Ufdjrw

here I have a jsp page which allow the user to apply his name, his age and his mastered programming language

<form action="./getPost" method="POST" >

 <label> name </label> <input type="text" name="name" > <br><br>
 <label> age </label> &nbsp <input type="text" name="age" > <br><br>


 <label> programming langage </label> <br>
 <input type="checkbox" name="fav" value="java"> java <br>
 <input type="checkbox" name="fav" value="php"> php <br>
 <input type="checkbox" name="fav" value="python"> python <br><br>

 <input type="submit" value="submit post">

 </form>

this is how the servlet get the data

 String name = request.getParameter("name");
 String age = request.getParameter("age");
 String[] lang = request.getParameterValues("fav");

 InsertPost.add(new Post(name, age, lang));

when I fill in all the fields of the form and click on the button it inserts the data into the database.
then I tested to submit it without selecting any checkbox which caused an error (java.lang.NullPointerException).
the issue is that I want to leave this optional means not required if the user wants to pick or not.
so how can I make the servlet handles null values ​​from checkboxes

How to solve this issue:

Option 1: (sending empty string instead of null)
Assuming that your table has a not-null constraint on field fav.

String name = request.getParameter("name");
String age = request.getParameter("age");
List<String> lang = request.getParameterValues("fav");
if(lang==null) 
 lang = new String[] "";

InsertPost.add(new Post(name, age, lang));
//not recommended as it will add 1-byte of empty string even if there is no fav language

Note:

You should put the InsertPost.add(...) call in a try-catch block to
handle exception during inserting data to DB and then show it on UI as a part of best
practices. Also, put a check if the name and age are null and handle it.

Option 2: (sending null and removing null constraint from the table on fav field)

//how you are doing it previously will work.
InsertPost.add(new Post(name, age, lang));

Cause of error

Your database is not expecting null value on filed favorite languages

//One suggestion: treat null and replace with empty String

 String name = (request.getParameter("name") == null ? "": request.getParameter("name"));
 String age = (request.getParameter("age") == null) ? "" : request.getParameter("age"));
 String[] lang = (request.getParameterValues("fav") == null) ? "": request.getParameterValues("fav"));

I hope it help you.