How to read XML file in Java
This tutorial shows how to read and parse an XML file in Java using a DOM parser.
1- Define XML file
Consider we have the following Students.xml file:
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<students> <student graduated="yes"> <id>1</id> <name>Hussein</name> </student> <student> <id>2</id> <name>Alex</name> </student> </students> |
2- Instantiate XML file
DOM parser loads the whole XML document into the memory and considers every XML tag as an element.
In order to instantiate a new Document object from an XML file, we do the following:
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File xmlFile = new File("students.xml"); DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parse(xmlFile); |
This is done only once and all the parsing operations afterward are done on the Document object.
3- Read the root node
To get the root node or element of an XML file, use the following method:
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doc.getDocumentElement() |
In students.xml, the root node is students.
4- Retrieve nodes by tag name
To retrieve all nodes of a specific tag name, use getElementsByTagName() method.
In the following example, we parse students.xml and print out all the defined students.
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private static void getAllStudents(Document doc) { NodeList studentNodes = doc.getElementsByTagName("student"); for(int i=0; i<studentNodes.getLength(); i++) { Node studentNode = studentNodes.item(i); if(studentNode.getNodeType() == Node.ELEMENT_NODE) { Element studentElement = (Element) studentNode; String studentId = studentElement.getElementsByTagName("id").item(0).getTextContent(); String studentName = studentElement.getElementsByTagName("name").item(0).getTextContent(); System.out.println("Student Id = " + studentId); System.out.println("Student Name = " + studentName); } } } |
The ELEMENT_NODE type refers to a non-text node that has sub-elements.
Calling the above method would give the following output:
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Student Id = 1 Student Name = Hussein Student Id = 2 Student Name = Alex |
In order to parse the whole XML file starting from the root node, you can recursively call getChildNodes() method as the following:
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private static void parseWholeXML(Node startingNode) { NodeList childNodes = startingNode.getChildNodes(); for(int i=0; i<childNodes.getLength(); i++) { Node childNode = childNodes.item(i); if(childNode.getNodeType() == Node.ELEMENT_NODE) { parseWholeXML(childNode); } else { // trim() is used to ignore new lines and spaces elements. if(!childNode.getTextContent().trim().isEmpty()) { System.out.println(childNode.getTextContent()); } } } } |
In this example, we parse the students.xml file and print out the text elements.
Running the above method would give the following output:
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1 Hussein 2 Alex |
5- Get Node by value
In order to search for a node by its value, you can use getElementsByTagName() method and check on the value of its text element.
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private static void getStudentById(Document doc, String textNodeName, String textNodeValue) { NodeList studentNodes = doc.getElementsByTagName("student"); for(int i=0; i<studentNodes.getLength(); i++) { Node studentNode = studentNodes.item(i); if(studentNode.getNodeType() == Node.ELEMENT_NODE) { Element studentElement = (Element) studentNode; NodeList textNodes = studentElement.getElementsByTagName(textNodeName); if(textNodes.getLength() > 0) { if(textNodes.item(0).getTextContent().equalsIgnoreCase(textNodeValue)) { System.out.println(textNodes.item(0).getTextContent()); System.out.println(studentElement.getElementsByTagName("name").item(0).getTextContent()); } } } } } |
In this example, we are looking for a student who has a specific id.
Now, if we call the method as:
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getStudentById(doc,"id", "2"); |
we get the following output:
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2 Alex |
6- Get Node by attribute value
In order to search for a node by the value of a specific attribute, you can use getElementsByTagName() along with getAttribute() methods as the following:
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private static void getGraduatedStudents(Document doc, String attributeName, String attributeValue) { NodeList studentNodes = doc.getElementsByTagName("student"); for(int i=0; i<studentNodes.getLength(); i++) { Node studentNode = studentNodes.item(i); if(studentNode.getNodeType() == Node.ELEMENT_NODE) { Element studentElement = (Element) studentNode; if(attributeValue.equalsIgnoreCase(studentElement.getAttribute(attributeName))) { String studentId = studentElement.getElementsByTagName("id").item(0).getTextContent(); String studentName = studentElement.getElementsByTagName("name").item(0).getTextContent(); System.out.println("Student Id = " + studentId); System.out.println("Student Name = " + studentName); } } } } |
In this example, we are looking for all graduated students i.e. students who have (graduated=”yes”) attribute.
Now, if we call the method as:
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getGraduatedStudents(doc, "graduated", "yes"); |
We get the following output:
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Student Id = 1 Student Name = Hussein |
7- Resources
You can download the full source code from this repository: Read-XML
