My lab4 work well on the localhost but it doesn't work in server I always get this 
FileNotFoundException: images/gaga.png (No such file or directory), 

               FileInputStream in = new FileInputStream("images/gaga.png" );

this the file input ?? where I should put my image in server? I put them in WWW folder but I am not sure 

still have  the same error 

java.io.FileNotFoundException: ../images/gaga.png (No such file or directory)

try single dot instead: ./images/FileName.png

if it does not work, you need some code to find your current path, some thing like

String path = request.getSession().getServletContext().getRealPath("/");

and put the image folders under www/lab4,

then the path to the image is path + "lab4/images/" + "gaga.png".

I found the code online, and I documented it as such, I think you should probably do the same if you choose to use it.

edit: by webcontent, I meant www/

I thought we weren't supposed to use absolute paths