Sending XPath a variable from Java
I have an XPath expression that searches for a static value. In this example, "test" is that value:
XPathExpression expr = xpath.compile("//doc[contains(., 'test')]/*/text()");
How c开发者_如何学运维an I pass a variable instead of a fixed string? I use Java with Eclipse. Is there a way to use the value of a Java String
to declare an XPath variable?
You can define a variable resolver and have the evaluation of the expression resolve variables such as $myvar
, for example:
XPathExpression expr = xpath.compile("//doc[contains(., $myVar)]/*/text()");
There's a fairly good explanation here. I haven't actually done this before myself, so I might have a go and provide a more complete example.
Update:
Given this a go, works a treat. For an example of a very simple implementation, you could define a class that returns the value for a given variable from a map, like this:
class MapVariableResolver implements XPathVariableResolver {
// local store of variable name -> variable value mappings
Map<String, String> variableMappings = new HashMap<String, String>();
// a way of setting new variable mappings
public void setVariable(String key, String value) {
variableMappings.put(key, value);
}
// override this method in XPathVariableResolver to
// be used during evaluation of the XPath expression
@Override
public Object resolveVariable(QName varName) {
// if using namespaces, there's more to do here
String key = varName.getLocalPart();
return variableMappings.get(key);
}
}
Now, declare and initialise an instance of this resolver in the program, for example
MapVariableResolver vr = new MapVariableResolver() ;
vr.setVariable("myVar", "text");
...
XPath xpath = factory.newXPath();
xpath.setXPathVariableResolver(vr);
Then, during evaluation of the XPath expression XPathExpression expr = xpath.compile("//doc[contains(., $myVar)]/*/text()");
, the variable $myVar
will be replaced with the string text
.
Nice question, I learnt something useful myself!
You don't need to evaluate Java (or whatever else PL variables in XPath). In C# (don't know Java well) I'll use:
string XPathExpression =
"//doc[contains(., " + myVar.ToString() + ")]/*/text()";
XmlNodelist result = xmlDoc.SelectNodes(XPathExpression);
Apart from this answer here, that explains well how to do it with the standard Java API, you could also use a third-party library like jOOX that can handle variables in a simple way:
List<String> list = $(doc).xpath("//doc[contains(., $1)]/*", "test").texts();
I use something similar to @brabster:
// expression: "/message/PINConfiguration/pinValue[../keyReference=$keyReference]";
Optional<Node> getNode(String xpathExpression, Map<String, String> variablesMap)
throws XPathExpressionException {
XPath xpath = XPathFactory.newInstance().newXPath();
xpath.setXPathVariableResolver(qname -> variablesMap.get(qname.getLocalPart()));
return Optional.ofNullable((Node) xpath.evaluate(xpathExpression, document,
XPathConstants.NODE));
}
Optional<Node> getNode(String xpathExpression) throws XPathExpressionException {
return getNode(xpathExpression, Collections.emptyMap());
}
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