[spring-cloud: 负载均衡]-源码分析
获取服务列表
ServiceInstanceListSupplier
ServiceInstanceListSupplier 接口是一个提供 ServiceInstance 列表的供应者，返回一个响应式流 Flux<List<ServiceInstance>>，用于服务发现。
public interface ServiceInstanceListSupplier extends Supplier<Flux<List<ServiceInstance>>> {String getServiceId();default Flux<List<ServiceInstance>> get(Request request) {return get();}static ServiceInstanceListSupplierBuilder builder() {return new ServiceInstanceListSupplierBuilder();}}
DelegatingServiceInstanceListSupplier
DelegatingServiceInstanceListSupplier 是一个抽象类，继承自 ServiceInstanceListSupplier，它通过委托给另一个 ServiceInstanceListSupplier 实例来实现其功能，同时支持选定服务实例的回调、初始化和销毁操作。
public abstract class DelegatingServiceInstanceListSupplier implements ServiceInstanceListSupplier, SelectedInstanceCallback, InitializingBean, DisposableBean {protected final ServiceInstanceListSupplier delegate;public DelegatingServiceInstanceListSupplier(ServiceInstanceListSupplier delegate) {Assert.notNull(delegate, "delegate may not be null");this.delegate = delegate;}public ServiceInstanceListSupplier getDelegate() {return delegate;}@Overridepublic String getServiceId() {return delegate.getServiceId();}@Overridepublic void selectedServiceInstance(ServiceInstance serviceInstance) {if (delegate instanceof SelectedInstanceCallback selectedInstanceCallbackDelegate) {selectedInstanceCallbackDelegate.selectedServiceInstance(serviceInstance);}}@Overridepublic void afterPropertiesSet() throws Exception {if (delegate instanceof InitializingBean) {((InitializingBean) delegate).afterPropertiesSet();}}@Overridepublic void destroy() throws Exception {if (delegate instanceof DisposableBean) {((DisposableBean) delegate).destroy();}}}
负载均衡实现
ReactorLoadBalancer
ReactorLoadBalancer 是基于 Reactor 实现的响应式负载均衡器，通过 Mono<Response<T>> 异步选择服务实例。
public interface ReactorLoadBalancer<T> extends ReactiveLoadBalancer<T> {@SuppressWarnings("rawtypes")Mono<Response<T>> choose(Request request);default Mono<Response<T>> choose() {return choose(REQUEST);}}
ReactorServiceInstanceLoadBalancer
ReactorServiceInstanceLoadBalancer 是一个标记接口，继承自 ReactorLoadBalancer，专门用于选择 ServiceInstance 对象的负载均衡器。
// RandomLoadBalancer, RoundRobinLoadBalancer
public interface ReactorServiceInstanceLoadBalancer extends ReactorLoadBalancer<ServiceInstance> {}
核心代码逻辑
推荐阅读：[spring-cloud: @LoadBalanced & @LoadBalancerClient]-源码分析
1. BlockingLoadBalancerInterceptor
// LoadBalancerInterceptor, RetryLoadBalancerInterceptor
public interface BlockingLoadBalancerInterceptor extends ClientHttpRequestInterceptor {}
LoadBalancerInterceptor
public class LoadBalancerInterceptor implements BlockingLoadBalancerInterceptor {private final LoadBalancerClient loadBalancer;private final LoadBalancerRequestFactory requestFactory;public LoadBalancerInterceptor(LoadBalancerClient loadBalancer, LoadBalancerRequestFactory requestFactory) {this.loadBalancer = loadBalancer;this.requestFactory = requestFactory;}public LoadBalancerInterceptor(LoadBalancerClient loadBalancer) {// for backwards compatibilitythis(loadBalancer, new LoadBalancerRequestFactory(loadBalancer));}// 重点!@Overridepublic ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution)throws IOException {URI originalUri = request.getURI();String serviceName = originalUri.getHost();Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);return loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));}}
2. BlockingLoadBalancerClient
ServiceInstanceChooser
ServiceInstanceChooser 接口用于通过负载均衡器选择与指定服务ID对应的服务实例，支持带请求上下文的选择。
public interface ServiceInstanceChooser {ServiceInstance choose(String serviceId);<T> ServiceInstance choose(String serviceId, Request<T> request);}
LoadBalancerClient
LoadBalancerClient 接口用于客户端负载均衡，选择服务实例并执行请求，同时提供将逻辑服务名重构为实际服务实例的 URI 的功能。
public interface LoadBalancerClient extends ServiceInstanceChooser {<T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException;<T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request) throws IOException;URI reconstructURI(ServiceInstance instance, URI original);}
// BlockingLoadBalancerClientAutoConfiguration
@SuppressWarnings({ "unchecked", "rawtypes" })
public class BlockingLoadBalancerClient implements LoadBalancerClient {// org.springframework.cloud.loadbalancer.config.LoadBalancerAutoConfiguration// LoadBalancerClientFactoryprivate final ReactiveLoadBalancer.Factory<ServiceInstance> loadBalancerClientFactory;public BlockingLoadBalancerClient(ReactiveLoadBalancer.Factory<ServiceInstance> loadBalancerClientFactory) {this.loadBalancerClientFactory = loadBalancerClientFactory;}// 重点！@Overridepublic <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException {String hint = getHint(serviceId);LoadBalancerRequestAdapter<T, TimedRequestContext> lbRequest = new LoadBalancerRequestAdapter<>(request, buildRequestContext(request, hint));Set<LoadBalancerLifecycle> supportedLifecycleProcessors = getSupportedLifecycleProcessors(serviceId);supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onStart(lbRequest));// 通过 choose 方法来选择一个合适的 ServiceInstanceServiceInstance serviceInstance = choose(serviceId, lbRequest);if (serviceInstance == null) {supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(new CompletionContext<>(CompletionContext.Status.DISCARD, lbRequest, new EmptyResponse())));throw new IllegalStateException("No instances available for " + serviceId);}return execute(serviceId, serviceInstance, lbRequest);}private <T> TimedRequestContext buildRequestContext(LoadBalancerRequest<T> delegate, String hint) {if (delegate instanceof HttpRequestLoadBalancerRequest) {HttpRequest request = ((HttpRequestLoadBalancerRequest) delegate).getHttpRequest();if (request != null) {RequestData requestData = new RequestData(request);return new RequestDataContext(requestData, hint);}}return new DefaultRequestContext(delegate, hint);}// 通过生命周期钩子函数来管理负载均衡请求的开始与结束，并处理可能的异常，确保负载均衡的执行过程有序@Overridepublic <T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request) throws IOException {if (serviceInstance == null) {throw new IllegalArgumentException("Service Instance cannot be null, serviceId: " + serviceId);}DefaultResponse defaultResponse = new DefaultResponse(serviceInstance);Set<LoadBalancerLifecycle> supportedLifecycleProcessors = getSupportedLifecycleProcessors(serviceId);Request lbRequest = request instanceof Request ? (Request) request : new DefaultRequest<>();supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onStartRequest(lbRequest, new DefaultResponse(serviceInstance)));try {T response = request.apply(serviceInstance);Object clientResponse = getClientResponse(response);supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(new CompletionContext<>(CompletionContext.Status.SUCCESS, lbRequest, defaultResponse, clientResponse)));return response;}catch (IOException iOException) {supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(new CompletionContext<>(CompletionContext.Status.FAILED, iOException, lbRequest, defaultResponse)));throw iOException;}catch (Exception exception) {supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(new CompletionContext<>(CompletionContext.Status.FAILED, exception, lbRequest, defaultResponse)));ReflectionUtils.rethrowRuntimeException(exception);}return null;}private <T> Object getClientResponse(T response) {ClientHttpResponse clientHttpResponse = null;if (response instanceof ClientHttpResponse) {clientHttpResponse = (ClientHttpResponse) response;}if (clientHttpResponse != null) {try {return new ResponseData(clientHttpResponse, null);}catch (IOException ignored) {}}return response;}private Set<LoadBalancerLifecycle> getSupportedLifecycleProcessors(String serviceId) {return LoadBalancerLifecycleValidator.getSupportedLifecycleProcessors(loadBalancerClientFactory.getInstances(serviceId, LoadBalancerLifecycle.class),DefaultRequestContext.class, Object.class, ServiceInstance.class);}@Overridepublic URI reconstructURI(ServiceInstance serviceInstance, URI original) {return LoadBalancerUriTools.reconstructURI(serviceInstance, original);}@Overridepublic ServiceInstance choose(String serviceId) {return choose(serviceId, REQUEST);}// 重点！通过负载均衡器同步选择一个服务实例并返回@Overridepublic <T> ServiceInstance choose(String serviceId, Request<T> request) {ReactiveLoadBalancer<ServiceInstance> loadBalancer = loadBalancerClientFactory.getInstance(serviceId);if (loadBalancer == null) {return null;}Response<ServiceInstance> loadBalancerResponse = Mono.from(loadBalancer.choose(request)).block();if (loadBalancerResponse == null) {return null;}return loadBalancerResponse.getServer();}private String getHint(String serviceId) {LoadBalancerProperties properties = loadBalancerClientFactory.getProperties(serviceId);String defaultHint = properties.getHint().getOrDefault("default", "default");String hintPropertyValue = properties.getHint().get(serviceId);return hintPropertyValue != null ? hintPropertyValue : defaultHint;}}
3. LoadBalancerRequestFactory
LoadBalancerRequestFactory 类用于创建封装负载均衡请求的 LoadBalancerRequest 实例，支持请求转换器和负载均衡客户端的配置。
public class LoadBalancerRequestFactory {private final LoadBalancerClient loadBalancer;private final List<LoadBalancerRequestTransformer> transformers;public LoadBalancerRequestFactory(LoadBalancerClient loadBalancer,List<LoadBalancerRequestTransformer> transformers) {this.loadBalancer = loadBalancer;this.transformers = transformers;}public LoadBalancerRequestFactory(LoadBalancerClient loadBalancer) {this.loadBalancer = loadBalancer;transformers = new ArrayList<>();}public LoadBalancerRequest<ClientHttpResponse> createRequest(final HttpRequest request, final byte[] body,final ClientHttpRequestExecution execution) {return new BlockingLoadBalancerRequest(loadBalancer, transformers,new BlockingLoadBalancerRequest.ClientHttpRequestData(request, body, execution));}}
LoadBalancerRequestTransformer
LoadBalancerRequestTransformer 接口允许在负载均衡过程中根据不同的服务实例自定义转换 HttpRequest，如修改请求头、URL 等，同时通过 @Order 注解控制其执行顺序。
@Order(LoadBalancerRequestTransformer.DEFAULT_ORDER)
public interface LoadBalancerRequestTransformer {int DEFAULT_ORDER = 0;HttpRequest transformRequest(HttpRequest request, ServiceInstance instance);
}
4. BlockingLoadBalancerRequest
BlockingLoadBalancerRequest 类实现了负载均衡请求接口，负责将原始 HTTP 请求封装为负载均衡请求，并支持应用请求转换器和执行负载均衡操作。
class BlockingLoadBalancerRequest implements HttpRequestLoadBalancerRequest<ClientHttpResponse> {private final LoadBalancerClient loadBalancer;private final List<LoadBalancerRequestTransformer> transformers;private final ClientHttpRequestData clientHttpRequestData;BlockingLoadBalancerRequest(LoadBalancerClient loadBalancer, List<LoadBalancerRequestTransformer> transformers,ClientHttpRequestData clientHttpRequestData) {this.loadBalancer = loadBalancer;this.transformers = transformers;this.clientHttpRequestData = clientHttpRequestData;}@Overridepublic ClientHttpResponse apply(ServiceInstance instance) throws Exception {HttpRequest serviceRequest = new ServiceRequestWrapper(clientHttpRequestData.request, instance, loadBalancer);if (this.transformers != null) {for (LoadBalancerRequestTransformer transformer : this.transformers) {serviceRequest = transformer.transformRequest(serviceRequest, instance);}}return clientHttpRequestData.execution.execute(serviceRequest, clientHttpRequestData.body);}@Overridepublic HttpRequest getHttpRequest() {return clientHttpRequestData.request;}static class ClientHttpRequestData {private final HttpRequest request;private final byte[] body;private final ClientHttpRequestExecution execution;ClientHttpRequestData(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) {this.request = request;this.body = body;this.execution = execution;}}}