How to set up a vanilla groovy project with main class executable via jar?

Question

I am getting very frustrated. I can't find a single, cohesive answer for my problem anywhere on the internet. Lots of documentation, nothing that brings it all together, though (that I can find).

All I need is someone to tell me:

• how to set up a groovy project (EDIT: Including where to put source files, in what directories, directory structure, etc.)
• assuming I haven't build groovy before
• or java before (I have, but work with me)
• in a way that I can specify a dependency (this is my dependency --> https://github.com/bpsm/edn-java ) so probably using maven or gradle
• one that has a main class and a main method (again, work with me)
• at the end of the build, I need a jar file that I can execute via java -jar <groovy-project>.jar which prints out "hello world"

As simply as possible.

Answer 1

I strongly recommend Gradle; it is very simple to setup (though I too struggled when learning it). I added the resulting project in my github .

Let's create a project structure from zero without an IDE. I presume you already have $JAVA_HOME set up .

1. Creating the project structure

1. Download Gradle and put it in your $PATH

2. Create your directory project (I created /tmp/gr8ex )

3. Switch to it and run gradle init [1]

4. Edit the build.gradle created file and add these line:

    plugins { // [2] id 'groovy' } repositories { mavenCentral() } // [3] dependencies { // [4] testCompile 'org.codehaus.groovy:groovy-all:2.4.8' compile 'org.codehaus.groovy:groovy-all:2.4.8' testCompile 'junit:junit:4.12' } 

Now the source files; we need to create the default directory structure that gradle uses (we can change it, but let's go with the defaults):

5. This is to create the source code dir:

    mkdir -p src/main/groovy 

6. And the test source folder:

    mkdir -p src/test/groovy 

7. The end result should look like this:

    gr8ex ├── build.gradle ├── gradle │ └── wrapper │ ├── gradle-wrapper.jar │ └── gradle-wrapper.properties ├── gradlew ├── gradlew.bat ├── settings.gradle └── src ├── main │ └── groovy └── test └── groovy 

2. Adding source code

1. Let's add a test package:

    mkdir -p src/test/groovy/org/gr8ex 

2. And a test. I'm using gedit src/test/groovy/org/gr8ex/HelloTest.groovy :

    package org.gr8ex class HelloTest extends GroovyTestCase { void 'test Hello should return "Hello, World!"' () { assert new Hello().world == "Hello, World!" } } 

3. Let's execute the test and check it fails:

    gradle test 

4. Yep, it failed:

    /tmp/gr8ex/src/test/groovy/org/gr8ex/HelloTest.groovy: 5: unable to resolve class Hello @ line 5, column 12. assert new Hello().world == "Hello, World!" ^ 1 error :compileTestGroovy FAILED 

5. Let's add source folder

    mkdir -p src/main/groovy/org/gr8ex 

6. And a source file (I used gedit src/main/groovy/org/gr8ex/Hello.groovy ). Note it already have our static main method:

    package org.gr8ex class Hello { def getWorld() { "Hello, World!" } static main(args) { println new Hello().world } } 

7. Test again (with gradle test ) and assert we get the message BUILD SUCCESSFUL :

    $ gradle test :compileJava UP-TO-DATE :compileGroovy :processResources UP-TO-DATE :classes :compileTestJava UP-TO-DATE :compileTestGroovy :processTestResources UP-TO-DATE :testClasses :test BUILD SUCCESSFUL Total time: 5.52 secs 

Done. Time to create our application jar.

3. Creating the jar executable

There is a couple of ways to achieve that (like the shadow plugin ). I'm going to stick with a "fatjar" approach.

1. Let's add a fatjar instruction in our build.gradle [5]:

    task fatjar(type: Jar) { manifest { attributes 'Main-Class': 'org.gr8ex.Hello' } from { configurations .runtime .collect { it.isDirectory() ? it : zipTree(it) } } with jar } 

2. Packaging it:

    gradle fatjar 

3. The resulting jar will be in builds/libs/gr8ex.jar . Let's execute it:

    $ java -jar build/libs/gr8ex.jar Hello, World! 

4. Profit! You can import this project with intellij and (I believe) eclipse.

---

[1]: Gradle creates some basic structure and add wrapper scripts so it can be executed without Gradle, if needed.

[2]: Here we are telling gradle that this project will use groovy

[3]: We tell gradle to use the mavencentral repository. JCenter is also very popular.

[4]: Here we are telling gradle that this project needs to use the groovy-all lib upon compilation and and testing phases

[5]: If you just stick with a jar {} instruction, like this answer , you will end with a very thin jar which will be missing the groovy libs. This "fatjar" packs your libs into the jar. You might want to tweak it a bit depending on your use case.

Answer 2

Eclipse may work pretty good with a Groovy Maven setup. You just need a pom.xml similar to this:

...
<plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.2</version>
        <configuration>
          <source>1.7</source>
          <target>1.7</target>
          <compilerId>groovy-eclipse-compiler</compilerId>
          <useIncrementalCompilation>false</useIncrementalCompilation>
        </configuration>
        <dependencies>
          <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy-eclipse-compiler</artifactId>
            <version>2.9.1-01</version>
          </dependency>
          <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy-eclipse-batch</artifactId>
            <version>2.3.7-01</version>
          </dependency>
          <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy</artifactId>
            <version>2.3.0</version>
          </dependency>
          <dependency>
            <groupId>org.apache.ivy</groupId>
            <artifactId>ivy</artifactId>
            <version>2.4.0</version>
          </dependency>
        </dependencies>
      </plugin>
      <plugin>
        <groupId>org.codehaus.groovy</groupId>
        <artifactId>groovy-eclipse-compiler</artifactId>
        <version>2.9.1-01</version>
        <extensions>true</extensions>
      </plugin>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <version>1.9.1</version>
        <executions>
          <execution>
            <id>add-source</id>
            <phase>generate-sources</phase>
            <goals>
              <goal>add-source</goal>
            </goals>
            <configuration>
              <sources>
                <source>wherever/you/like</source>          
              </sources>
            </configuration>
          </execution>
        </executions>
      </plugin>
...
<dependencies>
...
<dependency>
      <groupId>org.codehaus.groovy</groupId>
      <artifactId>groovy-all</artifactId>
      <version>${groovyVersion}</version>
      <scope>provided</scope>
    </dependency>
...
</dependencies>
...

The sources part is optional, as it should look for your sources in src/main/groovy and src/test/groovy. Eclipse should be able to configure your project as a maven project, and acquire automatically the Groovy nature as well.

A call to mvn install should generate a .jar file with your Groovy classes translated into .class files since you have configured a Groovy compiler in maven.

As for the main method, just do as you would normally with maven:

...
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <configuration>
        <archive>
            <manifest>
                <mainClass>my.mainClass</mainClass>
            </manifest>
        </archive>
    </configuration>
</plugin>
...