File system permission check

Question

Hi,
I'm trying to check whether an user has permission to explore a folder in the filesystem. I've reached to capture a NullPointerException when i use the list() mehod for the file object, but I wanted to check it before the exception has to be thrown.
When I search in the forum I find many information about checking if the code has permission, but I want to check the user, not the code.
Does anyone know how to do it?
(If someone found the information in the forum, please post a reference)
Thank you

Answer 1

I forgot that I've used canRead() before :-S
And, of course, it doesn't work.
Maybe some piece of code can help (I've tried to rewrite it in English, sorry for the translation problems ):
File f = new File(rutaBase);
            String[] rutasPosibles = null;
            int longTotal = 0;
            int longRoots;
            int longListado = 0;
            int k;
            if (!f.exists()) {
                Trazas.escribir("can't open dir: " + rutaBase);
            } else {
                Trazas.escribir("processing " + f.toString());
                Trazas.escribir("permissions on="+f.toString()+" canRead()="+f.canRead()+" canWrite()="+f.canWrite());
                    FilePermission perm = new FilePermission(rutaBase, "write");
                    boolean correct = false;
                    try {
                    AccessController.checkPermission(perm);
                    correct = true;
                    } catch (AccessControlException ace) {
                    Trazas.escribir("ACCESS CONTROL");
                    ace.printStackTrace();
                    correct = false;
                    } catch (Exception e) {
                    e.printStackTrace();
                    correct= false;
                    } finally{
                    Trazas.escribir("all correct: "+correct);
                longRoots = File.listRoots().length;
                try{
                longListado = f.list().length;
                }catch (SecurityException e){
                    Trazas.escribir("SECURITY!");
                    e.printStackTrace();
                }catch (NullPointerException e){
                    Trazas.escribir("NULL!");
                    e.printStackTrace();
                }catch (Exception e){
                    Trazas.escribir("OTRA");
                    e.printStackTrace();
                And the result is:
ListaDirectorioLocal$ListadoInternoLocal.generarListado(ListaDirectorioLocal.java:63).->processing S:\cuestionarios
ListaDirectorioLocal$ListadoInternoLocal.generarListado(ListaDirectorioLocal.java:64).->permissions on=S:\cuestionarios canRead()=true canWrite()=true
ListaDirectorioLocal$ListadoInternoLocal.generarListado(ListaDirectorioLocal.java:79).->all correct: true
ListaDirectorioLocal$ListadoInternoLocal.generarListado(ListaDirectorioLocal.java:92).->NULL!
java.lang.NullPointerExceptionSo I assume that neither canRead()/canWrite() from file nor checkPermission() from AccessController can be used to check if the user have permission to list the folder.
About IO and Applets, that's why I have my code signed. Once signed, I've had no problems in creating files and folders on my local-and-shared filesystem. I feel sorry for not being able to explain more clearly since the beginning. And maybe I must say my code is written using 1.4
I'm really grateful for your patience with me.