How to write data to smart card using java card? with example

can some one tell me how to write data in smart card using java card? i have this code i am using java card 2.2

private void writeName(APDU apdu) throws ISOException
{ 
    apdu.setIncomingAndReceive();
    byte[] apduBuffer = apdu.getBuffer();

    byte j = (byte)apduBuffer[4];

    userName = new byte[j];
    for (byte i=0; i<j; i++)
    {
        userName[(byte)i] = (byte)apduBuffer[5+i];
    }
}

Solution

If you are using JCOP plugin for developing the Applet, you can see .CAP files in the bin/ directory for each package. Now you will need to install each package in order of dependency. Suppose your application consists of packages A, B and C with your applet in C package. And B imports A and C imports B.

The order in which you will need to install the packages are A,B,C. Using JCOP, this can be accomplished by:

cm> install <pkgAID> package.cap

Once you have done this for the three packages, you will need to install the applet. This can be accomplished by:

cm> install -q <install params> <pkgAID> <AppletAID> packageC.cap

Once you do this you will see the applet in SELECTABLE state. Your JCOP shell console would look like :

Card Manager AID   :  A000000003000000
Card Manager state :  SECURED

    Application:  SELECTABLE (--------) A00000008710015553
    Application:  SELECTABLE (--------) "2PAY.SYS.DDF01"
    Application:  SELECTABLE (--------) A0004D6946617265
    Application:  SELECTABLE (--------) A0000000041010

And all those packages that are "modules" (libraries) are shown like this:

    Load File  :      LOADED (--------) A0000002994E6F53
     Module    :                        A0000002994E6F53656C656374
    Load File  :      LOADED (--------) A0000002990410  
     Module    :                        A00000029904101045

All those applets ini SELECTABLE state can now be selected and interacted with. If you want to send data to Applet with A00000008710015553, you will need to first select it. The interaction would be as shown below:

cm>  /select A00000008710015553
 => 00 A4 04 00 09 A0 00 00 00 87 10 01 55 53 00       ............US.
 (5273 usec)
 <= 90 00                                              ..
Status: No Error

Now, you can send data to the above Applet by using send command:

cm>  /send 00200000043131313100
 => 00 20 00 00 04 31 31 31 31 00                      . ...1111.
 (34423 usec)
 <= 90 00                                              ..
Status: No Error

These are all standard GP commands. I assumed that you are using a GP compliant card; you have mentioned nothing about it though.

I personally feel you will need to read through a bit on how JC Runtime Environment and JC VM works and it's relation with the API and a bit of GP spec before you delve into further.