Open the project you built in the Creating your first Gradle project lesson. Use a command-line, text editor, or an IDE as you prefer.

Adding the Java code

  • add a directory src/main/java for the main application code

  • create directories for the Java package com/tomgregory/languageapp

  • create a new file and open it for editing

  • paste in the following Java code:

    package com.tomgregory.languageapp;
    import java.nio.charset.StandardCharsets;
    public class SayHello {
        public static void main(String[] args) throws IOException {
            String language = args[0];
            InputStream resourceStream = SayHello.class.getClassLoader().getResourceAsStream(language + ".txt");
            assert resourceStream != null;
            BufferedReader bufferedInputStream = new BufferedReader(new InputStreamReader(resourceStream, StandardCharsets.UTF_8));

Adding the resources

  • create a new directory under src/main called resources
  • add a file en.txt with contents Hello!
  • add a file es.txt with contents Hola!

Building the application

  • open build.gradle and delete the comment.

  • insert this plugins configuration:

    plugins {
        id 'java'
  • see what Gradle tasks we have available:

    ./gradlew tasks (Linux/Mac)

    gradlew.bat tasks (Windows)

    All the tasks listed under Build tasks have been added to the project by the Java plugin.

  • to see all Gradle tasks, including compileJava and processResources, run:

    ./gradlew tasks --all (Linux/Mac)

    gradlew.bat tasks --all (Windows)

    These tasks appear under Other tasks.

  • compile the Java classes:

    ./gradlew compileJava (Linux/Mac)

    gradlew.bat compileJava (Windows)

  • look for output in build/classes/java/main

  • process resources:

    ./gradlew processResources (Linux/Mac)

    gradlew.bat processResources (Windows)

  • look for output in build/resources/main

  • generate a jar file:

    ./gradlew jar (Linux/Mac)

    gradlew.bat jar (Windows)

  • look for the jar file in build/libs

Running the application

  • run the following Java command:

    java -jar build/libs/get-going-with-gradle.jar en (Linux/Mac/Windows)

    You’ll see an error which says no main manifest attribute.

  • Add this jar configuration to the end of build.gradle:

    jar {
        manifest {
            attributes('Main-Class': 'com.tomgregory.languageapp.SayHello')
  • build the jar file again:

    ./gradlew jar (Linux/Mac)

    gradlew.bat jar (Windows)

  • rerun the Java command:

    java -jar build/libs/get-going-with-gradle.jar en (Linux/Mac/Windows)

    You should see the text Hello! output.

  • run the same Java command, but replace en with es for Spanish

    java -jar build/libs/get-going-with-gradle.jar es (Linux/Mac/Windows)

    You should see the text Hola! output.

Awesome! You’ve just built your first Java application with Gradle.

Testing the application

  • tests live in src/test/java, so under src create a new directory test/java

  • within this directory create directories com/tomgregory/languageapp for the same package structure

  • add a new file and open it for editing

  • paste in the following Java code:

    package com.tomgregory.languageapp;
    import org.junit.jupiter.api.Test;
    public class SayHelloTest {
        public void testSayHello() throws IOException {
            SayHello.main(new String[]{"en"});
  • try running the tests:

    ./gradlew test (Linux/Mac)

    gradlew.bat test (Windows)

    You’ll get an error here saying that it can’t find the org.junit.jupiter.api package.

  • add this dependency configuration block to build.gradle, after the plugins:

    dependencies {
        testImplementation 'org.junit.jupiter:junit-jupiter:5.6.3'
  • add this repositories configuration block, putting it just before the dependencies:

    repositories {
  • rerun the test command:

    ./gradlew test (Linux/Mac)

    gradlew.bat test (Windows)

    The build should be successful.

  • open the test report in a browser, located in build/reports/tests/test/index.html.

    You’ll see that 0 tests have been run.

  • add this test configuration block below the dependencies block:

    test {

    This configures tests to use the Junit 5 platform.

  • run the tests again:

    ./gradlew test (Linux/Mac)

    gradlew.bat test (Windows)

  • open the test report again in a browser, located in build/reports/tests/test/index.html. You should now see that 1 test was run, with a 100% success rate.

Commit your changes

  • get all the files ready to be committed:

    git add .

  • see what files are staged for commit:

    git status

  • Commit everything:

    git commit -m "Create Java project for language app."

Good work! You just built, run, and tested your first Java project with Gradle.