My XPath expression does not select anything in Java -


i evaluating xpath expression in java , supposed return single string value in return.
however, blank value.

sscce 

import javax.xml.xpath.*; import java.io.*; import org.xml.sax.*;  public class xpathbasic{     public static void main(string[] args){         xpathfactory factory;         xpath xpath;         xpathexpression xpathexpressioncompiled;         string xpathexpressionstring;         file xmlfile;         inputsource inputsource;          try{             factory = xpathfactory.newinstance();             xpath = factory.newxpath();             xpathexpressionstring = "/people/student[@scholarship='yes']/name";             xpathexpressioncompiled = xpath.compile(xpathexpressionstring);              xmlfile = new file("helloworld.xml");             inputsource = new inputsource(new fileinputstream(xmlfile));             string name = xpathexpressioncompiled.evaluate(inputsource);              if(name != null){                 system.out.println("name of student is: " + name);             }else{                 system.out.println("error");             }         }catch(xpathexpressionexception e){             system.out.println("there seems error expression: " + e.getmessage());         }catch(ioexception e){          }catch(exception e){          }      } }

xml 

<?xml version="1.0" encoding="utf-8" ?> <people xmlns="http://www.cmu.edu/ns/blank"  xmlns:xsi="http://www.w3.org/2001/xmlschema-instance" xsi:schemalocation="http://www.cmu.edu/ns/blank student.xsd">     <student scholarship="yes">         <name>john</name>         <course>computer technology</course>         <semester>6</semester>         <scheme>e</scheme>     </student>      <student scholarship="no">         <name>foo</name>         <course>industrial electronics</course>         <semester>6</semester>         <scheme>e</scheme>     </student> </people>

output

name of student is:

i expecting see john there. can please tell me went wrong ?

this mistake many of make! xpath sensitive namespaces. xml file contains namespaced elements , these namespaces required in xpath. in xml file can use default namespace, not in xpath.

try 

"/people[namespace-uri()='http://www.cmu.edu/ns/blank']/student[namespace-uri()='http://www.cmu.edu/ns/blank' , @scholarship='yes']/name[namespace-uri()='http://www.cmu.edu/ns/blank']"

and should work.

your system allows namespaces prefixes in xpath. these cannot empty. example might be:

"/a:people/a:student[@scholarship='yes']/a:name"

how map namespace prefix (a) depends on software. note prefix long mapped.


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