Tag Archives: XML

Parsing XML in Groovy using XmlSlurper

In my previous post I showed different ways in which we can parse XML document in Java. You must have noticed the code being too much verbose. Other JVM languages like Groovy, Scala provide much better support for parsing XML documents.

In this post I give you the code to parse the XML document in Grooy and one can compare the ease with which we can parse XML documents. I make use of XmlSlurper API in Groovy which loads the complete XML into a tree and this tree can be then navigated using Groovy’s version of XPath called GPath.

The XML document I am using is the same one used here and also the intent is to parse the XML and create a list of Employee object.

class XmlParserDemo {
  static void main(args){
    def empList = new ArrayList<Employee>();
    def emp;
    def employees = 
      new XmlSlurper().parse(ClassLoader.
          getSystemResourceAsStream("xml/employee.xml"));
    employees.employee.each{ node -> 
      emp = new Employee();
      emp.firstName = node.firstName
      emp.lastName = node.lastName
      emp.id = node.@id
      emp.location = node.location
      empList.add(emp)
    }
    empList.each{ empT -> println(empT)}
  }
}
class Employee{
  String firstName
  String lastName
  String id
  String location
  
  @Override
  public String toString(){
    return "${firstName} ${lastName}(${id}) in ${location}"
  }
}

The output is:

Rakesh Mishra(111) in Bangalore
John Davis(112) in Chennai
Rajesh Sharma(113) in Pune

And the XML is present in the “xml” package and is available in the classpath of the application. I am using the ClassLoader to load the XML resource.

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Parsing XML using DOM, SAX and StAX Parser in Java

I happen to read through a chapter on XML parsing and building APIs in Java. And I tried out the different parser available on a sample XML. Then I thought of sharing it on my blog so that I can have a reference to the code as well as a reference for anyone reading this. In this post I parse the same XML in different parsers to perform the same operation of populating the XML content into objects and then adding the objects to a list.

The sample XML considered in the examples is:

<employees>
  <employee id="111">
    <firstName>Rakesh</firstName>
    <lastName>Mishra</lastName>
    <location>Bangalore</location>
  </employee>
  <employee id="112">
    <firstName>John</firstName>
    <lastName>Davis</lastName>
    <location>Chennai</location>
  </employee>
  <employee id="113">
    <firstName>Rajesh</firstName>
    <lastName>Sharma</lastName>
    <location>Pune</location>
  </employee>
</employees>

And the obejct into which the XML content is to be extracted is defined as below:

class Employee{
  String id;
  String firstName;
  String lastName;
  String location;

  @Override
  public String toString() {
    return firstName+" "+lastName+"("+id+")"+location;
  }
}

There are 3 main parsers for which I have given sample code:

Using DOM Parser

I am making use of the DOM parser implementation that comes with the JDK and in my example I am using JDK 7. The DOM Parser loads the complete XML content into a Tree structure. And we iterate through the Node and NodeList to get the content of the XML. The code for XML parsing using DOM parser is given below.

public class DOMParserDemo {

  public static void main(String[] args) throws Exception {
    //Get the DOM Builder Factory
    DocumentBuilderFactory factory = 
        DocumentBuilderFactory.newInstance();

    //Get the DOM Builder
    DocumentBuilder builder = factory.newDocumentBuilder();

    //Load and Parse the XML document
    //document contains the complete XML as a Tree.
    Document document = 
      builder.parse(
        ClassLoader.getSystemResourceAsStream("xml/employee.xml"));


    List<Employee> empList = new ArrayList<>();

    //Iterating through the nodes and extracting the data.
    NodeList nodeList = document.getDocumentElement().getChildNodes();

    for (int i = 0; i < nodeList.getLength(); i++) {

      //We have encountered an <employee> tag.
      Node node = nodeList.item(i);
      if (node instanceof Element) {
        Employee emp = new Employee();
        emp.id = node.getAttributes().
            getNamedItem("id").getNodeValue();

        NodeList childNodes = node.getChildNodes();
        for (int j = 0; j < childNodes.getLength(); j++) {
          Node cNode = childNodes.item(j);

          //Identifying the child tag of employee encountered. 
          if (cNode instanceof Element) {
            String content = cNode.getLastChild().
                getTextContent().trim();
            switch (cNode.getNodeName()) {
              case "firstName":
                emp.firstName = content;
                break;
              case "lastName":
                emp.lastName = content;
                break;
              case "location":
                emp.location = content;
                break;
            }
          }
        }
        empList.add(emp);
      }

    }

    //Printing the Employee list populated.
    for (Employee emp : empList) {
      System.out.println(emp);
    }

  }
}

class Employee{
  String id;
  String firstName;
  String lastName;
  String location;

  @Override
  public String toString() {
    return firstName+" "+lastName+"("+id+")"+location;
  }
}

The output for the above will be:

Rakesh Mishra(111)Bangalore
John Davis(112)Chennai
Rajesh Sharma(113)Pune

Using SAX Parser

SAX Parser is different from the DOM Parser where SAX parser doesn’t load the complete XML into the memory, instead it parses the XML line by line triggering different events as and when it encounters different elements like: opening tag, closing tag, character data, comments and so on. This is the reason why SAX Parser is called an event based parser.

Along with the XML source file, we also register a handler which extends the DefaultHandler class. The DefaultHandler class provides different callbacks out of which we would be interested in:

  • startElement() – triggers this event when the start of the tag is encountered.
  • endElement() – triggers this event when the end of the tag is encountered.
  • characters() – triggers this event when it encounters some text data.

The code for parsing the XML using SAX Parser is given below:

import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

public class SAXParserDemo {

  public static void main(String[] args) throws Exception {
    SAXParserFactory parserFactor = SAXParserFactory.newInstance();
    SAXParser parser = parserFactor.newSAXParser();
    SAXHandler handler = new SAXHandler();
    parser.parse(ClassLoader.getSystemResourceAsStream("xml/employee.xml"), 
                 handler);
    
    //Printing the list of employees obtained from XML
    for ( Employee emp : handler.empList){
      System.out.println(emp);
    }
  }
}
/**
 * The Handler for SAX Events.
 */
class SAXHandler extends DefaultHandler {

  List<Employee> empList = new ArrayList<>();
  Employee emp = null;
  String content = null;
  @Override
  //Triggered when the start of tag is found.
  public void startElement(String uri, String localName, 
                           String qName, Attributes attributes) 
                           throws SAXException {
      
    switch(qName){
      //Create a new Employee object when the start tag is found
      case "employee":
        emp = new Employee();
        emp.id = attributes.getValue("id");
        break;
    }
  }

  @Override
  public void endElement(String uri, String localName, 
                         String qName) throws SAXException {
   switch(qName){
     //Add the employee to list once end tag is found
     case "employee":
       empList.add(emp);       
       break;
     //For all other end tags the employee has to be updated.
     case "firstName":
       emp.firstName = content;
       break;
     case "lastName":
       emp.lastName = content;
       break;
     case "location":
       emp.location = content;
       break;
   }
  }

  @Override
  public void characters(char[] ch, int start, int length) 
          throws SAXException {
    content = String.copyValueOf(ch, start, length).trim();
  }
    
}

class Employee {

  String id;
  String firstName;
  String lastName;
  String location;

  @Override
  public String toString() {
    return firstName + " " + lastName + "(" + id + ")" + location;
  }
}

The output for the above would be:

Rakesh Mishra(111)Bangalore
John Davis(112)Chennai
Rajesh Sharma(113)Pune

Using StAX Parser

StAX stands for Streaming API for XML and StAX Parser is different from DOM in the same way SAX Parser is. StAX parser is also in a subtle way different from SAX parser.

  • The SAX Parser pushes the data but StAX parser pulls the required data from the XML.
  • The StAX parser maintains a cursor at the current position in the document allows to extract the content available at the cursor whereas SAX parser issues events as and when certain data is encountered.

XMLInputFactory and XMLStreamReader are the two class which can be used to load an XML file. And as we read through the XML file using XMLStreamReader, events are generated in the form of integer values and these are then compared with the constants in XMLStreamConstants. The below code shows how to parse XML using StAX parser:

import java.util.ArrayList;
import java.util.List;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;

public class StaxParserDemo {
  public static void main(String[] args) throws XMLStreamException {
    List<Employee> empList = null;
    Employee currEmp = null;
    String tagContent = null;
    XMLInputFactory factory = XMLInputFactory.newInstance();
    XMLStreamReader reader = 
        factory.createXMLStreamReader(
        ClassLoader.getSystemResourceAsStream("xml/employee.xml"));
        
    while(reader.hasNext()){
      int event = reader.next();
      
      switch(event){
        case XMLStreamConstants.START_ELEMENT: 
          if ("employee".equals(reader.getLocalName())){
            currEmp = new Employee();
            currEmp.id = reader.getAttributeValue(0);
          }
          if("employees".equals(reader.getLocalName())){
            empList = new ArrayList<>();
          }
          break;
          
        case XMLStreamConstants.CHARACTERS:
          tagContent = reader.getText().trim();
          break;
          
        case XMLStreamConstants.END_ELEMENT:
          switch(reader.getLocalName()){
            case "employee":
              empList.add(currEmp);
              break;
            case "firstName":
              currEmp.firstName = tagContent;
              break;
            case "lastName":
              currEmp.lastName = tagContent;
              break;
            case "location":
              currEmp.location = tagContent;
              break;
          }
          break;
            
        case XMLStreamConstants.START_DOCUMENT:
          empList = new ArrayList<>();
          break;
      }

    }
    
    //Print the employee list populated from XML
    for ( Employee emp : empList){
      System.out.println(emp);
    }
      
  }
}

class Employee{
  String id;
  String firstName;
  String lastName;
  String location;
  
  @Override
  public String toString(){
    return firstName+" "+lastName+"("+id+") "+location;
  }
}

The output for the above is:

Rakesh Mishra(111) Bangalore
John Davis(112) Chennai
Rajesh Sharma(113) Pune

With this I have covered parsing the same XML document and performing the same task of populating the list of Employee objects using all the three parsers namely:

Using JAXB to generate Java Objects from XML document

Quite sometime back I had written about Using JAXB to generate XML from the Java, XSD. And now I am writing how to do the reverse of it i.e generating Java objects from the XML document. There was one comment mentioning that JAXB reference implementation and hence in this article I am making use of the reference implementation that is shipped with the JDK.
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Parsing XML is fun again- thanks to Groovy

I happened to work on Groovy while I was developing using Gaelyk and I found Groovy lot easier to write- I never thought of the types and this really helped me to make my codeGroov simpler and easier to write. And when you are dealing with RESTful APIs- you ought to be parsing XML,JSON and what not. As a Java programmer- I never enjoyed it. But Groovy really made parsing xml fun again. Continue reading

Using JAXB to generate XML from the Java, XSD

We can use JAXB to marshal the Java objects into XML using the given Schema and vice versa- unmarshal XML into Java objects. The xml schema can be specified in DTD, XSD or other format. The tool “xjc” is used to generate the annotated Java classes from the XSD schema. One can download the Java WSDP from here, it includes the JAXB implementation tools required. Here I will throw light on how to generate XML dynamically. Even I havent gone in depth with JAXB, but I found this really useful and thought of sharing it in the blog.

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JSON- JavaScript Object Notation

JSON- JavaScript Object NotationJSON

JSON (JavaScript Object Notation) is a lightweight data-interchange format based on the object notation of the JavaScript language. It does not require JavaScript to read or write; it is easy to parse by any language and libraries and tools exist in many languages to handle JSON.

It is:

  • easy for humans to read and write
  • easy for machines to parse and generate
  • based on a subset of the JavaScript Programming Language
  • text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages

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