What are Fat JARs and When Should You Use Them?

Understanding Fat JARs: A Comprehensive Guide

When it comes to Java application distribution, the term "fat JAR" often arises. But what does it truly mean? Let's delve into the different types of JARs to gain a clear understanding.

Types of JARs

Java Archive (JAR) files are essential for packaging Java applications for deployment. There are several variants of JARs, each with its own purpose:

• Skinny JAR: Includes only the code written by the developer.
• Thin JAR: Contains the application code along with its direct dependencies (e.g., libraries).
• Hollow JAR: An "application server" that houses the components necessary to run an application but lacks the application itself.
• Fat JAR (also known as Uber JAR): Combines the application code, direct dependencies, and the necessary components to execute the application independently.

Specifics of Fat JARs

Fat JARs are particularly useful when deploying applications to environments that lack a traditional application server. They contain everything required to run the application, including the necessary Java runtime environment (JRE), libraries, and other resources. This makes them ideal for standalone deployment on systems where installing a separate application server is impractical or undesirable.

Benefits of Fat JARs

Fat JARs offer several advantages:

• Portability: They can be deployed to any system with the JRE installed.
• Simple Deployment: The entire application is contained within a single file, making deployment a breeze.
• Reduced Footprint: Fat JARs typically have a smaller footprint compared to deploying an application to a full-fledged application server.

Considerations

While Fat JARs come with advantages, they also have potential drawbacks:

• Larger File Size: Fat JARs can grow considerably in size due to the inclusion of all necessary components.
• Maintenance: Maintaining Fat JARs can be more challenging as updates may require rebuilding and redeploying the entire package.

In summary, a fat JAR is a complete package that encompasses the application code, dependencies, and execution environment, allowing for standalone deployment. Whether to opt for a fat JAR or another type of JAR depends on the specific application requirements, deployment scenario, and infrastructure available.

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