如何以编程方式重新启动JavaWebStart应用程序

我正在尝试实现java web start应用程序的自动更新。逻辑：我正在从服务器获取jnlp文件，并将时间戳与当前时间戳进行比较。如果存在差异，则下载最新的文件并使用javaws命令重新启动应用程序。现在我有两个问题。 1.我无法获取本地jnlp文件（因为jnlp文件的位置对于前面提到的不同操作系统是不同的） 2.在终止当前正在运行的应用程序后，我无法找到一种优雅的方法来重新启动应用程序。如果有其他优雅的解决方案，我将不胜感激。谢谢

我的代码：

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Date;

import javax.swing.JOptionPane;

import org.apache.log4j.Logger;

import com.ibm.nzna.projects.qit.app.PropertySystem;

/**
 * QitUpdater . java
 * 
 * @Info Checks for updates for the JWS Application
 * 
 *       This program will try to use a given URL to connect online to check for
 *       a newer version of the jnlpFile. The program then compares the last
 *       modified dates of the local copy and the URL copy, and notifies the
 *       user if the URL copy is newer, via a Dialog box popup. The newer
 *       version can then, be downloaded and installed using JWS.
 * 
 * @Warnings If the server containing QIT changes its directory or location then
 *           the program will error out every time since the URL link is
 *           hard-coded.
 * 
 * @author Ashish Tyagi
 * @version 4/22/2013
 * 
 */
public abstract class QitUpdater {
//  constant which hold the location of property file and server location 
    public final static String jnlpFile = PropertySystem.getString(PropertySystem.PROPERTY_JNLP_FILE);
    public final static String fileDirectoryURL = PropertySystem.getString(PropertySystem.PROPERTY_JNLP_SERVER);
    static Logger logger = Logger.getLogger(QitUpdater.class.getName());


    // private variables
    private static HttpURLConnection huc;
    private static File oldFile = null;
    private static long localDate = 0;
    private static long remoteDate = 0;

    public static void checkUpdates(boolean displayErrors,boolean displayIsUpToDate,boolean autoRunner){
        logger.info("value of jnlp file: "+fileDirectoryURL+"/"+jnlpFile);
        if(jnlpFile !=null && fileDirectoryURL != null)
            checkForUpdates(displayErrors, displayIsUpToDate, autoRunner);
    }

    /**
     * Starts a new task to check for QIT updates.
     * 
     * If there is no connection or the program is up to date, then this method
     * returns normally. Otherwise, it will exit the old program and execute the
     * newer QIT program.
     * 
     * @param displayErrors
     *            will show all error messages in popups, if any occur. This is
     *            recommended to be false on boostrapping, so the 'offline user'
     *            is not annoyed.
     * 
     * @param displayIsUpToDate
     *            will show a popup letting the user know if their current
     *            version of QIT is up to date, if they have the most up to date
     *            version. Otherwise, it will ignore the popup.
     * 
     * @param autoRunNewer
     *            will automatically execute the newer JNLP file, if it is found
     *            or downloaded. This is recommended to be false if this method
     *            is being called from within a user action, like a button
     *            press. If it is set to false, a dialog will ask the user to
     *            restart QIT in order to finish updating the program, if an
     *            update was found.
     */
    public static void checkForUpdates(boolean displayErrors,
            boolean displayIsUpToDate, boolean autoRunNewer) {
        // Try to find a similarly named file
        // in the current local directory
        oldFile = new File(jnlpFile);

        if (oldFile.exists()) // find the JNLP file
        {
            // grab the local last modified date to compare
            localDate = oldFile.lastModified();
        }

        // Try to access the base URL
        int code = 404;
        try {
            URL u = new URL(fileDirectoryURL);
            huc = (HttpURLConnection) u.openConnection();
            huc.setRequestMethod("GET");
            huc.connect();
            code = huc.getResponseCode();
        } catch (MalformedURLException e) {
            if (displayErrors)
                printError("Error: Could not check for updates.\nMalformedURLException: "
                        + e.getMessage()
                        + "\n\nClick OK to continue using QIT.");
            return;
        } catch (IOException e) {
            if (displayErrors)
                printError("Error: Could not check for updates.\nIOException: "
                        + e.getMessage()
                        + "\n\nClick OK to continue using QIT.");
            return;
        }

        if (code == 200) {
            // 200 is a valid connection
            // scan URL for versions
            try {
                StringBuilder sb = new StringBuilder();
                sb.append(fileDirectoryURL).append("/").append(jnlpFile);
                URL u = new URL(sb.toString());
                huc = (HttpURLConnection) u.openConnection();
                huc.setRequestMethod("GET");
                huc.connect();

                // grab the last modified date
                remoteDate = huc.getLastModified();
            } catch (MalformedURLException e) {
                if (displayErrors)
                    printError("Error: Failed to download.\n\n"
                            + e.getMessage()
                            + "\n\nClick OK to continue using QIT.");
                return;
            } catch (IOException e) {
                if (displayErrors)
                    printError("Error: Failed to download.\n\n"
                            + e.getMessage()
                            + "\n\nClick OK to continue using QIT.");
                return;
            }

            // compare last modified dates of JNLP files
            if (remoteDate != localDate) {
                // found a newer version of JNLP

                // ask to download
                if (0 == printQuestion("An updated version of QIT is available.\n\nLast updated:\n"
                        + new Date(remoteDate).toString()
                        + "\n\nDo you want to download and install it?")) {
                    // download and install
                    try {
                        downloadUrlFile(jnlpFile, fileDirectoryURL + "/"
                                + jnlpFile);

                        oldFile.setLastModified(remoteDate);
                        // set the date to the date on the server

                        if (autoRunNewer) {
                            // run the JNLP file
                            try {
                                Runtime.getRuntime()
                                        .exec("javaws "+jnlpFile);

                                System.exit(0);// quit this version of QIT

                            } catch (IOException e) {
                                if (displayErrors)
                                    printError("Error:\n"
                                            + e.getMessage()
                                            + "\n\nClick OK to continue using QIT.");
                            }
                        } else
                            printInfo("In order to finish installing the\nupdate, QIT needs to be restarted.");

                    } catch (Exception e) {
                        if (displayErrors)
                            printError("Error: Failed to download " + jnlpFile
                                    + ".\n\n" + e.getMessage()
                                    + "\n\nClick OK to continue using QIT.");
                    }

                }
            } else {
                // modified dates are the same

                // try to launch the current JNLP
                if(oldFile.exists())
                {
                    // run the JNLP file
                    try {
                        Runtime.getRuntime()
                                .exec("javaws "+jnlpFile);

                        System.exit(0);// quit this version of QIT

                    } catch (IOException e) {
                        if (displayErrors)
                            printError("Error:\n"
                                    + e.getMessage()
                                    + "\n\nClick OK to continue using QIT.");
                    }
                }

                // up to date
                if (displayIsUpToDate)
                    printInfo("QIT is up to date.\n\nLast update was:\n"
                            + (new Date(localDate).toString())
                            + "\n\nClick OK to continue.");
            }
        }

        return;
    }

    /**
     * Downloads the urlString to the filename at the current directory.
     * 
     * @param filename
     * @param urlString
     * @throws MalformedURLException
     * @throws IOException
     */
    public static void downloadUrlFile(String filename, String urlString)
            throws MalformedURLException, IOException {
        BufferedInputStream in = null;
        FileOutputStream fout = null;

        try {
            URL url = new URL(urlString);
            huc = (HttpURLConnection) url.openConnection();
            in = new BufferedInputStream(url.openStream());
            fout = new FileOutputStream(filename);

            byte data[] = new byte[1024];
            int count;
            while ((count = in.read(data, 0, 1024)) != -1) {
                fout.write(data, 0, count);
            }
        } finally {
            if (in != null)
                in.close();
            if (fout != null)
                fout.close();
        }
    }

    /**
     * Display an error
     * 
     * @param e
     */
    private static void printError(String e) {
        JOptionPane.showMessageDialog(null, e, "Error",
                JOptionPane.ERROR_MESSAGE);
    }

    /**
     * Display some information
     * 
     * @param s
     */
    private static void printInfo(String s) {
        JOptionPane.showMessageDialog(null, s, "Information",
                JOptionPane.INFORMATION_MESSAGE);
    }

    /**
     * Prompt a Yes/No Question
     * 
     * @param String
     *            q
     * @return int 0 means YES, 1 means NO, -1 means they clicked "X" close
     */
    private static int printQuestion(String q) {
        return JOptionPane.showConfirmDialog(null, q, "Question",
                JOptionPane.YES_NO_OPTION);
    }
}

我正在尝试为我的JavaWebStart应用程序实现自动更新

使用JNLPAPI的

DownloadService

服务允许应用程序控制如何缓存自己的资源、确定当前缓存的资源、强制缓存资源以及从缓存中删除资源。JNLP客户端负责提供此服务的特定实现