[SOLVED] nullpointerexception while parsing wsdl using wsdl4j for listing of operations, input/output parameters

The code is working for a wsdl with only single operation but for wsdl with multiple operation tags, it is giving a nullpointer exception.

 Exception in thread "main" java.lang.NullPointerException
at project.Project.listInputs(Project.java:78)
at project.Project.main(Project.java:198)

The code:

package project;

 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashSet;
 import javax.xml.parsers.DocumentBuilderFactory;
 import javax.xml.parsers.ParserConfigurationException;
 import org.w3c.dom.Document;
 import org.w3c.dom.NodeList;
 import org.xml.sax.SAXException;

 /**
 *
 * @author karthikbv
 */
 public class Project {

     /**
     * @param args the command line arguments
     */
     public String[] listOperations(String filename) throws FileNotFoundException, SAXException,IOException, ParserConfigurationException 
     {
        Document d = (Document) DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new FileInputStream(filename));
        NodeList elements = d.getElementsByTagName("wsdl:operation");
        ArrayList<String> operations = new ArrayList<>();
        for (int i = 0; i < elements.getLength(); i++) {
            operations.add(elements.item(i).getAttributes().getNamedItem("name").getNodeValue());
        }
        return operations.toArray(new String[operations.size()]);
     }
     public String[] listOperationsUnique(String filename) throws   FileNotFoundException,SAXException, IOException, ParserConfigurationException 
     {
        String[] nonUnique = listOperations(filename);
        HashSet<String> unique = new HashSet<>(Arrays.asList(nonUnique));
        return unique.toArray(new String[unique.size()]);
     }
     public String[] listInputs(String filename) throws FileNotFoundException, SAXException,IOException, ParserConfigurationException, NullPointerException 
     {
        Document d1 = (Document) DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new FileInputStream(filename));
        NodeList elements1 = d1.getElementsByTagName("wsdl:input");
        NodeList elements ;
        NodeList ele = d1.getElementsByTagName("wsdl:message");        
        //ArrayList<String> tinput = new ArrayList<>();       
        ArrayList<String> tput = new ArrayList<>();
        ArrayList<String> input = new ArrayList<>();
        for(int k=0; k < elements1.getLength(); k++)
        {
            if(elements1.item(k).getAttributes().getNamedItem("message") != null)
            {
                input.add(elements1.item(k).getAttributes().getNamedItem("message").getNodeValue());
            }
        }
        String[] s,s1,s2;
        s1 = input.toArray(new String[input.size()]);
        s= this.listMessages(filename);
        for(int i=0;i<s1.length;i++)
        {
            for(int j=0;j<s.length;j++)
            {
                if((s1[i].substring(4)).equals(s[j]))
                {
                  for (int k = 0; k < ele.getLength(); k++) 
                  {
                    if(ele.item(k).getAttributes().getNamedItem("name").getNodeValue().equals(s[j]))
                    {
                        elements = ele.item(k).getChildNodes();
                        for(int l=0; l < elements.getLength(); l++)
                        {
                            if(elements.item(l).getAttributes() != null)
                            {
                                tput.add(elements.item(l).getAttributes().getNamedItem("type").getNodeValue());
                            }
                        }            
                    }
                  }   
                }
            }
        }
        s2 = tput.toArray(new String[tput.size()]);
        return s2;
        //return input.toArray(new String[input.size()]);
     }

     public String[] listMessages(String filename) throws FileNotFoundException, SAXException,IOException, ParserConfigurationException 
     {
        Document d = (Document) DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new FileInputStream(filename));
        NodeList elements = d.getElementsByTagName("wsdl:message");
        ArrayList<String> messages = new ArrayList<>();
        for (int i = 0; i < elements.getLength(); i++) 
        {
            if(elements.item(i).getAttributes().getNamedItem("name") != null)
            {
                messages.add(elements.item(i).getAttributes().getNamedItem("name").getNodeValue());
            }
        }
        return messages.toArray(new String[messages.size()]);
     }
     public String[] listMinputs(String filename) throws FileNotFoundException, SAXException,IOException, ParserConfigurationException, NullPointerException 
     {
        Document d1 = (Document) DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new FileInputStream(filename));
        NodeList melements1 = d1.getElementsByTagName("wsdl:part");
        ArrayList<String> minput = new ArrayList<>();
        int l,i;
        l = melements1.getLength();
        for(int k=0; k < l; k++)
        {
            if(melements1.item(k).getAttributes().getNamedItem("element") != null)
            {
                minput.add(melements1.item(k).getAttributes().getNamedItem("element").getNodeValue());
            }
        }
         return minput.toArray(new String[minput.size()]);
      }

    /**
     *
     * @param args
     * @throws FileNotFoundException
     * @throws SAXException
     * @throws IOException
     * @throws ParserConfigurationException
     */
    public static void main(String[] args) throws FileNotFoundException, SAXException, IOException, ParserConfigurationException, NullPointerException 
    {
        // TODO code application logic here
        Project p;
        p = new Project();
        System.out.println("Hi");
        String uri;
        uri = "C:/Users/karthikbv/Desktop/sample.wsdl";
        String[] s, s1;
        s = p.listOperationsUnique(uri);
        s1 = p.listInputs(uri);
        int len = s.length;
        int len1 = s1.length;
        System.out.println("Operations:");
        for(int i=0; i<len; i++)
        {
           System.out.println(s[i]); 
        }
        System.out.println("Input Params:");
        for(int i=0; i<len1; i++)
        {
           System.out.println(s1[i]); 
        }
    }
}