public PRAcroForm(PdfReader reader) 
{
        this.reader = reader;
        fields = new ArrayList();
        fieldByName = new HashMap();
        stack = new ArrayList();
}

Constructor

Parameters:

reader - reader of the input file

 public PRAcroForm.FieldInformation getField(String name) 
{
        return (FieldInformation)fieldByName.get(name);
}

 public ArrayList getFields() 
{
        return fields;
}

 public PRIndirectReference getRefByName(String name) 
{
        FieldInformation fi = (FieldInformation)fieldByName.get(name);
        if (fi == null) return null;
        return fi.getRef();
}

Given the title (/T) of a reference, return the associated reference

 protected  void iterateFields(PdfArray fieldlist,
    PRIndirectReference fieldDict,
    String title) 
{
        for (Iterator it = fieldlist.getArrayList().iterator(); it.hasNext();) {
            PRIndirectReference ref = (PRIndirectReference)it.next();
            PdfDictionary dict = (PdfDictionary) PdfReader.getPdfObjectRelease(ref);
            // if we are not a field dictionary, pass our parent's values
            PRIndirectReference myFieldDict = fieldDict;
            String myTitle = title;
            PdfString tField = (PdfString)dict.get(PdfName.T);
            boolean isFieldDict = tField != null;
            if (isFieldDict) {
                myFieldDict = ref;
                if (title == null) myTitle = tField.toString();
                else myTitle = title + '." + tField.toString();
            }
            PdfArray kids = (PdfArray)dict.get(PdfName.KIDS);
            if (kids != null) {
                pushAttrib(dict);
                iterateFields(kids, myFieldDict, myTitle);
                stack.remove(stack.size() - 1);   // pop
            }
            else {          // leaf node
                if (myFieldDict != null) {
                    PdfDictionary mergedDict = (PdfDictionary)stack.get(stack.size() - 1);
                    if (isFieldDict)
                        mergedDict = mergeAttrib(mergedDict, dict);
                    mergedDict.put(PdfName.T, new PdfString(myTitle));
                    FieldInformation fi = new FieldInformation(myTitle, mergedDict, myFieldDict);
                    fields.add(fi);
                    fieldByName.put(myTitle, fi);
                }
            }
        }
}

After reading, we index all of the fields. Recursive.

 protected PdfDictionary mergeAttrib(PdfDictionary parent,
    PdfDictionary child) 
{
        PdfDictionary targ = new PdfDictionary();
        if (parent != null) targ.putAll(parent);
        for (Iterator it = child.getKeys().iterator(); it.hasNext();) {
            PdfName key = (PdfName) it.next();
            if (key.equals(PdfName.DR) || key.equals(PdfName.DA) ||
            key.equals(PdfName.Q)  || key.equals(PdfName.FF) ||
            key.equals(PdfName.DV) || key.equals(PdfName.V)
            || key.equals(PdfName.FT)
            || key.equals(PdfName.F)) {
                targ.put(key,child.get(key));
            }
        }
        return targ;
}

merge field attributes from two dictionaries

 protected  void pushAttrib(PdfDictionary dict) 
{
        PdfDictionary dic = null;
        if (!stack.isEmpty()) {
            dic = (PdfDictionary)stack.get(stack.size() - 1);
        }
        dic = mergeAttrib(dic, dict);
        stack.add(dic);
}

stack a level of dictionary. Merge in a dictionary from this level

 public  void readAcroForm(PdfDictionary root) 
{
        if (root == null)
            return;
        hashMap = root.hashMap;
        pushAttrib(root);
        PdfArray fieldlist = (PdfArray)PdfReader.getPdfObjectRelease(root.get(PdfName.FIELDS));
        iterateFields(fieldlist, null, null);
}

Read, and comprehend the acroform

 public int size() 
{
        return fields.size();
}

Number of fields found