What is a JAR File and How To Open One

Usually, opening a jar is a matter of brute strength or tapping the edge of the lid against the kitchen counter. In the case of JAR files, it is a little more involved.

So what is a JAR file and how can you open it? Follow along in this article to learn more.

What is a JAR File?

A .jar file is a Java package file. It is similar to a ZIP file in Windows where a collection of files and resources are collected into a single file for easy transport or installation. The package is usually self-contained and will include everything required to make the package perform its intended use.

Java is completely different from JavaScript and all they really have in common is the name. Java is a programming language while JavaScript is primarily a web programming language that came out around the same time and interacts with HTML and CSS. They are not the same thing, this piece is only concerned with Java and not JavaScript.

Java is a programming language invented by Oracle in the 90s and has been around for over 20 years. It has two parts, a runtime that acts like an executable on your computer and a plug-in that works in a browser to perform actions.

To run Java files on your computer you need the Java Runtime Environment (JRE) installed in order to be able to open and run .jar files. Java runtimes are small packages written in Java that often work with a browser or application to perform a task like playing a video.

Is Java Insecure?

Java doesn’t have a very good reputation as it is thought to be full of security holes, this is only half true. The Java runtime is fine and does not have any significant vulnerabilities. The Java plug-in on the other hand does have issues. According to most security experts, the Java browser plug-in should only ever be used when absolutely necessary.

Java powers phones, computers, IoT devices, games, enterprise applications and all manner of things. You would be amazed at just how widespread Java is, which is also why it seems so insecure. The more prolific an OS, app, or programming language is, the more likely it is to be targeted for potential exploits and vulnerabilities, just ask Android, Microsoft, and Facebook.

If you want to get into programming or want to use Java applications on your computer, they are usually safe. Like any program, it depends entirely on the skill of the programmer. Java itself, as a programming language is not unsafe. Only the browser plug-in version of Java is regarded as unsafe.

Fortunately, we don’t use the Java plug-in to open .jar files. We use the Java Runtime Environment.

How to Open a JAR File

To open and use a .jar file, you need to have the Java Runtime Environment installed on your computer.

1. Download and install the JRE directly from Java here.
2. Select your .jar file and select open or double click it.

What happens next depends on how the .jar file has been made up. If it is an executable file, the program will execute like a Windows.exe file. Whatever the file was designed to do will happen once you open or double click. If the .jar file is a library you will be able to open it and browse its contents.

You can see if your compression tool of choice can extract the .jar file too if you don’t want to install the JRE. This will only work if the .jar file is a library file, which you won’t know until you try.

1. Right click your .jar file and select Open with.
2. Then, select your compression tool of choice, WinZip, 7-zip, WinRAR or whatever.
3. Allow the file to be extracted and browse the contents.

If you use Windows 10, you can choose how to open .jar files.

1. Click the Windows Start button and select Settings.
2. Now, select Apps.
3. Then, click on Default apps.
4. Next, scroll down and select Choose default apps by file type.
5. Scroll down to .jar and select the box to the right.
6. Finally, select the Java Platform or your compression tool of choice.

From now on, every time you double click a .jar file, it should open using the program you selected. Remember, .jar files come in two types, executables and libraries. If you select a compression tool such as WinZip as your default app and the .jar file is an executable, it will not execute but open. This may not be the behavior you want.

You can also open .jar files using PowerShell.

1. Open the folder containing the .jar file.
2. Then, hold down Shift and right-click in an empty space in that folder.
3. Now, select Open a PowerShell Windows here.
4. Type ‘java -jar [filename].jar’, without quotes, and hit Enter. Where you see [filename], change that to the actual name of the file.

If you have the JRE installed, the command will open the .jar file as you would expect it to.

Opening and Using Jar Files

Using .jar files isn’t complicated at all. As with most things on a computer, you just need the write app or command to run them. So that’s the basics of JAR files and how to open them.

Hope it helps! Feel free to share any thoughts or comments below.