JAR 文件主类未找到和 java.io.fileNotFoundException

Question

public class myapp extends Frame {

    public static void main(String args[]) {
        myapp mdi = new myapp();
    }

    static void Fatal(String s) {
        MessageBox mb = new MessageBox("JMF Error", s);
    }

    JMFrame jmframe = null;
    JDesktopPane desktop;
    FileDialog fd = null;
    CheckboxMenuItem AutoLoop = null;
    Player player = null;
    Player newPlayer = null;
    String filename;

    public myapp() {
        super("Java Media Player");

        // Add the desktop pane
        setLayout(new BorderLayout());
        desktop = new JDesktopPane();
        desktop.setDoubleBuffered(true);
        add("Center", desktop);
        setMenuBar(createMenuBar());

        setSize(640, 480);
        setVisible(true);

        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent we) {
                System.exit(0);
            }
        });

    }

    private MenuBar createMenuBar() {
        ActionListener al = new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                String command = ae.getActionCommand();
                if (command.equals("Open")) {
                    if (fd == null) {
                        fd = new FileDialog(myapp.this, "Open File",
                                FileDialog.LOAD);
                    }
                    fd.show();
                    if (fd.getFile() != null) {
                        String filename = fd.getDirectory() + fd.getFile();
                        openFile("file:" + filename);
                    }
                } else if (command.equals("Exit")) {
                    dispose();
                    System.exit(0);
                }
            }
        };

        MenuItem item;
        MenuBar mb = new MenuBar();

        Menu mnFile = new Menu("File");
        item = new MenuItem("Open");
        mnFile.add(item);
        item.addActionListener(al);
        mnFile.add(item = new MenuItem("Exit"));
        item.addActionListener(al);

        // Options Menu
        Menu mnOptions = new Menu("Options");
        AutoLoop = new CheckboxMenuItem("Auto replay");
        AutoLoop.setState(true);
        mnOptions.add(AutoLoop);

        Menu mn = new Menu("Help");
        MenuItem ball = new MenuItem("Build");
        ball.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(myapp.this,
                        "DEVELOPED BY DVM XLADOR");
            }
        });
        mn.add(ball);
        mb.add(mn);
        mb.add(mnFile);
        mb.add(mnOptions);
        mb.add(mn);
        return mb;
    }

    /**
     * Open a media file.
     */
    public void openFile(String filename) {
        String mediaFile = filename;
        Player player = null;
        // URL for our media file
        URL url = null;
        try {
            // Create an url from the file name and the url to the
            // document containing this applet.
            if ((url = new URL(mediaFile)) == null) {
                Fatal("Can't build URL for " + mediaFile);
                return;
            }

            // Create an instance of a player for this media
            try {
                player = Manager.createPlayer(url);
            } catch (NoPlayerException e) {
                Fatal("Error: " + e);
            }
        } catch (MalformedURLException e) {
            Fatal("Error:" + e);
        } catch (IOException e) {
            Fatal("Error:" + e);
        }
        if (player != null) {
            this.filename = filename;
            JMFrame jmframe = new JMFrame(player, filename);
            desktop.add(jmframe);
        }
    }
}

class JMFrame extends JInternalFrame implements ControllerListener {
    Player mplayer;
    Component visual = null;
    Component control = null;
    int videoWidth = 0;
    int videoHeight = 0;
    int controlHeight = 30;
    int insetWidth = 10;
    int insetHeight = 30;
    boolean firstTime = true;

    public JMFrame(Player player, String title) {
        super(title, true, true, true, true);
        getContentPane().setLayout(new BorderLayout());
        setSize(320, 10);
        setLocation(50, 50);
        setVisible(true);
        mplayer = player;
        mplayer.addControllerListener((ControllerListener) this);
        mplayer.realize();
        addInternalFrameListener(new InternalFrameAdapter() {
            public void internalFrameClosing(InternalFrameEvent ife) {
                mplayer.close();
            }
        });

    }

    public void controllerUpdate(ControllerEvent ce) {
        if (ce instanceof RealizeCompleteEvent) {
            mplayer.prefetch();
        } else if (ce instanceof PrefetchCompleteEvent) {
            if (visual != null)
                return;

            if ((visual = mplayer.getVisualComponent()) != null) {
                Dimension size = visual.getPreferredSize();
                videoWidth = size.width;
                videoHeight = size.height;
                getContentPane().add("Center", visual);
            } else
                videoWidth = 320;
            if ((control = mplayer.getControlPanelComponent()) != null) {
                controlHeight = control.getPreferredSize().height;
                getContentPane().add("South", control);
            }
            setSize(videoWidth + insetWidth, videoHeight + controlHeight
                    + insetHeight);
            validate();
            mplayer.start();
        } else if (ce instanceof EndOfMediaEvent) {
            mplayer.setMediaTime(new Time(0));
            mplayer.start();
        }
    }
}

D:\hadoop>jar cvf db.jar *.class
             added manifest
          adding: JMFrame$1.class(in = 600) (out= 377)(deflated 37%)
        adding: JMFrame.class(in = 2362) (out= 1329)(deflated 43%) 
            adding: myapp$1.class(in = 469) (out= 334)(deflated 28%)
            adding: myapp$2.class(in = 1330) (out= 807)(deflated 39%)
          adding: myapp$3.class(in = 631) (out= 436)(deflated 30%)
      adding: myapp.class(in = 3283) (out= 1787)(deflated 45%)

D:\hadoop>java -jar db.jar
  no main manifest attribute, in db.jar

---

I can compile my file with no issues but when it comes to creation of jar file it notifies me error of java.io.FileNotFoundException jni error please check your installation and also about manife.st file. Just correct my the segment of code where I made a mistake

Answer 1

How are you attempting to build your JAR? The problem looks like this is trying to build an executable JAR which will run by calling the main method in the Main class (this is a common default), but since you don't have a Main class it can't do this.

I'd suggest either change this configuration to call your actual class, or relocate your main method to a class with this name.

Answer 2

(Posting as a separate answer because the edit to the question shows a totally different issue)

The problem you're having running the JAR is that the JAR doesn't specify an entry point, so the jar command cannot execute it. Because you're not including a manifest when you create your JAR, jar is auto-generating an empty one for you.

To fix this, change your JAR-building command to:

jar cvfe db.jar myapp *.class

Then you'll be able to execute it as you were. (Note that myapp here is the fully-qualified class name. Since you haven't shown a package declaration, I've assumed you're using the default package. If not, make sure to include this here). You'll also find that if you unzip it and look inside META-INF/MANIFEST.MF there's now the line:

Main-Class: myapp

More on this here .