How to read all the values of an atrribute under an XML tag [dom4j]?

Question

I am using dom4j library(SAXReader) in java and want to know how can I read and fetch all the values of an XML attribute present in the child XML tags of some parent XML tags. for eg.

....
<ParentTag1>
 <ChildTag1 SomeAttributeName1 = "val1">....</ChildTag1>
 <ChildTag2>...</ChildTag2>
 <ChildTag3 SomeAttributeName1 = "val2">...</ChildTag3>
</ParentTag1>
....
<ParentTag2>
 <ChildTag1 SomeAttributeName2 = "val1">....</ChildTag1>
 <ChildTag2>...</ChildTag2>
 <ChildTag3 SomeAttributeName2 = "val2">...</ChildTag3>
</ParentTag2>
......

Let's say the attribute is SomeAttributeName1 Questions:

• How can I collect all the values of SomeAttributeName1 to a list or set ? eg. value set/list = {'val1', 'val2'}
  • While collecting the values for SomeAttributeName1, I want to make sure that I only look into child tags of a particular parent tag(here, only look into child tags of <ParentTag1> ) and not the complete XML, is it possible to do so ? If yes, please explain your answer using the same ?
  • Following above question, which is faster/efficient and why - reading child elements of <ParentTag1> OR reading complete XML to look for the values of SomeAttributeName1 ?

Thanks

Answer 1

Since DOM4J has built-in XPATH support, using that is probably the best apprach:

    List<String> values = doc.selectNodes("//ParentTag1//@SomeAttributeName1")
            .stream()
            .map(node -> node.getText())
            .collect(Collectors.toList());

The XPATH expression selects all Attribute nodes in all elements that have an ancestor element named ParentTag1.