Core J2ME™ Technology & MIDP phần 6 ppt

267 Example 10.4 OptionsList.java /* * Class OptionsList * * List to provide options for configuring of timer * */ import javax.microedition.lcdui.*; class OptionsList extends List implements CommandListener { private AnimatedTimer midlet; // Main midlet private Command cmBack; public OptionsList(String title, int listType, AnimatedTimer midlet) { // Call list constructor super(title, listType); // Save reference to MIDlet so we can // access the display manager class this.midlet = midlet; // Create the list entries append("Sleep interval", null); append("Start", null); append("Stop", null); // Create command and listen for events cmBack = new Command("Back", Command.BACK, 1); addCommand(cmBack); setCommandListener(this); } /* * Command event handling * */ public void commandAction(Command c, Displayable s) { // Event generated by the implicit list if (c == List.SELECT_COMMAND) { switch (getSelectedIndex()) { case 0: // Push current displayable and show the form // to adjust the timer sleep midlet.displayMgr.pushDisplayable(midlet.fmSleep); break; case 1: // Start timer and return to previous displayable midlet.cvTimer.startTimer(); midlet.displayMgr.popDisplayable(); break; Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 268 case 2: // Stop timer and return to previous displayable midlet.cvTimer.stopTimer(); midlet.displayMgr.popDisplayable(); break; } } else if (c == cmBack) { // Return to previous displayable midlet.displayMgr.popDisplayable(); } } } Example 10.5 SleepForm.java /* * Class SleepForm * * Form with gauge to adjust sleep interval of timer * */ import javax.microedition.lcdui.*; public class SleepForm extends Form implements CommandListener { private AnimatedTimer midlet; // Main midlet private Command cmBack, // Back to options list cmHome, // Go to main displayable (canvas) cmSave; // Save new sleep time private Gauge gaSleep; // Gauge to adjust sleep public SleepForm(String title, AnimatedTimer midlet) { // Call the form constructor super(title); // Save reference to MIDlet so we can // access the display manager class this.midlet = midlet; // Commands cmSave = new Command("Save", Command.SCREEN, 1); cmBack = new Command("Back", Command.BACK, 2); cmHome = new Command("Home", Command.SCREEN, 2); // Gauge to adjust the length of timer sleep gaSleep = new Gauge( " Timer Sleep " , true, 100, 1000); // Set to current sleep. Gauge holds values 0 to 100, // divide the current sleep (milliseconds) by 10 gaSleep.setValue(midlet.cvTimer.getSleep() / 10); // Add to form and listen for events append(gaSleep); addCommand(cmSave); addCommand(cmBack); addCommand(cmHome); Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 269 setCommandListener(this); } /* * Command event handling * */ public void commandAction(Command c, Displayable s) { if (c == cmSave) { // Gauge returns a value between 0 and 100 // We want milliseconds, so multiply by 10 midlet.cvTimer.setSleep(gaSleep.getValue() * 10); // Return to main midlet midlet.displayMgr.home(); } else if (c == cmBack) { // Pop the last displayable off the stack midlet.displayMgr.popDisplayable(); } else if (c == cmHome) { // Return to main midlet midlet.displayMgr.home(); } } } Example 10.6 DisplayManager.java /* * Use a stack to push and pop displayable objects * * public void pushDisplayable(Displayable) * public void popDisplayable() * public void home() * */ import javax.microedition.lcdui.*; import java.util.*; public class DisplayManager extends Stack { private Display display; // Reference to Display object private Displayable mainDisplayable; // Main displayable for MIDlet private Alert alStackError; // Alert for error conditions public DisplayManager(Display display, Displayable mainDisplayable) { // Only one display object per midlet, this is it this.display = display; this.mainDisplayable = mainDisplayable; Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 270 // Create an alert displayed when an error occurs alStackError = new Alert("Displayable Stack Error"); alStackError.setTimeout(Alert.FOREVER); // Modal } /* * Push the current displayable onto stack and set * the passed in displayable as active * */ public void pushDisplayable(Displayable newDisplayable) { push(display.getCurrent()); display.setCurrent(newDisplayable); } /* * Return to the main displayable object of MIDlet * */ public void home() { while (elementCount > 1) pop(); display.setCurrent(mainDisplayable); } /* * Pop displayable from stack and set as active * */ public void popDisplayable() { // If the stack is not empty, pop next displayable if (empty() == false) display.setCurrent((Displayable) pop()); else // On error show an alert // Once acknowldeged, set 'mainDisplayable' as active display.setCurrent(alStackError, mainDisplayable); } } Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 271 Chapter 11. RECORD MANAGEMENT SYSTEM (RMS) Topics in this Chapter • Persistent Storage Through the Record Store • Navigating with RecordEnumeration • Sorting with RecordComparator • Searching with RecordFilter • Notification of Changes with RecordListener • Exception Handling We can cover a lot of miles with the concepts we've covered upto this point. However, we are missing a significant capability that will eventually catch up with us. In fact, it is so ingrained into our daily computing we often take this concept for granted. I am referring to storing and retrieving of data. Whether the information is as simple as application preferences or as comprehensive as a product catalog, we need a way to manage application-related data. In desktop computing the options are obvious, CD-ROM, local drive, network drive, and so forth. It becomes a little more challenging with mobile devices. There are size and performance concerns, not to mention the differences between manufacturers as far as support (or lack of) for file systems and networking. The Record Management System (RMS) is a persistent storage environment within the MIDP. This chapter describes how you can read, write, sort and search data within a RMS. Persistent Storage Through the Record Store As an alternative to using a file system, the RMS uses non-volatile memory to store information. This record-oriented database, often referred to as a flat-file, can be thought of as a series of rows in a table, with a unique identifier for each row (see Table 11.1 ). Table 11.1. Record Store Record ID Data 1 Array of bytes 2 Array of bytes 3 Array of bytes Each record consists of a record id, an integer value that plays the role of primary key for the database and an array of bytes for storing the record data. A collection of records is known as a record store. A MIDlet can have any number of record stores (including none), where each is uniquely identified by its name. This idea needs to be carried one step further—if a MIDlet is part of MIDlet suite, record store names must also be unique within the suite. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 272 Naming Record Stores Each record store name can consist of up to 32 Unicode (16-bit) characters. Names are case sensitive. Names must be unique within a MIDlet suite. MIDlets that are packaged within a suite can access not only the record stores they create, but also those of other MIDlets in the suite. Figure 11–1 illustrates this concept. Figure 11-1. MIDlet access to record stores. The solid lines indicate access to record stores the MIDlet has created. Dashed lines represent access to record stores created by a different MIDlet within the same suite. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 273 Within "MIDlet Suite One," MIDlet #1 and MIDlet #2 can access all four record stores available as part of the suite. The same applies to "Suite Two." However, MIDlets in Suite One cannot access the record stores of Suite Two. Record store names within a suite must be unique. That is, Suite One must have all unique record store names. However, record store names in one suite may be duplicated in another. For example, Suite One and Suite Two both have record stores with the name "ABC" and "DEF." There are two values maintained by a record store that may be helpful for tracking database usage. Each is updated when a record is added, deleted or changed: 1. Version number is an integer value. Unfortunately, the starting value when creating a new record is not defined by the API. If you need to track version numbers, you can query the record store immediately after creation using getVersion() to determine the starting value. 2. Date and time stamp is a long integer that represents the number of milliseconds since midnight January 1 st , 1970. You can query this value by calling getLastModified(). Whenever a request is made to modify the record store, it is done in one fell swoop. That is, once a change is underway it is guaranteed to be completed before another begins. If a request(s) is made to update the record store while an operation is in progress, it will be queued, waiting for the current operation to finish. Removing Record Stores If a MIDlet suite is removed from a device, all record stores will be deleted as well. Record Store API This class is the heart of the RMS. Through this class we create, update, query and delete record stores (see Table 11.2 ). Table 11.2. RecordStore Class: javax.microedition.rms.RecordStore Method Description Constructors No constructor. See openRecordStore() Methods static RecordStore openRecordStore(String recordStoreName, boolean createIfNecessary) Open record store. Optionally, create the store if it does not already exist. void closeRecordStore() Close record store. static void deleteRecordStore(String recordStoreName) Delete record store. static String[] listRecordStores() List record stores in MIDlet suite. int addRecord(byte[] data, int offset, int numBytes) Add a record. void setRecord(int recordId, byte[] newData, int offset, int numBytes) record. Set (replace) data in a void deleteRecord(int recordId) Delete a record. byte[] getRecord(int recordId) Get byte array containing record data. int getRecord(int recordId, byte[] buffer, int offset) Get contents of record into b y te arra y Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 274 parameter copying data from specified offset. int getRecordSize(int recordId) Size in bytes of a record. int getNextRecordID() The number of the next record when adding a new record to the store. int getNumRecords() Number of records in the record store. long getLastModified() Last modified date of the record store. int getVersion() Record store version number. String getName() Name of the record store. int getSize() Total bytes occupied by record store. int getSizeAvailable() Current space (bytes) available for records. This will change as records are added/deleted. RecordEnumeration enumerateRecords( RecordFilter filter, RecordComparator comparator, boolean keepUpdated) Build an enumeration for traversing records in the record store. void addRecordListener (RecordListener listener) Add a listener to detect record store changes. void removeRecordListener (RecordListener listener) Remove listener. Example: Read and Write Records Now that we understand the basics of RMS, let's walk through two examples. Each will create a record store, write several records, read back those same records and delete the record store. The difference lies with how the data is manipulated before and after writing. More on that in a minute. We have two methods to write data into a record store: public int addRecord (byte[] data, int offset, int numBytes) public void setRecord (int recordId, byte[] newData, int offset, int numBytes) Regardless of which we choose, each accepts an array of bytes as the input. What will vary for our two examples is how we manage the array of data, for both reading and writing records. In our first example (Example 11.1 ), we will write String objects into the record store. Figure 11–2 shows the contents of the two records that were read from the record store. Figure 11-2. Reading and writing String objects Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 275 I've gone ahead and written several convenience methods for managing the record store. These include opening, closing and deleting. Each method Example 11.1 ReadWrite.java /* * ReadWrite.java * * Read and write to the record store. * * No GUI interface, all output is to the console * */ import java.io.*; import javax.microedition.midlet.*; import javax.microedition.rms.*; public class ReadWrite extends MIDlet { private RecordStore rs = null; static final String REC_STORE = "db_1"; public ReadWrite() { openRecStore(); // Create the record store // Write a few records and read them back writeRecord("J2ME and MIDP"); writeRecord("Wireless Technology"); readRecords(); closeRecStore(); // Close record store deleteRecStore(); // Remove the record store } public void destroyApp( boolean unconditional ) { } public void startApp() { // There is no user interface, go ahead and shutdown destroyApp(false); notifyDestroyed(); } public void pauseApp() { } public void openRecStore() { try { // Create record store if it does not exist rs = RecordStore.openRecordStore(REC_STORE, true ); } catch (Exception e) { Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 276 db(e.toString()); } } public void closeRecStore() { try { rs.closeRecordStore(); } catch (Exception e) { db(e.toString()); } } public void deleteRecStore() { if (RecordStore.listRecordStores() != null) { try { RecordStore.deleteRecordStore(REC_STORE); } catch (Exception e) { db(e.toString()); } } } public void writeRecord(String str) { byte[] rec = str.getBytes(); try { rs.addRecord(rec, 0, rec.length); } catch (Exception e) { db(e.toString()); } } public void readRecords() { try { byte[] recData = new byte[50]; int len; for (int i = 1; i <= rs.getNumRecords(); i++) { len = rs.getRecord( i, recData, 0 ); System.out.println("Record #" + i + ": " + new String(recData, 0, len)); System.out.println(" "); Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com [...]... the data back, we are assured to get the same information, in the same format That is, if we write an integer into the byte array, regardless of how the system running the JVM represents an integer ( 16 bits, 32 bits, etc.), we are guaranteed to get the expected results Once the streams are in place we call the appropriate methods based on the type of data we choose to write Next, we flush the stream,... PRECEDES Based on the sort algorithm in the compare() method, the first parameter precedes the second RecordComparator API Table 11.5 RecordComparator Interface: javax.microedition.rms.RecordComparator 2 86 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com Method int compare(byte[] rec1, byte[] rec2) Description Compare records to determine sort order See Table 11.4 for return values... moment to look at Figure 11–5 Notice that the records are sorted based on the "Name," which is the String we wrote in each record Figure 11-5 Records with multiple Java data types, sorted by "Name" 2 96 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com Example: Integer Sor t with Compound Records Using the same data as in the previous example, let's complicate things just a bit . append("Sleep interval", null); append("Start", null); append("Stop", null); // Create command and listen for events cmBack = new Command("Back",. Commands cmSave = new Command("Save", Command.SCREEN, 1); cmBack = new Command("Back", Command.BACK, 2); cmHome = new Command("Home", Command.SCREEN, 2); . System.out.println("UTF: " + strmDataType.readUTF()); System.out.println("Boolean: " + strmDataType.readBoolean()); System.out.println("Int: " + strmDataType.readInt());