12.2 The Oracle J2ME SODA SDK

The Oracle9i Lite database does not run on the MIDP platform. Instead, Oracle provides a Java object database for MIDP devices. The Oracle J2ME SDK (beta) supports the Oracle Simple Object Database Access (SODA) data store. Built on top of the standard RMS, SODA allows us to store, search, and retrieve Java data objects directly. The oracle.wireless.me.soda package contains six classes (see descriptions in Table 12.1).

Listing 12.2. The SODA demo

DBSession sess = new DBSession();



// Create a new DBClass with an INT field

// and a String field.

// The name of this DBClass is "dept". You can

// get it by its name using findClass() method

// in the sess object.

DBClass dept = sess.createClass(

    "dept",

    new DBAttr[] {

      new DBAttr("id", DBAttr.C_INT),

      new DBAttr("name", DBAttr.C_STRING)

    }

);



// Load a comma delimited database file.

// It will create a number of DBObjects

// under the "dept" DBClass.

DBLoader.loadCSV(dept, new InputStreamReader(in), dept.allAttr());



// Now, get all DBObjects (null match condition)

// in dept class in a DBCursor

DBCursor c = dept.createCursor(null, null);



// Iterate and get all field attributes

// in the DBClass.

DBAttr[] a = dept.getAttrs();

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

  System.out.print(a[i].name+", ");

  System.out.println();

  DBObject o;

  // Iterate through the cursor and get

  // data in each column (field).

  while ((o = c.next()) != null) {

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

      System.out.print(o.getString(i)+",");

      System.out.println();

    }

    c.close();

}



// Remember to release resources.

sess.close();

12.3 The IBM DB2e FastRecordStore

IBM DB2e (v8.1) provides a FastRecordStore class over the MIDP standard RMS record store. FastRecordStore packs several database rows into one RMS record and supports indexes for fast lookup. This results in much improved performance over the linear RMS record store.

To create a database table in a FastRecordStore, we have to first create the table in a DB2e backend database. Then, we synchronize the table to the MIDP device using IBM DB2e Sync. After the synchronization, a FastRecordStore with the same name as the backend table is created. We can now read or update data in the FastRecordStore via the TableMetaData class. All the changes we make on the MIDP client will be sent back to the backend table upon the next synchronization operation. For more information about database synchronization and the IBM Sync,

Note

In the FastRecordStore, each table row is packed into a byte array. Developers are required to manipulate those raw arrays manually. All rows start with a dirty byte and are followed by data in each column according to the following rules.

• If the column is not nullable, the data for the column is present.

• If the column is nullable there is a 1-byte boolean null indicator. If the indicator is true, no data follows. Otherwise, the column data follows.

To illustrate the above points, the SQL INSERT statement in Listing 12.3 can be interpreted as the Java code in Listing 12.4.

Listing 12.3. SQL script for a sample table

create table MyTable (a int, b int not null, c varchar(20),

                      id bigint not null primary key);

insert into MyTable values (null, 10, 'Have fun', 99);

Listing 12.4. Java code for the INSERT statement in Listing 12.3

DataOutputStream dout = new DataOutputStream(byteArrayOutStrm);

// The dirty byte

dout.writeByte(0);



// 'a' is null, no data follows

dout.writeBoolean(true);



// 'b', not nullable

// So there is no null indicator

dout.writeInt(10);



// 'c' is nullable, but not null

dout.writeBoolean(false);

dout.writeUTF("Have fun");



// 'id' not nullable

dout.writeLong(99);

The following code (Listing 12.5) demonstrates how to iterate through rows, delete a row, and read out data in a FastRecordStore.

Listing 12.5. Browse the FastRecordStore

  TableMetaData rs = ((MIDPISync)isync).getTableMetaDataByName(sName);

  int numCols = rs.getNumCols();

  FastRecordStore rms = FastRecordStore.openRecordStore(sName, false);

  Index index = new Index(rms, rs);

  FastRecordEnumeration enum = rms.enumerateRecords(null, null, false);



  // Iterate through rows

  while (enum.hasNextElement()) {

    int id = enum.nextRecordId();

    int recSize = rms.getRecordSize(id);

    byte data = new byte[recSize];

    recSize = rms.getRecord(id, data, 0);



    // Example: delete a row

    if (id == rowToDelete) {

      data[0] = ISync.ROW_DELETED;

      index.updateRecord(id, data, recSize);

      continue;

    }



    // Read out each field for each row

    ByteArrayInputStream bin = new ByteArrayInputStream(data);

    DataInputStream din = new DataInputStream(bin);

    din.readByte(); // dirty byte



    for (int c = 0; c < numCols; c++) {

    int type = rs.getType(c);

    boolean isNullable = rs.isNullable(c);

    boolean ind = false;

    if (isNullable) ind = din.readBoolean();

    if (ind) continue;

    switch (type) {

      case VARCHAR:

        strval = din.readUTF();

break;

      case INTEGER:

        intval = din.readInt();

break;

      // more ...

    }

  }

}