Skip to main content
Docs: template-java

Quick-Start

The Quick-Start guide explains how to get from an API to a functional Java project in a few steps. For more general information about first steps with ApiGear, see First Steps.

The quick start uses only the api feature. For all available features, see the overview.

1. Install the Code Generator​

ApiGear provides two powerful tools: a Studio and a Command Line Interface (CLI). The Studio is a graphical tool for creating, editing API modules and projects, while the CLI is a command-line tool for generating code from API modules. Both offer comprehensive functionality, including SDK template management, API project creation, code generation, API monitoring, and API simulation.

Download Studio
Download CLI

Install ApiGear Studio​

ApiGear Studio is available for macOS, Windows, and Linux. You can download it from the ApiGear Studio GitHub releases page.

For more detailed information on ApiGear Studio, refer to the dedicated studio documentation.

Install ApiGear CLI​

The ApiGear CLI is a versatile command-line tool for generating code from API modules. It's available for macOS, Windows, and Linux. Download the latest version from the ApiGear CLI GitHub releases page.

The CLI offers all the features available in the Studio.

For more detailed information on the ApiGear CLI, consult the dedicated CLI documentation.

2. Obtain the Template​

There are several methods to obtain the template: installation via the Studio, installation via the CLI, or cloning/downloading from GitHub.

This step is optional

The ApiGear Studio and the CLI detect the specified template in the solution document and install it automatically.

Optional steps (click to expand)

Installation via CLI​

When using the CLI, only the highlighted line needs to be executed. You can verify the successful installation using the template cache command.

$ apigear template install apigear-io/template-unreal@v3.2.2
$ apigear template cache
list of templates from the local cache

source                            | url                                               | installed | latest
apigear-io/template-unreal@v3.2.2 | https://github.com/apigear-io/template-unreal.git | <sha1>    | v3.2.2
...

Installation via Studio​

Installing the template through the Studio is straightforward:

  1. Open an existing project or create a new one
  2. Navigate to the Templates tab
  3. Click Install on the apigear-io/template-unreal entry
Installing the template
Figure: Installing the template

Cloning from GitHub​

If you need to inspect or modify the template's source code, cloning or downloading the repository is recommended. The repository doesn't need to be part of your project and can be stored anywhere on your computer.

$ git clone https://github.com/apigear-io/template-unreal.git

You can then configure the solution file to use your template by providing the relative path from the solution file to the template directory.

3. Set Up the Project​

A typical project requires two files: a solution file specifying the APIs and the template to use, and at least one API module file. Ideally, both should be placed in a folder named apigear, adjacent to each other.

Alternatively, you can use the Studio to create a new project and modify the two example files provided.

Solution File​

Create a solution file. The example below specifies:

  • Module files in line 8, here the helloworld.module.yaml module with the Hello API
  • The output directory for generated files in line 9
  • The template used to generate the code in line 10 (this can also be a path to a local copy of the template)
  • The enabled features of the template in line 13, here the stubs feature, which provides a simple implementation of interfaces.
helloworld.solution.yaml
schema: "apigear.solution/1.0"
name: hello_world_example
version: "0.1.0"

targets:
  - name: ue_docs
    inputs:
      - helloworld.module.yaml
    output: ../ue_docs
    template: apigear-io/template-unreal@v3.2.2
    force: true
    features:
      - stubs
Targets

You can extend this solution file with additional targets, each for a different technology with a different template. The module.yaml file is technology-independent and can be used with any template.

Template Version

We highly recommend specifying the exact version of the template. Otherwise, a newer version will be automatically downloaded and used for code generation. This can lead to unexpected behavior if file structures or code changes in the template.

note

Set the force parameter to true if you want to always override all generated files. When set to false, some files, such as implementations (stub feature), won't be updated. API files are always updated regardless of this setting.

API Module File​

Use your preferred text editor to create the helloworld.module.yaml file with the following example content:

helloworld.module.yaml
schema: apigear.module/1.0
name: io.world
version: "1.0.0"

interfaces:
  - name: Hello
    properties:
      - { name: last, type: Message }
    operations:
      - name: say
        params:
          - { name: msg, type: Message }
          - { name: when, type: When }
        return:
          type: int
    signals:
      - name: justSaid
        params:
          - { name: msg, type: Message }
enums:
  - name: When
    members:
      - { name: Now, value: 0 }
      - { name: Soon, value: 1 }
      - { name: Never, value: 2 }
structs:
  - name: Message
    fields:
      - { name: content, type: string }

4. Generate Code​

Generate via CLI​

The following snippet demonstrates how to run the CLI and provides an example output:

$ apigear generate solution apigear/helloworld.solution.yaml
10:52:20 INF generated 21 files in 30ms. (20 write, 0 skip, 1 copy) topic=gen
  • The generate command instructs the CLI to generate code
  • The solution parameter specifies that we want to process a solution file

Generate via Studio​

  1. Open the project
  2. Navigate to the Solutions tab
  3. Click Run on the helloworld.solution.yaml entry
Generating code
Figure: Generating code

5. Use the generated Java project​

Prerequisites

The easiest way to work with the generated code is Android Studio, which manages the SDK, Gradle, and JDK for you.

For command-line builds, you need JDK 17 or later (see Eclipse Adoptium), Gradle 8.7+, and the Android SDK with compileSdk 35. The minimum supported Android version is API 33 (Android 13 / Tiramisu).

Project folder structure​

For the code generation we assume that both ApiGear files reside in an apigear subfolder next to the generated files. In this case, the folder structure should look similar to this.

📂hello-world
 ┣ 📂apigear
 ┃ ┣ 📜helloworld.solution.yaml
 ┃ ┗ 📜helloworld.module.yaml
 ┣ 📂java_hello_world
 ┃ ┗ 📂ioWorld
 ┃   ┗ 📂ioWorld_api/src/main/java/ioWorld/ioWorld_api
 ┃     ┣ 📜IHello.java
 ┃     ┣ 📜IHelloEventListener.java
 ┃     ┣ 📜AbstractHello.java
 ┃     ┣ 📜Message.java
 ┃     ┗ 📜When.java

The generated code is a Gradle multi-module project with separate source files per type.

Create and run an example​

The api feature generates separate files for each type: the When enum, the Message struct, the IHello interface, the IHelloEventListener event listener, and the AbstractHello abstract base class. You can implement the interface and use it in your project:

import ioWorld.ioWorld_api.*;

import java.util.concurrent.CompletableFuture;

public class HelloExample {
    // A simple implementation of the Hello interface
    static class MyHello extends AbstractHello {
        private Message last = new Message();

        @Override
        public int say(Message msg, When when) {
            System.out.println("say called: " + msg.content + " (" + when + ")");
            return 42;
        }

        @Override
        public CompletableFuture<Integer> sayAsync(Message msg, When when) {
            return CompletableFuture.supplyAsync(() -> say(msg, when));
        }

        @Override
        public void setLast(Message last) {
            if (!last.equals(this.last)) {
                this.last = last;
                fireLastChanged(last);
            }
        }

        @Override
        public Message getLast() {
            return last;
        }

        @Override
        public boolean _isReady() {
            return true;
        }
    }

    public static void main(String[] args) {
        MyHello hello = new MyHello();

        // Use a struct (all-args or no-arg constructor)
        Message msg = new Message("Hello World");

        // Call an operation
        int result = hello.say(msg, When.Now);
        System.out.println("Result: " + result);

        // Subscribe to property changes and signals
        hello.addEventListener(new IHelloEventListener() {
            @Override
            public void onLastChanged(Message newValue) {
                System.out.println("last changed: " + newValue.content);
            }

            @Override
            public void onJustSaid(Message msg) {
                System.out.println("justSaid signal: " + msg.content);
            }

            @Override
            public void on_readyStatusChanged(boolean isReady) {
                System.out.println("ready: " + isReady);
            }
        });

        // Set a property (triggers onLastChanged)
        hello.setLast(msg);
    }
}
tip

For more features, check the features overview.