1、场景：这里有两个服务，user-server和store-server
1.1、user服务
接口：
package com.lkx.user.controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
/**
* @Author: lkx
* @Date: 2023/8/23/13:20
* @Description:
*/
@RestController
public class UserController {
@GetMapping("/testUser")
public Object testUser() {
return "HelloWorld";
}
}
1.2、store服务
配置类：
package com.lkx.store.config;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.web.client.RestTemplate;
/**
* @Author: lkx
* @Date: 2023/8/23/13:18
* @Description:
*/
@SpringBootConfiguration
@ComponentScan(basePackages = {"com.lkx.store"})
public class AppConfig {
@Bean
@LoadBalanced
public RestTemplate restTemplate() {
return new RestTemplate();
}
}
接口：
package com.lkx.store.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
/**
* @Author: lkx
* @Date: 2023/8/23/13:20
* @Description:
*/
@RestController
public class StoreController {
@Autowired
private RestTemplate restTemplate;
@GetMapping("/testStore")
public Object testStore() {
/**
* 原生调用方式实际上存在一种问题
* 每多一次新地址的调用 都要维护一个全地址 这样维护起来相对就比较复杂了
*
* Ribbon ：这个组件实际上就是为了来做服务的发现的
* Ribbon最终服务的调用还是使用的是 restTemplate
*/
// 原生调用
return restTemplate.getForObject("http://192.168.230.1:8081/testUser",String.class);
// Ribbon调用
// return restTemplate.getForObject("http://user-server/testUser",String.class);
}
}
代码中，store服务通过url（ip地址加端口/方法）去调用user服务的接口，这是原生的调用方式。可以成功调用。Ribbon调用通过服务名称也可成功.
2、Ribbon的实现原理。
解释：两个服务启动时，会将自己的服务名称，以及IP地址和端口注册到注册中心，当有服务调用时，就会拉取注册中心的注册表，里面包含了所有的注册信息。当我们使用Ribbon方式去调用其他服务时，ribbon的拦截器会拦截请求，然后根据拉取到的注册信息，去找到服务名称对应的ip地址和端口，然后重组请求地址，最后以原生的RestTemplate方式去实现服务的调用。
3、源码跟踪
配置类中，我们在设置Bean RestTemplate时，加了一个注解@LoadBalanced。这个注解尤为重要，它就是Ribbon实现原理最为重要的一环。
@LoadBalanced 源码：
/*
* 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 org.springframework.beans.factory.annotation.Qualifier;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Annotation to mark a RestTemplate bean to be configured to use a LoadBalancerClient.
* @author Spencer Gibb
*/
@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Qualifier
public @interface LoadBalanced {
}
这里的解释翻译是：标记一个RestTemplate bean来配置使用LoadBalancerClient。那么，这个LoadBalancerClient是什么呢？
/*
* 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 org.springframework.cloud.client.ServiceInstance;
import java.io.IOException;
import java.net.URI;
/**
* Represents a client-side load balancer.
* @author Spencer Gibb
*/
public interface LoadBalancerClient extends ServiceInstanceChooser {
/**
* Executes request using a ServiceInstance from the LoadBalancer for the specified
* service.
* @param serviceId The service ID to look up the LoadBalancer.
* @param request Allows implementations to execute pre and post actions, such as
* incrementing metrics.
* @return The result of the LoadBalancerRequest callback on the selected
* ServiceInstance.
*/
<T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException;
/**
* Executes request using a ServiceInstance from the LoadBalancer for the specified
* service.
* @param serviceId The service ID to look up the LoadBalancer.
* @param serviceInstance The service to execute the request to.
* @param request Allows implementations to execute pre and post actions, such as
* incrementing metrics.
* @return The result of the LoadBalancerRequest callback on the selected
* ServiceInstance.
*/
<T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request) throws IOException;
/**
* Creates a proper URI with a real host and port for systems to utilize.
* Some systems use a URI with the logical service name as the host,
* such as http://myservice/path/to/service. This will replace the
* service name with the host:port from the ServiceInstance.
* @param instance
* @param original A URI with the host as a logical service name.
* @return A reconstructed URI.
*/
URI reconstructURI(ServiceInstance instance, URI original);
}
翻译一下注释：Represents a client-side load balancer.这是一个客户端负载平衡器。而@LoadBalanced注解标记的RestTemplate就是来配置这个平衡器的，这里我们就需要找到这个配置类，同文件夹下有一个LoadBalancerAutoConfiguration，给它的解释是功能区的自动配置（客户端负载平衡）
@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 LoadBalancerInterceptor loadBalancerInterceptor) {
return restTemplate -> {
List<ClientHttpRequestInterceptor> list = new ArrayList<>(
restTemplate.getInterceptors());
list.add(loadBalancerInterceptor);
restTemplate.setInterceptors(list);
};
}
}
而在这个配置类里就有我们的ribbon的拦截器设置了。然后进入LoadBalancerInterceptor拦截器,通过拦截器的执行代码，然后到RibbonLoadBalancerClient的execute方法，这个方法就是通过我们的key来找到对应的服务器去执行请求，后面方法太多，就不一 一叙述，最后发现，最底层调用的还是原生的请求去实现调用的。
