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See:
Description
| Interface Summary | |
| RecordComparator | An interface defining a comparator which compares two records (in an implementation-defined manner) to see if they match or what their relative sort order is. |
| RecordEnumeration | An interface representing a bidirectional record store Record enumerator. |
| RecordFilter | An interface defining a filter which examines a record to see if it matches (based on an application-defined criteria). |
| RecordListener | A listener interface for receiving Record Changed/Added/Deleted events from a record store. |
| Class Summary | |
| RecordStore | A class representing a record store. |
| Exception Summary | |
| InvalidRecordIDException | Thrown to indicate an operation could not be completed because the record ID was invalid. |
| RecordStoreException | Thrown to indicate a general exception occurred in a record store operation. |
| RecordStoreFullException | Thrown to indicate an operation could not be completed because the record store system storage is full. |
| RecordStoreNotFoundException | Thrown to indicate an operation could not be completed because the record store could not be found. |
| RecordStoreNotOpenException | Thrown to indicate that an operation was attempted on a closed record store. |
The Mobile Information Device Profile provides a mechanism for MIDlets to persistently store data and later retrieve it. This persistent storage mechanism is modeled after a simple record oriented database and is called the Record Management System.
The MIDP provides a mechanism for MIDlets to persistently store data and retrieve it later. This persistent storage mechanism, called the Record Management System (RMS), is modeled after a simple record-oriented database.
A record store consists of a collection of records that will remain persistent across multiple invocations of a MIDlet. The platform is responsible for making its best effort to maintain the integrity of the MIDlet's record stores throughout the normal use of the platform, including reboots, battery changes, etc.
Record stores are created in platform-dependent locations, which are not exposed to MIDlets. The naming space for record stores is controlled at the MIDlet suite granularity. MIDlets within a MIDlet suite are allowed to create multiple record stores, as long as they are each given different names. When a MIDlet suite is removed from a platform, all record stores associated with its MIDlets MUST also be removed. MIDlets within a MIDlet suite can access one another's record stores directly. New APIs in MIDP 2.0 allow for the explicit sharing of record stores if the MIDlet creating the RecordStore chooses to give such permission.
Sharing is accomplished through the ability to name a RecordStore in another MIDlet suite and by defining the accessibilty rules related to the Authentication of the two MIDlet suites.
RecordStores are uniquely named using the unique name of the MIDlet suite plus the name of the RecordStore. MIDlet suites are identified by the MIDlet-Vendor and MIDlet-Name attributes from the application descriptor.
Access controls are defined when RecordStores to be shared are created. Access controls are enforced when RecordStores are opened. The access modes allow private use or shareable with any other MIDlet suite.
Record store names are case sensitive and may consist of any combination of up to 32 Unicode characters. Record store names MUST be unique within the scope of a given MIDlet suite. In other words, MIDlets within a MIDlet suite are not allowed to create more than one record store with the same name; however, a MIDlet in one MIDlet suite is allowed to have a record store with the same name as a MIDlet in another MIDlet suite. In that case, the record stores are still distinct and separate.
No locking operations are provided in this API. Record store
implementations ensure that all individual record store
operations are atomic, synchronous, and serialized so that no
corruption occurs with multiple accesses. However, if a MIDlet
uses multiple threads to access a record store, it is the
MIDlet's responsibility to coordinate this access, or unintended
consequences may result. For example, if two threads in a MIDlet
both call RecordStore.setRecord() concurrently on
the same record, the record store will serialize these calls
properly, and no database corruption will occur as a result.
However, one of the writes will be subsequently overwritten by
the other, which may cause problems within the
MIDlet. Similarly, if a platform performs transparent
synchronization of a record store or other access from below, it
is the platform's responsibility to enforce exclusive access to
the record store between the MIDlets and synchronization
engine.
This record store API uses long integers for time/date stamps,
in the format used by System.currentTimeMillis()
. The record store is time stamped with the last time it was
modified. The record store also maintains a version, which is an
integer that is incremented for each operation that modifies the
contents of the record store. These are useful for
synchronization engines as well as applications.
Records are arrays of bytes. Developers can use
DataInputStream and DataOutputStream
as well as ByteArrayInputStream and
ByteArrayOutputStream to pack and unpack different
data types into and out of the byte arrays.
Records are uniquely identified within a given record store by
their recordId , which is an integer value. This
recordId is used as the primary key for the
records. The first record created in a record store will have
recordId equal to 1, and each subsequent
recordId will monotonically increase by one. For
example, if two records are added to a record store, and the
first has a recordId of 'n', the next will have a
recordId of (n+1). MIDlets can create other indices
by using the RecordEnumeration class.
The example uses the Record Management System to store and retrieve high scores for a game. In the example, high scores are stored in separate records, and sorted when necessary using a RecordEnumeration.
import javax.microedition.rms.*;
import java.io.DataOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.io.EOFException;
/**
* A class used for storing and showing game scores.
*/
public class RMSGameScores
implements RecordFilter, RecordComparator
{
/*
* The RecordStore used for storing the game scores.
*/
private RecordStore recordStore = null;
/*
* The player name to use when filtering.
*/
public static String playerNameFilter = null;
/*
* Part of the RecordFilter interface.
*/
public boolean matches(byte[] candidate)
throws IllegalArgumentException
{
// If no filter set, nothing can match it.
if (this.playerNameFilter == null) {
return false;
}
ByteArrayInputStream bais = new ByteArrayInputStream(candidate);
DataInputStream inputStream = new DataInputStream(bais);
String name = null;
try {
int score = inputStream.readInt();
name = inputStream.readUTF();
}
catch (EOFException eofe) {
System.out.println(eofe);
eofe.printStackTrace();
}
catch (IOException eofe) {
System.out.println(eofe);
eofe.printStackTrace();
}
return (this.playerNameFilter.equals(name));
}
/*
* Part of the RecordComparator interface.
*/
public int compare(byte[] rec1, byte[] rec2)
{
// Construct DataInputStreams for extracting the scores from
// the records.
ByteArrayInputStream bais1 = new ByteArrayInputStream(rec1);
DataInputStream inputStream1 = new DataInputStream(bais1);
ByteArrayInputStream bais2 = new ByteArrayInputStream(rec2);
DataInputStream inputStream2 = new DataInputStream(bais2);
int score1 = 0;
int score2 = 0;
try {
// Extract the scores.
score1 = inputStream1.readInt();
score2 = inputStream2.readInt();
}
catch (EOFException eofe) {
System.out.println(eofe);
eofe.printStackTrace();
}
catch (IOException eofe) {
System.out.println(eofe);
eofe.printStackTrace();
}
// Sort by score
if (score1 < score2) {
return RecordComparator.PRECEDES;
}
else if (score1 > score2) {
return RecordComparator.FOLLOWS;
}
else {
return RecordComparator.EQUIVALENT;
}
}
/**
* The constructor opens the underlying record store,
* creating it if necessary.
*/
public RMSGameScores()
{
//
// Create a new record store for this example
//
try {
recordStore = RecordStore.openRecordStore("scores", true);
}
catch (RecordStoreException rse) {
System.out.println(rse);
rse.printStackTrace();
}
}
/**
* Add a new score to the storage.
*
* @param score the score to store.
* @param playerName the name of the play achieving this score.
*/
public void addScore(int score, String playerName)
{
//
// Each score is stored in a separate record, formatted with
// the score, followed by the player name.
//
int recId; // returned by addRecord but not used
ByteArrayOutputStream baos = new ByteArrayOutputStream();
DataOutputStream outputStream = new DataOutputStream(baos);
try {
// Push the score into a byte array.
outputStream.writeInt(score);
// Then push the player name.
outputStream.writeUTF(playerName);
}
catch (IOException ioe) {
System.out.println(ioe);
ioe.printStackTrace();
}
// Extract the byte array
byte[] b = baos.toByteArray();
// Add it to the record store
try {
recId = recordStore.addRecord(b, 0, b.length);
}
catch (RecordStoreException rse) {
System.out.println(rse);
rse.printStackTrace();
}
}
/**
* A helper method for the printScores methods.
*/
private void printScoresHelper(RecordEnumeration re)
{
try {
while(re.hasNextElement()) {
int id = re.nextRecordId();
ByteArrayInputStream bais = new ByteArrayInputStream(recordStore.getRecord(id));
DataInputStream inputStream = new DataInputStream(bais);
try {
int score = inputStream.readInt();
String playerName = inputStream.readUTF();
System.out.println(playerName + " = " + score);
}
catch (EOFException eofe) {
System.out.println(eofe);
eofe.printStackTrace();
}
}
}
catch (RecordStoreException rse) {
System.out.println(rse);
rse.printStackTrace();
}
catch (IOException ioe) {
System.out.println(ioe);
ioe.printStackTrace();
}
}
/**
* This method prints all of the scores sorted by game score.
*/
public void printScores()
{
try {
// Enumerate the records using the comparator implemented
// above to sort by game score.
RecordEnumeration re = recordStore.enumerateRecords(null, this,
true);
printScoresHelper(re);
}
catch (RecordStoreException rse) {
System.out.println(rse);
rse.printStackTrace();
}
}
/**
* This method prints all of the scores for a given player,
* sorted by game score.
*/
public void printScores(String playerName)
{
try {
// Enumerate the records using the comparator and filter
// implemented above to sort by game score.
RecordEnumeration re = recordStore.enumerateRecords(this, this,
true);
printScoresHelper(re);
}
catch (RecordStoreException rse) {
System.out.println(rse);
rse.printStackTrace();
}
}
public static void main(String[] args)
{
RMSGameScores rmsgs = new RMSGameScores();
rmsgs.addScore(100, "Alice");
rmsgs.addScore(120, "Bill");
rmsgs.addScore(80, "Candice");
rmsgs.addScore(40, "Dean");
rmsgs.addScore(200, "Ethel");
rmsgs.addScore(110, "Farnsworth");
rmsgs.addScore(220, "Farnsworth");
System.out.println("All scores");
rmsgs.printScores();
System.out.println("Farnsworth's scores");
RMSGameScores.playerNameFilter = "Farnsworth";
rmsgs.printScores("Farnsworth");
}
}
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