用于分析xml属性文件的XPath查询

我有以下xml文档:

<!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">  
<properties>  
    <comment>My Happy Configuration</comment>  
    <entry key="HappyKey">Happy Key</entry>  
    <entry key="SadKey">Sad Key</entry>  
    <entry key="AngryKey">Angry Key</entry>  
    <entry key="ConfusedKey">Confused Key</entry>  
    ...
</properties>

/properties/entry[@key='HappyKey']  

我预计这会带来快乐,但它不会带来任何回报。