java - Android : nonwritablechannelException and ClosedChannelException -

i'm using filelock, don't know why meet nonwritablechannelexception exception :

public static list<string> readfromfile(context ctx, string filename) {         try {             fileinputstream fis = ctx.openfileinput(filename);             // lock file             filelock lock = fis.getchannel().trylock(); // exception here             // unlock file             lock.release();             return null;         } catch (exception e) {             log.i(tag, "cannot read file");             e.printstacktrace();         }         return null; } 

and meet exception when writting file: exception closedchannelexception

public static boolean savetofile(context ctx, list<string> lst, string filename) {         try {             fileoutputstream fos = ctx.openfileoutput(filename, context.mode_private);             // lock file             filelock lock = fos.getchannel().lock();             packageobject obj = new packageobject(lst);             objectoutputstream writer = new objectoutputstream(fos);             writer.writeobject(obj);             writer.close();             // unlock file             lock.release(); // exception @ line                 fos.close();             return true;         } catch (exception e) {             log.i(tag, "cannot write file");             e.printstacktrace();         }         return false;     } 

on android developer page, explain exception is:

a nonwritablechannelexception thrown when attempting write channel not open writing.

but still cannot explain why. please me figure out why meet exception please.

thanks :)

"a nonwritablechannelexception thrown when attempting write channel not open writing."

you opened file/channel using openfileinput ... opening reading not writing. if want take lock on file, have open write using openfileoutput instead ... or maybe well.