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}