我正在使用jmf从网络摄像头捕获图像。 我已经连接了摄像头，它工作得很好。 我使用以下代码从网络摄像头捕获图像： -
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGEncodeParam;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Date;
import java.util.Iterator;
import java.util.Vector;
import javax.media.Buffer;
import javax.media.CannotRealizeException;
import javax.media.CaptureDeviceInfo;
import javax.media.CaptureDeviceManager;
import javax.media.Manager;
import javax.media.NoPlayerException;
import javax.media.Player;
import javax.media.control.FrameGrabbingControl;
import javax.media.format.VideoFormat;
import javax.media.util.BufferToImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
public class FrameGrab extends JPanel implements ActionListener {
private Player player = null;
private BufferedImage buffImg = null;
private Timer timer;
private FrameGrabbingControl frameGrabber;
public FrameGrab() {
// Create capture device
Vector devices = CaptureDeviceManager.getDeviceList(null);
CaptureDeviceInfo cdi = null;
for (Iterator i = devices.iterator(); i.hasNext();) {
cdi = (CaptureDeviceInfo) i.next();
/* Get the first Video For Windows (VFW) capture device.
* Use the JMF registry tool in the bin directory of the JMF
* distribution to detect available capture devices on your
* computer.
*/
if (cdi.getName().startsWith("vfw:"))
break;
}
// start the Timer with 3s intervals
new Timer(2000, this).start();
try {
player = Manager.createRealizedPlayer(cdi.getLocator());
player.start();
} catch (NoPlayerException e) {
e.printStackTrace();
} catch (CannotRealizeException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
// Grab a frame from the capture device
frameGrabber = (FrameGrabbingControl) player
.getControl("javax.media.control.FrameGrabbingControl");
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
if (buffImg != null) {
g.drawImage(buffImg, 0, 0, this);
}
}
private void writeImagetoFile(BufferedImage img,String aFileName,int width,int height,double quality)
{
try{
FileOutputStream fos = new FileOutputStream(aFileName);
JPEGImageEncoder encoder2 =JPEGCodec.createJPEGEncoder(fos);
JPEGEncodeParam param2 = encoder2.getDefaultJPEGEncodeParam(img);
param2.setQuality((float) quality, true);
encoder2.encode(img,param2);
fos.close();
}catch(Exception ex){}
}
private void grab() {
Buffer buf=null;
try{
Thread.sleep(2000);
buf = frameGrabber.grabFrame();
}catch(Exception ex){ex.printStackTrace();}
// Convert frame to an buffered image so it can be processed and saved
Image img = (new BufferToImage((VideoFormat) buf.getFormat())
.createImage(buf));
buffImg = new BufferedImage(img.getWidth(this), img.getHeight(this),
BufferedImage.TYPE_INT_RGB);
writeImagetoFile(buffImg,"c:/image.jpg",100,100,100);
Graphics2D g = buffImg.createGraphics();
g.drawImage(img, null, null);
g.setColor(Color.darkGray);
g.setFont(new Font("Tahoma", Font.PLAIN, 12)
.deriveFont(AffineTransform.getRotateInstance(1.57)));
g.drawString((new Date()).toString(), 5, 5);
}
public static void createAndShowGui() {
JFrame frame = new JFrame("Frame Grabber");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new FrameGrab());
frame.setSize(328, 270);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
/*
* (non-Javadoc)
*
* @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
*/
public void actionPerformed(ActionEvent e) {
grab();
repaint();
}
}
通过运行此程序，我得到以下异常：
java.lang.NullPointerException
at writepdffile.FrameGrab.grab(FrameGrab.java:99)
at writepdffile.FrameGrab.actionPerformed(FrameGrab.java:137)
at javax.swing.Timer.fireActionPerformed(Timer.java:271)
at javax.swing.Timer$DoPostEvent.run(Timer.java:201)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at writepdffile.FrameGrab.grab(FrameGrab.java:102)
at writepdffile.FrameGrab.actionPerformed(FrameGrab.java:137)
at javax.swing.Timer.fireActionPerformed(Timer.java:271)
at javax.swing.Timer$DoPostEvent.run(Timer.java:201)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
我不明白为什么会产生这样的异常...... 请一些人帮我，我是jfm的新手。
先谢谢
答案 0 :(得分：1)
好的，如果您遇到NullPointerException的问题，当您未通过jmf注册表进行配置时会发生这种情况。当您为Windows安装jmf时，会有与之关联的jmf注册应用程序。您必须打开它，选择设置并选择捕获设备。如果您的设备以vfw（Windows视频）开头，如vfw:Microsoft Image Capture(win 32):0，则提交它，这是最后一步。
我认为你已经将类路径设置为包含jmf.jar和其他jar文件的jmf的lib文件夹。然后你可以正常运行jmf的程序。如果您遇到任何问题，请告诉我