COMPILE_SDK_VERSION = 26
BUILD_TOOLS_VERSION = 26.0.0
MIN_SDK_VERSION = 19
TARGET_SDK_VERSION = 26
VERSION_CODE = 1
VERSION_NAME = 1.0

android {
    compileSdkVersion COMPILE_SDK_VERSION as int
    buildToolsVersion BUILD_TOOLS_VERSION
    defaultConfig {
        applicationId "com.xtao.simpledemo"
        minSdkVersion MIN_SDK_VERSION as int
        targetSdkVersion TARGET_SDK_VERSION as int
        versionCode VERSION_CODE as int
        versionName VERSION_NAME
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile(‘proguard-android.txt‘), ‘proguard-rules.pro‘
            buildConfigField("int", "TARGET_SDK_VERSION", "${TARGET_SDK_VERSION}")
        }
        debug {
            buildConfigField("int", "TARGET_SDK_VERSION", "${TARGET_SDK_VERSION}")
            resValue("string", "VERSION_NAME", "${VERSION_NAME}")
        }
    }
}

int targetSDKVersion = BuildConfig.TARGET_SDK_VERSION;

ResourceBundle bundle = ResourceBundle.getBundle("gradle");//gradle为properties的文件名
String result = bundle.getString("test_key");//test_key是properties文件中的key值

Properties properties = new Properties();
InputStream is = this.getClassLoader().getResourceAsStream("gradle.properties");//path
properties.load(is);
String result= properties.getProperty("test_key");//test_key是properties文件中的key值

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/VERSION_NAME"/>