java Mongodb 查询数组

{
  "FOLDER_ID": "aaa",
  "UUID": "zsw",
  "_id": ObjectId("4f90c83c5b313c4bd9c271d5"),
  "file_list": [
    {
      "file_id": "2",
      "file_name": "歌曲",
      "file_size": "34MB",
      "last_modified": "2001-3-3",
      "thumb_img_uri": "www.google.cn"
    }
  ],
  "subfolder_list": [
    {
      "folder_id": "1",
      "label": "我的文档"
      "ast_modified": "2001-3-21",
      "thumb_img_uri": "www.baidu.com"
    }
  ]
}

BasicDBObject query = new BasicDBObject(); 
    	   BasicDBObject field = new BasicDBObject(); 
    	   field.put("file_list", 1); 
    	   DBCursor cursor = coll.find(query, field); 
    	   while(cursor.hasNext()){ 
    	        BasicDBObject result = (BasicDBObject) cursor.next(); 
    	        int i = result.size();
    	        System.out.println("Result Size: "+i);
    	        System.out.println(result);

{ "_id" : { "$oid" : "4f90c83c5b313c4bd9c271d5"} , "file_list" : [ { "file_id" : "2" , "file_name" : "歌曲" , "file_size" : "34MB" , "last_modified" : "2001.3-3" , "thumb_img_uri" : "www.google.cn"}]}

   BasicDBObject query = new BasicDBObject(); 
    	   BasicDBObject field = new BasicDBObject(); 
    	   field.put("file_list", 1); 
    	   DBCursor cursor = coll.find(query, field); 
    	   while(cursor.hasNext()){ 
    	        BasicDBObject result = (BasicDBObject) cursor.next(); 
    	        int i = result.size();
    	        System.out.println("Result Size: "+i);
    	        System.out.println(result);
    	        ArrayList<BasicDBObject> versi=(ArrayList<BasicDBObject>)result.get("file_list");
    	        for(BasicDBObject embedded:versi){
    	        	String file_name  = embedded.getString("file_name");
    	        	System.out.println("file_name:"+file_name);
    	        }

{ "_id" : { "$oid" : "4f90c83c5b313c4bd9c271d5"} , "file_list" : [ { "file_id" : "2" , "file_name" : "歌曲" , "file_size" : "34MB" , "last_modified" : "2001.3-3" , "thumb_img_uri" : "www.google.cn"}]}file_name:歌曲