IDE-Style program running

Question

My Goal

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I am attempting to make a Java program in which a user can select any .class or .jar file from their computer. My program w

Answer 1

If you don't want the other program (which you call through it's main method) to be able to shut down the JVM you're running in, you have, as I see it, three options:

1. Using a SecurityManager

Set up the SecurityManager so that it prevents the System.exit call:

public class Test {
    public static void main(String args[]) {
        SecurityManager sm = System.getSecurityManager();
        System.setSecurityManager(new SecurityManager() {
            @Override
            public void checkExit(int status) {
                throw new SecurityException("Client program exited.");
            }
        });

        try {
            System.out.println("hello");
            System.exit(0);
            System.out.println("world");
        } catch (SecurityException se) {
            System.out.println(se.getMessage());
        }
    }
}

Prints:

hello
Client program exited.

This is probably the nicest solution. This is the way application servers prevent an arbitrary servlet from terminating the entire server.

2. Separate JVM

Run the other program in a separate JVM, using for instance ProcessBuilder

import java.io.*;

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

        ProcessBuilder pb = new ProcessBuilder("java", "other.Program");
        pb.redirectErrorStream();
        Process p = pb.start();
        InputStream is = p.getInputStream();
        int ch;
        while ((ch = is.read()) != -1)
            System.out.print((char) ch);
        is.close();
        System.out.println("Client program done.");
    }
}

3. Use shutdown hooks instead

Don't disallow the termination of the JVM, but instead add shutdown-hooks that cleans up the "hub" and exits gracefully. (This option probably only makes sense if your running one "external" program at a time.)

import java.io.*;

public class Test {

    public static void main(String args[]) throws IOException {

        Runtime.getRuntime().addShutdownHook(new Thread() {
            public void run() { 
                System.out.println("Uninitializing hub...");
                System.out.println("Exiting gracefully.");
            }
        });

        // Run client program
        System.out.println("Running... running... running...");
        System.exit(0);

     }
}

Prints:

Running... running... running...
Uninitializing hub...
Exiting gracefully.