Lost your JAR files?
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A JAR file is an archive file based on the famous ZIP file format and has the potential to hold a big number of files into one. JAR files often store a wide range of small data, such as CLASS files, a manifest file and application resources (as in sound clips, images, security certificates, and directories).
Cellphone devices with Java availability apply this technology to store game files, web browsers and add-ons. JAR files can easily contain hundreds or thousands of pieces into one single compressed file, so they are easy to share, easy to transfer.
What Is a JAR File?
By definition, nowadays they’ve considered another type of archiving tool but early on, they developed to make Java applets and their requisite components, downloadable for a browser in only one HTTP transaction. Therefore, the need to open a new connection for each item was eliminated.
This led to a speedy process as the applet could be loaded onto a web page and function much faster. Not to mention reducing the file size which was another time-saving factor itself. Besides, the digital signature created by the applet’s author for every single entry in a JAR file is an attractive feature that allows origin authentication possible.
1. JAR Files Attractive Features
- A JAR file is based on a zip archive.
- This archive format can handle class, audio and image files stored in one place.
- JAR file is the only cross-platform archive format.
- It is Backward-compatible with applet code.
- Written in java, it is an open standard and fully extendable.
- Perfect for packaging pieces of a java applet.
- It contains a manifest file and potentially signature file.
2. Difference Between JAR and WAR Files
Both JAR and WAR files are archive format, though there are obvious differences between them:
Comparison Parameters |
JAR File |
WAR File |
| Extension | JAR file has the .jar extension | WAR file has the .war extension. |
| Abbreviation | Stands for Java Archive | Stands for Web Application Resource or Web Application Archive |
| Types of Files and Applications | JAR files package many files into one to use as a library, plugin, and so on. It allows Java Runtime Environment (JRE) to deploy a complete application of the classes and the associated resources in one single request. | WAR files' only usage is allowing testing and deploying a web application easily. |
| Structure | Structurally, a JAR file can be very diverse. | A WAR file comes with a predefined structure with WEB-INF and META-INF directories. |
| Necessities | If you build a JAR file as executable without using additional software, you’re able to run a JAR from the command line. | To execute a WAR, you’ll require a server. |
| Formats Used | Any format | Servlet |
| Contains | It contains compiled Java source code, manifest file, XML-based configuration data, JSON-based data files, images and audio. | It consists of servlet, JSP,XML, HTML, CSS and JavaScript files. |
How to Create and Edit a JAR File?
Here is the basic format of the command for creating a JAR file:
- jar cf jar-file input-file(s)
- The "c" option suggests that you want to "create" a JAR file. The "f" option means that you want the output to go to a file rather than to stdout.
- The "c" and "f" can appear in either order but without any space between them.
- "Jar-file" is the name you are choosing for your JAR file which can be any other name. JAR filenames commonly have a .jar extension.
- This command will generate a JAR file and place it in the current directory. It also creates a default manifest file for the JAR archive.
Video Tutorial on How to Create Executable Jar File in Eclipse IDE
For editing a JAR file:
While .txt contents of JAR files can be easily opened with Notepad, handling your files manually can result in losing precious data. If you want to edit a JAR file without damaging it, install dedicated software. Currently, several JAR editors are available online, but it might take a while to find the right fit.
Note: Make sure always have a copy of your file beforehand.
How to Open a JAR File?
JAR files are ZIP compressed, thus to see their contents, various types of file decompressors are usable including 7-Zip, RARLAB WinRAR and WinZip (Windows), WinZip Mac (Mac), and PeaZip (Linux, macOS, and Windows).
Extraction with these programs typically goes like this:
- First right-click on the file, then select the "Open with" option and pick the default program.
- Click the browse button in the "Open With" window to launch the File Explorer window.
- Afterward, find the .exe file for the software you want as the default program to open your JAR files.
- "Jar-file" is the name you are choosing for your JAR file which can be any other name. JAR filenames commonly have a .jar extension.
- This command will generate a JAR file and place it in the current directory. It also creates a default manifest file for the JAR archive.
Note: Once you extracted your JAR files, simply click on them, to view the inside files. Most data are text files, however additional software to view others might be needed.
How to Run a JAR File?
Usually, to run a JAR file, you must have the Java Runtime Environment (JRE) installed. With JRE, all you need to do is double-click on the file’s name. However, this method only works for executable files, otherwise, at best you can only view the files.
Windows:
JRE is commonly installed on Windows, so you can open a JAR file simply by double-clicking on them. Although as we said not all JAR files are executables and easy to open.
Mac:
After double-clicking JAR files, on a Mac, “Apple Jar Launcher” (a macOS program) sends the JAR file to JRE, or JVM, eventually runs the file.
Cellphones:
Some mobile devices have JRE built-in by default or you can just install it. Afterward, you can open Java applications in web browsers such as Firefox, Safari, and Edge (except for Chrome).
How to Repackage a JAR File?
JAR repacking process can be tricky due to the folder structure. To repack a JAR file, continue as below:
- First, remove the old .jar: rm JAR_NAME.jar
- Go inside the folder: cd JAR_NAME
- Pack the jar referencing the parent folder: jar cf ../JAR_NAME.jar *
In the end, you'll have the JAR_NAME.jar in the parent folder, where the original file was unpacked from.
How to Convert a JAR File?
1. Converting with decompilers:
Using Java decompilers, you can decompile the CLASS files in your JAR files. For that to happen, you are only required to upload the file and choose the decompiler.
2. Converting JAR to APK:
There is an urgent need for JAR to APK file conversion if you decided to use a Java application on Android. That’s why you should run the file in an Android emulator, that automatically creates an APK file for you. Although to get a Java program on Android, it is much easier to compile the APK from the source code.
3. Converting JAR to WAR:
With programming applications like Eclipse, you can make executable JAR files. However, you can’t convert a JAR file to a WAR file directly. Bear in mind that a WAR file’s structure is different from a JAR file. In that regard, just build a WAR, then add the file directory into the lib. Then you’ll get access to the JAR file’s components.
4. Converting JAR to ZIP:
It is a simple trick for opening jar files. You can rename the file extension from .jar to .zip, making a pseudo-zip that is recognizable by programs like 7-Zip or PeaZip.
How to Recover a JAR File?
Like other archive formats, JAR files are delicate and you need to handle them carefully so as not to corrupt them. To recover unsaved or deleted JAR files, the main procedure is essentially the same as in other file formats. There is a recommended recovery protocol to follow when encountering lost data:
- Don't add new data to your device containing JAR files in need of recovery.
- The recovery process must be the first thing you do.
- Use the best tools for recovery from the beginning, because every failure means lessening your chance of full recovery.
Recover a JAR File with Wondershare Recoverit:
Wondershare Recoverit is famous worldwide software, dedicated to restoring lost data with a wide range of formats, and a very effective way of bringing back deleted JAR files. This program helps you fast, in only 3 steps:
Step 1 Select a location where you lost JAR files
Select a hard disk drive where you lost your JAR files, click "Start" to scanning lost JAR files.
Step 2 Scan the hard disk drive to search lost files
Recoverit will start an all-around scan. Usually, it will take a few minutes to finish the scanning. Sometimes, a few hours are required if many large-sized files are present.
Step 3 Preview and recover JAR files
After the scan, you can find JAR files from "Archive" item on the "File Type". Before you recover, you can preview all the file names contained in the recoverable JAR file. Then check and recover them by clicking the "Recover" button.
Conclusion
In this brief, we reviewed in detail what a JAR file is, and its obvious differences from a WAR file. We also summarized how to create, edit, run, repackage, convert and recover a JAR file, eager to offer a comprehensive insight to enthusiast users.
FAQs
What does JAR stand for?
JAR stands for Java Archive, and used for storing Java programs and games, compressing them into a single file.
What program is used to open a JAR file?
WinZip and PeaZip are among the programs that both Windows and Mac users can use to open JAR files. However, to run a JAR file, Windows users can use JRE (Java Runtime Environment) and Mac users can use Apple Jar Launcher.
Does JAR and WAR formats have the same application?
No. WAR files' only usage is allowing testing and deploying a web application easily. On the other hands, JAR files package many files into one to use as a library, plugin, and so on.
How to recover a JAR file?
Using third-party software is the most valid approach for bringing back your lost CAB files. In this case, our recommendation is Wondershare Recoverit data recovery software.
