How to run async bash command in java?

Question

I'm trying to run an async bash command from a java file and wait for it to finish before I continue the java code execution.

At this moment I've tried using Callable like so:

class AsyncBashCmds implements Callable{

    @Override
    public String call() throws Exception {
        try {
            String[] cmd = { "grep", "-ir", "<" , "."};

            Runtime.getRuntime().exec(cmd); 

            return "true"; // need to hold this before the execution is completed.

        } catch (Exception e) {
            return "false";
        }
    }
}

and I call it like so:

ExecutorService executorService = Executors.newFixedThreadPool(1);
Future<String> future =  executorService.submit(new runCPPinShell(hookResponse));
String isFinishedRunningScript = future.get();

Thanks!!!

What's going wrong: you say that you are trying the command. But you don't say what's going wrong? DOes (it appear that) nothing happens at all? Do you get an error message/code? Does the bash command run but do the wrong thing? — jalanb
– jalanb, Commented Apr 25, 2020 at 1:46
the command is executed but the java code does not wait for it to finish — H.Epstein
– H.Epstein, Commented Apr 25, 2020 at 15:28

Johannes Kuhn · Accepted Answer · 2020-04-25 15:13:20Z

1

An easier way is to use Java 9+ .onExit():

private static CompletableFuture<String> runCmd(String... args) {
    try {
        return Runtime.getRuntime().exec(args)
            .onExit().thenApply(pr -> "true");
    } catch (IOException e) {
        return CompletableFuture.completedFuture("false");
    }
}

Future<String> future = runCmd("grep", "-ir", "<" , ".");
String isFinishedRunningScript = future.get(); // Note - THIS will block.

If you want to block anyway, use .waitFor().

answered Apr 25, 2020 at 15:13

Johannes Kuhn

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2 Comments

H.Epstein Over a year ago

I get this error : cannot find symbol symbol: method onExit() location: class java.lang.Process I assume I do not use Java 9+ ?

H.Epstein Over a year ago

I am not running Java 9+ but .waitFor() solved it for me, Thanks!

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