springCloud的LoadBalance源码分析

最新推荐文章于 2025-06-04 17:59:27 发布

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最新推荐文章于 2025-06-04 17:59:27 发布 · 1.3k 阅读

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文章标签：

#eureka #ribbon #loadBalance #springcloud

本文详细分析了SpringCloud中的LoadBalancer核心类、LoadBalanced注解及其功能，以及源码实现。通过@LoadBalanced注解，RestTemplate能实现自动负载均衡。源码解析包括LoadBalancerAutoConfiguration配置类的条件判断，以及RibbonAutoConfiguration中如何创建Ribbon实现的负载均衡客户端。文章还提及Eureka客户端默认使用Ribbon的原因。

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springCloud的LoadBalance源码分析

欢迎查看Eetal的第二十篇博客–SpringCloud的LoadBalance源码分析

LoadBalanced注解与功能

通过在创建的RestTemplate上加入LoadBalanced注解，则该RestTemplate会自动成为负载均衡的RestTeplate，请求的url的hostname会作为服务名称去解析
用法如下

	@LoadBalanced
	@Bean
    public RestTemplate restTemplate() {
   
   
        return new RestTemplate();
    }
	
	public String requestTest(){
   
   
	String url = "http://8781-eurekaClient/getClient2Info";
	return restTemplate.getForObject(url, String.class);
		}

等价于以下写法

@Autowired
	RestTemplate restTemplate;
	
	@Autowired
    private LoadBalancerClient client;
	
	@RequestMapping("/getProviderInfo")
	public String getProviderInfo() {
   
   
		ServiceInstance instance = client.choose("8780-eurekaClient");
        String url = "http://" + instance.getHost() + ":" + instance.getPort() + "/getInfo";
        return restTemplate.getForObject(url, String.class);
	}

源码分析

1.LoadBalanced注解

@Target({
   
    ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Qualifier
public @interface LoadBalanced {
   
   

}

这里注意，该注解被标记了@Qualifier注解，后续使用@Autowired注解注入时，如果注解的属性也被LoadBalanced注解，则只装载一样被LoadBalanced注解的符合autowired的对象
2.LoadBalnceAutoConfigure

@Configuration
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {
   
   

	@LoadBalanced
	@Autowired(required = false)
	private List<RestTemplate> restTemplates = Collections.emptyList();

	@Autowired(required = false)
	private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();

	@Bean
	public SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(
			final ObjectProvider<List<RestTemplateCustomizer>> restTemplateCustomizers) {
   
   
		return () -> restTemplateCustomizers.ifAvailable(customizers -> {
   
   
			for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
   
   
				for (RestTemplateCustomizer customizer : customizers) {
   
   
					customizer.customize(restTemplate);
				}
			}
		});
	}

	@Bean
	@ConditionalOnMissingBean
	public LoadBalancerRequestFactory loadBalancerRequestFactory(
			LoadBalancerClient loadBalancerClient) {
   
   
		return new LoadBalancerRequestFactory(loadBalancerClient, this.transformers);
	}

	@Configuration
	@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
	static class LoadBalancerInterceptorConfig {
   
   

		@Bean
		public LoadBalancerInterceptor ribbonInterceptor(
				LoadBalancerClient loadBalancerClient,
				LoadBalancerRequestFactory requestFactory) {
   
   
			return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
		}

		@Bean
		@ConditionalOnMissingBean
		public RestTemplateCustomizer restTemplateCustomizer(
				final LoadBalanc