Expose Backend

Your stack:

Goal

Turn a Groovy class into a remotely callable backend service using Graftcode Gateway - no Spring, no REST routes, no OpenAPI specs needed.

What You'll See

Create a small Groovy class with public methods.
Host it through Graftcode Gateway using Docker.
Explore the exposed methods in Graftcode Vision - your service is now accessible from any app as a strongly-typed client.

Prerequisites

Docker installed and running
JDK 21 and Maven only if you build outside Docker - the Maven base image below already provides both for docker build

Step 1. Create a project folder

Create a new folder and set up a Maven project:

mkdir groovy-energy-service
cd groovy-energy-service

Create a pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                             http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>energy-service</artifactId>
    <version>1.0.0</version>

    <properties>
        <groovy.version>4.0.24</groovy.version>
        <maven.compiler.source>21</maven.compiler.source>
        <maven.compiler.target>21</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.apache.groovy</groupId>
            <artifactId>groovy</artifactId>
            <version>${groovy.version}</version>
        </dependency>
    </dependencies>

    <build>
        <sourceDirectory>src/main/groovy</sourceDirectory>
        <plugins>
            <plugin>
                <groupId>org.codehaus.gmavenplus</groupId>
                <artifactId>gmavenplus-plugin</artifactId>
                <version>3.0.2</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Step 2. Write a Groovy class with public methods

Create the directory structure and a file src/main/groovy/energy/EnergyPriceCalculator.groovy:

package energy

class EnergyPriceCalculator {
    static int getPrice() {
        return new Random().nextInt(5) + 100
    }
}

This is a plain Groovy class - no annotations, no frameworks, no special interfaces. Groovy methods are public by default, so methods you define here become available for remote consumption once hosted through Graftcode Gateway. Vision and MCP may also list inherited Groovy runtime methods such as getMetaClass and setMetaClass.

Step 3. Host it with Graftcode Gateway

Create a Dockerfile in the project root:

FROM maven:3.9-eclipse-temurin-21

WORKDIR /usr/app

COPY . /usr/app/

RUN mvn package -q

RUN apt-get update \
 && apt-get install -y wget \
 && wget -O /usr/app/gg.deb https://github.com/grft-dev/graftcode-gateway/releases/latest/download/gg_linux_amd64.deb \
 && dpkg -i /usr/app/gg.deb \
 && rm /usr/app/gg.deb \
 && apt-get clean \
 && rm -rf /var/lib/apt/lists/*

EXPOSE 80
EXPOSE 81

CMD ["gg","--modules", "/usr/app/target/energy-service-1.0.0.jar"]

The key line is the last one - gg (Graftcode Gateway) reads your compiled JAR, discovers all public methods in your Groovy classes, and exposes them automatically. Port 80 handles service calls, port 81 serves Graftcode Vision.

Build and run the container:

docker build --no-cache --pull -t myenergyservice-groovy:test .
docker run -d -p 80:80 -p 81:81 --name graftcode_demo_groovy myenergyservice-groovy:test

Your Groovy service is now running and exposed through Graftcode Gateway.

Step 4. Explore the service in Graftcode Vision

Open http://localhost:81/GV in your browser.

You will see all public methods from your Groovy class - their names, parameter types, and return types. Graftcode Vision also provides:

A "Try it out" button to call methods live, directly from the browser.
A package manager command (npm, NuGet, PyPI, Maven, etc.) to install this service as a strongly-typed client in any other application.

Step 5. Run with a Project Key (recommended for real-world usage)

Everything above works without any account - perfect for learning and local development. When you're ready for real-world usage, create a free account at portal.graftcode.com, set up a project, and copy its Project Key.

Then pass the key when starting your gateway:

CMD ["gg", "--modules", "/usr/app/target/energy-service-1.0.0.jar", "--projectKey", "YOUR_PROJECT_KEY"]

A Project Key gives you:

Stable registry URL - consumers always find and update your Graft through a permanent address, so install commands don't change when you redeploy.
Portal visibility - see all your gateways and exposed services in one place at gateways.graftcode.com.
Access control - decide who can download your Grafts using package manager authentication and permissions.
MCP endpoint - Graftcode Gateway automatically exposes an MCP (Model Context Protocol) endpoint alongside your service, making your methods callable by AI agents and LLM-based tools out of the box.

Step 6. Call it from another app

Your service is now accessible from any application. From Graftcode Vision, select your target package type - for example npm - and copy the generated install command. That installs a Graft: a strongly-typed client that lets any app call your service methods directly.

The generated npm package name is derived from Maven coordinates (for this sample it looks like @graft/maven-groupid_com-example_artifactid_energy-service@1.0.0). Always copy the exact command from Vision or Gateway logs.

If Gateway logs "Uploading UGM successful" but npm install or Maven restore returns 404, the package may not be available yet. Recheck the registry URL from Vision/logs, retry the install, or call methods through the MCP endpoint at http://localhost:81/mcp while troubleshooting.

import com.graft.maven.energypricecalculator.EnergyPriceCalculator

def price = EnergyPriceCalculator.getPrice()
println price

No REST clients, no request/response models, no endpoint URLs in your code. When you add or update a public method, consumers update their Graft with a single package manager command.