After searching high and low, I have made this work.
The key issue is that processing uses the rxtx java library (RXTX-2.1-7) for serial communications.
The RXTX wiki says:

"rxtx tries to detect ports on by scanning /dev for files matching any of a set of known-good prefixes, such as 'ttyS', 'ttym', and since 2.2 'ttyUSB' and so on. "

And since the bluetooth device is named  rfcomm* it cannot be detected.
The trick is to create a sym link to fool rxtx (use a ttyS device that is not yet assigned):

1. $ sudo ln -s  /dev/rfcomm0 /dev/ttyS99

Then, connect:

1. $ sudo rfcomm connect 0
2.  Connected /dev/rfcomm0 to 00:12:11:19:08:54 on channel 1
3.  Press CTRL-C for hangup

At this point the red led on the JY-MCU becomes solid and processing can detect it:

1. println(Serial.list());

output is:

1. [0] "/dev/ttyACM0"
2. [1] "/dev/ttyS99"

So, serial communication can work.
To summarize, the following process will allow a processing script to communicate via a serial port with a JY-MCU device in a BlueZ linux framework

One time setup:
1. power up the JY-MCU,
2. use the following command to get its hardware address, mine is 00:12:11:19:08:5

1. $ hcitool scan

3. use that to create the /etc/bluetooth/rfcomm.conf file; you'll note that I chose 0 for the rfcomm device,
   we need that for connection later:       

1. $ cat /etc/bluetooth/rfcomm.conf
2.         rfcomm0 {
3.             bind yes;
4.             device 00:12:11:19:08:54;
5.             channel    1;
6.             comment "Linvor Bluetooth Module";
7.         }

4. use BlueMan to pair the JY-MCU.
That ends the one-time setup.

Then, every time you want to use the JY-MCU
 1. create the sym link:

1.  $ sudo ln -s  /dev/rfcomm0 /dev/ttyS99

2. connect to the JY-MCU:

1. $ sudo rfcomm connect 0
2.  Connected /dev/rfcomm0 to 00:12:11:19:08:54 on channel 1
3.  Press CTRL-C for hangup

3. you can now run a processing script and connect to the JY-MCU with the code:

1. String portName = "/dev/ttyS99";
2. myPort = new Serial(this, portName, 9600);

4. after running the processing script, be sure to CTRL-C at the
    command line to disconnect the JY-MCU.

That should do it!
Ciao,
Bob

May i know where do i need to type those codes to? i am still a newbie. pls help me

@Ch Khuan :   please tell me exactly what you want to do. Otherwise I can't know how to help you!
Ciao,
Bob

i am currently using window 7 and i don't know where to start. For example,

1. $ sudo ln -s  /dev/rfcomm0 /dev/ttyS99       

i don't know where i should copy this code to. Same as the other codes below. May u guide me?

Look at the subject of this thread: the "Linux" part is a strong hint that these commands won't work in Windows 7!
It is good that you searched about your problem, whatever it is, but instead of reviving an old thread, you should have made your own, or send a private message if you wanted direct assistance.