can't figure out how to set up gradle build with nested projects

Question

Since two days I am trying to figure out how to get the following to compile.

I have an android studio project called "Margin", which shall use the library "hbci4java", which in turn uses the project "cryptalgs4java".

The directory structure is as follows:

Margin
+-# app
| +-# build
| +-# libs
| | +-# hbci4java
| |   +-# src
| |   | +-# org/kapott/hbci
| |   | | +-# manager
| |   | | | +-- HBCIHandler.java
| |   | | | +-- ...
| |   | | +-- ...
| |   | +-- ...
| |   |
| |   +-# thirdparty
| |   | +-# cryptalgs4java
| |   |   +-# src
| |   |   +-- build.gradle
| |   |   +-- ...(other files)
| |   |
| |   +-- build.gradle
| |   +-- settings.gradle
| |
| +-# src
| | +-+ main
| | | +-# java
| | | | +-# de/bvs/margin
| | | |   +-# activities
| | | |   |  +-- MainActivity.java
| | | |   |  +-- ...
| | | |   + ...
| | | |
| | | +-- ...
| | +-- ...
| |
| +-- build.gradle
| +-- ...
|
+-# build
+-# gradle
+-- build.gradle
+-- gradle.properties
+-- settings.gradle
+-- ...

The app containing MainActivity compiled well before I added the libs directory structure, and it still does, as long as I don't tell android studio anything about this directory. However, I want to use the hbci4java project within my project. Let's say, I want to create a HBCIHandler object within my Mainactivity.

I know, I have to tell the build system, that it shall use the hbci4java library. But i'm overhelmed by the different gradle files:

I understand that Margin/app/libs/hbci4java/thirdparty/cryptalgs4java/buid.gradle is used to build the cryptalgs4java, when standing alone. It contains the following:

apply plugin: 'java'

repositories {
  mavenCentral()
}

sourceCompatibility = 1.5
compileJava.options.encoding = 'ISO-8859-1'

version = '2.5.13-SNAPSHOT'

sourceSets{
    main {
        java {
            srcDir 'src/java'
        }
        output.classesDir 'classes'
    }
}

Also Margin/app/libs/hbci4java/build.gradle and Margin/app/libs/hbci4java/settings.gradle seem to be clear to me, when just building the hbci4java project:

apply plugin: 'java'

repositories {
    mavenCentral()
}

dependencies {
    compile project(':thirdparty/cryptalgs4java')
    testCompile group: 'junit', name: 'junit', version: '4.+'
}

sourceCompatibility = 1.5
compileJava.options.encoding = 'ISO-8859-1'
compileTestJava.options.encoding = 'ISO-8859-1'

version = '2.5.13-SNAPSHOT'

sourceSets{
    main {
        java {
            srcDir 'src'
        }
        output.classesDir 'classes'
    }

    test {
        java {
            srcDirs 'test'
        }
    }
}

settings:

include 'thirdparty/cryptalgs4java'

But I'm totally not sure how the building of the android project works, and how I can make it aware of the library project.

Here are the contents of the remaining gradle files:

Margin/app/build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 22
    buildToolsVersion "22.0.1"

    defaultConfig {
        applicationId "de.bvs.margin.margin"
        minSdkVersion 19
        targetSdkVersion 22
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:22.2.0'
}

Margin/build.gradle:

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.2.3'
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

and Margin/settings.gradle:

include ':app'

I tried several locations to place the libs folder and also tried to mention it in the different gradle files, with no success so far.

I hope, anybody can help me figure out, how to use the libs and make android studio aware of them.

best wishes, Stephan

Answer 1

After fiddeling a bit more, i found out that the following does the trick:

add the following lines to Margin/settings.gradle:

include ':app:libs:hbci4java', ':thirdparty/cryptalgs4java'
project(':thirdparty/cryptalgs4java').projectDir = new File('app/libs/hbci4java/thirdparty/cryptalgs4java')

add

compile project(':app:libs:hbci4java')

to the dependencies section in Margin/app/build.gradle

Now, gradle is able to resync and android studio will allow to add the project hbci4java as dependency in Margin.