can't find all field of a pdf (acroform) - pdfbox

Question

Considering this pdf
With this code I except retrieve all field but I get half of them:
pdfOriginal.getDocumentCatalog().getAcroForm().getFields().forEach(field -> {
System.out.println(field.getValueAsString());
});
What is wrong here ? It seems all annotations are not in aocroform reference, what is the correct way to add form field annotation into acroform object?
Update 1
The wierd thing here if I tried to set field's value which is not referenced/found in getAcroForm.getFields() like this :
doc.getDocumentCatalog().getAcroForm().getField("fieldNotInGetFields").setValue("a");
This works
Update 2
It seems using doc.getDocumentCatalog().getAcroForm().getFieldTree() retrieve all fields. I don't understand why doc.getDocumentCatalog().getAcroForm().getFields() not ?
What is the correct way retrieve all fields of a pdf acroform.getFieldTree() or acroform.getFields() (I need retrieve them to set them partialValue)

Answer 1

From the java doc on method public List<PDField> getFields() we can read:
A field might have children that are fields (non-terminal field) or does not have children which are fields (terminal fields).
In my case some fields contain non-terminal field so to print them all we need check if we are in a PDNonTerminalField like :
document.getDocumentCatalog().getAcroForm().getFields().forEach(f -> {
listFields(f);
});
// loop over PDNonTerminalField otherwise print field value
public static void listFields(PDField f){
if(f instanceof PDNonTerminalField) {
((PDNonTerminalField) f).getChildren().forEach(ntf-> {
listFields(ntf);
});
}else {
System.out.println(f.getValueAsString());
}
}