[英]InputStream exception while evaluating Xpath
I get : javax.xml.transform.TransformerException: Unable to evaluate expression using this context
我得到: javax.xml.transform.TransformerException: Unable to evaluate expression using this context
at com.sun.org.apache.xpath.internal.XPath.execute(Unknown Source)
at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.eval(Unknown Source)
at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(Unknown Source)
at XPathImplementation.evaluate(XPathImplementation.java:136)
at Main.main(Main.java:23)
Caused by: java.lang.RuntimeException: Unable to evaluate expression using this context
at com.sun.org.apache.xpath.internal.axes.NodeSequence.setRoot(Unknown Source)
at com.sun.org.apache.xpath.internal.axes.LocPathIterator.execute(Unknown Source)
While trying to evaluate an Xpath expression using InputStream
object , I've tried to debug it however found nothing wrong (and of course I missed something ..) . 在尝试使用InputStream
对象评估Xpath表达式时,我尝试调试它,但是没有发现任何错误(当然,我也错过了什么..)。 Here's the code: 这是代码:
From Main: 从主要:
XPathProject m = new XPathImplementation();
m.loadXML("books.xml");
String q = "inventory/book/chapter[3]/preceding-sibling::chapter//title";
Object ob = m.evaluate(q, null, XPathConstants.NODESET);
We use this evaluate
method : 我们使用这种evaluate
方法:
public Object evaluate(String expression, Node source, QName returnType) throws XPathExpressionException,IllegalArgumentException,NullPointerException, TransformerException
{
...
InputStream is = nodeToInputStream(source);
Object returnedObject= xpath.evaluate(expression, is, returnType); // it happens here !!
... more code
}
Auxiliary method nodeToInputStream
: 辅助方法nodeToInputStream
:
/*
* Convert Node object into InputStream object
*/
private InputStream nodeToInputStream(Node node) throws TransformerException {
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
StreamResult outputTarget = new StreamResult(outputStream);
Transformer t = TransformerFactory.newInstance().newTransformer();
t.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
t.transform(new DOMSource(node), outputTarget);
return new ByteArrayInputStream(outputStream.toByteArray());
}
Any idea where did I go wrong ? 知道我哪里出错了吗? 10x! 10倍!
Well m.evaluate(q, null, XPathConstants.NODESET);
好m.evaluate(q, null, XPathConstants.NODESET);
passes in a null reference to the evaluate method so you create new DOMSource(null)
I think which does not seem to make sense to me and probably results in that error later where a relative XPath inventory/book/chapter[3]/preceding-sibling::chapter//title
is evaluated. 将null引用传递给评估方法,因此您创建了new DOMSource(null)
我认为这对我而言似乎没有意义,并且可能会在稍后导致相对于XPath inventory/book/chapter[3]/preceding-sibling::chapter//title
被评估。
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