JAR, WAR & EAR

JAR – Java ARchive
It’s a file format based on the ZIP file format and similar to ZIP format this is also used for aggregating many files (many be of different types) into one aggregate file. This aggregate file will have (.jar) extension. Application development using Java uses JAR files for many useful purposes. One of the most common use is to package all the .class files, image files, and other files required by an Applet into a JAR file, so that the download of a single file will have all the components downloaded at the client machine. Otherwise, we would require those many HTTP Connections to individually download each of the components and this will of course be a very tedious and time-consuming effort. Another popular usage is to bundle all the .class files, and other required component files of a typical subsystem into a JAR file and include that JAR file into the CLASSPATH of another Java application which requires the services of that subsystem. The maintenance and deployment becomes very easier in this case.

Source Code : Running an executable JAR from command-line

Steps : Steps to Create a Jar File

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Intro: jar-The Java Archive Tool

Tutorial: Lesson: Packaging Programs in JAR Files