英文:
Find index of nested XML tag
问题
假设我有一个像这样的XML：
<body>
<nested attr="bla">
<name>foo</name>
</nested>
<nested attr="blub">
<name>bar</name>
</nested>
<nested attr="bli">
<name>baz</name>
</nested>
</body>
现在我想要的是一种通过特定值获取`nested`标签索引的方法。例如，`bar`的索引将是1（或者如果从1开始计数则为2）。
我已经使用了Apache CachedXPathApi完成了这个任务：
public int getIndex(String path, String value) throws TransformerException {
NodeIterator it = cachedXPathAPI.selectNodeIterator(document, path);
Node node;
int i = 0;
while((node = it.nextNode()) != null) {
if(node.getTextContent().equals(value)) {
return i;
}
++i;
}
return -1;
}
这对于从属性`attr`获取索引很有效，就像这样：
```getIndex("/body/nested/@attr", "blub")```
但我不知道如何为嵌套的值执行此操作。如果我使用```/body/nested/name```，那么它显然只会计算`nested`中的`name`标签，这不是我想要的。
我该如何解决这个问题，无论是通过更改Java代码还是甚至使用特殊的XPath表达式？
英文:
suppose I have an XML like this:
<body>
<nested attr="bla">
<name>foo</name>
</nested>
<nested attr="blub">
<name>bar</name>
</nested>
<nested attr="bli">
<name>baz</name>
</nested>
</body>
What I want now is a way to get the index of the nested tag with a certain value. So for example the index of bar would be 1 (or 2 if you count from 1).
I have already done this using Apache CachedXPathApi:
public int getIndex(String path, String value) throws TransformerException {
NodeIterator it = cachedXPathAPI.selectNodeIterator(document, path);
Node node;
int i = 0;
while((node = it.nextNode()) != null) {
if(node.getTextContent().equals(value)) {
return i;
}
++i;
}
return -1;
}
Which works fine for getting the index from the attribute attr like this:
getIndex("/body/nested/@attr", "blub")
But I don't know how to do this for the nested values. If I use /body/nested/name then it will obviously only ever count the name tags within nested which is not what I want.
How can I solve this, either by changing the Java Code or maybe even with a special XPath expression?
答案1
得分: 1
如果我正确理解您的问题，您想要在您的代码中获取 <Nested> 标签的索引。请查看以下代码：
public static void main(String[] args) throws TransformerException, SAXException, IOException, ParserConfigurationException {
String xmlString = "<body>\r\n" +
" <nested attr=\"bla\">\r\n" +
" <name>foo</name>\r\n" +
" </nested>\r\n" +
" <nested attr=\"blub\">\r\n" +
" <name>bar</name>\r\n" +
" </nested>\r\n" +
" <nested attr=\"bli\">\r\n" +
" <name>baz</name>\r\n" +
" </nested>\r\n" +
"</body>";
CachedXPathAPI cachedXPathAPI = new CachedXPathAPI();
DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document document = builder.parse(new InputSource(new StringReader(xmlString)));
NodeList list = cachedXPathAPI.selectNodeList(document, "/body/nested");
for(int i=0; i<list.getLength(); i++ ) {
String value = list.item(i).getAttributes().getNamedItem("attr").getTextContent();
System.out.println(list.item(i).getNodeName()+" @Index "+i+" attr:: "+value);
}
}
result
nested @Index 0 attr:: bla
nested @Index 1 attr:: blub
nested @Index 2 attr:: bli
英文:
If I understood ur question correctly U want to have the index of the <Nested> tag in ur code, Look at the below code
public static void main(String[] args) throws TransformerException, SAXException, IOException, ParserConfigurationException {
String xmlString = "<body>\r\n" +
" <nested attr=\"bla\">\r\n" +
" <name>foo</name>\r\n" +
" </nested>\r\n" +
" <nested attr=\"blub\">\r\n" +
" <name>bar</name>\r\n" +
" </nested>\r\n" +
" <nested attr=\"bli\">\r\n" +
" <name>baz</name>\r\n" +
" </nested>\r\n" +
"</body>";
CachedXPathAPI cachedXPathAPI = new CachedXPathAPI();
DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document document = builder.parse(new InputSource(new StringReader(xmlString)));
NodeList list = cachedXPathAPI.selectNodeList(document, "/body/nested");
for(int i=0; i<list.getLength(); i++ ) {
String value = list.item(i).getAttributes().getNamedItem("attr").getTextContent();
System.out.println(list.item(i).getNodeName()+" @Index "+i+" attr:: "+value);
}
}
result
nested @Index 0 attr:: bla
nested @Index 1 attr:: blub
nested @Index 2 attr:: bli
答案2
得分: 1
只评估这个XPath表达式：
count(/*/*[name='bar']/preceding-sibling::*) + 1
基于XSLT的验证：
以下转换简单地评估XPath表达式，并输出此评估的结果：
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:value-of select="count(/*/*[name='bar']/preceding-sibling::*) + 1"/>
</xsl:template>
</xsl:stylesheet>
当应用于提供的XML文档时：
<body>
<nested attr="bla">
<name>foo</name>
</nested>
<nested attr="blub">
<name>bar</name>
</nested>
<nested attr="bli">
<name>baz</name>
</nested>
</body>
会产生期望的正确结果：
2
II. 更新
在评论中，楼主描述了另一种情况，即XML文档中没有满足筛选条件的元素。在这种情况下，上面的表达式返回1，这是不正确的。
以下是一个在所有情况下都返回正确结果的XPath表达式：
(boolean(/*/*[name='bar'])) * (count(/*/*[name='bar']/preceding-sibling::*) + 1)
这是将前一个XPath表达式（上面的）乘以另一个XPath表达式（在其左侧），该表达式在没有满足筛选谓词的元素时计算为0，否则为1。
基于XSLT的验证 表明，当存在满足条件的元素时，此XPath表达式评估为正确的基于1的索引值；当不存在这样的元素时，评估为0。我们利用了隐式转换 number(false()) 为 0，以及 number(true()) 为 1 的事实。
以下是后一个示例：
<body>
<nested attr="bla">
<name>foo</name>
</nested>
<nested attr="blub">
<name>barr</name>
</nested>
<nested attr="bli">
<name>baz</name>
</nested>
</body>
在这里，没有任何元素具有字符串值为 bar 的 name 子元素。当我们应用转换：
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:value-of select="(boolean(/*/*[name='bar'])) * (count(/*/*[name='bar']/preceding-sibling::*) + 1)"/>
</xsl:template>
</xsl:stylesheet>
将产生正确的期望结果：
0
英文:
Just evaluate this XPath expression:
count(/*/*[name='bar']/preceding-sibling::*) + 1
XSLT-based verification:
The following transformation simply evaluates the XPath expression and outputs the result of this evaluation:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:value-of select="count(/*/*[name='bar']/preceding-sibling::*) +1"/>
</xsl:template>
</xsl:stylesheet>
When applied on the provided XML document:
<body>
<nested attr="bla">
<name>foo</name>
</nested>
<nested attr="blub">
<name>bar</name>
</nested>
<nested attr="bli">
<name>baz</name>
</nested>
</body>
the wanted, correct result is produced:
2
II. Update
In a comment the OP described another case, where there is no element in the XML document that satisfies the filtering condition. In such case the previous expression (above) returns 1 and this is incorrect.
Here is an XPath expression that returns the correct result in all cases:
(boolean(/*/*[name='bar'])) * (count(/*/*[name='bar']/preceding-sibling::*) +1)
This is the previous XPath expression, multiplied by another XPath expression (on its left) which evaluates to 0 if there is no element that satisfies the filtering predicate, and to 1 otherwise.
The XSLT-based verification shows that this XPath expression evaluates to the correct 1-based index values in the case when a satisfying element exists, and to 0 when no such element exists. Here we take advantage of the fact that the implicit conversion number(false()) is 0 and number(true()) is 1 .
Here is the latter example:
<body>
<nested attr="bla">
<name>foo</name>
</nested>
<nested attr="blub">
<name>barr</name>
</nested>
<nested attr="bli">
<name>baz</name>
</nested>
</body>
Here no element has a <name> child with string value 'bar'. And when we apply the transformation:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:template match="/">
<xsl:value-of select=
"(boolean(/*/*[name='bar'])) * (count(/*/*[name='bar']/preceding-sibling::*) +1)"/>
</xsl:template>
</xsl:stylesheet>
the correct, wanted result is produced:
0
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