Building a Java project with Gradle (practical)

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 SayHello.java and open it for editing

paste in the following Java code:

package com.tomgregory.languageapp;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
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));

        System.out.println(bufferedInputStream.readLine());
    }
}

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 SayHelloTest.java and open it for editing

paste in the following Java code:

package com.tomgregory.languageapp;

import org.junit.jupiter.api.Test;

import java.io.IOException;

public class SayHelloTest {
    @Test
    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 {
    mavenCentral()
}
```
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 {
    useJUnitPlatform()
}
```
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.