Executing a Jar file from an Java application

Question

I have 2 methods I wrote to try and execute a Jar file from my Java application and they both are not doing anything. The Java Runtime Environment is installed on the C: drive and by default its Path points to a directory on the C: drive. The Jar file I am trying to execute is located on the E: drive.

Jar location: E:\\Demo Folder\\MyDemo.jar

I tried to execute MyDemo.jar using the following 2 methods:

Method 1:

try {
    Runtime.getRuntime().exec("cmd /c start %SystemDrive%\\java -jar " + "E:/Demo Folder/MyDemo.jar");
} catch (IOException ex) {
    System.err.println(ex.getMessage());
}

Method 2:

try {
    File dirFile = new File("E:/Demo Folder/");
    ProcessBuilder pb = new ProcessBuilder("java", "-jar", "E:/Demo Folder/MyDemo.jar");
    pb.directory(dirFile);
    Process p = pb.start();
} catch (Exception ex) {
    System.err.println(ex.getMessage());
}

Answer 1

Didn't you try to put your invocation logic inside a, say, E:/Demo Folder/rundemo.bat` (or .cmd) file, and call that .bat from your java instead? That's usually more sane and easy to troubleshoot.

Answer 2

I'm guessing the problem is the space in the path of the jar file. Try this:

new ProcessBuilder("java", "-jar", "\"E:/Demo Folder/MyDemo.jar\"");

Answer 3

To launch a external java executable application you must first locate the java.exe file (Which loads the JVM) and pass the argument of -jar to indicate loading of a executable JAR file. In both methods you provided you had minor errors within your code.

In method one:

cmd /c start %SystemDrive%\\\\java -jar

%SystemDrive% is being treated as a string literal as java is unaware of Windows specific environment variables.

In method two:

"java", "-jar", "E:/Demo Folder/MyDemo.jar"

You are assuming that java.exe has been added to PATH environmental variables which may not be the case. Also, from your usage of the "%" operators, I am assuming you are on a windows machine, which uses \\ for directories therefore... "E:/Demo Folder/MyDemo.jar" may not return a valid location.

Try the following segment of code:

try {
    File dirFile = new File("E:\\Demo Folder\\");
    ProcessBuilder pb = new ProcessBuilder(System.getProperty("java.home") + File.separator + "bin" + File.separator + "java", "-jar", new File(dirFile, "MyDemo.jar").getAbsolutePath());
    pb.directory(dirFile);
    Process p = pb.start();
} catch (Exception ex) {
    System.err.println(ex.getMessage());
}