/*
* Copyright 2013-2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.cloud.client.loadbalancer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.springframework.beans.factory.SmartInitializingSingleton;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestInterceptor;
import org.springframework.web.client.RestTemplate;
/**
* Auto configuration for Ribbon (client side load balancing).
*
* @author Spencer Gibb
* @author Dave Syer
*/
//表示这是一个配置类
@Configuration
//必须存在RestTemplate类
@ConditionalOnClass(RestTemplate.class)
//必须存在LoadBalancerClient类型的bean
@ConditionalOnBean(LoadBalancerClient.class)
public class LoadBalancerAutoConfiguration {
//所有被@LoadBalanced注解修饰的RestTemplate
@LoadBalanced
@Autowired(required = false)
private List<RestTemplate> restTemplates = Collections.emptyList();
//对于所有被@LoadBalanced注解修饰的RestTemplate,调用SmartInitializingSingleton的
//customize方法
@Bean
public SmartInitializingSingleton loadBalancedRestTemplateInitializer(
final List<RestTemplateCustomizer> customizers) {
return new SmartInitializingSingleton() {
@Override
public void afterSingletonsInstantiated() {
for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
for (RestTemplateCustomizer customizer : customizers) {
customizer.customize(restTemplate);
}
}
}
};
}
//对于所有被@LoadBalanced注解修饰的RestTemplate,增加loadBalancerInterceptor属性
@Bean
@ConditionalOnMissingBean
public RestTemplateCustomizer restTemplateCustomizer(
final LoadBalancerInterceptor loadBalancerInterceptor) {
return new RestTemplateCustomizer() {
@Override
public void customize(RestTemplate restTemplate) {
List<ClientHttpRequestInterceptor> list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
}
};
}
//产生一个LoadBalancerInterceptor类型的bean,包含loadBalancerClient类型的bean
@Bean
public LoadBalancerInterceptor ribbonInterceptor(
LoadBalancerClient loadBalancerClient) {
return new LoadBalancerInterceptor(loadBalancerClient);
}
}
LoadBalancerAutoConfiguration配置类的作用是将所有被@LoadBalanced注解修饰的RestTemplate bean增LoadBalancerInterceptor拦截器bean,而LoadBalancerInterceptor又包含loadBalancerClient,这样当用RestTemplate调用时,会首先调用拦截器方法,在拦截器方法里使用loadBalancerClient真正实现负载均衡以及url转换,达到服务名到真正的host之间的转换和负载均衡;