Import an external module to Android Project in Android Studio (http://alexzh.com/tutorials/import-an-external-module-in-android-studio/)

app-module-build.gradle

//ExternalModulesInProject/Application/app
apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.0"
    defaultConfig {
        applicationId "com.alexzh.application"
        minSdkVersion 14
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.0.0'
    testCompile 'junit:junit:4.12'

    compile project(':simpledateformatter')
}

application-settings.gradle

//ExternalModulesInProject/Application
include ':app'

include ':simpledateformatter'
project(':simpledateformatter').projectDir = new File(settingsDir, '../simpledateformatter')

simpledateformatter-module-build.gradle

//ExternalModulesInProject/simpledateformatter
apply plugin: 'java'

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
}

sourceCompatibility = "1.7"
targetCompatibility = "1.7"