爪哇国新游记之三十四----Dom4j的XPath操作

Dom4j是Java访问XML的利器之一，另一个是JDom。记得当年因为粗掌握点JDomAPI但项目要求使用Dom4j还闹一阵情绪，现在看来真是没必要，只花一些时间成本就进去一个新世界绝对是值得做的一件事。更何况JDom因无人更新而停顿了。

Dom4j有两个包，一个是dom4j-1.6.1.jar，它提供基本的XML API支持，如访问节点，属性等。

还有一个是jaxen-1.1-beta-9.jar，它提供XPath支持。

关于XPath的语法，请见转载：XPath基本语法

言归正传，下面请看例程。

1.访问节点群

XML样本：

<applications>
    <application name='chat'>
        <mtLanguage source='ar_ar' target='en_us' />
        <mtLanguage source='zh_cn' target='en_us' />
        <mtLanguage source='zh_tw' target='en_us' />
        <mtLanguage source='en_us' target='ar_ar' />
        <mtLanguage source='en_us' target='zh_cn' />
        <mtLanguage source='en_us' target='zh_tw' />
        <mtLanguage source='en_us' target='fr_fr' />
        <mtLanguage source='en_us' target='de_de' />
        <mtLanguage source='en_us' target='it_it' />
        <mtLanguage source='en_us' target='ja_jp' />
        <mtLanguage source='en_us' target='ko_kr' />
        <mtLanguage source='en_us' target='pt_br' />
        <mtLanguage source='en_us' target='ru_ru' />
        <mtLanguage source='en_us' target='es_es' />
        <mtLanguage source='fr_fr' target='en_us' />
        <mtLanguage source='de_de' target='en_us' />
        <mtLanguage source='it_it' target='en_us' />
        <mtLanguage source='ja_jp' target='en_us' />
        <mtLanguage source='ko_kr' target='en_us' />
        <mtLanguage source='pt_br' target='en_us' />
        <mtLanguage source='ru_ru' target='en_us' />
        <mtLanguage source='es_es' target='en_us' />
    </application>
    <application name='doc'>
        <mtLanguage source='ar_ar' target='en_us' />
        <mtLanguage source='zh_cn' target='en_us' />
        <mtLanguage source='zh_tw' target='en_us' />
        <mtLanguage source='en_us' target='ar_ar' />
        <mtLanguage source='en_us' target='zh_cn' />
        <mtLanguage source='en_us' target='zh_tw' />
        <mtLanguage source='en_us' target='fr_fr' />
        <mtLanguage source='en_us' target='de_de' />
        <mtLanguage source='en_us' target='hi_in' />
        <mtLanguage source='en_us' target='it_it' />
        <mtLanguage source='en_us' target='ja_jp' />
        <mtLanguage source='en_us' target='ko_kr' />
        <mtLanguage source='en_us' target='pt_br' />
        <mtLanguage source='en_us' target='ru_ru' />
        <mtLanguage source='en_us' target='es_es' />
        <mtLanguage source='en_us' target='ur_pk' />
        <mtLanguage source='fr_fr' target='en_us' />
        <mtLanguage source='de_de' target='en_us' />
        <mtLanguage source='hi_in' target='en_us' />
        <mtLanguage source='it_it' target='en_us' />
        <mtLanguage source='ja_jp' target='en_us' />
        <mtLanguage source='ko_kr' target='en_us' />
        <mtLanguage source='pt_br' target='en_us' />
        <mtLanguage source='ru_ru' target='en_us' />
        <mtLanguage source='es_es' target='en_us' />
        <mtLanguage source='ur_pk' target='en_us' />
    </application>
</applications>

现在，如果我想要访问属性为chat的application节点下的所有mtLanguage子节点，XPath应该这样写：

//applications/application[@name='chat']/mtLanguage

而具体操作的Java语句是：

Document doc= DocumentHelper.parseText(responseXML);// 这个responseXML就是上面的XML样例
List<?> elms=doc.selectNodes("//applications/application[@name='chat']/mtLanguage");
System.out.println("There are "+elms.size()+" language pairs available in text translation");

for(Object obj:elms){
     Element elm=(Element)obj;
     System.out.println("From "+elm.attributeValue("source")+" to "+elm.attributeValue("target"));
}

执行上面语句输出如下：

There are 22 language pairs available in text translation
From ar_ar to en_us
From zh_cn to en_us
From zh_tw to en_us
From en_us to ar_ar
From en_us to zh_cn
From en_us to zh_tw
From en_us to fr_fr
From en_us to de_de
From en_us to it_it
From en_us to ja_jp
From en_us to ko_kr
From en_us to pt_br
From en_us to ru_ru
From en_us to es_es
From fr_fr to en_us
From de_de to en_us
From it_it to en_us
From ja_jp to en_us
From ko_kr to en_us
From pt_br to en_us
From ru_ru to en_us
From es_es to en_us

2.访问特定节点

XML样本：

<rep sts="OK" a="trep" tl="zh-CN">
    <docs>
        <d dt="ndoc" did="d20160223213120480009045125076363146" lang="en-US"
            ctime="2016-02-23T21:31:20" mtime="2016-02-23T21:31:20" orig="1"
            mime="text/x-mt-xml" wc="2">
            <p pid="1" wc="2">
                <s sid="1">
                    <t tid="1" tt="orig" wc="2">Good evening</t>
                </s>
            </p>
        </d>
        <d dt="ndoc" did="d20160223213120480009045125076363146" lang="zh-CN"
            ctime="2016-02-23T21:31:20" mtime="2016-02-23T21:31:20" orig="0"
            mime="text/x-mt-xml" sc="100.00" wc="1">
            <p pid="1" wc="1">
                <s sid="1">
                    <t tid="1" tt="mt" src="mt" sc="100.00" wc="1">晚上好</t>
                </s>
            </p>
        </d>
    </docs>
</rep>

如果我想得到上文中“晚上好”这段文字，XPath应该这样写

//rep/docs/d[last()]/p/s/t

对应的Java代码是：

Document doc= DocumentHelper.parseText(responseXML);
Element elm = (Element) doc.selectSingleNode("//rep/docs/d[last()]/p/s/t");
targetTxt=elm.getText();

3.取属性

XML样本：

<rep sts="OK" a="trep" tl="zh-CN">
    <docs>1</docs>
</rep>

要取根节点rep的sts属性，XPath可以这样写：

//rep/@sts

而对应的Java语句是：

System.out.println("XML="+responseXML);
Document doc= DocumentHelper.parseText(responseXML);
Attribute attr = (Attribute) doc.selectSingleNode("//rep/@sts");      

return attr.getText();