I am retrieving XML tag values by evaluate path, assume I have 3 tags with book info: Book info consists of : Name - year - Author and in 1 tag Author name has been missed and doesn't come in my tags, I want to have an array that shows 1 author name + null value which shows that 2 tags hasn't been specified, like below: As you see second tag consist of no author name and the third tag doesn't have any author name tag as below: I really appreciate for any guidance/ hint/ help. :-)
Author: [John Smith,null,null]
My XML File:
<?xml version="1.0" encoding="UTF-8"?>
<perldata>
<item key="book">
<item key="name">My Book Name</item>
<item key="year">2019</item>
<item key="author">John Smith</item>
</item>
<item>
<item key="name">Anonymous Book Name 1</item>
<item key="year">2018</item>
<item key="author"></item>
</item>
<item>
<item key="name">Her Book Name</item>
<item key="year">2018</item>
</item>
</perldata>
This shows that the third tag does not consist of Author name tag. I don't know how to show null value in EvaluateXpath: ( Really need help)
String fileName="book.xml";
Document document = getDocument(fileName);
// Defining Variables
// String xpathExpression = "";
FileWriter fw = null;
BufferedWriter bw = null;
PrintWriter pw = null;
//Using Document Builder
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
documentBuilderFactory.setNamespaceAware(true);
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
Document doc1 = documentBuilder.parse(fileName);
/*******Get attribute values using xpath******/
XPathFactory xpathFactory = XPathFactory.newInstance();
XPath xpath = xpathFactory.newXPath();
try{
fw = new FileWriter("/root/Desktop/book.txt");
bw = new BufferedWriter(fw);
pw = new PrintWriter(bw)
pw.println("BookName: "+evaluateXpath(document, "/perldata/item[@key=book]/item[@key='name']/text()"));
pw.println("year: "+evaluateXpath(document, "/perldata/item[@key=book]/item[@key='year']/text()"))
pw.println("Author: "+evaluateXpath(document, "/perldata/item[@key=book]/item[@key='author']/text()"))
pw.flush(); }
catch (IOException e)
{ e.printStackTrace(); } } }
private static List<String> evaluateXPath(Document document, String xpathExpression) throws Exception
{
// Create XPathFactory object
XPathFactory xpathFactory = XPathFactory.newInstance();
// Create XPath object
XPath xpath = xpathFactory.newXPath();
List<String> values = new ArrayList<>();
try
{
// Create XPathExpression object
XPathExpression expr = xpath.compile(xpathExpression);
// Evaluate expression result on XML document
NodeList nodes = (NodeList) expr.evaluate(document, XPathConstants.NODESET);
for (int i = 0; i < nodes.getLength(); i++) {
values.add(nodes.item(i).getNodeValue());
}
} catch (XPathExpressionException e) {
e.printStackTrace();
}
return values;
}
private static Document getDocument(String fileName) throws Exception
{
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(fileName);
return doc;
}
}
Summary:
Trim the tag's text content, and check if the resulting string is empty or not.
Details:
The XML in the question only has one tag containing key="book". I assume all 3 sections should have this, so we know each one represents a book.
Therefore, I will assume you have an XML file like the following, which includes one empty "author" tag, and one completely missing "author" tag:
<?xml version="1.0" encoding="UTF-8"?>
<perldata>
<item key="book">
<item key="name">My Book Name</item>
<item key="year">2019</item>
<item key="author">John Smith</item>
</item>
<item key="book">
<item key="name">Anonymous Book Name 1</item>
<item key="year">2018</item>
<item key="author"></item>
</item>
<item key="book">
<item key="name">Her Book Name</item>
<item key="year">2018</item>
</item>
<item key="book">
<item key="name">Another Book Name</item>
<item key="year">2019</item>
<item key="author">Jane Jones</item>
</item>
</perldata>
Assuming the above, you can print out all names (including null names) as follows:
File file = new File("C:/tmp/Book2.xml");
FileInputStream fis = new FileInputStream(file);
DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = builderFactory.newDocumentBuilder();
Document xmlDocument = builder.parse(fis);
XPath xPath = XPathFactory.newInstance().newXPath();
NodeList bookNodes = (NodeList) xPath.compile("//item[@key='book']")
.evaluate(xmlDocument, XPathConstants.NODESET);
List<String> authors = new ArrayList();
for (int i = 0; i < bookNodes.getLength(); i++) {
Node bookNode = bookNodes.item(i);
Node authorNode = (Node) xPath.compile("./item[@key='author']")
.evaluate(bookNode, XPathConstants.NODE);
if (authorNode == null) {
authors.add(null);
} else {
String s = authorNode.getTextContent().trim();
authors.add(s.isEmpty() ? null : s);
}
}
System.out.println(authors);
The final print statement gives this:
[John Smith, null, null, Jane Jones]
Additional notes:
This loops through all the <item key="book"> sections in the file. For each section, it then performs this targeted search, but only within that section:
Node authorNode = (Node) xPath.compile("./item[@key='author']")
.evaluate(bookNode, XPathConstants.NODE);
The evaluate uses the current bookNode as its starting point.
After that, we can check all the possible outcomes:
key="author" tag - and it contains an author's name.key="author" tag - but there is no name in it.key="author" tag for this book node.