Get element by attribute value variables (xpath) [duplicate] - xpath

Question

I want to pass a parameter into an XPath expression.
(//a/b/c[x=?],myParamForXAttribute)
Can I do this with XPath 1.0 ? (I tried string-join but it is not there in XPath 1.0)
Then how can I do this ?
My XML looks like
<a>
<b>
<c>
<x>val1</x>
<y>abc</y>
</c>
<c>
<x>val2</x>
<y>abcd</y>
</c>
</b>
</a>
I want to get <y> element value where x element value is val1
I tried //a/b/c[x='val1']/y but it did not work.

Answer 1

Given that you're using the Axiom XPath library, which in turn uses Jaxen, you'll need to follow the following three steps to do this in a thoroughly robust manner:
Create a SimpleVariableContext, and call context.setVariableValue("val", "value1") to assign a value to that variable.
On your BaseXPath object, call .setVariableContext() to pass in the context you assigned.
Inside your expression, use /a/b/c[x=$val]/y to refer to that value.
Consider the following:
package com.example;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.impl.common.AxiomText;
import org.apache.axiom.om.util.AXIOMUtil;
import org.apache.axiom.om.xpath.DocumentNavigator;
import org.jaxen.*;
import javax.xml.stream.XMLStreamException;
public class Main {
public static void main(String[] args) throws XMLStreamException, JaxenException {
String xmlPayload="<parent><a><b><c><x>val1</x><y>abc</y></c>" +
"<c><x>val2</x><y>abcd</y></c>" +
"</b></a></parent>";
OMElement xmlOMOBject = AXIOMUtil.stringToOM(xmlPayload);
SimpleVariableContext svc = new SimpleVariableContext();
svc.setVariableValue("val", "val2");
String xpartString = "//c[x=$val]/y/text()";
BaseXPath contextpath = new BaseXPath(xpartString, new DocumentNavigator());
contextpath.setVariableContext(svc);
AxiomText selectedNode = (AxiomText) contextpath.selectSingleNode(xmlOMOBject);
System.out.println(selectedNode.getText());
}
}
...which emits as output:
abcd

Answer 2

It depends on the language in which you're using XPath.
In XSLT:
"//a/b/c[x=$myParamForXAttribute]"
Note that, unlike the approach above, the three below are open to XPath injection attacks and should never be used with uncontrolled or untrusted inputs; to avoid this, use a mechanism provided by your language or library to pass in variables out-of-band. [Credit: Charles Duffy]
In C#:
String.Format("//a/b/c[x={0}]", myParamForXAttribute);
In Java:
String.format("//a/b/c[x=%s]", myParamForXAttribute);
In Python:
"//a/b/c[x={}]".format(myParamForXAttribute)