JAR (Java Archive) is a platform-independent file format that allows many files to be combined into a single compressed file. The JAR files created for J2EE applications are EAR files (Enterprise JAR files).
The JAR file format is based on the popular ZIP file format. Unlike ZIP files, JAR files are used not only for compression and distribution, but also for deploying and packaging libraries, components, and plug-in programs, and can be used directly by tools like compilers and the JVM. Special files, such as manifests and deployment descriptors, are included in JARs to instruct tools on how to handle a particular JAR.
A JAR file can be used
□ for distributing and working with libraries
□ as a building unit for applications and extensions
□ as a deployment unit for components, applets, or plug-in applications
□ as a deployment unit for components, applets, or plug-in programs
□ for packaging auxiliary resources associated with components
The JAR file format offers a number of advantages and features, many of which are not provided by traditional compression formats such as ZIP or TAR. They include:
- Security.
The contents of a JAR file can be digitally signed. This allows tools that recognize the signature to selectively grant you software security privileges that other files cannot, and to detect whether the code has been tampered with.
- Reduce download time.
If an applet is bundled into a JAR file, the browser can download the applet's class files and associated resources in a single HTTP transaction, rather than opening a new connection for each file.
- Compression.
The JAR format allows you to compress files for more efficient storage.
- Transfer platform extensions.
The Java Extensions Framework provides a way to add functionality to the core Java platform, packaged in JAR files (Java 3D and JavaMail are examples of extensions developed by Sun).
- Package sealing.
Packages stored in JAR files can optionally be sealed to enhance version consistency and security. Sealing a package means that all classes in the package must be found in the same JAR file.
- Package version control.
A JAR file can contain data about the files it contains, such as vendor and version information.
- Portability.
The mechanisms for handling JAR files are a standard part of the core Java platform API.
JAR in cell phone e-books
JAVA cell phone e-books are generally formatted as JAR and JAD, where the JAD file is a description file that describes the information in the jar file. Some cell phones do not support direct reading of JAR (which is caused by the security policy of the phone), then you need a JAD file. Such phones are only in the minority. java runs on top of the java virtual machine, also known as the JVM, and many low-end models can also support java, so it is destined to be quite a wide range of java format. Because java can provide rich interactive behavior, so in the support of graphics, multimedia, do the most excellent, in addition, the reader and the text is packaged together (jar), so only need to install can read, do not need to install another reader or download e-books.
Compared to previous e-book reading devices, the biggest advantage of a cell phone is that it is convenient and portable. And its shortcomings are the screen reading limitations, as well as less readable resources. The current cell phone design, showing the size of the polarization of the situation, a trend is more and more small, take the road of dexterity, delicate, another trend is more and more large, take the road of rich features and perfect, close to the PDA, there is no doubt that only this trend is suitable for the development of cell phone e-books. For the majority of users at present, each screen displays a few lines of the phone to read tens of thousands of words of e-books, there is still a great deal of inconvenience.
At present, the software that can produce e-books has mBookMaker developed by Palm Books, and so on, and those who want to convert their own text into e-books may want to try it.
Due to the different hardwares of different brands of cell phones, not all cell phones can support mobile eBooks. Comparatively speaking, Nokia, Motorola and other brands of cell phones, as long as they can support JAVA, then there must be a suitable e-book.
But there are some already very good JAR reading software, you can directly read TXT.HTML.UMD and other formats of the novel. For example, Anyview 3.0 is a very good cell phone e-book software
The production of cell phone e-books require a certain degree of patience, if you do not have the patience, you can also go directly to some of the cell phone e-books that have been done to provide the download site: