Creating Java library file with IntelliJ IDEA

Question

I'm trying to create a library which could be used in other projects. I've written one class with several static methods to do some stuff. I wanted to try it out but I am not able to use the imported JAR file.

I have compiled my code as an artifact and took the JAR file from "out" folder and then copied it to another project. After that I went to "Project structure", tab "Libraries" and I pressed the plus button. I've found the JAR file and selected it, afterwards IDEA asked me to specify dependencies so I did, but when I want to use it in code I am not able to do so. It can't even be imported.

Any ideas why it ignores my library? Thanks!

What should I do in order to create a JAR library with IntelliJ IDEA, that is usable in other projects?

Answer 1

You are running into a very common dependency management problem.

IMO the real answer is to use a build system like Maven, Ant, or Gradle (I'd go Gradle myself). What you are trying to do is manual, hard to reproduce, and brittle.

Every time you make a change you will have to go through manual steps to create a new JAR. And you really don't understand your dependencies.

To go all out with best practices you would be to have real build system that publishes to a continuous integration server, which compiles and runs tests. On successful completion of the tests, the JARs are published to an artifact server (Nexus/Artifactory).

The people you are sharing with would consume the JARs via the build system by declaring dependencies on your JAR.

Answer 2

I figured out what my problem was. When I created the library I was trying to make it simple. Too simple, unfortunately. I had a package with a class in it that was compiled into a JAR. Structure shown below:

foo
 |
 |_ MyLib.java 

However in order to use classes from a created JAR library they have to be placed in packages. That means if I have:

foo
 |
 |_bar
 |  |
 |  |_MyInnerLib.java
 |
 |_MyOuterLib.java

I am able to import and use methods from MyInnerLib but MyOuterLib isn't reachable nor importable. This was the error I was making.