The preamble character triggers the listener to buffer the input. The event handler is onBarcodeReceived
Below is a successful barcode buffer in the ignition debug console
13:44:35.339 [AWT-EventQueue-0] DEBUG PMIBarcodeController - ------- Resetting elapsed time: 13334. Looking for preamble of: \\u003f
13:44:35.355 [AWT-EventQueue-0] DEBUG PMIBarcodeController - ------- Preamble found: \u003f. Start buffering...
13:44:35.386 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, Slash, char: \u003f (?)
13:44:35.401 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 16 buffer: 3 echo 0
13:44:35.417 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.417 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, Shift, char: \uffff (?)
13:44:35.417 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 52 buffer: 6 echo 0
13:44:35.417 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.433 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, Q, char: \u0051 (Q)
13:44:35.433 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 67 buffer: 7 echo 0
13:44:35.433 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.464 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, 3, char: \u0033 (3)
13:44:35.464 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 100 buffer: 10 echo 0
13:44:35.464 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.480 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, 4, char: \u0034 (4)
13:44:35.480 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 119 buffer: 13 echo 0
13:44:35.495 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.511 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, 7, char: \u0037 (7)
13:44:35.511 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 140 buffer: 16 echo 0
13:44:35.511 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.526 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, 8, char: \u0038 (8)
13:44:35.526 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 156 buffer: 19 echo 0
13:44:35.526 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.542 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, 2, char: \u0032 (2)
13:44:35.542 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 172 buffer: 22 echo 0
13:44:35.542 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.558 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, 1, char: \u0031 (1)
13:44:35.558 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 188 buffer: 25 echo 0
13:44:35.558 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.573 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, 0, char: \u0030 (0)
13:44:35.573 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 207 buffer: 28 echo 0
13:44:35.573 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.589 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Keyevent ID: 402, Enter, char: \u000a (
)
13:44:35.589 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Handled: true Buffering: true Elapsed Time: 220 buffer: 31 echo 0
13:44:35.589 [AWT-EventQueue-0] DEBUG PMIBarcodeController - -
13:44:35.589 [AWT-EventQueue-0] DEBUG PMIBarcodeController - ########## Possible preamble = Keyevent ID: 402, Enter, char: \u000a (
)
13:44:35.792 [AWT-EventQueue-0] DEBUG PMIBarcodeController - *** Input Timeout KeyEventHandler SI (readtime 200) ***
13:44:35.792 [AWT-EventQueue-0] DEBUG PMIBarcodeController - si.buffer: [Key Pressed, Slash, ?]
[Key Released, Slash, ?]
[Key Pressed, Q, Q]
[Key Released, Shift, \uFFFF]
[Key Released, Q, Q]
[Key Pressed, 3, 3]
[Key Released, 3, 3]
[Key Pressed, 4, 4]
[Key Released, 4, 4]
[Key Pressed, 7, 7]
[Key Released, 7, 7]
[Key Pressed, 8, 8]
[Key Released, 8, 8]
[Key Pressed, 2, 2]
[Key Released, 2, 2]
[Key Pressed, 1, 1]
[Key Released, 1, 1]
[Key Pressed, 0, 0]
[Key Released, 0, 0]
[Key Pressed, Enter, \n]
[Key Released, Enter, \n]
13:44:35.792 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Barcode Scanner 1 si.Regex target ?Q3478210
pattern: \u003f.* = found: true
13:44:35.792 [AWT-EventQueue-0] DEBUG PMIBarcodeController - Barcode Scanner 1 Decode Results: Default
13:44:35.808 [AWT-EventQueue-0] DEBUG PMIBarcodeController - value[0] = Q3478210
{u'Default': [Q3478210]}
13:44:35.823 [AWT-EventQueue-0] DEBUG PMIBarcodeController - si.buffer:
13:44:35.823 [AWT-EventQueue-0] DEBUG PMIBarcodeController - si.echo :
13:44:35.823 [AWT-EventQueue-0] DEBUG PMIBarcodeController - *** End of Input Timeout, Elapsed Time: 458
13:44:46.526 [AWT-EventQueue-0] DEBUG PMIBarcodeController - ------- Resetting elapsed time: 10699. Looking for preamble of: \\u003f