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Bruce Scharlau, University of Aberdeen, 2010 Java ME Record Management System Mobile Computing.

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Presentation on theme: "Bruce Scharlau, University of Aberdeen, 2010 Java ME Record Management System Mobile Computing."— Presentation transcript:

1 Bruce Scharlau, University of Aberdeen, 2010 Java ME Record Management System Mobile Computing

2 Bruce Scharlau, University of Aberdeen, 2010 Mobiles + (Tunnels | Hills) = Lost connection

3 Bruce Scharlau, University of Aberdeen, 2010 Only commercial databases for Java ME handsets No widely available databases for Java ME on CLDC There are some open source packages if youre using CDC – see information page

4 Bruce Scharlau, University of Aberdeen, 2010 A RecordStore is NOT a database A RecordStore is an array of bytes with MIDP 2.0 a RecordStore can be shared across MIDlet suites RecordStore names must be unique

5 Bruce Scharlau, University of Aberdeen, 2010 Set the MIDlet-Data-Size attribute when using RMS Any MIDlet suite that uses RMS should specify the minimum number of bytes of data storage it requires, by setting the MIDlet- Data-Size attribute, in both the JAR manifest and the application descriptor. If the MIDlet-Data-Size attribute is missing, the device assumes the MIDlet suite requires no space for data storage.

6 Bruce Scharlau, University of Aberdeen, 2010 RecordStore if LILO Im telling you, its last in, last out No transactions then. Hmm

7 Bruce Scharlau, University of Aberdeen, 2010 If multiple apps share an RMS you need to write the logic for this RMS operations are thread-safe, but threads must still coordinate the reading and writing of data to the same record store. This is especially important if your RecordStore is shared in a MIDlet suite.

8 Bruce Scharlau, University of Aberdeen, 2010 RecordStore uses ID not index 1Tom6789 2Jane3680 3Henry1472 1Tom6789 2Jane3680 3Henry1472 4Mary8547 1Tom6789 2Jane3680 3Henry1472 4Mary8547 1Tom6789 2Jane3680 3Henry3456 4Mary8547 5Sarah Start with three Remove Jane, add Mary Remove Tom Change data, add row

9 Bruce Scharlau, University of Aberdeen, 2010 recordID = 1 for first record Yes, but when its gone its gone Auto- increment, nice. And it always starts at 1

10 Bruce Scharlau, University of Aberdeen, 2010 RecordStore Methods All are static so can be called without instance Can acquire a list of all record stores with String[ ] listRecordStores() Create/open record store with RecordStore openRecordStore(myStore, true) boolean to create or not if doesnt exist Delete via void deleteRecordStore(myStore)

11 Bruce Scharlau, University of Aberdeen, 2010 Adding Items myRecords.addRecord(myBytes, 0, myBytes.length); byteArray of data to be written to the store Offset from which to start writing the data How much of byteArray should be written

12 Bruce Scharlau, University of Aberdeen, 2010 Modifying a Record Same as writing to a record, but must also pass in the recordID as the first parameter myRecords.addRecord(recordID, myBytes, 0, myBytes.length);

13 Bruce Scharlau, University of Aberdeen, 2010 Reading a record Either: –A) byte [ ] recordData = myRecords.getRecord(1) –B) byte[ ] myBuffer = new byte[BIG_ENOUGH]; int readRecord = myRecords.getRecord(1, myBuffer, 0); Instead of creating a new byte array to hold the result, this version uses one from the application

14 Bruce Scharlau, University of Aberdeen, 2010 Meta Information long lastModified() timestamp of store String getName() of the store int getNextRecordID() to be added to the store int getRecordSize(int myRecord) for the size of the specified record int getSize() of the complete store

15 Bruce Scharlau, University of Aberdeen, 2010 Custom Objects Problem – how to serialise objects and their attributes? Create class and then write variables to bytes and then store this object to the array Reverse the process to recreate the object

16 Bruce Scharlau, University of Aberdeen, 2010 Custom Object - class class AuctionItems { String descriptionAI; String summaryAI; String startPriceAI; long startDateAI; } Create class to hold variables for custom object, which can then be passed around as required

17 Bruce Scharlau, University of Aberdeen, 2010 Write Custom object private byte[] getBytes() throws IOException{ ByteArrayOutputStream baos = new ByteArrayOutputStream(); DataOutputStream dos = new DataOutputStream(baos); dos.writeUTF(descriptionAI); dos.writeUTF(summaryAI); dos.writeUTF(startPriceAI); dos.writeLong(startDateAI); dos.close(); baos.close(); return baos.toByteArray(); } * Variables from Form * Could also write out Int, Long, Short, and others * Variables from Form * Could also write out Int, Long, Short, and others

18 Bruce Scharlau, University of Aberdeen, 2010 Read Custom Object public AuctionJ2meItems(byte[] data) throws RecordStoreNotOpenException, InvalidRecordIDException, RecordStoreException, IOException { ByteArrayInputStream bais = new ByteArrayInputStream(data); DataInputStream dis = new DataInputStream(bais); this.descriptionAI = dis.readUTF(); this.summaryAI = dis.readUTF(); this.startPriceAI = dis.readUTF(); this.startDateAI = dis.readLong(); } A read from the store is the constructor for object and gets used like this: byte[] inputData = auctionItems.getRecord(item); AuctionItems ai = new AuctionItems(inputData); item is an int

19 Bruce Scharlau, University of Aberdeen, 2010 Could write your own implementation to make RMS work like JDBC To make working with RMS like using JDBC, and Java objects, need to write structure to handle this

20 Bruce Scharlau, University of Aberdeen, 2010 Use either brute force or enumeration to traverse a RecordStore Because record IDs are fixed, they are not continuous. A deleted record ID is not filled by an incoming record, so iteration doesnt work. RecordStore is NOT a database as shown by this operation

21 Bruce Scharlau, University of Aberdeen, 2010 Fetch records one by one in a simple way... RecordStore rs =... // an open record store int lastID = rs.getNextRecordID(); int numRecords = rs.getNumRecords(); int count = 0; for( int id = 1; id < lastID && count < numRecords; ++id ){ try { byte[] data = rs.getRecord( id );... // process the data ++count; } catch( InvalidRecordIDException e ){ // just ignore and move to the next record } catch( RecordStoreException e ){ // a more general error that should be handled // somehow break; }...

22 Bruce Scharlau, University of Aberdeen, 2010 You can also use RecordEnumeration RecordStore rs =... // an open record store RecordEnumeration enum = rs.enumerateRecords( null, null, false ); try { while( enum.hasNextElement() ){ int id = enum.nextRecordId(); byte[] data = rs.getRecord( id );... // do something here } } catch( RecordStoreException e ){ // handle the error here }...

23 Bruce Scharlau, University of Aberdeen, 2010 Sorting Objects Use RecordEnumerations to sort through records using compare() –Returns either: EQUIVALENT, FOLLOWS or PRECEDES Can also use enumerateRecords() with its RecordFilter to sift through recordStore

24 Bruce Scharlau, University of Aberdeen, 2010 Use RecordComparator to sort records for display import javax.microedition.rms.*; import java.lang.*; public class MyComparator implements RecordComparator { public int compare(byte rec1[], byte rec2[]) { String recstr1 = new String(rec1); String recstr2 = new String(rec2); int num = recstr1.compareTo(recstr2); if (num != 0) { return ( num < 0 ? RecordComparator.PRECEDES : RecordComparator.FOLLOWS); } else { return RecordComparator.EQUIVALENT; }

25 Bruce Scharlau, University of Aberdeen, 2010 Dukes Auction MIDlet retrieves list of auction items AuctionMIDlet Servlet Database Send query to db AuctionItems ResultSet returned Vector returned AuctionJ2meItems Creates vector of these Serialises to RMS

26 Bruce Scharlau, University of Aberdeen, 2010 Call the servlet with byte hc = (HttpConnection) Connector.open(url); baos = new ByteArrayOutputStream(); dos = new DataOutputStream(baos); dos = hc.openDataOutputStream(); dos.writeByte(OPERATION_LIST_ALL_ITEMS); dos.close(); Use DataInput/ OutputStreams and ByteArrayOutputStream to manage data

27 Bruce Scharlau, University of Aberdeen, 2010 The servlet responds to the call private void j2me_selectItem(DataInputStream call, DataOutputStream result, String quantity) throws IOException, SQLException { AuctionItems auctionI = new AuctionItems(); Vector items = new Vector (); items = auctionI.getJ2meAuctionItems("all"); Iterator iter = items.iterator(); while (iter.hasNext()) { AuctionJ2meItems aItem = new AuctionJ2meItems(); aItem = (AuctionJ2meItems) iter.next(); result.writeUTF("next"); result.writeUTF(aItem.descriptionAI); result.writeUTF(aItem.summaryAI); result.writeUTF(aItem.startPriceAI); result.writeLong(aItem.startDateAI); } return; } Use AuctionItems and AuctionJ2meItems Write stream to MIDlet

28 Bruce Scharlau, University of Aberdeen, 2010 MIDlet captures stream and writes object to RMS inputStream = hc.openDataInputStream(); int contentLength = (int) hc.getLength(); String k = ""; inputStream.skipBytes(4); while (inputStream.available() > 0) { k = inputStream.readUTF(); if (k.equals("next")) { aItem = new AuctionJ2meItems(inputStream.readUTF(), inputStream.readUTF(), inputStream.readLong()); ByteArrayOutputStream baos2 = new ByteArrayOutputStream(); DataOutputStream dos2 = new DataOutputStream(baos2); aItem.serialize(dos2); byte[] b = baos2.toByteArray(); try { auctionItemStore.addRecord(b, 0, b.length); } catch (Exception e) { // more code left out here

29 Bruce Scharlau, University of Aberdeen, 2010 Then we can read the RecordStore into a form with read(1); private void read(int item) throws RecordStoreNotOpenException, InvalidRecordIDException, RecordStoreException, IOException { byte[] inputData = auctionItemStore.getRecord(item); AuctionJ2meItems ai = new AuctionJ2meItems(inputData); ai.print(); // set up form … readForm.append(description); readForm.append(summary); readForm.append(startPrice); readForm.append(startDate); description.setString(ai.descriptionAI); summary.setString(ai.summaryAI); startPrice.setString(ai.startPriceAI); startDate.setString(String.valueOf(new java.util.Date(ai.startDateAI))); // add commnds to form … readForm.setCommandListener(this); display.setCurrent(readForm); } Notice that we convert startDataAI to Date from long Use AuctionJ2meItem object

30 Bruce Scharlau, University of Aberdeen, 2010 Navigate through records with previous and next commands } else if (c == mPrevCommand) { try { if (currentId == 1) { Alert alertPrev = new Alert("No previous records"); alertPrev.setTimeout(Alert.FOREVER); alertPrev.addCommand(mReadAuctionCommand); alertPrev.setCommandListener(this); display.setCurrent(alertPrev); } else { currentId--; read(currentId); } catch (RecordStoreNotOpenException e) { // pl;us other exceptions … } else if (c == mNextCommand) { try { currentId++; read(currentId); … Check for no record, and keep track of recordID

31 Bruce Scharlau, University of Aberdeen, 2010 Using AuctionJ2meItem on server and handset causes issues Closely couples the code between the two Explore alternatives before coupling code May be able to use interoperable option

32 Bruce Scharlau, University of Aberdeen, 2010 The more classes in the app the more memory it consumes Each class in the app will need to be loaded All classes in MIDP are loaded dynamically at the start during class verification Keeping classes small, and to a minimum is therefore important in mobile Java

33 Bruce Scharlau, University of Aberdeen, 2010 Summary RMS is similar to database, with significant differences that you need to accommodate Map the bytes to objects for convenience Sometimes need to share code across platforms (server and Java ME client) to ease programming


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