build.gradle

apply plugin: 'com.android.application'


def loadProperties(String sourceFileName) {
    def config = new Properties()
    def propFile = new File(sourceFileName)
    if (propFile.canRead()) {
        System.out.println("Loading property file: " + propFile.absolutePath)
        config.load(new FileInputStream(propFile))
        for (Map.Entry property in config) {
            System.out.println("setting " + property.key)
            project.ext[property.key] = property.value;
        }
        return true;
    } else {
        System.err.println("Couldn't load property file: " + propFile.absolutePath)
        return false;
    }
}

buildscript {
    repositories {
        mavenCentral()
        jcenter()
    }

    dependencies {
    }
}
loadProperties("config.properties")
android {
    compileSdkVersion 23
    buildToolsVersion "23.0.1"
    sourceSets {
        main {
            jniLibs.srcDir 'jniLibs'
        }
    }
    defaultConfig {
        applicationId "com.riantono.devs"
        minSdkVersion 16
        targetSdkVersion 23
        ........
      resValue "string", "API_URL", project.ext.get("API_URL")
    }
    buildTypes {
        debug {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            zipAlignEnabled false
            shrinkResources false
        }
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            zipAlignEnabled false
            shrinkResources false
    }
    lintOptions {
        abortOnError false
    }
}
repositories {
    mavenCentral()
    jcenter()
}
dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:multidex:1.0.0'
    compile 'com.android.support:appcompat-v7:23.1.0'
}

sample.config.properties

API_URL="https://themoviedb.org"