Java Application Deployment

For desktop computers, there are different ways to install an application. In order to install new software properly, the user needs to insert the medium containing the software into the computer system and start the installation. It is common practice for a wizard to guide the user through a predefined procedure for installing the software. Software or software updates can be downloaded from the Internet using a Web browser as well. When the software is downloaded, the installation usually needs to be initiated by the user or system administrator.

For limited devices, software installation is different. PDA software is usually installed through a connection to the desktop computer; for example, a serial cable or an Infrared Data Association (IrDA) connection. The installation is initiated on the desktop computer.

Using devices that provide a wireless Internet connection, it seems quite straightforward to download applications from the Internet directly to the device without going through a desktop PC.

A downloaded application must be saved in the device's storage, installed, and inspected by the platform. Applications of that kind can be launched and later deleted from the device when the user no longer needs it. A mechanism covering these issues is called Java Application Manager (JAM).

JAM Implementation

The JAM reference implementation is generally described in the CLDC reference implementation (RI) by SUN. In the RI documentation, the JAM is divided into the following steps:

  • Installing the application to the device

  • Executing the application

  • Updating the installed application

  • Deleting the application from the target device

In order to use the JAM mechanism, the KVM version that is used should support this feature. The RI does not state how the implementation platform has to support browsing of descriptor files in the Internet, for example, but describes all the information that needs to be included in a descriptor file. A complete specification of how JAM should be implemented is given in the J2ME profiles.

The Descriptor File

The Java Application Descriptor (JAD) file is downloaded into the device and analyzed by the platform. According to the information that is stored in the descriptor file, the platform decides whether the related JAR file containing the application classes should be downloaded or rejected. The association between the descriptor file and the JAR file is shown in Figure 2.2.

Figure 2.2. The association between JAD and JAR file including a KVM application.


A JAD descriptor file consists of readable text including name-value pairs describing properties of its associated Java application. Each line of the descriptor file holds one attribute, where an attribute consists of a name and a value, separated by a colon. The following attribute describes the file size of the application JAR file:

Jar-File-Size: 2123

The application developer is responsible for maintaining the JAD and JAR files. Additionally, the descriptor file and the associated JAR file must be placed on the same Web site.

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