Mobile Devices Programming - MIDlet to Servlet Communication

By : Omer Guinko

Published Date : February 18, 2010

1- Introduction

The Java Platform, Micro Edition (Java ME) is essentially a version of Java specially made for mobile devices. This platform consists of a wide variety of applications programming interfaces (API), a virtual machine that executes the generated Java Bycode, and a set of development tools.

Application written in Java ME will run on just about any device that supports the APIs.
To specify the level of functionality that a particular device supports, we must reference two things: the configuration and the profile.

Configurations
A configuration describes the lowest number of libraries and virtual-machine features that must be supported in a device. Currently there are two: Connected Device Configuration (CDC) and the Connected Limited Device Configuration (CLDC)
The configurations and profiles are generally described in terms of their minimum amount of ROM and RAM

Connected Device Configuration
A connected device configuration has, at a minimum, 512KB of read-only memory (ROM) and 256KB of random access memory (RAM).

The CDC is designed for devices like television set-top boxes, car navigation systems, and high-end PDAs.

Connected Limited Device Configuration (CLDC)
The CLDC is designed for devices with 160KB to 512KB of total memory, including a minimum of 160KB of ROM and 32KB of RAM.

Specially, the CLDC targets the minimum hardware requirements and the low-level API in a range of devices. It encompasses mobile phones, pagers, PDAs and other devices with similar size.

Profiles
A profile is layered on top of a configuration, adding the APIs and the specification necessary to develop applications for a specific family of devices.

Mobile Information Device Profile (MIDP)
The MIDP provides a more specific set of hardware requirements for mobile phone devices in the area of the memory, input, display size, display number of colors and networking. It also provides a set of APIs specially for developing mobile phone applications. According to the MIDP2.0 specification (JSR-118), a mobile information device has the following characteristics:

• A minimum of 256KB ROM for the MIDP implementation (this is in addition to the CLDC)
• A minimum of 128KB of RAM for the Java runtime heap
• A minimum of 8KB of nonvolatile writable memory for persistent data
• A screen set of at least 96x54 pixels
• Some capacity for input, either by keypad, keyboard, or touch screen
• Two-way network connection, possibly intermittent

 

2- MIDP Applications

The APIs available to a MIDP application come from packages in both CLDC and MIDP, as shown in Figure 2.1.

Figure 2.1

Optionally device vendors may also supply Java APIs to access device-specific features.

Each device implements some kind of operating system (OS). Layered on top of the device OS is the CLDC (including the JVM) and the MIDP APIs.

MIDP applications use only the CLDC and the MIDP APIs. Device-specific applications may also use Java APIs supplied by the device vendor. Figure 2.2 shows a map of the possibilities.

Figure 2.2