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.

## Persistent Storage

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.

### Record Store

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 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 accessibility 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

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.

### Example:

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");
        }
    }

@since MIDP 1.0