J2ME 101, Part 3: Inside the Record Management System

/*--------------------------------------------------
* ReadWritePrimitives.java
*-------------------------------------------------*/
import java.io.*;
import javax.microedition.midlet.*;
import javax.microedition.rms.*;

public class ReadWritePrimitives extends MIDlet
{
     private RecordStore rs = null;    // Record store
     static final String REC_STORE = "rms2"; // Name of record store

     public ReadWritePrimitives()
     {
       openRecStore();   // Create the record store

       writeTestData();  // Write a series of records
       readStream();     // Read back the records

       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
       {
         // The second parameter indicates that the record store
       		 // should be created if it does not exist
         rs = RecordStore.openRecordStore(REC_STORE, true);
       }
       catch (Exception e)
       {
         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());
         }
       }
     }

     /*--------------------------------------------------
     * Create three arrays to write to record store
     *-------------------------------------------------*/
     public void writeTestData()
     {
       boolean[] booleans = {true,false};
       int[] integers = {17 , 4};
       String[] strings = {"Golf", "Tennis"};

       writeStream(booleans, integers, strings);
     }

     /*--------------------------------------------------
     * Write to record store using streams.
     *-------------------------------------------------*/
     public void writeStream(boolean[] bData, int[] iData, String[] sData)
     {
       try
       {
          // Write data into an internal byte array
         ByteArrayOutputStream strmBytes = new ByteArrayOutputStream();

         // Write Java data types into the above byte array
         DataOutputStream strmDataType = new DataOutputStream(strmBytes);

         byte[] record;

         for (int i = 0; i < sData.length; i++)
         {
           // Write Java data types
           strmDataType.writeBoolean(bData[i]);
           strmDataType.writeInt(iData[i]);
           strmDataType.writeUTF(sData[i]);

           // Clear any buffered data
           strmDataType.flush();

           // Get stream data into byte array and write record
           record = strmBytes.toByteArray();
           rs.addRecord(record, 0, record.length);

           // Toss any data in the internal array so writes
           // starts at beginning (of the internal array)
           strmBytes.reset();
         }

         strmBytes.close();
         strmDataType.close();

       }
       catch (Exception e)
       {
         db(e.toString());
       }
     }

     /*--------------------------------------------------
     * Read from the record store using streams
     *-------------------------------------------------*/
     public void readStream()
     {
       try
       {
         // Allocate space to hold each record
         byte[] recData = new byte[50];

         // Read from the specified byte array
         ByteArrayInputStream strmBytes = new ByteArrayInputStream(recData);

         // Read Java data types from the above byte array
         DataInputStream strmDataType = new DataInputStream(strmBytes);

         for (int i = 1; i <= rs.getNumRecords(); i++)
         {
           // Get data into the byte array
           rs.getRecord(i, recData, 0);

           // Read back the data types
           System.out.println("Record #" + i);
           System.out.println("Boolean: " + strmDataType.readBoolean());
           System.out.println("Integer: " + strmDataType.readInt());
           System.out.println("String: " + strmDataType.readUTF());
           System.out.println("--------------------");

           // Reset so read starts at beginning of array
           strmBytes.reset();
         }

         strmBytes.close();
         strmDataType.close();

       }
       catch (Exception e)
       {
         db(e.toString());
       }
     }

     /*--------------------------------------------------
     * Simple message to console for debug/errors
     *-------------------------------------------------*/
     private void db(String str)
     {
       System.err.println("Msg: " + str);
     }
}