An example from the jcop Tools Training, on EF of linear structure with records of fixed size

Package  Com. NXP. Id. jcop. Training. filesystem;  Import  Javacard. Framework. Applet;  Import  Javacard. Framework. iso7816;  Import  Javacard. Framework. isoexception;  Import  Javacard. Framework. APDU;  Import  Javacard. Framework. jcsystem;  Import  Javacard. Framework. util; Public   Class Filesystemapplet Extends  Applet {  Private   Final   Static   Short File_version = ( Short ) 0x0100 ;  //  INS bytes      Private   Final   Static  Byte Ins_select_file = ( Byte ) 0xa4 ;  Private   Final   Static   Byte Ins_read_binary = ( Byte ) 0xb0 ;  Private   Final   Static   Byte Ins_update_binary = ( Byte ) 0xd6;  //  SW1 sw2      Public   Static   Final   Short Sw_lc_inconsistent_with_p1p2 = ( Short ) 0x6a87 ;  Public   Static   Final   Short Sw_wrong_parameter_p1p2 = ( Short ) 0x6b00 ; //  File Allocation Table      Private   Static   Final   Byte Fat_ef_1_id = 1 ;  Private   Static   Final   Byte Fat_ef_2_id = 2 ;  //  Fixed File      Private   Final  Static   Byte [] Ef_1_cvca_pubkey = {(  Byte ) 0x04 ,(  Byte ) 0x9d ,( Byte ) 0xdc ,( Byte ) 0x9e ,( Byte ) 0xbb ,( Byte ) 0xd2 ,( Byte ) 0xe0 ,( Byte ) 0x84 ,( Byte ) 0xbd,(  Byte ) 0x69 ,( Byte ) 0xe4 ,( Byte ) 0xca ,( Byte ) 0x22 ,( Byte ) 0x2a ,( Byte ) 0x3c ,( Byte ) 0xcf ,( Byte ) 0x76 ,(  Byte ) 0x03 ,( Byte ) 0x3e ,( Byte ) 0x47 ,(Byte ) 0x6b ,( Byte ) 0x04 ,( Byte ) 0xc7 ,( Byte ) 0xe5 ,( Byte ) 0x6e ,(  Byte ) 0x40 ,( Byte ) 0x9e ,( Byte ) 0x2b ,( Byte ) 0xa1 ,(  Byte ) 0xb9 ,( Byte ) 0xb7 ,(Byte ) 0x59 ,( Byte ) 0xb6 ,( Byte ) 0x79 ,( Byte ) 0xe2 ,( Byte ) 0x4c ,( Byte ) 0x7a ,(  Byte ) 0xae ,( Byte ) 0x45 ,( Byte ) 0x26 ,( Byte ) 0xe8 ,( Byte ) 0xc1 ,( Byte ) 0x81 ,( Byte ) 0x65 ,( Byte ) 0x99 ,(  Byte ) 0x7c ,( Byte ) 0x60 ,( Byte ) 0x29 ,( Byte ) 0x57 ,( Byte ) 0xf3 ,( Byte ) 0x8b ,( Byte ) 0xe8 ,( Byte ) 0x07 ,(  Byte ) 0x03 ,( Byte ) 0xe5 ,( Byte ) 0xb7 ,( Byte ) 0x7a };  //  Dynamic File      Private   Static   Byte  [] Ee_ef_2_data;  //  Filesystem      Private  Object [] ee_filesystem;  // File selection flag      Private   Static   Byte  [] Ram_selectedfile;  Public  Filesystemapplet () {ee_ef_2_data = New   Byte [( Short ) 0x3fff]; //  Persistent 16 K  Ee_filesystem = New Object [fat_ef_2_id + 1]; //  Persistent filesystem reference Ee_filesystem [fat_ef_1_id] = (Object) ef_1_cvca_pubkey; ee_filesystem [fat_ef_2_id] = (Object) ee_ef_2_data;  //  Transient reference to the selected file Ram_selectedfile = jcsystem. maketransientbytearray (( Short ) 0 , Jcsystem. clear_on_deselect );}  Public   Static   Void Install ( Byte [] Barray, Short Boffset, Byte  Blength ){  //  GP-compliant javacard applet Registration          New  Com. NXP. Id. jcop. Training. filesystem. filesystemapplet (). Register (barray ,(  Short ) (Boffset + 1 ), Barray [boffset]);}  Public   Void Process (APDU ){  //  Good practice: Return 9000 on select          If  (Selectingapplet () {util. setshort (APDU. getbuffer (),(  Short ) 0 , File_version); APDU. setoutgoingandsend ((  Short ) 0 ,( Short ) 2 );  Return  ;}  Byte [] Buf =APDU. getbuffer ();  Short Ram_tempshort = 0; //  Our fast stack variable  //  Retrieve P1P2 from APDU Buffer          Short Ram_p1p2 = ( Short  ) (Util. getshort (BUF, iso7816.offset _ P1 ));  Switch  (BUF [iso7816.offset _ ins]) {  Case  Ins_select_file: If (Ram_p1p2! = 0x0000) //  Only select by file supported  Isoexception. throwit (iso7816.sw _ incorrect_p1p2); ram_tempshort = APDU. setincomingandreceive ();  If (Ram_tempshort! = 2) //  File is 2 byte, located in the data field  Isoexception. throwit (iso7816.sw _ wrong_length); ram_tempshort = Util. getshort (BUF, iso7816.offset _ CDATA ); Switch  (Ram_tempshort ){  Case  (Fat_ef_1_id): ram_selectedfile = ( Byte  []) Ee_filesystem [fat_ef_1_id];  Break  ;  Case  (Fat_ef_2_id): ram_selectedfile = ( Byte  []) Ee_filesystem [fat_ef_2_id];  Break ;  Default  : Isoexception. throwit (iso7816.sw _ file_not_found );}  //  Switch              Break  ;  Case Ins_read_binary: //  Class 2 APDU (header and Le, not data field)              If (Ram_selectedfile = Null ) // File must have been selected before (sfid not supported in this example)  Isoexception. throwit (iso7816.sw _ file_not_found );  If (Ram_p1p2 &( Short ) 0x8000) = ( Short ) 0x8000) //  Highest bit shall be 0 (sfid not supported in this example)  Isoexception. throwit (iso7816.sw _ incorrect_p1p2 );  //  Offset encoded in P1/P2, 15 lowest Bit Ram_tempshort =APDU. setoutgoing ();  //  Check if Le! = 0 <-- no response expected              If (Ram_tempshort = 0 ) Isoexception. throwit (iso7816.sw _ wrong_length );  //  Check offset              If (Ram_p1p2> = Ram_selectedfile.length) isoexception. throwit (iso7816.sw _ incorrect_p1p2 );  //  If Le = 256 --> output maximum remaining              If (Ram_tempshort = 0x0100 ) Ram_tempshort = ( Short ) (Ram_selectedfile.length- Ram_p1p2 );  Else  {  //  Check expected length                  If (( Short ) (Ram_p1p2 + ram_tempshort)> Ram_selectedfile.length) isoexception. throwit (iso7816.sw _ wrong_length);} util. arraycopynonatomic (ram_selectedfile, ram_p1p2, Buf ,( Short ) 0 , Ram_tempshort); APDU. setoutgoinglength (ram_tempshort); APDU. sendbytes ((  Short ) 0 , Ram_tempshort );  Break  ;  Case  Ins_update_binary:  If (Ram_selectedfile = Null ) //  File must have been selected before (sfid not supported in this example) Isoexception. throwit (iso7816.sw _ file_not_found );  //  Update only allowed for dynamic File              If (Ram_selectedfile = ( Byte  []) Ee_filesystem [fat_ef_1_id]) isoexception. throwit (iso7816.sw _ file_invalid );  //  Check offset and length Ram_tempshort = APDU. setincomingandreceive ();  If (Ram_p1p2> = ram_selectedfile.length) |(((  Short ) Ram_p1p2 + ram_tempshort)> = ram_selectedfile.length) | (Ram_tempshort = 0 ) Isoexception. throwit (iso7816.sw _ wrong_length); util. arraycopynonatomic (BUF, iso7816.offset _ CDATA, ram_selectedfile, ram_p1p2, ram_tempshort );  Break  ;  Default  :  //  Good practice: if you don't know the instruction, say so: Isoexception. throwit (iso7816.sw _ ins_not_supported );}}}  /*  * Tasks * 0. create a second dymanic file EF_3: Max file size = 210 byte * 1. fill EF_3 with pseudo do random numbers * 2. read and Write into EF3 * Advanced * 3. create a cyclic file ef_4: Max file size = 50 byte * 4. write 2 time 120 bytes into ef_4 --> observe overwriting ** check out the scripts folder  */ 

And the corresponding test script ..

# Select DF/Select |Fileapp # select ef_1/Send 00a40000020001 9000# Read Binary/Send 00b0000504*9000/send 00b0000000*9000/send 00b000007f 6700# Select ef_2/Send 00a40000020002 9000# UPDATE BINARY/Send limit 9000/send limit 6700# Read Binary/Send 00b000a020 000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f9000