Calling a command line program in Java

Question

I am making a GUI for a command line program using JavaFX.

If I just pack the program inside the .JAR, can I call it? Or do I need to extract the program into the local machine first before making a process? I ask because since a .JAR is a ZIP file, I suppose you can't just run a file inside the .JAR because it is compressed or something.

The command line program that you want to launch, is it a Java program? Or like a native binary? — aioobe, May 26 '15 at 05:48
Then it's the operating system that launches the program. Unless the operating system in question is able to launch programs from within zip-files (which I doubt) you would have to extract the binary and write it to disk before launching. — aioobe, May 26 '15 at 05:49
this is a good question and I can imagine future visitors struggling with a similar use case so I took the time to write an exhaustive answer. — aioobe, May 26 '15 at 06:22

score 1 · Answer 1 · answered May 26 '15 at 05:49

1

You have to extract your program first to let the os execute it. There's no way to 'stream' it to ram and execute from there.

answered May 26 '15 at 05:49

chris

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score 1 · Accepted Answer · edited May 23 '17 at 11:51

You'd have to do this in two steps:

Extract the binary and write it to disk (because the OS is probably only able to launch the program if it's a file on disk)
Launch the program, preferably using ProcessBuilder.

Here's a complete demo:

test.c

#include <stdio.h>

int main() {
    printf("Hello world\n");
    return 0;
}

Test.java

import java.io.*;
import java.nio.file.*;
import java.nio.file.attribute.PosixFilePermission;
import java.util.Collections;

public class Test {
    public static void main(String[] args) throws Exception {

        Path binary = Paths.get("mybinary");
        Files.copy(Test.class.getResourceAsStream("mybinary"), binary);

        System.out.println("Launching external program...");

        // Needed for Linux at least
        Files.setPosixFilePermissions(binary,
                Collections.singleton(PosixFilePermission.OWNER_EXECUTE));

        Process p = new ProcessBuilder("./mybinary").inheritIO().start();
        p.waitFor();
        System.out.println("External program finished.");
    }
}

Demo

$ cc mybinary.c -o mybinary
$ ./mybinary
Hello world
$ javac Test.java
$ jar -cvf Test.jar Test.class mybinary
$ rm mybinary Test.class
$ ls
mybinary.c  Test.jar  Test.java
$ java -cp Test.jar Test
Launching external program...
Hello world
External program finished.

Further reading:

Calling a command line program in Java

2 Answers2

Here's a complete demo: