfig {

    @LoadBalanced
    @Bean
    WebClient.Builder webClientBuilder(){
        return WebClient.builder();
    }

    @Bean
    WebClient webClient(){
        return webClientBuilder().build();
    }
}

3.3使用?

@RestController
@RequestMapping("/consume/")
public class ConsumeController {

    @Autowired
    private WebClient webClient;

    @GetMapping("hello")
    public String test(){
        return "hello,consumer";
    }


    @GetMapping("provide")
    public Mono<String> provide(){
        String url = "http://service-provider/provide/hello";
        Mono<String> result = webClient.get().uri(url).retrieve().bodyToMono(String.class);
        return result;
    }
}

原理：底层会使用ReactiveLoadBalancer

引入webFlux

    @Autowired
    private ReactorLoadBalancerExchangeFilterFunction lbFunction;

    @GetMapping("provide2")
    public Mono<String> provide2(){
        String url = "http://service-provider/provide/hello";
        Mono<String> result = WebClient.builder()
                .filter(lbFunction)
                .build()
                .get()
                .uri(url)
                .retrieve()
                .bodyToMono(String.class);
        return result;
    }

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