problem with JMF and capture device

i try to u开发者_如何学运维se JMF on applet for read data from webcam . but in below code :

String str2 = "vfw:Microsoft WDM Image Capture (Win32):0"; di = CaptureDeviceManager.getDevice(str2); ml = di.getLocator();

Capturedevicemanager.getdevice(str2); method returned null value .

tnx