* ��parameters������װ��query string��
*
* @return query string�����û�в�������<code>null</code>
*/
public String toQueryString() {
QueryStringParser parser = new QueryStringParser();
for (Object element : keySet()) {
String key = (String) element;
Object[] values = getObjects(key);
if (isEmptyArray(values)) {
continue;
}
for (Object valueObject : values) {
if (valueObject == null || valueObject instanceof String) {
parser.append(key, (String) valueObject);
}
}
}
return parser.toQueryString();
}