loadBalancer 第4 章：ServiceInstanceListSupplier

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李延 LV6 2021-06-23

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# 作用

在ReactorServiceInstanceLoadBalancer中我们知道，它就是通过ServiceInstanceListSupplier对象获取到当前请求所有符合要求的实例，再进行筛选实现负载均衡的。

# 加载

ServiceInstanceListSupplier是通过loadBalancerClientFactory加载。

同样我们在LoadBalancerClientConfiguration类中找到加载过程。

```java

@Bean
		@ConditionalOnBean(ReactiveDiscoveryClient.class)
		@ConditionalOnMissingBean
		@ConditionalOnProperty(value = "spring.cloud.loadbalancer.configurations", havingValue = "default",
				matchIfMissing = true)
		public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(
				ConfigurableApplicationContext context) {
			return ServiceInstanceListSupplier.builder().withDiscoveryClient().withCaching().build(context);
		}
```
这里有多个，我们只挑选了默认加载的那个。

# 主要方法withBlockingDiscoveryClient

```java

public ServiceInstanceListSupplierBuilder withBlockingDiscoveryClient() {
		if (baseCreator != null && LOG.isWarnEnabled()) {
			LOG.warn("Overriding a previously set baseCreator with a blocking DiscoveryClient baseCreator.");
		}
		this.baseCreator = context -> {
			DiscoveryClient discoveryClient = context.getBean(DiscoveryClient.class);

return new DiscoveryClientServiceInstanceListSupplier(discoveryClient, context.getEnvironment());
		};
		return this;
	}
```

这里我们看到通过上下文加载DiscoveryClient对象的过程。而DiscoveryClient对象就是提供每个serviceId实例的对象。

这个对象在nacos也可以找到它的实现：NacosDiscoveryClient

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