Is it possible to declare a variable in Gradle usable in Java?

Here are two ways to pass value from Gradle to use in Java;

Generate Java Constants

android {    buildTypes {        debug {            buildConfigField "int", "FOO", "42"            buildConfigField "String", "FOO_STRING", "\"foo\""            buildConfigField "boolean", "LOG", "true"        }        release {            buildConfigField "int", "FOO", "52"            buildConfigField "String", "FOO_STRING", "\"bar\""            buildConfigField "boolean", "LOG", "false"        }    }}

You can access them with BuildConfig.FOO

Generate Android resources

android {    buildTypes {        debug{            resValue "string", "app_name", "My App Name Debug"        }        release {            resValue "string", "app_name", "My App Name"        }    }}

You can access them in the usual way with @string/app_name or R.string.app_name

An example of usage an Api App Key in an Android application (Java and XML)

gradle.properties

AppKey="XXXX-XXXX"

build.gradle

buildTypes {//...    buildTypes.each {        it.buildConfigField 'String', 'APP_KEY_1', AppKey        it.resValue 'string', 'APP_KEY_2', AppKey    }}

Usage in java code

Log.d("UserActivity", "onCreate, APP_KEY: " + getString(R.string.APP_KEY_2));BuildConfig.APP_KEY_1

Usage in xml code

<data android:scheme="@string/APP_KEY_2" />

• Link to an example of Api App Key usage in an Android application
• Using String Constants Generated by Gradle Build Configurations

Example using system properties, set in build.gradle, read from Java application (following up from question in comments):

Basically, using the test task in build.gradle, with test task method systemProperty setting a system property that's passed at runtime:

apply plugin: 'java'group = 'example'version = '0.0.1-SNAPSHOT'repositories {    mavenCentral()    // mavenLocal()    // maven { url 'http://localhost/nexus/content/groups/public'; }}dependencies {    testCompile 'junit:junit:4.8.2'    compile 'ch.qos.logback:logback-classic:1.1.2'}test {  logger.info '==test=='  systemProperty 'MY-VAR1', 'VALUE-TEST'}

And here's the rest of the sample code (which you could probably infer, but is included here anyway): it gets a system property MY-VAR1, expected at run-time to be set to VALUE-TEST:

package example;import org.slf4j.Logger;import org.slf4j.LoggerFactory;public class HelloWorld {  static final Logger log=LoggerFactory.getLogger(HelloWorld.class);  public static void main(String args[]) {    log.info("entering main...");    final String val = System.getProperty("MY-VAR1", "UNSET (MAIN)");    System.out.println("(main.out) hello, world: " + val);    log.info("main.log) MY-VAR1=" + val);  }}

Testcase: if MY-VAR is unset, the test should fail:

package example;...public class HelloWorldTest {    static final Logger log=LoggerFactory.getLogger(HelloWorldTest.class);    @Test public void testEnv() {        HelloWorld.main(new String[]{});        final String val = System.getProperty("MY-VAR1", "UNSET (TEST)");        System.out.println("(test.out) var1=" + val);        log.info("(test.log) MY-VAR1=" + val);        assertEquals("env MY-VAR1 set.", "VALUE-TEST", val);    }}

Run (note: test is passing):

$ gradle cleanTest test:cleanTest:compileJava UP-TO-DATE:processResources UP-TO-DATE:classes UP-TO-DATE:compileTestJava UP-TO-DATE:processTestResources UP-TO-DATE:testClasses UP-TO-DATE:testBUILD SUCCESSFUL

I've found that the tricky part is actually getting the output from gradle... So, logging is configured here (slf4j+logback), and the log file shows the results (alternatively, run gradle --info cleanTest test; there are also properties that get stdout to the console, but, you know, why):

$ cat app.logINFO Test worker example.HelloWorld - entering main...INFO Test worker example.HelloWorld - main.log) MY-VAR1=VALUE-TESTINFO Test worker example.HelloWorldTest - (test.log) MY-VAR1=VALUE-TEST

If you comment out "systemProperty..." (which, btw, only works in a test task), then:

example.HelloWorldTest > testEnv FAILED    org.junit.ComparisonFailure at HelloWorldTest.java:14

For completeness, here is the logback config (src/test/resources/logback-test.xml):

<configuration>    <appender name="FILE" class="ch.qos.logback.core.FileAppender">        <file>app.log</file>        <layout class="ch.qos.logback.classic.PatternLayout">            <pattern>%d %p %t %c - %m%n</pattern>        </layout> </appender> <root level="info">     <appender-ref ref="FILE"/></root></configuration> 

Files:

• build.gradle
• src/main/java/example/HelloWorld.java
• src/test/java/example/HelloWorldTest.java
• src/test/resources/logback-test.xml