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Gradle + Eclipse : use class from existing project in a new project

I know there are a lot of questions that seem similar. I have also spent a few hours getting to grips with Gradle multiprojects. But I still don't understand what the best course of action is here. Incidentally I am using Groovy as my coding language, but explanations referencing Java would be just as good.
I have developed an Eclipse Gradle project, "ProjectA", which in particular has a class, IndexManager, which is responsible for creating and opening and querying Lucene indices.
Now I am developing a new Eclipse Gradle project, "ProjectB", which would like to use the IndexManager class from ProjectA.
This doesn't really mean that I would like both projects to be part of a multiproject. I don't want to compile the latest version of ProjectA each time I compile ProjectB - instead I would like ProjectB to be dependent on a specific version of ProjectA's IndexManager. With the option of upgrading to a new version at some future point. I.e. much as with the sorts of dependencies you get from Maven or JCenter...
Both projects have the application plugin, so ProjectA produces an executable .jar file whose name incorporates the version. But currently this contains only the .class files, the resource files, and a file called MANIFEST.MF containing the line "Manifest-Version: 1.0". Obviously it doesn't contain any of the dependencies (e.g. Lucene jar files) needed by the .class files.
The application plugin also lets you produce a runnable distribution: this consists of an executable file (2 in fact, one for *nix/Cygwin, one for Windows), but also all the .jar dependencies needed to run it.
Could someone explain how I might accomplish the task of packaging up this class, IndexManager (or alternatively all the classes in ProjectA possibly), and then including it in my dependencies clause of ProjectB's build.gradle... and then using it in a given file (Groovy or Java) of ProjectB?
Or point to some tutorial about the best course of action?

One possible answer to this which I seem to have found, but find a bit unsatisfactory, appears to be to take the class which is to be used by multiple projects, here IndexManager, and put it in a Gradle project which is specifically designed to be a Groovy library. To this end, you can kick it off by creating the project directory and then:
$ gradle init --type groovy-library
... possible to do from the Cygwin prompt, but not from within Eclipse as far as I know. So you then have to import it into Eclipse. build.gradle in this library project then has to include the dependencies needed by IndexManager, in this case:
compile 'org.apache.lucene:lucene-analyzers-common:6.+'
compile 'org.apache.lucene:lucene-queryparser:6.+'
compile 'org.apache.lucene:lucene-highlighter:6.+'
compile 'commons-io:commons-io:2.6'
compile 'org.apache.poi:poi-ooxml:4.0.0'
compile 'ch.qos.logback:logback-classic:1.2.1'
After this, I ran gradle jar to create the .jar which contains this IndexManager class, initially without any fancy stuff in the manifest (e.g. name, version). And I put this .jar file in a dedicated local directory.
Then I created another Gradle project to use this .jar file, the critical dependency here being
compile files('D:/My Documents/software projects/misc/localJars/XGradleLibExp.jar' )
The file to use this class looks like this:
package core
import XGradleLibExp.IndexManager
class Test {
public static void main( args ) {
println "hello xxx"
Printer printer = new Printer()
IndexManager im = new IndexManager( printer )
def result = im.makeIndexFromDbaseTable()
println "call result $result"
}
}
class Printer {
def outPS = new PrintStream(System.out, true, 'UTF-8' )
}
... I had designed IndexManager to use an auxiliary class, which had a property outPS. Groovy duck-typing means you just have to supply anything with such a property and hopefully things work.
The above arrangement didn't run: although you can do build and installdist without errors, the attempt to execute the distributed executable fails because the above 6 compile dependency lines are not present in build.gradle of the "consumer" project. When you put them in this "consumer" Gradle project's build.gradle, it works.
No doubt you can add the version to the generated .jar file, and thus keep older versions for use with "consumer" projects. What I don't understand is how you might harness the mechanism which makes the downloading and use of the dependencies needed by the .jar as automatic as we are used to for things obtained from "real repositories".
PS in the course of my struggles today I seem to have found that Gradle's "maven-publish" plugin is not compatible with Gradle 5.+ (which I'm using). This may or may not be relevant: some people have talked of using a "local Maven repository". I have no idea whether this is the answer to my problem... Await input from an über-Gradle-geek... :)

You should be able to update the Eclipse model to reflect this project-to-project dependency. It looks something like this (in ProjectB's build.gradle):
apply plugin: 'eclipse'
eclipse {
classpath.file.whenMerged {
entries << new org.gradle.plugins.ide.eclipse.model.ProjectDependency('/ProjectA')
}
project.file.whenMerged {
// add a project reference, which should show up in /ProjectB/.project's <projects> element
}
}
These changes may be to the running data model, so they may not actually alter the .classpath and .project files. More info can be found here: https://docs.gradle.org/current/dsl/org.gradle.plugins.ide.eclipse.model.EclipseModel.html
This issue is discussed here: http://gradle.1045684.n5.nabble.com/Gradle-s-Eclipse-DSL-and-resolving-dependencies-to-workspace-projects-td4856525.html and a bug was opened but never resolved here: https://issues.gradle.org/browse/GRADLE-1014

Gradle - one project, multiple packages, multiple jars

I'm asking you about a very basic question but I hope you can find the time to help me:
I'm trying to realise a java-project, that can spit out several different programs which partially have dependencies on other projects of mine.
In order to keep it simple, I want to have all the code in one project, run by Gradle, so if I make changes to a central library (the database connector for example) all the child-programs automatically recieve the changes.
An example could look like this:
project:
program_A
central_library
program_B
output:
program_A.jar (including central library)
program_B.jar (including central library)
Now I'm having serious troubles finding a correct buildscript for this and was wondering if someone here could help me out.
P.S. : Since I'm new to this, if I should realize this through different modules within the Gradleproject instead of different packages in the Gradleprojects sourcefile, feel free to tell me :)

One way to approach this is to have a root project, that holds the three other projects inside of it.
Specify the sub-projects inside its settings.gradle file:
rootProject.name = 'RootProject'
include 'program_A'
include 'central_library'
include 'program_B'
With this in place, program_a can depend on central_library by adding a dependency in its build.gradle:
dependencies {
compile project(':central_library')
}
I have a similar setup in one of my projects, although the "central library" is the root project and the submodules are test environments.

Create a root directory and put each library or program into its own sub-directory.
Create a gradle project in each subproject.
You can for example create a skeleton gradle project by running
gradle init --type=java-library
or
gradle init --type=java-application
Then in the root directory create a gradle multi-module project. Basically
run only
gradle init
and then create a settings.gradle and list all sub-projects there.
This is actually described very well in the gradle documentation:
https://guides.gradle.org/creating-multi-project-builds/

If I understand correctly, what you want to do is, when you change your local projects, you want other projects to see those details. For this you need to publish your projects to some kind of repo, like maven repo. You can do this from command line gradle publishToMavenLocal, or gradle build pTMl. You can also do this in build.gradle file with something like the following:
task sourceJar (type : Jar) {
classifier = constants.extSources
from sourceSets.main.allSource
}
publications {
mavenJava(MavenPublication) {
from components.java
artifact(sourceJar) {
classifier "sources" //classifier = constants.extSources
}
}
}

gradle include library from another project

I have this project setup (in Android AIDE):
|---Project1
| |---App
| |---Lib
|
|---Project2
|---App
I want add project 1 Lib as dependency (or linked source, because i only need to access 1 class from the library) to Project2.
Project2 settings.gradle:
include ':Lib'
project(':Lib').projectDir = new File(settingsDir, '../Project1/Lib')
Project2 build.gradle:
compile project(':Lib')
I am getting the following error:
Project dependency 'Lib' not found.
Is there anything wrong with the folder path? I didn't find any good solution for this problem and i am not very familiar with gradle.
If i would instead link the library source folder to Project2 i tried to add the following lines to the build.gradle (under android section):
sourceSets {
main.java.srcDirs += '/../Project1/Lib/src/main/'
}
I could access the source if i used the full path down to the folder with the class file but with the problem that when i instantiated the class from the Lib in Project2 it gave me the error that the class was not found inside the package.
Do both projects need to have the same package names? What would be the best solution to manage this without having the Library as an standalone library?

Gradle multi project - sharing source code between projects

In a gradle multi project (java), it is possible to share source code so that each project has access to it and compiles against it?
For example, sub projects 'mouse', 'cat', 'dog', containing a single java class in each - Mouse.java Cat.java, and Dog.java respectively. Each of these classes extends Animal.java.
A caveat is that when any given sub-project (e.g, 'mouse') is being built, it has some compile time dependencies defined (from maven central) and it requires that Animal.java gets compiled using those some dependencies. The same goes for the other projects. So, I can't compile and jar up Animal.java and then use that jar as a dependency of the 3 projects. Animal must get recompiled together with the source of the dependent project. The result should be mouse.jar, cat.jar, and dog.jar, each in their respective project build dir (as usual) and each also containing their version of Animal.class.
I understand that the example isn't very intuitive (as Animal should be generic enough to be compiled independently). It's the best I could find to simulate the hard to explain scenario I'm trying to solve.
Is that possible to do in Gradle?
Thank you.

solved this with sourceSets. Added the parent project main source set to the sub projects:
e.g, added to build.gradle of project 'mouse':
sourceSets {
main.java.srcDir project(':animal').sourceSets.main.java
}

Android Studio: add project as library

I want to add this project as library to my project in android studio.
this is what I tried,
I have my project directory as f:/my project/my app/src
and my library in f:/my project/my library/src
I import the module (the library) by going to file > import module > selecting the library
then I got to file > project structure > modules > dependencies tab > select my project > add module dependency apply ok and then done
however when I use the code from the library I get the usual syntax error (the class ... could not be found)
also I noticed this popup (see image)
I am new to android studio or intelliJ, how do I fix this.
Thanks!

Edit the settings.gradle file (in directory f:/my project), it must contains something like this:
include 'my app','my library'
If this file don't exists: create it manually. The settings.gradle contains the list of gradle modules in a multi-module project.
Then you must add the dependency to your library in app. To do so edit the my app/build.gradle and add this line :
dependencies {
compile project(':my library')
}
I also notice that you don't use default structure for your projects (i.e. you put the code in src/ instead of src/main/java) so you will have to overwrite some values of the default fileSet in the build.gradle of your projects. Be sure to have something like this in my app/build.gradle and my library/build.gradle :
android {
sourceSets {
main {
java.srcDirs = ['src']
}
}
}