<RESPONSE>
<SINGLE>
<KEY name="id"><VALUE>2</VALUE>
</KEY>
<KEY name="username"><VALUE>admin</VALUE>
</KEY>
<KEY name="password"><VALUE>$2y$10$7M7tcqJDwqmKZRenKGyB8.SYLMkErOSRgrLDd/bxDCBMJyVpTMKlO</VALUE>
</KEY>
<KEY name="firstname"><VALUE>Admin</VALUE>
</KEY>
<KEY name="lastname"><VALUE>User</VALUE>
</KEY>
<KEY name="email"><VALUE>nihar.cbsh@gmail.com</VALUE>
</KEY>
<KEY name="skype"><VALUE></VALUE>
</KEY>
<KEY name="phone"><VALUE null="null"/>
</KEY>
<KEY name="city"><VALUE></VALUE>
</KEY>
<KEY name="country"><VALUE></VALUE>
</KEY>
<KEY name="lang"><VALUE>en</VALUE>
</KEY>
<KEY name="avatar"><VALUE null="null"/>
</KEY>
<KEY name="timemodified"><VALUE>1401336631</VALUE>
</KEY>
我从moodle中的rest webservice获得了这个xml响应。我想从特定键获取用户名值。我怎么能得到它?