How to close a program if is already open in Java

Question

I'm writing this server, and I want to check if the same program is already running, if is running close the program.

Say I run ServerA

Then I run ServerB (which is the same server)

I want to close ServerA so ServerB can run successfully.

Answer 1

Okay I manage to do it like so...

public static void main(String[] args){
    String PIDtoKill = readPIDFile();
    if(!PIDtoKill.isEmpty())
        killPID(PIDtoKill);
    saveThisPIDtoFile();
}

Method used....

private static String readPIDFile() {
    try {
        for (String line : Files.readAllLines(Paths.get("C:\\Users\\MyUser\\Desktop\\PIDsRunning.txt")))
            return line;
    }
    catch (IOException e1) {
        e1.printStackTrace();
    }
    return "";
}

private static void saveThisPIDtoFile() {
    String pid = ManagementFactory.getRuntimeMXBean().getName();
    pid = pid.substring(0, pid.indexOf("@"));

    List<String> lines = Arrays.asList(pid);
    Path file = Paths.get("C:\\Users\\MyUser\\Desktop\\PIDsRunning.txt");

    try {
        Files.write(file, lines, Charset.forName("UTF-8"));
    }
    catch (IOException e) {
        e.printStackTrace();
    }
}

private static void killPID(String pIDtoKill) {
    try {
        Runtime.getRuntime().exec("taskkill /F /PID " + pIDtoKill);
    }
    catch (IOException e) {
        e.printStackTrace();
    }
}

Answer 2

In case you want to close the program if it is open
You can go for:
System.exit(0);
There are many other exit codes but 0 seems to suit your requirement.

Answer 3

Using the system to kill the process by pid is one solution.

One can use RMI (Remote Method Invocation) to create single instance applications, or in your case send a kill call so the application can terminate on its own. (A graceful termination, requiring the app to be still functioning.)

You could also use an OSGi container: that play with module life cycles the best.