LoadBalancerInterceptor负载均衡拦截器

LoadBalancerAutoConfiguration负载均衡自动配置 里面调用

public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {

    private LoadBalancerClient loadBalancer;

    //注入LoadBalancerClient 的实现  (唯一的实现就是RibbonLoadBalancerClient
    public LoadBalancerInterceptor(LoadBalancerClient loadBalancer) {
        this.loadBalancer = loadBalancer;
    }
    
    //拦截
    @Override
    public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
            final ClientHttpRequestExecution execution) throws IOException {
            
        //从请求url里面拿到服务名
        final URI originalUri = request.getURI();
        String serviceName = originalUri.getHost();
        
        //loadBalancer执行 根据服务名选择实例  发起请求  的过程
        return this.loadBalancer.execute(serviceName,
                new LoadBalancerRequest() {
      //等负载均衡选中了具体的服务以后 会来回调这个apply方法
                    @Override
                    public ClientHttpResponse apply(final ServiceInstance instance) throws Exception {
                            
                        HttpRequest serviceRequest = new ServiceRequestWrapper(request,
                                instance);
//serviceRequest换成getUrl重写过的 继续拦截链
                        return execution.execute(serviceRequest, body);
                    }

                });
    }

    private class ServiceRequestWrapper extends HttpRequestWrapper {

        private final ServiceInstance instance;

        public ServiceRequestWrapper(HttpRequest request, ServiceInstance instance) {
            super(request);
            this.instance = instance;
        }

        @Override
        public URI getURI() {
            
            //之前看的RibbonLoadBalancerClient.reconstructURI
            URI uri = LoadBalancerInterceptor.this.loadBalancer.reconstructURI(
                    this.instance, getRequest().getURI());
            return uri;
        }

    }

}

这个负载均衡器的拦截 完全靠注入的LoadBalancerClient决定怎么做
拦截里面 转到LoadBalancerClient.execute 里面会选中具体的服务实例 再来回调apply方法
回调的方法 里面穿的HttpRequest的getUrl 重写 里面也用LoadBalancerClient.reconstructURI 吧原来的url换掉