J2MEでのカメラスナップショットヌルポインタの例外

Question

私はこれに長い時間を費やしましたが、まだ成功していません。イメージをキャプチャしてサーバーに送信するアプリケーションでは、以下のようなNullPointerExceptionが発生します。

java.lang.NullPointerException: 0 

at Files.CameraMIDlet.snap(CameraMIDlet.java:120) 
at Files.CameraForm.commandAction(CameraForm.java:116) 
at javax.microedition.lcdui.Display$ChameleonTunnel.callScreenListener(), bci=46 
at com.sun.midp.chameleon.layers.SoftButtonLayer.processCommand(), bci=74 
at com.sun.midp.chameleon.layers.SoftButtonLayer.soft2(), bci=173 
at com.sun.midp.chameleon.layers.SoftButtonLayer.keyInput(), bci=78 
at com.sun.midp.chameleon.CWindow.keyInput(), bci=38 
at javax.microedition.lcdui.Display$DisplayEventConsumerImpl.handleKeyEvent(), bci=17 
at com.sun.midp.lcdui.DisplayEventListener.process(), bci=277 
at com.sun.midp.events.EventQueue.run(), bci=179 
at java.lang.Thread.run(Thread.java:722) 

誤差は以下のコードで、CameraFormにmidlet.snap();でもCameraMIDletにbyte[] image = videoControl.getSnapshot("encoding = jpeg");で起こると。

CameraFormのコードはここにある：

package Files; 

import javax.microedition.media.*; 

import javax.microedition.lcdui.*; 

import javax.microedition.media.control.*; 

import java.io.IOException; 

class CameraForm extends Form implements CommandListener { 

private final CameraMIDlet midlet; 

private final Command exitCommand; 

private Command captureCommand = null; 

private Command showImageCommand = null; 


private Player player = null; 

private static VideoControl videoControl = null; 

private boolean active = false; 

private StringItem messageItem; 

public CameraForm(CameraMIDlet midlet) { 
    super("Camera"); 
    this.midlet = midlet; 
    messageItem = new StringItem("Message", "start"); 
    append(messageItem); 
    exitCommand = new Command("EXIT", Command.EXIT, 1); 
    addCommand(exitCommand); 
    setCommandListener(this); 
    try { 
     //creates a new player and set it to realize 
     player = Manager.createPlayer("capture://video"); 
     player.realize(); 
     //Grap the Video control and set it to the current display 
     videoControl = (VideoControl) (player.getControl("VideoControl")); 
     if (videoControl != null) { 
      append((Item) (videoControl.initDisplayMode(
        VideoControl.USE_GUI_PRIMITIVE, null))); 
      captureCommand = new Command("CAPTURE", Command.SCREEN, 1); 
      addCommand(captureCommand); 
      messageItem.setText("OK"); 
     } else { 
      messageItem.setText("No video control"); 
     } 
    } catch (IOException ioe) { 
     messageItem.setText("IOException: " + ioe.getMessage()); 
    } catch (MediaException me) { 
     messageItem.setText("Media Exception: " + me.getMessage()); 
    } catch (SecurityException se) { 
     messageItem.setText("Security Exception: " + se.getMessage()); 
    } 
} 

* the video should be visualized on the sreen 
* therefore you have to start the player and set the videoControl visible 

synchronized void start() { 
    if (!active) { 
     try { 
      if (player != null) { 
       player.start(); 
      } 
      if (videoControl != null) { 
       videoControl.setVisible(true); 
            //midlet.snap(); 
      } 
     } catch (MediaException me) { 
      messageItem.setText("Media Exception: " + me.getMessage()); 
     } catch (SecurityException se) { 
      messageItem.setText("Security Exception: " + se.getMessage()); 
     } 
     active = true; 
    } 
} 

* to stop the player. First the videoControl has to be set invisible 
* than the player can be stopped 

synchronized void stop() { 
    if (active) { 
     try { 
      if (videoControl != null) { 
       videoControl.setVisible(false); 
      } 
      if (player != null) { 
       player.stop(); 
      } 
     } catch (MediaException me) { 
      messageItem.setText("Media Exception: " + me.getMessage()); 
     } 
     active = false; 
    } 
} 

* on the captureCommand a picture is taken and transmited to the server 

public void commandAction(Command c, Displayable d) { 
    if (c == exitCommand) { 
     midlet.cameraFormExit(); 
    } else { 
     if (c == captureCommand) { 

         midlet.snap(); 

     } 

    } 
} 


} 

CameraMIDletのためのコードは以下の通りです：

package Files; 

import java.io.*; 

import javax.microedition.midlet.*; 

import javax.microedition.lcdui.*; 

import javax.microedition.io.*; 

import javax.microedition.media.control.*; 

import java.io.IOException; 

import javax.microedition.media.MediaException; 


public class CameraMIDlet extends MIDlet { 


private CameraForm cameraSave = null; 

private DisplayImage displayImage = null; 

    CameraForm captureThread; 

    private static VideoControl videoControl; 

    private StringItem messageItem; 

public CameraMIDlet() { 
} 
/* 
* startApp() 
* starts the MIDlet and generates cameraSave, displayImage, database 
* 
**/ 

public void startApp() { 
    Displayable current = Display.getDisplay(this).getCurrent(); 
    if (current == null) { 
     //first call 
     cameraSave = new CameraForm(this); 
     displayImage = new DisplayImage(this); 
     Display.getDisplay(this).setCurrent(cameraSave); 
     cameraSave.start(); 

    } else { 
     //returning from pauseApp 
     if (current == cameraSave) { 
      cameraSave.start(); 
     } 
     Display.getDisplay(this).setCurrent(current); 
    } 
} 
public void pauseApp() { 
    if (Display.getDisplay(this).getCurrent() == cameraSave) { 
     cameraSave.stop(); 
    } 
} 
public void destroyApp(boolean unconditional) { 
    if (Display.getDisplay(this).getCurrent() == cameraSave) { 
     cameraSave.stop(); 
    } 
} 
private void exitRequested() { 
    destroyApp(false); 
    notifyDestroyed(); 
} 
void cameraFormExit() { 
    exitRequested(); 
} 
/** 
* restart the camera again 
* 
*/ 
void displayCanvasBack() { 
    Display.getDisplay(this).setCurrent(cameraSave); 
    cameraSave.start(); 
} 


/** 
* the byte[] of the image should be transmitted to a server 
* 
**/ 
void buildHTTPConnection(byte[] byteImage) { 
    displayImage.setImage(byteImage); 
    Display.getDisplay(this).setCurrent(displayImage); 
    HttpConnection hc = null; 
    OutputStream out = null; 
    try { 
     //enode the image data by the Base64 algorithm 
     String stringImage = Base64.encode(byteImage); 
     // URL of the Sevlet 
     String url = new String(
       "http://ip-adress:8080/C:/Users/HASENDE/Documents/NetBeansProjects/Mobile/pics"); 
     // Obtain an HTTPConnection 
     hc = (HttpConnection) Connector.open(url); 
     // Modifying the headers of the request 
     hc.setRequestMethod(HttpConnection.POST); 
     // Obtain the output stream for the HttpConnection 
     out = hc.openOutputStream(); 

     out.write(stringImage.getBytes());   
    } catch (IOException ioe) { 
     StringItem stringItem = new StringItem(null, ioe.toString()); 
    } finally { 
     try { 
      if (out != null) 
       out.close(); 
      if (hc != null) 
       hc.close(); 
     } catch (IOException ioe) { 
     } 
    } 
    // ** end network 
} 
/** 
* stop the camera, show the captured image and transmit the image to a server 
**/ 
void transmitImage(byte[] image) { 
    cameraSave.stop(); 
    Display.getDisplay(this).setCurrent(displayImage); 
    buildHTTPConnection(image); 
} 

    public void snap(){ 
       try { 
     byte[] image = videoControl.getSnapshot("encoding = jpeg"); 
     transmitImage(image); 
     messageItem.setText("Ok"); 
    } catch (MediaException me) { 
      messageItem.setText("Media Exception: " + me.getMessage()); 
     } 

     } 
} 

Answer 1

バグを見つけるに近い99％を取得NPEをスローするステートメントを識別することによって：

byte[] image = videoControl.getSnapshot("encoding = jpeg"); 

上記のNPEは、videoControlがnullであることを意味します。ここでCameraMIDletを見ると、videoControlはnullで初期化され、他のものに変更されることはありません。そのため、NPEを取得しています。ちなみに、CameraFormコードからは、そこに定義されているvideoControlオブジェクトを使用するように見えますが、あなたはそうしませんでした。

サイドノート。 CameraFormは複数のスレッドで使用されるように設計されているようです（​​修飾子があります）。この場合、videoControlも同期された方法で取得することをお勧めします。また、その場合には、activeフラグの定義におけるvolatile修飾子を追加します。代わりに、フォームの写真を使用キャンバスを取得するための

private volatile boolean active = false; // in CameraForm 

Answer 2

を、写真 チェックfollwingコードはここに

public class ImageCaptureCanvas extends Canvas { 

    UrMidlet midlet; 
    VideoControl videoControl; 
    Player player; 
    SnapShotCanvas snap; 
    private Display display; 



    public ImageCaptureCanvas(UrMidlet midlet) throws MediaException { 
     this.midlet = midlet; 

     this.display = Display.getDisplay(midlet); 
     this.setFullScreenMode(true); 

     try { 
      player = Manager.createPlayer("capture://image"); 
      player.realize(); 
      videoControl = (VideoControl) player.getControl("VideoControl"); 

     } catch (Exception e) { 
      dm(e.getClass().getName()); 
     } 

     videoControl.initDisplayMode(VideoControl.USE_DIRECT_VIDEO, this); 
     try { 
      videoControl.setDisplayLocation(0,0); 
      videoControl.setDisplaySize(getWidth(), getHeight()); 

     } catch (MediaException me) { 
      try { 
       videoControl.setDisplayFullScreen(true); 
      } catch (MediaException me2) { 
      } 
     } 
     dm("icc10"); 
     videoControl.setVisible(true); 
     dm("icc11"); 
     player.start(); 
     this.display.setCurrent(this); 
    } 

    public void dm(String message) { 
     Form form = new Form("Error"); 
     form.append(message); 
     display.setCurrent(form); 
    } 

    public void paint(Graphics g) { 
    } 

    protected void keyPressed(int keyCode) { 
     boolean prv=false; 
     int actn=getGameAction(keyCode); 
     switch (keyCode) { 
      case KEY_NUM5: 
       prv=true; 
       Thread t = new Thread() { 

        public void run() { 
         try { 
          byte[] raw = videoControl.getSnapshot(null); 
          Image image = Image.createImage(raw, 0, raw.length); 

          snap = new SnapShotCanvas(image); 
          display.setCurrent(snap); 
         } catch (Exception e) { 
          dm(e.getClass().getName() + " " + e.getMessage()); 
         } 
        } 
       }; 
       t.start(); 
       break; 
     } 
     if(!prv){ 
      switch (actn) { 
      case Canvas.FIRE: 
       Thread t1 = new Thread() { 

        public void run() { 
         try { 
          byte[] raw = videoControl.getSnapshot(null); 
          Image image = Image.createImage(raw, 0, raw.length); 

          snap = new SnapShotCanvas(image); 
          display.setCurrent(snap); 

         } catch (Exception e) { 
          dm(e.getClass().getName() + " " + e.getMessage()); 
         } 
        } 
       }; 
       t1.start(); 
       break; 

     } 
     } 

    } 
} 

SnapShotCanvasコード

をキャプチャ

class SnapShotCanvas extends Canvas { 

    private Image image; 

    public SnapShotCanvas(Image image) { 
     this.image = image; 
     setFullScreenMode(true); 
    } 

    public void paint(Graphics g) { 
     g.drawImage(image, getWidth()/2, getHeight()/2, Graphics.HCENTER | Graphics.VCENTER); 
    } 
}