persistent storage record stores mini databases – represent data as byte records record...

Persistent Storage

Record Stores mini databases – represent data as byte records Record Management System (RMS) API

Files and Directories FileConnection API

Contacts and Calendars Personal Information Management (PIM) API

RMS vs FileConnection API

FileConnection familiar (simpler) to use provides access to images, sounds, etc.

needs security privileges may not be supported on older devices

RMS vs FileConnection API

FileConnection familiar (simpler) to use provides access to images, sounds, etc.

needs security privileges may not be supported on older devices

RMS available on all MIDP devices does not require security privileges may be more appropriate for some applications

more cumbersome to use

RecordStores Mini databases that consist of a collection of records (byte arrays)

Could be shared across MIDlets



Creating Record Stores (via static methods)

RecordStore openRecordStore(String name, boolean create)

RecordStore openRecordStore(String name, boolean create, int auth, boolean writable)

auth = AUTHMODE_ANY – accessible by all midlets

AUTHMODE_PRIVATE – restricted to this midlet



Creating Record Stores (via static methods)

RecordStore openRecordStore(String name, boolean create)

RecordStore openRecordStore(String name, boolean create, int auth, boolean writable)

auth = AUTHMODE_ANY – accessible by all midlets

AUTHMODE_PRIVATE – restricted to this midlet

Manipulating Record Storesint addRecord(byte[] data, int offset, int numBytes)

void deleteRecord(int recordID)

byte[] getRecord(int recordID)

void setRecord(int recordID, byte[] data, int offset, int numBytes)

int getNumRecords()

int getRecordSize(int recordID)

Writing to RecordStore

void saveRecords(String rsName)

{

RecordStore rs = RecordStore.openRecordStore(rsName, true);

String[] data = {“Mickey”, “Minnie”, “Donald”, “Tom”, “Jerry”};

for (int i = 0; i < data.length; ++i) {

byte[] bytes = data[i].getBytes();

rs.addRecord(bytes, 0, bytes.length);

}

rs.closeRecordStore();

}

// NOTE: The RecordStore methods throw exceptions – put try/catch.

Reading from RecordStore

void readRecords(String rsName)

{


for (int i = 1; i <= rs.getNumRecords(); ++i) {

byte[] record = rs.getRecord(i);

String name = new String(record);

mainScreen.append(name);

}


}

// NOTE: The RecordStore methods throw exceptions – put try/catch.

// Typically will use RecordEnumeration to traverse

Enumerating Records RecordEnumeration – an interface for sequential traversal of a RecordStore

interface RecordEnumeration

{

bool hasNextElement();

bool hasPreviousElement();

byte[] nextRecord();

byte[] previousRecord();

int numRecords();

... ... ...

}

Enumerating Records RecordEnumeration – an interface for sequential traversal of a RecordStore

interface RecordEnumeration

{

bool hasNextElement();

bool hasPreviousElement();

byte[] nextRecord();

byte[] previousRecord();

int numRecords();

... ... ...

}

To get an enumerator for a RecordStore:

RecordEnumeration enumerateRecords(RecordFilter f, RecordComparator c,

boolen keepUpdated);

ordering criterion

selection criterion

Enumerating Records

void processRecords(String rsName)

{


RecordEnumeration records = rs.enumerateRecords(null, null, true);

while (records.hasNextElement()) {

byte[] rawData = records.nextRecord();

String name = new String(rawData);


}


}

RecordFilter Interface

Use to retrieve only those records that match a certain criterion

interface RecordFilter

{

boolean matches(byte[] record);

}

return true iff record satisfies the criterion

RecordFilter Interface

Use to retrieve only those records that match a certain criterion

interface RecordFilter

{

boolean matches(byte[] record);

}

Filter for records that start with CompSci:

class CompSciFilter implements RecordFilter

{

boolean matches(byte[] record)

{

String data = new String(record);

return data.startsWith(“CompSci”);

}

}

return true iff record satisfies the criterion

RecordComparator Interface

Use to create an ordering criterion for retrieving the records

interface RecordComparator

{

int compare(byte[] r1, byte[] r2)

}

return FOLLOWS if r1 comes after r2 in sorted order

PRECEDES if r1 comes before r2 in sorted order

EQUIVALENT if r1 and r2 are considered equal

RecordComparator Interface Retrieve by decreasing size

class DescSizeSorter implements RecordComparator

{

boolean compare(byte[] r1, byte[] r2)

{

String s1 = new String(r1);

String s2 = new String(r2);

if (s1.size() > s2.size()) {

return ???

}

else if (s1.size() < s2.size()) {

return ???

}

else {

return ???

}

}

Enumerating Records Traverse only CompSci records in decreasing order of length

void processRecords(String rsName)

{


CompSciFilter filter = new CompSciFilter();

DecSizeSorter order = new DecSizeSorter();

RecordEnumeration records = rs.enumerateRecords(filter, order, true);

while (records.hasNextElement()) {

byte[] rawData = records.nextRecord();

String name = new String(rawData);


}


}

Input/Output Streams An abstract representation of stream of data

ByteArrayInputStream/ByteArrayOutputStream --- abstraction for

reading from / writing to a byte array

OutputStream

ByteArrayOutputStream

DataOutputStream

InputStream

ByteArrayInputStream

DataInputStream

ByteArrayInput/Output Streams Provide a mechanism for reading from / writing to a byte array (only bytes)

Allow the buffer to grow as needed (on writing to)

Selected methods (ByteArrayInput):

int size() – current size of buffer

void write(int b) – write a byte to the buffer

void write(byte[] b, int off, int len) – write len bytes starting off

byte[] toByteArray() – return the buffer in a byte array

Example:ByteArrayOutputStream os = new ByteArrayOutputStream();

os.write(‘C’);

os.write(‘S’);

os.write(1);

byte[] data = os.toByteArray();

DataInput/Output Stream Provide convenient mechanism for reading from / writing to a stream

(supports all of the primitive types)

Selected methods (DataOutputStream):

DataOutputStream(OutputStream os)

void writeInt(int v)

void writeDouble(double v)

void writeUTF(String s) -- write machine-independentt encoding of v

void flush() -- forces any written values to be written to stream

Selected methods (DataInputStream):

DataInputStream(InputStream os)

int readInt()

double readDouble()

String readUTF()

long skip(long n) – skip n bytes (return how many actually skipped)

int available() – how many bytes can be read without waiting

DataInput/Output Stream Example (writing)

ByteArrayOutputStream os = new ByteArrayOutputStream();

DataOutputStream output = new DataOutputStream(os);

output.writeUTF(‘Comp Sci’);

output.writeInt(391);

output.writeDouble(4.3);

byte[] = os.toByteArray();

Example (reading)

byte[] data = ... // data stored in somehow

ByteArrayInputStream is = new ByteArrayInputStream(data);

DataInputStream input = new DataOutputStream(is);

String name = input.readUTF();

int code = input.readInt();

double maxgrade = input.readDouble(4.3);

Files and Directories Generic Connection Framework (Connections and Connector classes)

ConnectorTypeConnection = (TypeConnection) Connector.open(url)

Connection

InputConnection

OutputConnection

FileConnection SocketConnection HttpConnection

DataInputStream openDataInputStream()

int getPort()String getHost()String getURL()String getResponseMessage()

DataOutputStream openDataOutputStream()OutputStream openOutputStream()

void close()

int getPort()String getAddress()String getLocalAddress()

InputStream openInputStream()

File Manipulation Example (writing)

FileConnection fc = (FileConnection) Connector.open( filename );

DataOutputStream output = fc.getDataOutputStream();

output.writeInt(2);

output.writeUTF(“CS 112”);

output.writeUTF(“CS 391”);

output.close();

fc.close();

Example (reading)FileConnection fc = (FileConnection) Connector.open( filename );

DataInputStream input = fc.getDataInputStream();

int numRecords = input.readInt();

String name1 = input.readUTF();

String name2 = input.readUTF();

output.close();

fc.close();

persistent storage record stores mini databases – represent data as byte records record...

Documents