javax.microedition.rms
Class RecordStore

java.lang.Object
  javax.microedition.rms.RecordStore

public class RecordStore
extends Object

A class representing a record store. A record store consists of a collection of records which will remain persistent across multiple invocations of the 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 the 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 the record stores associated with its MIDlets will also be removed. These APIs only allow the manipulation of the MIDlet suite's own record stores, and does not provide any mechanism for record sharing between MIDlets in different MIDlet suites. MIDlets within a MIDlet suite can access each other's record stores directly.

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, a MIDlets within a MIDlet suite are is not allowed to create more than one record store with the same name, however a MIDlet in different one MIDlet suites are is allowed to each 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 no corruption will occur 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. Similarly, if a platform performs transparent synchronization of a record store, it is the platform's responsibility to enforce exclusive access to the record store between the MIDlet and synchronization engine.

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 one (1). Each subsequent record added to a RecordStore will be assigned a recordId one greater than the record added before it. That is, 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.

This record store 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 RecordStore. These are useful for synchronization engines as well as other things.

Version:

MIDP 1.0

Author:

Jim Van Peursem

Method Summary

int	addRecord(byte[] data, int offset, int numBytes) Adds a new record to the record store.
void	addRecordListener(RecordListener listener) Adds the specified RecordListener.
void	closeRecordStore() This method is called when the MIDlet requests to have the record store closed.
void	deleteRecord(int recordId) The record is deleted from the record store.
static void	deleteRecordStore(String recordStoreName) Deletes the named record store.
RecordEnumeration	enumerateRecords(RecordFilter filter, RecordComparator comparator, boolean keepUpdated) Returns an enumeration for traversing a set of records in the record store in an optionally specified order.
long	getLastModified() Returns the last time the record store was modified, in the format used by System.currentTimeMillis().
String	getName() Returns the name of this RecordStore.
int	getNextRecordID() Returns the recordId of the next record to be added to the record store.
int	getNumRecords() Returns the number of records currently in the record store.
byte[]	getRecord(int recordId) Returns a copy of the data stored in the given record.
int	getRecord(int recordId, byte[] buffer, int offset) Returns the data stored in the given record.
int	getRecordSize(int recordId) Returns the size (in bytes) of the MIDlet data available in the given record.
int	getSize() Returns the amount of space, in bytes, that the record store occupies.
int	getSizeAvailable() Returns the amount of additional room (in bytes) available for this record store to grow.
int	getVersion() Each time a record store is modified (record added, modified, deleted), it's version is incremented.
static String[]	listRecordStores() Returns an array of the names of record stores owned by the MIDlet suite.
static RecordStore	openRecordStore(String recordStoreName, boolean createIfNecessary) Open (and possibly create) a record store associated with the given MIDlet suite.
void	removeRecordListener(RecordListener listener) Removes the specified RecordListener.
void	setRecord(int recordId, byte[] newData, int offset, int numBytes) Sets the data in the given record to that passed in.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

addRecord

public int addRecord(byte[] data,
                     int offset,
                     int numBytes)
              throws RecordStoreNotOpenException,
                     RecordStoreException,
                     RecordStoreFullException

Adds a new record to the record store. The recordId for this new record is returned. This is a blocking atomic operation. The record is written to persistent storage before the method returns.

Parameters:

data - the data to be stored in this record. If the record is to have zero-length data (no data), this parameter may be null.

offset - the index into the data buffer of the first relevant byte for this record.

numBytes - the number of bytes of the data buffer to use for this record (may be zero).

Returns:

the recordId for the new record.

Throws:

RecordStoreNotOpenException - if the record store is not open.

RecordStoreException - if a different record store-related exception occurred.

RecordStoreFullException - if the operation cannot be completed because the record store has no more room.

NullPointerException - if data is null but numBytes is greater than zero.

addRecordListener

public void addRecordListener(RecordListener listener)

Adds the specified RecordListener. If the specified listener is already registered, it will not be added a second time. When a record store is closed, all listeners are removed.

Parameters:

listener - the RecordChangedListener to add.

See Also:

removeRecordListener(javax.microedition.rms.RecordListener)

closeRecordStore

public void closeRecordStore()
                      throws RecordStoreNotOpenException,
                             RecordStoreException

This method is called when the MIDlet requests to have the record store closed. Note that the record store will not actually be closed until closeRecordStore() is called as many times as openRecordStore() was called. In other words, the MIDlet needs to make a balanced number of close calls as open calls before the record store is closed.

When the record store is closed, all listeners are removed. If the MIDlet attempts to perform operations on the RecordStore object after it has been closed, the methods will throw a RecordStoreNotOpenException.

Throws:

RecordStoreNotOpenException - if the record store is not open.

RecordStoreException - if a different record store-related exception occurred.

deleteRecord

public void deleteRecord(int recordId)
                  throws RecordStoreNotOpenException,
                         InvalidRecordIDException,
                         RecordStoreException

The record is deleted from the record store. The recordId for this record is NOT reused.

Parameters:

recordId - the ID of the record to delete.

Throws:

RecordStoreNotOpenException - if the record store is not open.

InvalidRecordIDException - if the recordId is invalid.

RecordStoreException - if a general record store exception occurs.

deleteRecordStore

public static void deleteRecordStore(String recordStoreName)
                              throws RecordStoreException,
                                     RecordStoreNotFoundException

Deletes the named record store. MIDlet suites are only allowed to operate on their own record stores, including deletions. If the record store is currently open by a MIDlet when this method is called, or if the named record store does not exist, a RecordStoreException will be thrown.

Parameters:

recordStoreName - the MIDlet suite unique record store to delete.

Throws:

RecordStoreException - if a record store-related exception occurred.

RecordStoreNotFoundException - if the record store could not be found.

enumerateRecords

public RecordEnumeration enumerateRecords(RecordFilter filter,
                                          RecordComparator comparator,
                                          boolean keepUpdated)
                                   throws RecordStoreNotOpenException

Returns an enumeration for traversing a set of records in the record store in an optionally specified order.

The filter, if non-null, will be used to determine what subset of the record store records will be used.

The comparator, if non-null, will be used to determine the order in which the records are returned.

If both the filter and comparator are null, the enumeration will traverse all records in the record store in an undefined order. This is the most efficient way to traverse all of the records in a record store.

The first call to RecordEnumeration.nextRecord() returns the record data from the first record in the sequence. Subsequent calls to RecordEnumeration.nextRecord() return the next consecutive record's data. To return the record data from the previous consecutive from any given point in the enumeration, call previousRecord(). On the other hand, if after creation the first call is to previousRecord(), the record data of the last element of the enumeration will be returned. Each subsequent call to previousRecord() will step backwards through the sequence.

Parameters:

filter - if non-null, will be used to determine what subset of the record store records will be used.

comparator - if non-null, will be used to determine the order in which the records are returned.

keepUpdated - if true, the enumerator will keep its enumeration current with any changes in the records of the record store. Use with caution as there are possible performance consequences. If false the enumeration will not be kept current and may return recordIds for records that have been deleted or miss records that are added later. It may also return records out of order that have been modified after the enumeration was built. Note that any changes to records in the record store are accurately reflected when the record is later retrieved, either directly or through the enumeration. The thing that is risked by setting this parameter false is the filtering and sorting order of the enumeration when records are modified, added, or deleted.

Returns:

an enumeration for traversing a set of records in the record store in an optionally specified order.

Throws:

RecordStoreNotOpenException - if the record store is not open.

See Also:

RecordEnumeration.rebuild()

getLastModified

public long getLastModified()
                     throws RecordStoreNotOpenException

Returns the last time the record store was modified, in the format used by System.currentTimeMillis().

Returns:

the last time the record store was modified, in the format used by System.currentTimeMillis().

Throws:

RecordStoreNotOpenException - if the record store is not open.

getName

public String getName()
               throws RecordStoreNotOpenException

Returns the name of this RecordStore. Not synchronized as the name is immutable.

Returns:

the name of this RecordStore.

Throws:

RecordStoreNotOpenException - if the record store is closed

getNextRecordID

public int getNextRecordID()
                    throws RecordStoreNotOpenException,
                           RecordStoreException

Returns the recordId of the next record to be added to the record store. This can be useful for setting up pseudo-relational relationships. That is, if you have two or more record stores whose records need to refer to one another, you can predetermine the recordIds of the records that will be created in one record store, before populating the fields and allocating the record in another record store. Note that the recordId returned is only valid while the record store remains open and until a call to addRecord().

Returns:

the record id of the next record to be added to the record store.

Throws:

RecordStoreNotOpenException - if the record store is not open.

RecordStoreException - if a different record store-related exception occurred.

getNumRecords

public int getNumRecords()
                  throws RecordStoreNotOpenException

Returns the number of records currently in the record store.

Returns:

the number of records currently in the record store.

Throws:

RecordStoreNotOpenException - if the record store is not open.

getRecord

public byte[] getRecord(int recordId)
                 throws RecordStoreNotOpenException,
                        InvalidRecordIDException,
                        RecordStoreException

Returns a copy of the data stored in the given record.

Parameters:

recordId - the id of the record to use in this operation.

Returns:

the data stored in the given record. Note that if the record has no data, this method will return null.

Throws:

RecordStoreNotOpenException - if the record store is not open.

InvalidRecordIDException - if the recordId is invalid.

RecordStoreException - if a general record store exception occurs.

See Also:

setRecord(int, byte[], int, int)

getRecord

public int getRecord(int recordId,
                     byte[] buffer,
                     int offset)
              throws RecordStoreNotOpenException,
                     InvalidRecordIDException,
                     RecordStoreException

Returns the data stored in the given record.

Parameters:

recordId - the id of the record to use in this operation.

buffer - the byte array in which to copy the data.

offset - the index into the buffer in which to start copying.

Returns:

the number of bytes copied into the buffer, starting at index offset.

Throws:

RecordStoreNotOpenException - if the record store is not open.

InvalidRecordIDException - if the recordId is invalid.

RecordStoreException - if a general record store exception occurs.

See Also:

setRecord(int, byte[], int, int)

getRecordSize

public int getRecordSize(int recordId)
                  throws RecordStoreNotOpenException,
                         InvalidRecordIDException,
                         RecordStoreException

Returns the size (in bytes) of the MIDlet data available in the given record.

Parameters:

recordId - the id of the record to use in this operation.

Returns:

the size (in bytes) of the MIDlet data available in the given record.

Throws:

RecordStoreNotOpenException - if the record store is not open.

InvalidRecordIDException - if the recordId is invalid.

RecordStoreException - if a general record store exception occurs.

getSize

public int getSize()
            throws RecordStoreNotOpenException

Returns the amount of space, in bytes, that the record store occupies. The size returned includes any overhead associated with the implementation, such as the data structures used to hold the state of the record store, etc.

Returns:

the size of the record store in bytes.

Throws:

RecordStoreNotOpenException - if the record store is not open.

getSizeAvailable

public int getSizeAvailable()
                     throws RecordStoreNotOpenException

Returns the amount of additional room (in bytes) available for this record store to grow. Note that this is not necessarily the amount of extra MIDlet-level data which can be stored, as implementations may store additional data structures with each record to support integration with native applications, synchronization, etc.

Returns:

the amount of additional room (in bytes) available for this record store to grow.

Throws:

RecordStoreNotOpenException - if the record store is not open.

getVersion

public int getVersion()
               throws RecordStoreNotOpenException

Each time a record store is modified (record added, modified, deleted), it's version is incremented. This can be used by MIDlets to quickly tell if anything has been modified. The initial version number is implementation dependent. The increment is a positive integer greater than 0. The version number only increases as the RecordStore is updated.

Returns:

the current record store version.

Throws:

RecordStoreNotOpenException - if the record store is not open.

listRecordStores

public static String[] listRecordStores()

Returns an array of the names of record stores owned by the MIDlet suite. Note that if the MIDlet suite does not have any record stores, this function will return NULL. The order of RecordStore names returned is implementation dependent.

Returns:

an array of the names of record stores owned by the MIDlet suite. Note that if the MIDlet suite does not have any record stores, this function will return NULL.

openRecordStore

public static RecordStore openRecordStore(String recordStoreName,
                                          boolean createIfNecessary)
                                   throws RecordStoreException,
                                          RecordStoreFullException,
                                          RecordStoreNotFoundException

Open (and possibly create) a record store associated with the given MIDlet suite. If this method is called by a MIDlet when the record store is already open by a MIDlet in the MIDlet suite, this method returns a reference to the same RecordStore object.

Parameters:

recordStoreName - the MIDlet suite unique name, not to exceed 32 characters, of the record store.

createIfNecessary - if true, the record store will be created if necessary.

Returns:

the RecordStore object for this record store.

Throws:

RecordStoreException - if a record store related exception occurred.

RecordStoreNotFoundException - if the record store could not be found.

RecordStoreFullException - if the operation cannot be completed because the record store is full.

removeRecordListener

public void removeRecordListener(RecordListener listener)

Removes the specified RecordListener. If the specified listener is not registered, this method does nothing.

Parameters:

listener - the RecordChangedListener to remove.

See Also:

addRecordListener(javax.microedition.rms.RecordListener)

setRecord

public void setRecord(int recordId,
                      byte[] newData,
                      int offset,
                      int numBytes)
               throws RecordStoreNotOpenException,
                      InvalidRecordIDException,
                      RecordStoreException,
                      RecordStoreFullException

Sets the data in the given record to that passed in. After this method returns, a call to getRecord(int recordId) will return an array of numBytes size containing the data supplied here.

Parameters:

recordId - the id of the record to use in this operation.

newData - the new data to store in the record.

offset - the index into the data buffer of the first relevant byte for this record.

numBytes - the number of bytes of the data buffer to use for this record.

Throws:

RecordStoreNotOpenException - if the record store is not open.

InvalidRecordIDException - if the recordId is invalid.

RecordStoreException - if a general record store exception occurs.

RecordStoreFullException - if the operation cannot be completed because the record store has no more room.

See Also:

getRecord(int)