process does not run when executing Java

Question

I am trying to run a .class file in java. Here's what I've tried:

Runtime rt = Runtime.getRuntime();
Process pr = rt.exec("cd target/classes/; java -cp ./ SoundHandler Correct; cd ../../");

I did some googling and the best I could come up with was to tack this on to the end:

pr.getInputStream();
pr.getErrorStream();
pr.getOutputStream();

This did not help. I want to run a .class file in java. Thanks!

The .class file does not seem to run from when I execute the command from inside java. — Sushila Jyothi Lévêque, Sep 22 '18 at 17:19
It does not play the sound or print "This is a test" (for debug). I know the command does not run because it does not play the sound I provided in the arguments. The command or the SoundHandler class itself does not raise any errors when I run the command from terminal in the same directory. — Sushila Jyothi Lévêque, Sep 22 '18 at 17:47
This question is not a dupe. I am simply cd to where the .class file is. — Sushila Jyothi Lévêque, Feb 23 '19 at 22:08

skandigraun · Accepted Answer · 2018-09-22T19:50:18.710

0

You are giving three commands to the runtime to execute - but only one parameter. It is trying to execute it as one command - however such a command does not exist.

If the command consists of multiple elements (command and arguments), they should be passed as a String array, so the runtime can differentiate them. If you are using shell commands, (like cd), then the command should be passed to the shell as a parameter.

Try something like this:

//if you are using unix-like OS. For Windows change sh -c to cmd /k
String[] cmd = new String[] {"sh", "-c", "cd target/classes/ && java -cp ./ SoundHandler Correct"};
Runtime rt = Runtime.getRuntime();
Process pr = rt.exec(cmd)

For debugging the process, you can read the command's output on the following way:

InputStream is = pr.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);

String line;
while ((line = br.readLine()) != null){
    System.out.println("MSG: " + line);
}

A bit of update after some chat conversation: the main idea was working, but classpath needed some investigation.

edited Sep 22 '18 at 19:50

answered Sep 22 '18 at 17:26

skandigraun

741
8
21

What's the error/output you get? – skandigraun Sep 22 '18 at 17:56
None. It just continues with the main .class file. – Sushila Jyothi Lévêque Sep 22 '18 at 17:57
There has to be something on the inputstream of the process. – skandigraun Sep 22 '18 at 17:58
I tried `pr.getOutputStream` and `pr.getErrorStream`, but nothing changes – Sushila Jyothi Lévêque Sep 22 '18 at 18:00
Try to add an `echo success` to the start of end or the command (the last element of the cmd array). Also, note that you need to check the inputstream of the process, since this is the commands' output is written. – skandigraun Sep 22 '18 at 18:02
I did that, it did not output anything, even with `pr.getInputStream`. – Sushila Jyothi Lévêque Sep 22 '18 at 18:05
How do you read the inputstream? At least a "success" message should be displayed. – skandigraun Sep 22 '18 at 18:06
`pr.getInputStream`. I obviously can't print it and understand it... – Sushila Jyothi Lévêque Sep 22 '18 at 18:07
See my edit.... – skandigraun Sep 22 '18 at 18:11
It turns out line = br.readLine() is null. – Sushila Jyothi Lévêque Sep 22 '18 at 18:23
You put that code before or after executing the process? (Should be after) – skandigraun Sep 22 '18 at 18:24
I put it after.. – Sushila Jyothi Lévêque Sep 22 '18 at 18:26
I'm trying to start a chat, because it is going to take long otherwise. So just flooding this comment part and hoping that the option will pop up - don't know why the option is not more visible... – skandigraun Sep 22 '18 at 18:32
So adding a new comment... the chat option is still not available. – skandigraun Sep 22 '18 at 18:32
Well, let's add another one, I can feel that this will be lucky comment. – skandigraun Sep 22 '18 at 18:33
1

Apparently it was not, still no chat link. – skandigraun Sep 22 '18 at 18:33
Chat link chat link – skandigraun Sep 22 '18 at 18:33
Why there is no chat link – skandigraun Sep 22 '18 at 18:33
I can't chat. Not enough rep. – Sushila Jyothi Lévêque Sep 22 '18 at 18:33
What? That needs also rep? Wow. I gave you all the rep I could. – skandigraun Sep 22 '18 at 18:35
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/180585/discussion-between-sushila-jyothi-leveque-and-skandigraun). – Sushila Jyothi Lévêque Sep 22 '18 at 18:36

process does not run when executing Java

1 Answers1