How to parse XML using XPATH

Question

I want to scan following XML and fetch value of id based on condition name=task2 and value=efg.

<node1>
<node2>
    <node3>
        <id>ABC-123</id>
        <condition>
            <task name="task1" operation="and" value="abc" />
            <task name="task2" operation="and" value="efg" />
            <task name="task3" operation="and" value="hij" />
            <task name="task4" operation="or" value="klm" />
            <task name="task5" operation="and" value="nop" />
            <task name="task6" value="uvw" />
        </condition>
    </node3>
    <node3>
        <id>XYZ-987</id>
        <condition>
            <task name="task1" operation="and" value="cde" />
            <task name="task2" operation="and" value="abc" />
            <task name="task5" operation="and" value="nop" />
        </condition>
    </node3>
    <node3>
        <id>RST-567</id>
        <condition>
            <task name="task2" operation="and" value="efg" />
            <task name="task8" operation="and" value="jkl" />
            <task name="task9" operation="and" value="rst" />
            <task name="task10" value="xyz" />
        </condition>
    </node3>
</node2>
</node1>

I am able to scan and get result as count = 2, using

 String expression = "//node3/condition/task[@name='"+condition.getKey()+"' and @value='"+condition.getValue()+"']";

But not the value of id using following code

String expression = "//node3/condition/task[@name='"+condition.getKey()+"' and @value='"+condition.getValue()+"']/node3/id";

How to get values "ABC-123" and "RST-567" which would be the correct result?

Referring following blog and w3c links
https://xjaphx.wordpress.com/2011/12/24/android-xml-adventure-parsing-xml-using-xpath/
http://www.w3schools.com/xml/xml_xpath.asp
http://www.w3schools.com/xsl/xpath_operators.asp

Please choose tags wisely. XPath is a subset of XQuery, and there is no XQuery support on android (without additional libraries, which you do not seem to use). I removed the XQuery tag due to being not related to your question. — Jens Erat
– Jens Erat, Commented Feb 24, 2016 at 9:33

har07 · Accepted Answer · 2016-02-24 09:30:56Z

1

You can nest predicates (expression in []) to achieve that, for example :

//node3[condition/task[@name='task2' and @value='efg']]/id

answered Feb 24, 2016 at 9:30

har07

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2 Comments

Abhinav Tyagi Over a year ago

Thanks :) BTW, which is the best approach, yours or WERO's? Need solution with faster processing.

Mathias Müller Over a year ago

@AbhinavTyagi har07's solution is very likely faster than wero's, because using the following-sibling:: axis is probably more costly. It depends on the kinds of optimizations your XPath engine makes and usually, the differences do not matter.

wero · Accepted Answer · 2016-02-24 09:26:28Z

1

You can select the ids and filter for the tasks with a following sibling condition:

/node1/node2/node3/id[following-sibling::condition/task[@name='task2' and @value='efg']]

To select only the text values use

/node1/node2/node3/id/text()[../following-sibling::condition/task[@name='task2' and @value='efg']]

answered Feb 24, 2016 at 9:26

wero

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4 Comments

Abhinav Tyagi Over a year ago

Got the result from the first option but second option with text returned exception during evaluation.

Abhinav Tyagi Over a year ago

something with String Reader...! passing xml as string to input source InputSource inputSrc = new InputSource(new StringReader(xml)); XPath xpath = XPathFactory.newInstance().newXPath(); String result = (String)xpath.evaluate(expression, inputSrc, XPathConstants.STRING);

wero Over a year ago

that seems to be another problem. Comments are not a good place to discuss exceptions, but you can always post another question.

Abhinav Tyagi Over a year ago

I am fine with your first option :)

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