What is .jar?
.jar (Java Archive) is a ZIP-based package format used to bundle compiled Java bytecode (.class files), resources, and metadata into a single file. JARs are used for Java libraries, command-line tools, desktop apps, and components that run on the Java Virtual Machine (JVM).
This quick guide explains when to use .jar files, how to open them on any device, and how to share them instantly with FileXhost.
When to use .jar files
- You are distributing a Java library or reusable component.
- You want to ship a self-contained Java CLI or desktop application.
- You are packaging code and resources for use on the JVM or in application servers.
- You need a standard way to deliver Java artifacts between services, build systems, or repositories.
How to open .jar files
JAR files can be executed with the Java Runtime (`java -jar file.jar`) when they contain an appropriate manifest specifying the main class. They can also be opened as ZIP archives using archive tools or IDEs to inspect contained classes, resources, and metadata. Build tools like Maven, Gradle, and IntelliJ IDEA treat JARs as first-class artifacts for dependencies and packaging. When you upload JAR files to FileXhost, they can be shared as downloadable builds for teammates, CI/CD systems, or users.
Algorithm details
JAR files follow the standard ZIP file structure with additional metadata in the META-INF directory, including the MANIFEST.MF file. The manifest can declare the main entry point class, classpath information, and metadata such as version, vendor, and capabilities. Inside the archive, compiled .class files contain JVM bytecode produced by Java or other JVM languages like Kotlin and Scala.
Browser & platform support
- Desktop: Browsers download JAR files as binaries; they do not execute them directly. Historically, Java applets used JARs in browsers, but this model is now deprecated.
- Mobile: Mobile platforms do not run standard JAR files directly; Android uses APK/AAB formats instead of plain JARs.
- OS: Operating systems can associate JAR files with the Java Runtime for double-click execution when properly configured, but this depends on installed Java and OS settings.
Format comparison
| Feature | Details |
|---|---|
| JAR vs WAR | WAR files are specialized JARs for web applications, containing web.xml, JSPs, and web resources deployed to application servers. |
| JAR vs ZIP | JAR builds on top of ZIP by adding Java-specific metadata such as the manifest and, optionally, signatures. |
| JAR vs JMOD | JMOD is a module format introduced with Java 9 for packaging Java modules; JAR remains the common format for libraries and applications. |
| JAR vs Native Binary | JARs require a JVM to run, while native binaries execute directly on the OS; tools like GraalVM can ahead-of-time compile JAR-based apps to native images. |
How to create jar files
- Build Tools: Use Maven, Gradle, or Ant to compile Java code and package it as a JAR.
- JDK Tools: Use the `jar` command-line tool from the JDK to create or update archives manually.
- IDEs: Export Java projects as JARs from IDEs like IntelliJ IDEA, Eclipse, or NetBeans.
- CI/CD Pipelines: Automated build pipelines produce JAR artifacts for deployment and distribution.
How to convert jar files
- FileXhost: Upload JAR artifacts to FileXhost to share builds and libraries with collaborators or downstream systems.
- Archive Tools: Open JARs with ZIP utilities to extract or replace resources without changing code.
- Repackaging: Use build tools to repackage JARs into shaded or fat JARs that include dependencies.
- Native Images: Use tools like GraalVM native-image to compile JAR-based applications into platform-specific binaries.
Advantages & disadvantages
Advantages
- Standard format for Java libraries and applications on the JVM
- ZIP-based, easy to inspect, compress, and transport
- Integrates seamlessly with Maven Central and other artifact repositories
Disadvantages
- Requires a compatible Java Runtime Environment to execute
- Managing dependency versions across many JARs can be complex
- Not directly executable on platforms without installed Java or a JVM distribution
Tools & software
Build & Dependency Tools
Maven, Gradle, Ant, sbt
IDEs
IntelliJ IDEA, Eclipse, NetBeans
Runtime & Utilities
Java Runtime Environment (JRE), Java Development Kit (JDK), jar CLI tool
Frequently asked questions
How do I run a JAR file?
If the JAR is executable and has a Main-Class defined in its manifest, use `java -jar file.jar`. Otherwise, add it to your classpath and run the appropriate main class via the Java command.
Can I open a JAR file without Java?
You can inspect a JAR with any ZIP-capable tool, but you need a JVM or compatible runtime to execute the bytecode it contains.
What is a fat or shaded JAR?
A fat or shaded JAR packages your application code together with its dependencies into a single JAR, simplifying distribution at the cost of a larger file size.
Is a JAR file safe to run?
JARs can contain arbitrary code. Only run JAR files from trusted sources and consider using tools like code signing, checksums, or sandboxed environments to verify integrity and security.
Technical specs
- File type
- Executable
- Extension
- .jar
- MIME type
- application/java-archive, application/x-java-archive, application/octet-stream
- Compression
- Uncompressed
- Max file size on FileXhost
- Up to 25 MB per file on the free plan and up to 1 GB on Pro FileXhost accounts.
Share .jar files instantly
Upload your .jar file to FileXhost to get a clean, shareable URL in seconds. View the file in a modern browser, protect access with optional settings, and let others download it without any confusing ads or cluttered file pages.
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