Bootstrap3 input输入框插入glyphicon图标的方法

<div class="form-group has-feedback">
<label class="col-md-2 control-label" for="username">用户名</label>
<div class="col-md-6">
<span class="glyphicon glyphicon-user form-control-feedback"></span>
<input type="text" class="form-control" id="username" name="username" placeholder="用户名" autofocus>
</div>
</div>
<div class="form-group has-feedback">
<label class="col-md-2 control-label" for="password">密　码</label>
<div class="col-md-6">
<i></i>
<span class="glyphicon glyphicon-lock form-control-feedback"></span>
<input type="password" class="form-control" id="password" name="password" placeholder="密码">
</div>
</div>

form-control-feedback{
right:0 //改称 left:0
}