hugb_hello_world

(T-303-HUGB, Hugbúnaðarfræði, 2016-3)

Sample program used to show students Gradle in action.

What was done

####NOTE: I used gradle 3.1 in the lecture.

Create project

• Git clone hugb_hello_world project
• Run gradle init --type java-library to create basic folder structure.
• Run gradle check to check if everything is working as it should.

Project content

• build.gradle (The gradle build file that we use)
• gradle (Folder containing the gradle wrapper)
• gradlew (Linux/Unix script to run the gradle wrapper)
• gradlew.bat (Windows script to run the gradle wrapper)
• settings.gradle (Settings file for gradle, not used in our example, can for example contain definitions if we have multiple projects)
• src (Source folder for our code)

Show basic gradle tasks

• Checkout list of gradle tasks (./gradlew tasks if we use the wrapper, gradle tasks if using the gradle install on the machine)

Create basic code

• Navigate to src/main/java and delete Library.java (just a demo file that we do not use)
• Navigate to scr/test/java and delete LibraryTest.java.
• Create folders for code under src/main/java (mkdir -p com/bangsapabbi/helloworld)
• Navigate to the new folder and create HelloWorld.java

package com.bangsapabbi.helloworld;

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello world");
    }
}

• Check if everything builds.
• Add the application plugin* to run the program.

apply plugin: 'application'

mainClassName = "com.bangsapabbi.helloworld.HelloWorld"

• Extract the "Hello World!" message to World class to be able to show basic unit tests.

package com.bangsapabbi.helloworld;

public class HelloWorld {
    public static void main(String[] args) {
        World world = new World();
        System.out.println(world.greet());
    }
}

package com.bangsapabbi.helloworld;

public class World {
    public String greet() {
        return "Hello world!";
    }
}

Testing

• Navigate to src/test/java
• Create folder structure (mkdir -p com/bangsapabbi/helloworld)
• Add WorldTest.java file.

package com.bangsapabbi.helloworld;

import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class WorldTest {

    @Test
    public void greetResultsInHello() {
        World world = new World();
        assertEquals("Hello world!", world.greet());
    }

}

• Run tests using gradle test
• Change test and see the build fail.
• Open build/reports/test to view detailed test report.

bin folder

• Create bin folder
• Create clean script
• chmod +x on the clean file.

#!/bin/bash

./gradlew clean

Gson (Not part of the project in git)

• Goto http://search.maven.org/
• Search for gson
• Click the version number
• Here we can find the dependency string that we need.

compile 'com.google.code.gson:gson:2.3'

Refactoring World class to include gson output.

package com.bangsapabbi.helloworld;

import com.google.gson.Gson;

public class World {

    private String greeting = "Hello world!";

    public String greet() {
        return greeting;
    }

    public String jsonGreet() {
        return new Gson().toJson(this);
    }
}

• Add the following line to HelloWorld.java to output json.

System.out.println(world.jsonGreet());