SAX XML NullPointerException in character() method

Question

I'm having issues when parsing my xml file. Everything works fine unless I am trying to push values into my parameters Vector.
class SAXLoader extends DefaultHandler {
    private static String className, //name of the class for module in xml
            methodName,              //name of the method for the class
            path;                    //path to jar. should be in URI format
    private Vector params;      //parameters to the method
    private boolean isClassName,     //true if element begins className tag
            isMethodName,            //true if element begins methodName tag
            isParameter,             //true if element begins parameter tag
            isPath;                  //true if element begins path tag
    //=======================init()================================
    //opens XML file specified and parses it for className,
    //the methodName,and the path to the JAR
    //This should be called before doing any of the getter methods
    //=============================================================
    public void init() {
        try {
            XMLReader xmlreader = XMLReaderFactory.createXMLReader();
            SAXLoader handler = new SAXLoader();
            xmlreader.setContentHandler(handler);
            xmlreader.setErrorHandler(handler);
            try {
                FileReader r = new FileReader("myclass.xml");
                xmlreader.parse(new InputSource(r));
            } catch (FileNotFoundException e) {
                System.out.println("File Not Found!");
                e.printStackTrace();
            } catch (NullPointerException e) {
                System.out.println("Parse Error!");
                e.printStackTrace();
        } catch (Exception e) {
            System.out.println("XML Reader Error!");
            e.printStackTrace();
public void characters(char ch[], int start, int length) {
        String temp = "";
        for (int i = start; i < start + length; i++) {
            switch (ch) {
case '\\':
// System.out.print("\\\\");
break;
case '"':
// System.out.print("\\\"");
break;
case '\n':
// System.out.print("\\n");
break;
case '\r':
// System.out.print("\\r");
break;
case '\t':
// System.out.print("\\t");
break;
default:
temp += ch[i];
break;
if (isClassName) {
className = temp;
} else if (isMethodName) {
methodName = temp;
} else if (isPath) {
path = temp;
} else if (isParameter) {
System.out.println("zomg!: " + temp);
params.add(temp);
} //end of characters(...
Right there at params.add(temp);
I'm using this DefaultHandler based class to parse an XML file for information regarding a user's own class [its classname, its methodname, and the methods parameters].
Any clues?
Message was edited by:
nick.mancuso
Message was edited by:
nick.mancuso

Answer 1

You don't actually allocate the params Vector, at least not on the code you've posted. You want something like:
private Vector params = new Vector();or better yet:
private List params = new LinkedList();perhaps.
But even better yet...I suspect that having a handful of global temp variables like that isn't going to work. In my experience, when using SAX you pretty much have to create a stack to hold the current place in the XML tree. That's how you traverse trees, with stacks. Then instead of setting isMethodName, isParameter, etc. (which I presume you do in open/close tag handlers) you define an enumeration of values like "class", "method", "parameter", and then have a stack of those values, or something.