public static void testIndex() throws UnknownHostException {
        MongoClient  mgoLocal   = new MongoClient("");
        DBCollection collection = mgoLocal.getDB("test_index").getCollection("url");

        // create unique index
        DBObject indexFileds = new BasicDBObject();
        indexFileds.put("url", 1);
        collection.ensureIndex(indexFileds, "url_1", true);

        // insert document
        String str = "http://www.biomedcentral.com/bmcgeriatr/search/results?drpAddedInLast=&txtSearch4=&txtSearch3=&txtSearch2=bmc+geriatrics&txtSearch1=dementia%2C+or+alzheimer&drpToDate=&drpOrderBy=by+date&drpFromDate=&page=8&jou_id=2009&itemsPerPage=25&portal_id=&excludePhrase1=&excludeField1=&search-button=Search&drpField1=&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&journalAbbreviation=bmcgeriatr&drpField3=%5BAU%5D&drpField2=%5BTA%5D&drpPhrase4=&excludeSearchText1=&drpField4=&drpPhrase3=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&journalIssn=&drpPhrase2=exact&drpPhrase1=&articleType=&saveHistory=false";
        for (int i = 0; i < 10000; i++) {
            DBObject doc = new BasicDBObject();
            doc.put("url", str);
            collection.insert(doc);
        }
        
        // count
        System.out.println(collection.count());        // ==> 10000
        
        // query count
        DBObject query = new BasicDBObject();
        query.put("url", str);
        System.out.println(collection.count(query));   // ==> 0
    }