ArrayList Problem while parsing XML...

[Joe Budden]

Background Information:

I am writing a program that parses a "question/answer" database composed of a XML file. I am using XMLReader to do my parsing. During the startElement function, if the tag is "question" then a new Question object will be pushed onto a stack. However, if it's a simple element just such as the answer then a StringBuffer will be pushed onto the stack. The characters method will append to the StringBuffer and then the SB will be applied to the attribute of the Question object. Lastly, the Question object will be added to an ArrayList. The code works great up until after the 'xr.parse(new InputSource(r));' statement is done parsing the document..

Sample XML file:

 
<database>
<question>
<title> Some question for content </title>
<answer> Some solution! </answer>
<contact> Someone </contact>
<category> Something </category>
<subcategory> Some </subcategory>
</question>
<question>
<title> Some question for content </title>
<answer> Some solution! </answer>
<contact> Someone </contact>
<category> Something </category>
<subcategory> Some </subcategory>
</question>
<question>
<title> Some question for content </title>
<answer> Some solution! </answer>
<contact> Someone </contact>
<category> Something </category>
<subcategory> Some </subcategory>
</question>
</database>
   

Using various debug out statements, the size of the ArrayList is intact throughout the endDocument(), startElement(), etc, methods. However, after the parsing is done, the array list's size is 0. I am completely stumped as to why this is happening. Here is the source:

import java.io.FileReader;
import java.util.*;
import org.xml.sax.XMLReader;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.helpers.XMLReaderFactory;
import org.xml.sax.helpers.DefaultHandler;
 
 
public class FAQParser extends DefaultHandler implements java.io.Serializable {
 
    public Stack stack = new Stack();
    public boolean isStackReadyForText;
    public ArrayList listOfQuestions = new ArrayList();
    public Question question;
    public int id = 1;
 
    public FAQParser() {
super();
    }
 
    public void parse(String filename) throws Exception {

System.out.println("DEBUG: *** Beginning of parse()");

XMLReader xr = XMLReaderFactory.createXMLReader();
FAQParser handler = new FAQParser();
xr.setContentHandler(handler);
xr.setErrorHandler(handler);

                // However, if I do this below, then it does show as part of the ArrayList.
//listOfQuestions.add(new Question());

FileReader r = new FileReader(filename);
xr.parse(new InputSource(r));

System.out.println("DEBUG: *** End of parse(): with a size of: " + listOfQuestions.size());
// Above reports 0 after finished.
 

    }

   
  
    //////////////////////////////////////////////////////
/////////////////// Event Handlers ///////////////////
//////////////////////////////////////////////////////
 
 public void startDocument() {
 System.out.println("DEBUG: Start of document encountered.");
 }
 
 public void endDocument() {
 
 System.out.println("**** DEBUG: End of document encountered. " + listOfQuestions.size() + " questions found in the ArrayList!");

 }
 
 
    public void startElement(String uri, String localName, String qName, Attributes attribs) {


isStackReadyForText = false;


if (localName.equals("database")) {

System.out.println("DEBUG: Beginning <database> tag found.");

}

// Complex Elements
// ----------------

else if (localName.equals("question") ) {
    
stack.push(new Question());


}

// Simple Elements
// ---------------

else if((localName.equals("title") || localName.equals("answer") || localName.equals("contact") || localName.equals("category") || localName.equals("subcategory"))) {
    
stack.push(new StringBuffer());


    
isStackReadyForText = true;

}

// If not one of our above cases, then do nothing.
else {

    // do nothing

   }
   

}
    
 
    // receive notification of the end of an element
     public void endElement(String uri, String localName, String qName) {
 



        isStackReadyForText = false;

if (!localName.equals("database")) {

Object tmp = stack.pop();



// Complex Elements
if(localName.equals("question")) {

   question = (Question)tmp;
question.setId(id);

listOfQuestions.add(question);

System.out.println("**** DEBUG: Question was added to ArrayList");
id++;
}

// Simple Elements
else if (localName.equals("title")) {

 ((Question)stack.peek()).setTitle(tmp.toString());

 
}

else if (localName.equals("answer")) {

((Question)stack.peek()).setAnswer(tmp.toString());


}

else if (localName.equals("contact")) {

((Question)stack.peek()).setContact(tmp.toString());

}

else if (localName.equals("category")) {

((Question)stack.peek()).setCategory(tmp.toString());

}

else if (localName.equals("subcategory")) {

((Question)stack.peek()).setSubcategory(tmp.toString());


}

// Unknown Element, case will never occur
else {
stack.push(tmp);

}

}
 }
 
 
    // receive notification of character data
    public void characters(char ch[], int start, int length) {


if (isStackReadyForText == true)
{
((StringBuffer) stack.peek()).append(ch, start, length);

}

else {

}
        
        }


public static void main(String args[]) {

try { 
  
            String file = new String(args[0]);
            FAQParser p = new FAQParser();
p.parse(file);

 
        } catch (Exception e) { e.printStackTrace(); } 
}
     } 
 
 

And the Question object class:

 
public class Question {
 
 
 
    private String title;
    private String answer;
    private String contact;
    private String category;
    private String subcategory;
    private int id;
 
    public Question() {

this.title = "Default Title";
this.answer = "Default Answer";
this.contact = "Default Contact";
this.category = "Default Category";
this.subcategory = "Default Subcategory";
 
    }
 
 
 
    public void setTitle(String title) {
 
        this.title = title;
 
    }
 
 
 
    public String getTitle() { 
 
        return title;
 
    }
 
 
 
    public void setAnswer(String answer) {
 
        this.answer = answer;
 
    }
 
 
 
    public String getAnswer() {
 
        return answer;
 
    }
 
 
 
    public void setContact(String contact) {
 
        this.contact = contact;
 
    }
 
 
 
    public String getContact() {
 
        return contact;
 
    }
 
 
 
    public void setCategory(String category) {
 
        this.category = category;
 
    }
 
 
 
    public String getCategory() {
 
        return category;
 
    }
 
 
 
    public void setSubcategory(String subcategory) {
 
        this.subcategory = subcategory;
 
    }

public String getSubcategory() {
return subcategory;
}
 
 
 
    public void setId(int id) {
 
        this.id = id;
 
    }
 
 
 
    public int getId() {
 
        return id;
 
    }
 
}
   

After running the program:
 
DEBUG: *** Beginning of parse()
DEBUG: Start of document encountered.
DEBUG: Beginning <database> tag found.
**** DEBUG: Question was added to ArrayList
**** DEBUG: Question was added to ArrayList
**** DEBUG: Question was added to ArrayList
**** DEBUG: End of document encountered. 3 questions found in the ArrayList!
 
DEBUG: *** End of parse(): with a size of: 0
 
As you can see, when it reaches the end of the document, the 3 Question objects are successfully in the array.. However, after the parse function finishes, another check shows that it's of size 0.
 

Sorry for the such lengthy thread, but I've tried every single option in the book and I can't find the bug. Please help me. Thank you.

[ June 12, 2006: Message edited by: Joe Budden ]
[ June 12, 2006: Message edited by: Joe Budden ]

[Paul Clapham]

Well, this seems to be rather a common thing to do. Somewhere you create an FAQParser object. So far so good. But inside its parse() method:

FAQParser handler = new FAQParser();

you create a second FAQParser object. This second FAQParser is the one that does the parsing, since you set it to be the ContentHandler for the XMLReader. But at the end, you disregard it and look in the first FAQParser for results. Naturally there aren't any because it wasn't involved in the parsing.

You only need one FAQParser. So in the parse() method, don't create another one. Just use the one you already have.