Create a Java REST Application JAR without using Gradle/Maven?

Question

Using Gradle I know the way to create a fat jar that is ran in Spring Boot embedded Tomcat Server is:

1. Gradle clean build bootRun

I am wondering though how to create a fat jar manually using only command line in order to create and run the same exact same jar as above?

I know to create an run a very simple java application it is:

javac myApp.java
java myApp

But how to create a fat jar that contains all the projects dependencies and then run it? Without using a tool like gradle or maven ?

Answer 1

Basically, you could just jar up your class(es) with a manifest that specifies where main() is. For a classic "Hello World" class named Hello, the manifest would look like this...

Manifest-Version: 1.0
Main-Class: Hello
Class-Path: .

You would build it like this...

$ jar cvmf MANIFEST.MF Hello.jar Hello.class 
added manifest
adding: Hello.class(in = 415) (out= 285)(deflated 31%)

and execute it like this...

$ java -jar Hello.jar
Hello World

You could do the same with a more complex app with jar dependencies (including an embedded Tomcat), but you would need to unzip all the dependent jars into a directory, and include that in the jar. A build tool, like Gradle, can make that easier.