Fundamentals of Java ME MIDP Programming : Non-GUI APIs in MIDP

1. Record Management System

MIDP provides a simple record-based persistent storage mechanism known as the Record Management System (RMS). It's a package that allows the MIDlet application to store persistent data within a controlled environment, while maintaining system security. It provides a simple, non-volatile data store for MIDlets while they are not running. The classes making up the RMS are contained in the javax.microedition.rms package.

Essentially, the RMS is a very small, basic database. It stores binary data in a Record within a RecordStore. MIDlets can add, remove and update the records in a RecordStore. The persistent data storage location is implementation-dependent and is not exposed to the MIDlet. A RecordStore is, by default, accessible across all MIDlets within a suite, and MIDP extends access to MIDlets with the correct access permissions from other MIDlet suites. When the parent MIDlet suite is removed from the device, its record stores are also removed, regardless of whether a MIDlet in another suite is making use of them.

Here is a short example of how to use RMS for writing and reading persistent data from the device:

// saving data to RMS
public int saveToStore(byte[] data) {
  int recordID = 0;
  try {
    RecordStore store = RecordStore.openRecordStore("ImageStore", true);
    recordID = store.addRecord(data, 0, data.length);
    store.closeRecordStore();
  }
  catch(RecordStoreException rse) {
    rse.printStackTrace();
  }
  return recordID;
}
// reading data from RMS
public byte[] loadFromStore(String storeName, int recordID) {
  byte[] data = null;
  try {
    RecordStore store = RecordStore.openRecordStore("ImageStore", false);
    data = store.getRecord(recordID);
    store.closeRecordStore();
  }
  catch(RecordStoreException rse) {
    rse.printStackTrace();
  }
  return data;
}

					  

2. Media API

MIDP includes the Media API which provides limited, audio-only multimedia. It is a subset of the optional and much richer JSR-135 Mobile Media API, which currently ships on most Symbian OS phones.

The MIDP Media API provides support for tone generation and audio playback of WAV files if the latter is supported by the underlying hardware. Since MIDP is targeted at the widest possible range of devices, not just feature-rich smartphones, the aim of the Media API is to provide a lowest common denominator of functionality suitable for the capabilities of all MIDP devices.

3. Networking – Generic Connection Framework

CLDC has defined a streamlined approach to networking, known as the Generic Connection Framework (GCF). The framework seeks to provide a consistent interface for every network connection between the MIDP classes and the underlying network protocols. It doesn't matter what kind of connection is being opened; the interface remains the same. For instance, if you're opening a socket or an HTTP connection, you are still going to use the same Connector.open() method. MIDP has support for many protocols, although HTTP and HTTPS are mandatory. Java ME on Symbian OS also supports other optional protocols, such as sockets, server sockets and datagrams.

4. Push Registry