What is an uber jar?

Question

I am reading Maven documentation and came across the name uber-jar.

What does an uber-jar mean and what are its features/advantages?

Answer 1

ubar jar is also known as fat jar i.e. jar with dependencies.
There are three common methods for constructing an uber jar:

1. Unshaded: Unpack all JAR files, then repack them into a single JAR. Works with Java's default class loader. Tools maven-assembly-plugin
2. Shaded: Same as unshaded, but rename (i.e., "shade") all packages of all dependencies. Works with Java's default class loader. Avoids some (not all) dependency version clashes. Tools maven-shade-plugin
3. JAR of JARs: The final JAR file contains the other JAR files embedded within. Avoids dependency version clashes. All resource files are preserved. Tools: Eclipse JAR File Exporter

for more

Answer 2

Paxdiablo's definition is really good.

In addition, please consider delivering an uber-jar is sometimes quite useful, if you really want to distribute a software and don't want customer to download dependencies by themselves. As a draw back, if their own policy don't allow usage of some library, or if they have to bind some extra-components (slf4j, system compliant libs, arch specialiez libs, ...) this will probably increase difficulties for them.

You can perform that :

• basically with maven-assembly-plugin
• a bit more further with maven-shade-plugin

A cleaner solution is to provide their library separately; maven-shade-plugin has preconfigured descriptor for that. This is not more complicated to do (with maven and its plugin).

Finally, a really good solution is to use an OSGI Bundle. There is plenty of good tutorials on that :)

For further configuration, please read those topics :

• Should you provide dependent libraries in client jar?
• Best practices in building and deploying Clojure applications: good tutorials?

Answer 3

The different names are just ways of packaging java apps.

Skinny – Contains ONLY the bits you literally type into your code editor, and NOTHING else.

Thin – Contains all of the above PLUS the app’s direct dependencies of your app (db drivers, utility libraries, etc).

Hollow – The inverse of Thin – Contains only the bits needed to run your app but does NOT contain the app itself. Basically a pre-packaged “app server” to which you can later deploy your app, in the same style as traditional Java EE app servers, but with important differences.

Fat/Uber – Contains the bit you literally write yourself PLUS the direct dependencies of your app PLUS the bits needed to run your app “on its own”.

Source: Article from Dzone

Reposted from: https://stackoverflow.com/a/57592130/9470346

Answer 4

A self-contained, executable Java archive. In the case of WildFly Swarm uberjars, it is a single .jar file containing your application, the portions of WildFly required to support it, an internal Maven repository of dependencies, plus a shim to bootstrap it all. see this

Answer 5

According to uber-JAR Documentation Approaches: There are three common methods for constructing an uber-JAR:

Unshaded Unpack all JAR files, then repack them into a single JAR. Tools: Maven Assembly Plugin, Classworlds Uberjar

Shaded Same as unshaded, but rename (i.e., "shade") all packages of all dependencies. Tools: Maven Shade Plugin

JAR of JARs The final JAR file contains the other JAR files embedded within. Tools: Eclipse JAR File Exporter, One-JAR.

Answer 6

For Java Developers who use SpringBoot, ÜBER/FAT JAR is normally the final result of the package phase of maven (or build task if you use gradle).

Inside the Fat JAR one can find a META-INF directory inside which the MANIFEST.MF file lives with all the info regarding the Main class. More importantly, at the same level of META-INF directory you find the BOOT-INF directory inside which the directory lib lives and contains all the .jar files that are the dependencies of your application.