springCloudAlibaba-学习笔记
Declarative REST Client: Feign creates a dynamic implementation of an interface decorated with JAX-RS or Spring MVC annotations
Feign:假装，伪装。OpenFeign可以将提供者提供的Restful服务伪装为接口进行消费，消费者只需要使用feign接口 + 注解的方式即可直接调用提供者提供的Restful服务，而无需在使用RestTemplate
JAX-RS：Java api extensions of RESTful web services。
OpenFeign具有负载均衡功能，其可以对指定的微服务采用负载均衡方式进行消费、访问。老版本的OpenFeign默认采用Ribbon负载均衡器。但是由于Netflix不再维护Ribbon，所有Springcloud2021.x开始集成OpenFeign中已彻底丢弃Ribbon，而是采用SpringCloud自行研发的SpringCloud Loadbalancer作为负载均衡器。
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-loadbalancer</artifactId>
</dependency>
/**
* 描述: feign接口， 参见提供端controller
* @author Vic.xu
* @date 2023-10-20 16:43
*/
@FeignClient(value = "depart-provider", path = "/provider/depart")
public interface DepartService {
@PostMapping("/save")
boolean save(@RequestBody Depart depart);
@DeleteMapping("/delete/{id}")
boolean delete(@PathVariable("id") int id);
@PutMapping("/update")
boolean update(@RequestBody Depart depart);
@GetMapping("/get/{id}")
Depart get(@PathVariable("id") int id);
@GetMapping("/list")
List<Depart> list();
}
@EnableFeignClients
# default is global, can be changed to a real feignName
spring.cloud.openfeign.client.config.default.connectTimeout=5000
spring.cloud.openfeign.client.config.default.readTimeout=1
spring.cloud.openfeign.compression.request.enabled=true
spring.cloud.openfeign.compression.request.mime-types=text/xml,application/xml,application/json
spring.cloud.openfeign.compression.request.min-request-size=2048
httpclient：spring.cloud.openfeign.httpclient.enabled=truespring.cloud.openfeign.httpclient.hc5.enabled=falseokhttp: spring.cloud.openfeign.okhttp.enabled=falsefeign 的远程调用底层实现技术默认采用的是jdk的URLConnection，同时还支持Httpclient和Okhttp。
由于jdk的URLConnection不支持连接池，通信效率很低，所以生产中是不会使用该默认实现的，所在在spring cloud OpenFeign中直接将默认实现该为HttpClient，同是也支持OkHttp.
Client feignClient: If Spring Cloud LoadBalancer is on the classpath, FeignBlockingLoadBalancerClient is used. If none of them is on the classpath, the default feign client is used.
加上LoadBalancer 依赖后默认负载均衡（轮询的方式）
启动类上加：@LoadBalancerClients(defaultConfiguration = DepartConfig.class)
编写随机策略：
public class DepartConfig {
private static final Logger LOGGER = LoggerFactory.getLogger(DepartConfig.class);
/**
* 配置随机均衡策略
*/
@Bean
public ReactorLoadBalancer<ServiceInstance> randomLoadbalancer(Environment environment, LoadBalancerClientFactory factory){
//获取负载均衡客户端名称，即提供者服务名称
String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
ObjectProvider<ServiceInstanceListSupplier> lazyProvider =
factory.getLazyProvider(name, ServiceInstanceListSupplier.class);
LOGGER.info("获取负载均衡客户端名称，即提供者服务名称:{}", name);
//从所有provider实例中指定名称的实例列表中随机选择一个实例
// 参数1：获取指定名称的所有provider实例列表
//参数2：指定要获取的provider实例名称
return new RandomLoadBalancer(lazyProvider, name);
}
}
ReactorLoadBalancer相关实现类：随机、轮询、nacos