Execute a Java program from our Java program

Question

I used

Runtime.getRuntime().exec(\"_____\")

but it throws a IOException as below:

java.io.IOException: Create         


        

Answer 1

java.io.IOException: CreateProcess: c:/ error=5
        at java.lang.Win32Process.create(Native Method)
        at java.lang.Win32Process.<init>(Win32Process.java:63)
        at java.lang.Runtime.execInternal(Native Method)

If I recall correctly, error code 5 means access denied. This could be because your path is incorrect (trying to execute "c:/") or you are bumping against your OS security (in which case, look at the permissions).

If you are having trouble locating the Java executable, you can usually find it using system properties:

public class LaunchJre {

    private static boolean isWindows() {
        String os = System.getProperty("os.name");
        if (os == null) {
            throw new IllegalStateException("os.name");
        }
        os = os.toLowerCase();
        return os.startsWith("windows");
    }

    public static File getJreExecutable() throws FileNotFoundException {
        String jreDirectory = System.getProperty("java.home");
        if (jreDirectory == null) {
            throw new IllegalStateException("java.home");
        }
        File exe;
        if (isWindows()) {
            exe = new File(jreDirectory, "bin/java.exe");
        } else {
            exe = new File(jreDirectory, "bin/java");
        }
        if (!exe.isFile()) {
            throw new FileNotFoundException(exe.toString());
        }
        return exe;
    }

    public static int launch(List cmdarray) throws IOException,
            InterruptedException {
        byte[] buffer = new byte[1024];

        ProcessBuilder processBuilder = new ProcessBuilder(cmdarray);
        processBuilder.redirectErrorStream(true);
        Process process = processBuilder.start();
        InputStream in = process.getInputStream();
        while (true) {
            int r = in.read(buffer);
            if (r <= 0) {
                break;
            }
            System.out.write(buffer, 0, r);
        }
        return process.waitFor();
    }

    public static void main(String[] args) {
        try {
            Runtime.getRuntime().exec("c:/");

            List cmdarray = new ArrayList();
            cmdarray.add(getJreExecutable().toString());
            cmdarray.add("-version");
            int retValue = launch(cmdarray);
            if (retValue != 0) {
                System.err.println("Error code " + retValue);
            }
            System.out.println("OK");
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

(Tested Windows XP, Sun JRE 1.6; Ubuntu 8.04, OpenJDK JRE 1.6)

This is the equivalent of running:

java -version

You may also want to look at the "java.library.path" system property (and "path.separator") when trying to locate the executable.