1. Outline-session 9 (09-April-2009)
>> J2ME Record Management System
-Introduction
-RMS
-Record Store
-Record Store-MIDlet
-Record Store –Scope
-Record Store –Two attribute
-Record Store –API
-Record Enumeration

2. Introduction
• Just like ordinary desktop-based programs, MIDlets need a
facility to store data permanently.
• Cell phones and other mobile devices are quite limited when
compared to desktop systems.
• NO file system nor relational database in a MIDP-based
environment.
• MIDP provides the persistence storage package
javax.microedition.rms for storing data.
• The package is called Record Management System (RMS)
provides a simple record-oriented database.

3. RMS(Record Management System)
•
•
•
•
RMS is a system for managing records.
A record is an individual data item.
No data type. A record is represented by an array of bytes.
A record can contain a number, a string, an array, an image -anything that a sequence of bytes can represent.
• Manipulating byte array is difficult.
• A simple way is to use String as it has a rich API to manipulate
and convert it to and from byte array is simple.

4. Where are the fields?
• Don't be confused by the term record. The answer is simple:
– In RMS a record doesn't have any fields.
• A record consists of an array of single binary field of variable
size identified by a record Id.
• This keeps RMS small and flexible -- important attributes for a
MIDP subsystem.
• The programmer has to handle type conversion, comparison,
etc.

5. Record Stores
• A record store is an ordered collection of records.
• Each record must belong to a record store, and all record
access occurs through the record store.
• In fact, the record store guarantees that records are read and
written atomically, with no possibility of data corruption.

6. Record Stores
• When a record is created, the record store assigns it a unique
identifier, an integer called the record ID.
• The first record added to a record store has a record ID of 1,
the second a record ID of 2, and so on.

7. Record Stores-MIDlet
• A MIDlet can have any number of record stores (including
none)
• Each record store is uniquely identified by its name
• MIDlet is part of MIDlet suite, record store names must also
be unique within the suite
• MIDlets that are packaged within a suite can access not only
the record stores they create, but also those of other MIDlets
in the suite

8. Record Stores-Scope
• Within "MIDlet Suite One," MIDlet #1 and MIDlet #2 can
access all four record stores available as part of the suite.
• MIDlets in Suite One cannot access the record stores of Suite
Two.

9. Record Stores-Two attribute
>> There are two values maintained by a record store that may
be helpful for tracking database usage
1. Version Number:
–
–
–
–
Version number is an integer value.
the starting value when creating a new record is not defined by the
API
If you need to track version numbers, you can query the
record store immediately after creation using getVersion() to
determine the starting value.
1. Date and Timestamp:
–
–
is a long integer that represents the number of milliseconds since
midnight January 1st, 1970. You can query this value by calling
getLastModified().

10. Record Store API
>>This class is the heart of the RMS. Through this class we create, update,
query and delete record stores

11. Record Store API
>>This class is the heart of the RMS. Through this class we create, update,
query and delete record stores

12. Manage Record Store
•
•
•
•
To open a record store, you simply need to call the openRecordStore
method.
– public static RecordStore openRecordStore(
String recordStoreName,
boolean createIfNecessary)
throws RecordStoreException, RecordStoreFullException,
RecordStoreNotFoundException
createIfNecessary determines whether the record store, if not existed, will
be created or a RecordStoreNotFoundException will be thrown.
The following opens a record store named "Address."
RecordStore rs = RecordStore.openRecordStore("Address",
true);
The record store will be created if it does not exist.

13. Manage Record Store
•
•
closeRecordStore() method closes an open record.
rs.closeRecordStore();
Remember to clean up after yourself as much as possible.
•
To delete a record store and its contained records, call the static
deleteRecordStore() method.
RecordStore.deleteRecordStore("Address");
•
To find out all the record stores available to a particular MIDlet suite, call
the listRecordStores() method:
public static String[] listRecordStores()

14. Adding records
• The MIDlet invokes the addRecord() method
of RecordStore class to insert a new record
into the record store.
– public int addRecord(byte[] data, int offset, int numBytes)
inserts a record represented by an array of bytes data with offset as
its starting index and numBytes as its length.
String brand = "Honda";
byte bytes[] = brand.getBytes();
int recID = rs.addRecord(bytes,0,bytes.length);

15. Manage Record Store
•
•
closeRecordStore() method closes an open record.
rs.closeRecordStore();
Remember to clean up after yourself as much as possible.
•
To delete a record store and its contained records, call the static
deleteRecordStore() method.
RecordStore.deleteRecordStore("Address");
•
To find out all the record stores available to a particular MIDlet suite, call
the listRecordStores() method:
public static String[] listRecordStores()

16. Retrieving Record
• There are two versions to retrieve a record:
public int getRecord(int recordId, byte[] buffer, int offset)
– copies the data stored in the given record to the byte array
represented by buffer.
public byte[] getRecord(int recordId)
– returns a new copy of the data represented by recordId.
byte[] retrieved = new byte[rs.getRecordSize(recID)];
rs.getRecord(id, retrieved, 0);
String retrievedString = new String(retrieved);
byte[] retrieved = rs.getRecord(recID);
String retrievedString = new String(retrieved);

17. Update Record
• To update a record use the method
setRecord:
public void setRecord(int recordId,
byte[] newData, int offset, int numBytes)
– sets new information, a stream of bytes (newData) with offset as its
starting index and numBytes as its length, at the record location
represented by recordId.
String brand = "Toyota";
byte data[] = newappt.getBytes();
rs.setRecord(recID, data, 0, data.length());

18. Deleting Record
• The MIDlet invokes the deleteRecord()
method to delete a record from the record
store.
public void deleteRecord(int recordId)
– deletes the record represented by recordId. The
recordId is not reused.
rs.deleteRecord(1);

19. Record Enumeration
•
The RecordEnumeration (A.K.A enumerator) class provides methods for
moving forward and back through a record store.
• you might prefer to enumerate through the records, sorting alphabetically
Enumeration Implementation
RecordEnumeration re = rs.enumerateRecords(null,null,false);
while (re.hasNextElement())
{
// Get the next record into a String
String str = new String(re.nextRecord());
... do something ...
}

20. Record Enumeration
•
Key Methods in enumeration
>> nextRecord() to move forward
>>previousRecord() to move back
>>previousRecord(), whichh will return the last record
• An enumerator maintains in internal index of the record store
1. You can make calls to reindex() whenever you update, delete or add a
record.
2. A record listener can be established to notify you of changes to the record
store
3. Whenever a change occurs, the listener will call one of three methods,
depending on whether the change was an add, delete or update

21. Record Enumeration-API