How to automatically answer user prompts in Java?

Question

I'm using a compiled Java file which takes a filename as a parameter and then asks for a username and password (via user input). I am trying to automate this from a shell script, but am running into problems. I'm unable to access the java code, which is why I am having trouble.
So the code is called the following way

java javaprogram /home/user/securityfile

So, you pass the file, and then it asks you for username and password. After entering those, it's done.

Now, I have tried to put the user input into a file and pass it in, but I get an error.

java javaprogram /home/user/securityfile < userinputfile

userinput file contains the following text (First line is the username, second line is the password):

MattSmith
MSpassword136

Does anyone have any ideas? Maybe I am doing it wrong?

Here is the error message:

Exception in thread "main" java.lang.NullPointerException at ilex.util.UserAuthFile.main(UserAuthFile.java:297)

Thanks

If you just want to figure out what the Java program is doing, perhaps try decompiling it? Or, since it sounds like this is a Linux system, you could try using strace to see exactly how it's interacting with the console. Note that any mechanism to read a password securely on the console won't work with a pipe; you'll probably need a pty instead. — Daniel Pryden
– Daniel Pryden, Commented Apr 16, 2018 at 21:56
Try (echo "user"; sleep 1; echo "password") | java javaprogram /home/user/securityfile. If that works you can refactor to read from file without too much work. — LMC
– LMC, Commented Apr 16, 2018 at 22:46
May be that app will never read from System.in since it requires an interactive console System.console(). Some info here. — LMC
– LMC, Commented Apr 16, 2018 at 23:20

LMC · Accepted Answer · 2018-04-18 17:47:35Z

2

Try (echo "user"; sleep 1; echo "password") | java javaprogram /home/user/securityfile

If that works you can refactor to read from file without too much work. If it doesn't, may be that app will never read from System.in since it requires an interactive console System.console(). Some info here.

answered Apr 18, 2018 at 17:47

LMC

14.4k3 gold badges34 silver badges62 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

jonesy19 Over a year ago

You were spot on, I was doomed from the beginning. System.console() is what it is using. Thanks for the help.

Collectives™ on Stack Overflow

How to automatically answer user prompts in Java?

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related