Question

As the title says, I’m wondering if it is possible for a program written in Java (and only java) to relaunch himself (preferably a .jar) with administrator privileges, showing in the way the native Windows UAC (in order to make it more trustable for the user), i did my homework and found out that it is possible to accomplish this using bridges between c++ and java, but i would really like to do this as a pure java project.

P.S: In the remote case that this result to be impossible, can someone show me the “easy” way to do this using another language (i mean, I’ve found tutorials, but they are to complicated for something I think it should not be that complicated).

P.S2: In case it is possible to accomplish this, would it work, on other platforms (OS X, Linux)

Answer 1

It cannot be done in pure java.

Best bet would be to write this to a file:

@echo Set objShell = CreateObject("Shell.Application") > %temp%\sudo.tmp.vbs
@echo args = Right("%*", (Len("%*") - Len("%1"))) >> %temp%\sudo.tmp.vbs
@echo objShell.ShellExecute "%1", args, "", "runas" >> %temp%\sudo.tmp.vbs
@cscript %temp%\sudo.tmp.vbs

and save it as something.bat in Windows temp directory (as we have access to this).

You would then execute this from your application using Runtime or ProcessBuilder and exit your application (System.exit(0);).

You should add an immediate start up check to your application that checks if the program has elevation, if it has proceed if not re-run the batch and exit.

Here is an example I made (this must be run when compiled as a Jar or it wont work):

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import javax.swing.JOptionPane;

/**
 *
 * @author David
 */
public class UacTest {

    public static String jarName = "UacTest.jar", batName = "elevate.bat";

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        if (checkForUac()) {//uac is on
            JOptionPane.showMessageDialog(null, "I am not elevated");
            //attempt elevation
            new UacTest().elevate();
            System.exit(0);
        } else {//uac is not on
            //if we get here we are elevated
            JOptionPane.showMessageDialog(null, "I am elevated");
        }

    }

    private static boolean checkForUac() {
        File dummyFile = new File("c:/aaa.txt");
        dummyFile.deleteOnExit();

        try {
            //attempt to craete file in c:/
            try (FileWriter fw = new FileWriter(dummyFile, true)) {
            }
        } catch (IOException ex) {//we cannot UAC muts be on
            //ex.printStackTrace();
            return true;
        }
        return false;
    }

    private void elevate() {
        //create batch file in temporary directory as we have access to it regardless of UAC on or off
        File file = new File(System.getProperty("java.io.tmpdir") + "/" + batName);
        file.deleteOnExit();

        createBatchFile(file);

        runBatchFile();

    }

    private String getJarLocation() {
        return getClass().getProtectionDomain().getCodeSource().getLocation().getPath().substring(1);
    }

    private void runBatchFile() {
        //JOptionPane.showMessageDialog(null, getJarLocation());

        Runtime runtime = Runtime.getRuntime();
        String[] cmd = new String[]{"cmd.exe", "/C",
            System.getProperty("java.io.tmpdir") + "/" + batName + " java -jar " + getJarLocation()};
        try {
            Process proc = runtime.exec(cmd);
            //proc.waitFor();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    private void createBatchFile(File file) {
        try {
            try (FileWriter fw = new FileWriter(file, true)) {
                fw.write(
                        "@echo Set objShell = CreateObject(\"Shell.Application\") > %temp%\\sudo.tmp.vbs\r\n"
                        + "@echo args = Right(\"%*\", (Len(\"%*\") - Len(\"%1\"))) >> %temp%\\sudo.tmp.vbs\r\n"
                        + "@echo objShell.ShellExecute \"%1\", args, \"\", \"runas\" >> %temp%\\sudo.tmp.vbs\r\n"
                        + "@cscript %temp%\\sudo.tmp.vbs\r\n"
                        + "del /f %temp%\\sudo.tmp.vbs\r\n");
            }
        } catch (IOException ex) {
            //ex.printStackTrace();
        }
    }
}