bug fixed for AfterFilter, fix #3217

Author: wenshao

src/main/java/com/alibaba/fastjson/serializer/AfterFilter.java

@@ -11,10 +11,11 @@ public abstract class AfterFilter implements SerializeFilter {
     private final static Character                   COMMA           = Character.valueOf(',');
 
     final char writeAfter(JSONSerializer serializer, Object object, char seperator) {
+        JSONSerializer last = serializerLocal.get();
         serializerLocal.set(serializer);
         seperatorLocal.set(seperator);
         writeAfter(object);
-        serializerLocal.set(null);
+        serializerLocal.set(last);
         return seperatorLocal.get();
     }
 

src/test/java/com/alibaba/json/bvt/issue_3300/Issue3217.java

@@ -0,0 +1,98 @@
+package com.alibaba.json.bvt.issue_3300;
+
+import com.alibaba.fastjson.JSON;
+import com.alibaba.fastjson.serializer.AfterFilter;
+import junit.framework.TestCase;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Issue3217 extends TestCase {
+
+    public void test_for_issue() throws Exception {
+        RefAfterFilterTest refAfterFilterTest = new RefAfterFilterTest();
+
+        List<Item> items = new ArrayList<Item>(2);
+        Category category = new Category("category");
+        items.add(new Item("item1",category));
+        items.add(new Item("item2",category));
+
+        System.out.println(JSON.toJSONString(items,refAfterFilterTest));
+    }
+
+    public static class RefAfterFilterTest extends AfterFilter {
+
+        private Category category = new Category("afterFilterCategory");
+
+        @Override
+        public void writeAfter(Object object) {
+
+            if (object instanceof Item) {
+
+                this.writeKeyValue("afterFilterCategory", category);
+                /*多加一个属性报错,原因是category是object也触发了writeAfter,当前线程变量serializer被设置为null了serializerLocal.set(null);
+                 *这两个write换个顺序就不会报错
+                 */
+                this.writeKeyValue("afterFilterTwo", "two");
+
+            }
+        }
+    }
+
+    public static class Category {
+
+        private String name;
+
+        public Category(String name){
+            this.name = name;
+        }
+
+        public String getName() {
+            return name;
+        }
+
+        public void setName(String name) {
+            this.name = name;
+        }
+    }
+
+    public static class Item {
+
+        private String name;
+
+        private Category category;
+
+        private String barcode;
+
+
+        public Item(String name,Category category){
+            this.name = name;
+            this.category = category;
+        }
+
+        public String getName() {
+            return name;
+        }
+
+        public void setName(String name) {
+            this.name = name;
+        }
+
+        public Category getCategory() {
+            return category;
+        }
+
+        public void setCategory(Category category) {
+            this.category = category;
+        }
+
+        public String getBarcode() {
+            return barcode;
+        }
+
+        public void setBarcode(String barcode) {
+            this.barcode = barcode;
+        }
+
+    }
+}