java ee - Display list of files in webpage using servlet -

i'm new java ee, , want display in webpage list of pdf thumbnails. these pdf stored in folder in src/main/webapp/pdf, , want read folder filenames. here code :

@override public void doget(httpservletrequest req, httpservletresponse res) {     try {         res.setcontenttype("application/json");         res.setcharacterencoding("utf-8");          printwriter out = res.getwriter();         file pdffolder = new file("/pdf");          (file pdf : pdffolder.listfiles()) { // line 27             out.println(pdf.getname());         }     } catch (ioexception e) {         log.log(level.severe, e.getmessage());     } } 

when run code, nullpointerexception :

java.lang.nullpointerexception     com.multi.services.listfiles.doget(listfiles.java:27)     javax.servlet.http.httpservlet.service(httpservlet.java:621)     javax.servlet.http.httpservlet.service(httpservlet.java:728) 

here structure :

what want have web service reads pdf folder , returns json containing pdf filenames, , call service in javascript using ajax.

can me make script running ? or has better solution ?

thanks :)

a quote javadoc of file.listfiles()

returns null if abstract pathname not denote directory, or if i/o error occurs.

so path not correct (as current directory of servlet container undefined). have these possibilities here:

• use absolute path (this appropriate, if store pdf outside of webapp)

• use getrealpath() (this should suitable use case; pdfs part of webapp):

file pdffolder =   new file(req.getsession().getservletcontext().getrealpath("/pdf"));