Java Reference
In-Depth Information
PDAP adds a CommConnection and a FileConnection for serial port and file access to the
generic connection framework, which are described in detail in Chapter 6 .
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.
 
 
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