NullPointerException

[shalini gnana]

I tried to change the content of the attribute in the xml using
DOM.Its throwing nullpointer exception...

    import java.io.File;
import java.util.*;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
 

public class parser
{
    public Document parseXmlFile(String filename,boolean validating)
    {
        try 
        {
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            factory.setValidating(validating);
            Document doc = factory.newDocumentBuilder().parse(new File(filename));
   
        } 
        catch (Exception ex) 
        {
 
        }
         return null;
    }
    
    public void changeData()
    {
      Document doc = parseXmlFile("infilename.xml", false);
    
    // Obtain an element
      Element element = doc.getDocumentElement();
    //Element element = doc.getElementById("key");
    
    // Determine the presence of an attribute
    boolean has = element.hasAttribute("value");      // true
    
    // Get an attribute value; returns null if not present
    String attrValue = element.getAttribute("value"); // value1
    
    // Change the value of an attribute
    element.setAttribute("value", "newValue1");
    
    // If an attribute is not specified in the XML but has a
    // default value, the attribute is automatically created
    element = doc.getElementById("key2");
    has = element.hasAttribute("value");       // true
    attrValue = element.getAttribute("value"); // value2
    
    // If the attribute value contains special characters,
    // they are automatically converted to entities when the
    // document in dumped
    element.setAttribute("value", "a<\"'&>z");
 
    }
    
    public static void main(String [] args)
    {
        parser Parser = new parser();
        Document doc = Parser.parseXmlFile("C:/Documents and Settings/map.xml", false);
        Parser.changeData();
        
    }
    
}

This is my xml:

    ?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE map [ <!ELEMENT map (entry*) >
                    <!ELEMENT entry EMPTY >
                    <!ATTLIST entry key   ID    #REQUIRED
                                    value CDATA "mydefault"> ]>
    <map>
        <entry key="key1" value="value1"/>
        <entry key="key2" />
    </map>

[Suraj Berwal]

The problem is you are not using the Document class instance you have created in second line of your main method.

public static void main(String [] args)
    {
        parser Parser = new parser();
        Document doc = Parser.parseXmlFile("C:/Documents and Settings/map.xml", false);
        Parser.changeData();
        
    }

You are creating a new instance of Document class in the changeData() method.

public void changeData()
    {
      Document doc = parseXmlFile("infilename.xml", false);
    

You need to pass the object of the Document class to the changeData() method in your main method. Modify your change Data() method to accpet the Document object in its parameters.

Try and see if it works. Post your output if it doesn't work.

Thanks,
Suraj

[shalini gnana]

Its no throwing any error,now...
But the attribute "value1" is not changing into newValue1..

Thank you...

[William Brogden]

But the attribute "value1" is not changing into newValue1..

Where are you looking? The original file won't be changed unless you write over it - there is no magic link between the DOM and the text file.

Bill

[shalini gnana]

element.setAttribute("value", "newValue1");

I tried to set value to the attribute,but its not getting
edited...Can anyone say,how to edit?

[William Brogden]

I guess I am going to have to repeat myself:

Where are you looking? The original file won't be changed unless you write over it - there is no magic link between the DOM and the text file.

Bill