代理接口的修改，提供刷星代理API。downloader 下载错误时，提供request,exception,proxyProvider三个参数，

webmagic-core/src/main/java/us/codecraft/webmagic/downloader/AbstractDownloader.java

@@ -3,6 +3,7 @@ package us.codecraft.webmagic.downloader;
 import us.codecraft.webmagic.Page;
 import us.codecraft.webmagic.Request;
 import us.codecraft.webmagic.Site;
+import us.codecraft.webmagic.proxy.ProxyProvider;
 import us.codecraft.webmagic.selector.Html;
 
 /**
@@ -38,7 +39,7 @@ public abstract class AbstractDownloader implements Downloader {
     protected void onSuccess(Request request) {
     }
 
-    protected void onError(Request request) {
+    protected void onError(Request request, Throwable throwable, ProxyProvider proxyProvider) {
     }
 
 }

webmagic-core/src/main/java/us/codecraft/webmagic/downloader/HttpClientDownloader.java

@@ -87,7 +87,7 @@ public class HttpClientDownloader extends AbstractDownloader {
             return page;
         } catch (IOException e) {
             logger.warn("download page {} error", request.getUrl(), e);
-            onError(request);
+            onError(request,e,proxyProvider);
             return page;
         } finally {
             if (httpResponse != null) {

webmagic-core/src/main/java/us/codecraft/webmagic/proxy/ProxyProvider.java

@@ -19,6 +19,13 @@ public interface ProxyProvider {
      */
     void returnProxy(Proxy proxy, Page page, Task task);
 
+    /**
+     *  代理IP是珍贵资源，有可能代理提供者内部代理没有过期，就一直提供某个IP，但这个IP又不可以使用，所以提供一种方式通知提供者，这个代理该刷新了
+     *
+     * @param task  下载任务
+     */
+    void refreshProxy(Task task);
+
     /**
      * Get a proxy for task by some strategy.
      * @param task the download task

webmagic-core/src/main/java/us/codecraft/webmagic/proxy/SimpleProxyProvider.java

@@ -30,6 +30,11 @@ public class SimpleProxyProvider implements ProxyProvider {
         this.pointer = pointer;
     }
 
+    @Override
+    public void refreshProxy(Task task) {
+
+    }
+
     public static SimpleProxyProvider from(Proxy... proxies) {
         List<Proxy> proxiesTemp = new ArrayList<Proxy>(proxies.length);
         for (Proxy proxy : proxies) {