用于获取属性值的 Xpath 表达式在 Java 中失败
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Xpath expression for getting an attribute value fails in Java
提问by Jonathan
I am trying to get an attribute value from an XML file, but my code fails with the exception below:
我试图从 XML 文件中获取属性值，但我的代码失败并出现以下异常：
11-15 16:34:42.270: DEBUG/XpathUtil(403): exception = javax.xml.xpath.XPathExpressionException: javax.xml.transform.TransformerException: Extra illegal tokens: '@', 'source'
11-15 16:34:42.270: DEBUG/XpathUtil(403): 异常 = javax.xml.xpath.XPathExpressionException: javax.xml.transform.TransformerException: 额外的非法标记: '@', 'source'
Here is the code I use to get the node list:
这是我用来获取节点列表的代码：
private static final String XPATH_SOURCE = "array/extConsumer@source";
mDocument = XpathUtils.createXpathDocument(xml);
NodeList fullNameNodeList = XpathUtils.getNodeList(mDocument,
XPATH_FULLNAME);
And here is my XpathUtilsclass:
这是我的XpathUtils课：
public class XpathUtils {
private static XPath xpath = XPathFactory.newInstance().newXPath();
private static String TAG = "XpathUtil";
public static Document createXpathDocument(String xml) {
try {
Log.d(TAG , "about to create document builder factory");
DocumentBuilderFactory docFactory = DocumentBuilderFactory
.newInstance();
Log.d(TAG , "about to create document builder ");
DocumentBuilder builder = docFactory.newDocumentBuilder();
Log.d(TAG , "about to create document with parsing the xml string which is: ");
Log.d(TAG ,xml );
Document document = builder.parse(new InputSource(
new StringReader(xml)));
Log.d(TAG , "If i see this message then everythings fine ");
return document;
} catch (Exception e) {
e.printStackTrace();
Log.d(TAG , "EXCEPTION OCCURED HERE " + e.toString());
return null;
}
}
public static NodeList getNodeList(Document doc, String expr) {
try {
Log.d(TAG , "inside getNodeList");
XPathExpression pathExpr = xpath.compile(expr);
return (NodeList) pathExpr.evaluate(doc, XPathConstants.NODESET);
} catch (Exception e) {
e.printStackTrace();
Log.d(TAG, "exception = " + e.toString());
}
return null;
}
// extracts the String value for the given expression
public static String getNodeValue(Node n, String expr) {
try {
Log.d(TAG , "inside getNodeValue");
XPathExpression pathExpr = xpath.compile(expr);
return (String) pathExpr.evaluate(n, XPathConstants.STRING);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
I get an exception thrown in the getNodeListmethod.
我在getNodeList方法中抛出异常。
Now, according to http://www.w3schools.com/xpath/xpath_syntax.asp, to get an attribute value, you use the "@" sign. But for some reason, Java is complaining about this symbol.
现在，根据http://www.w3schools.com/xpath/xpath_syntax.asp，要获取属性值，请使用“@”符号。但出于某种原因，Java 抱怨这个符号。
回答by vanje
Try
尝试
array/extConsumer/@source
as your XPath expression. This selects the source attribute of the extConsumer element.
作为您的 XPath 表达式。这将选择 extConsumer 元素的源属性。
回答by Anon
Put a slash before the attribute spec:
在属性规范前加一个斜杠：
array/extConsumer/@source
回答by Pops
The w3schools page you linked to also says "Predicates are always embedded in square brackets." You just appended the @source. Try
您链接到的 w3schools 页面也说“谓词总是嵌入在方括号中”。您刚刚附加了@source. 尝试
private static final String XPATH_SOURCE = "array/extConsumer[@source]";
EDIT:
To be clear, this is if you're looking for a single item, which is what your original wording led me to believe. If you want to collect a bunch of source attributes, see the answers by vanje and Anon that suggest using a slash instead of square brackets.
编辑：
要清楚，这是如果您正在寻找单个项目，这就是您的原始措辞让我相信的。如果您想收集一堆源属性，请参阅 vanje 和 Anon 的答案，建议使用斜杠而不是方括号。
