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Apache Wicket Interview Questions and Answers

Ques. How to keep file validation in apache-wicket if no file has been selected?
To fix it, just override the validateOnNullValue() method like this :

FileUploadField fileUpload = new FileUploadField("fileupload",new Model<FileUpload>());
fileUpload .add(new AbstractValidator() { 
       public boolean validateOnNullValue(){
       return true;
protected void onValidate(IValidatable validatable) { 
FileUpload fileUpload = (FileUpload) validatable.getValue();
    protected String resourceKey() {
   return "yourErrorKey";
Now, when no file is selected, and submit button is clicked, validation will be performed.
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