diff --git a/webmagic-core/src/main/java/us/codecraft/webmagic/oo/PageModelExtractor.java b/webmagic-core/src/main/java/us/codecraft/webmagic/oo/PageModelExtractor.java
index e743e06..83a4d31 100644
--- a/webmagic-core/src/main/java/us/codecraft/webmagic/oo/PageModelExtractor.java
+++ b/webmagic-core/src/main/java/us/codecraft/webmagic/oo/PageModelExtractor.java
@@ -39,7 +39,7 @@ class PageModelExtractor {
         this.clazz = clazz;
         initTargetUrlPatterns();
         fieldExtractors = new ArrayList<FieldExtractor>();
-        if (clazz.isAssignableFrom(AfterExtractor.class)) {
+        if (AfterExtractor.class.isAssignableFrom(clazz)) {
             try {
                 afterExtractor = (AfterExtractor) clazz.newInstance();
             } catch (Exception e) {
@@ -50,9 +50,9 @@ class PageModelExtractor {
             field.setAccessible(true);
             ExtractBy extractBy = field.getAnnotation(ExtractBy.class);
             if (extractBy != null) {
-                if (!extractBy.multi() && !field.getType().isAssignableFrom(String.class)) {
+                if (!extractBy.multi() && !String.class.isAssignableFrom(field.getType())) {
                     throw new IllegalStateException("Field " + field.getName() + " must be string");
-                } else if (extractBy.multi() && !field.getType().isAssignableFrom(List.class)) {
+                } else if (extractBy.multi() && !List.class.isAssignableFrom(field.getType())) {
                     throw new IllegalStateException("Field " + field.getName() + " must be list");
                 }
                 String value = extractBy.value();
@@ -82,9 +82,9 @@ class PageModelExtractor {
             }
             ExtractByUrl extractByUrl = field.getAnnotation(ExtractByUrl.class);
             if (extractByUrl != null) {
-                if (!extractByUrl.multi() && !field.getType().isAssignableFrom(String.class)) {
+                if (!extractByUrl.multi() && !String.class.isAssignableFrom(field.getType())) {
                     throw new IllegalStateException("Field " + field.getName() + " must be string");
-                } else if (extractByUrl.multi() && !field.getType().isAssignableFrom(List.class)) {
+                } else if (extractByUrl.multi() && !List.class.isAssignableFrom(field.getType())) {
                     throw new IllegalStateException("Field " + field.getName() + " must be list");
                 }
                 String regexPattern = extractByUrl.value();
diff --git a/webmagic-core/src/test/java/us/codecraft/webmagic/oo/OschinaBlog.java b/webmagic-core/src/test/java/us/codecraft/webmagic/oo/OschinaBlog.java
index b8c7e4a..c82ef23 100644
--- a/webmagic-core/src/test/java/us/codecraft/webmagic/oo/OschinaBlog.java
+++ b/webmagic-core/src/test/java/us/codecraft/webmagic/oo/OschinaBlog.java
@@ -1,5 +1,7 @@
 package us.codecraft.webmagic.oo;
 
+import us.codecraft.webmagic.Page;
+
 import java.util.List;
 
 /**
@@ -8,7 +10,7 @@ import java.util.List;
  * Time: 下午10:18 <br>
  */
 @TargetUrl("http://my.oschina.net/flashsword/blog/*")
-public class OschinaBlog {
+public class OschinaBlog implements AfterExtractor<OschinaBlog>{
 
     @ExtractBy("//title")
     private String title;
@@ -19,4 +21,7 @@ public class OschinaBlog {
     @ExtractBy(value = "//div[@class='BlogTags']/a/text()", multi = true)
     private List<String> tags;
 
+    @Override
+    public void afterProcess(Page page, OschinaBlog oschinaBlog) {
+    }
 }
diff --git a/webmagic-core/src/test/java/us/codecraft/webmagic/oo/TestFetcher.java b/webmagic-core/src/test/java/us/codecraft/webmagic/oo/TestFetcher.java
index e8e3799..f4525f0 100644
--- a/webmagic-core/src/test/java/us/codecraft/webmagic/oo/TestFetcher.java
+++ b/webmagic-core/src/test/java/us/codecraft/webmagic/oo/TestFetcher.java
@@ -1,8 +1,12 @@
 package us.codecraft.webmagic.oo;
 
+import org.junit.Ignore;
 import org.junit.Test;
 import us.codecraft.webmagic.Site;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * @author yihua.huang@dianping.com <br>
  * @date: 13-8-1 <br>
@@ -10,12 +14,15 @@ import us.codecraft.webmagic.Site;
  */
 public class TestFetcher {
 
-//    @Ignore("takes long")
+    @Ignore("takes long")
     @Test
     public void test() {
+        System.out.println(List.class.isAssignableFrom(ArrayList.class));
         OOSpider.create(Site.me().addStartUrl("http://my.oschina.net/flashsword/blog/145796"), OschinaBlog.class)
                 .run();
 
     }
 
+
+
 }