The following code shows how to combine dropdown button with input group.
<!DOCTYPE html>
<html>
<head>
<script type='text/javascript'
src='http://code.jquery.com/jquery-git2.js'></script>
<link rel="stylesheet" type="text/css"
href="http://getbootstrap.com/assets/css/docs.css">
<link rel="stylesheet" type="text/css"
href="http://getbootstrap.com/dist/css/bootstrap.css">
<script type='text/javascript'
src="http://getbootstrap.com/dist/js/bootstrap.js"></script>
</head><!-- ww w . j av a 2 s.co m-->
<body style='margin:30px'>
<div class="input-group">
<input type="text" class="form-control " placeholder="username">
<div class="input-group-btn">
<button type="button" class="btn btn-default dropdown-toggle"
data-toggle="dropdown">
Dropdown <span class="caret"></span>
</button>
<ul class="dropdown-menu">
<li><a href="#">Dropdown link</a></li>
<li><a href="#">Dropdown link</a></li>
</ul>
</div>
</div>
</body>
</html>