ReadWriteStreams.java Source code

Introduction

Here is the source code for ReadWriteStreams.java

Source

/*--------------------------------------------------
* ReadWriteStreams.java
*
* Use streams to read and write Java data types
* to the record store.
*
* No GUI interface, all output is to the console
*
* Example from the book:     Core J2ME Technology
* Copyright John W. Muchow   http://www.CoreJ2ME.com
* You may use/modify for any non-commercial purpose
*-------------------------------------------------*/
import java.io.*;
import javax.microedition.midlet.*;
import javax.microedition.rms.*;

public class ReadWriteStreams extends MIDlet {
    private RecordStore rs = null; // Record store
    static final String REC_STORE = "db_1"; // Name of record store

    public ReadWriteStreams() {
        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() {
        String[] strings = { "Text 1", "Text 2" };
        boolean[] booleans = { false, true };
        int[] integers = { 1, 2 };

        writeStream(strings, booleans, integers);
    }

    /*--------------------------------------------------
    * Write to record store using streams.
    *-------------------------------------------------*/
    public void writeStream(String[] sData, boolean[] bData, int[] iData) {
        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.writeUTF(sData[i]);
                strmDataType.writeBoolean(bData[i]);
                strmDataType.writeInt(iData[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 {
            // Careful: Make sure this is big enough!
            // Better yet, test and reallocate if necessary      
            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("UTF: " + strmDataType.readUTF());
                System.out.println("Boolean: " + strmDataType.readBoolean());
                System.out.println("Int: " + strmDataType.readInt());
                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
    * When used with Exceptions we should handle the 
    * error in a more appropriate manner.
    *-------------------------------------------------*/
    private void db(String str) {
        System.err.println("Msg: " + str);
    }
}