GitHub Webhooks - Java

Java - Basic Handler

Spring Boot REST controller for handling GitHub webhooks.

@RestController
public class WebhookController {
    private static final String SECRET = "your_secret";

    @PostMapping("/webhook")
    public String handle(HttpServletRequest req) throws IOException {
        String payload = readPayload(req);
        String signature = req.getHeader("X-Hub-Signature-256");

        if (!verifySignature(signature, payload)) {
            return "Invalid signature";
        }

        String event = req.getHeader("X-GitHub-Event");
        if ("push".equals(event)) {
            runDeployScript();
        }
        return "OK";
    }
}

Java - Read Payload

Read the request body for signature verification.

private String readPayload(HttpServletRequest request) throws IOException {
    StringBuilder payload = new StringBuilder();
    try (BufferedReader reader = request.getReader()) {
        String line;
        while ((line = reader.readLine()) != null) {
            payload.append(line);
        }
    }
    return payload.toString();
}

Java - Verify Signature

Verify GitHub webhook signature using HMAC SHA-256.

private boolean verifySignature(String signature, String payload) {
    if (signature == null) return false;

    String expected = "sha256=" +
        Hex.encodeHexString(HmacUtils.hmacSha256(SECRET, payload));

    return expected.equals(signature);
}

Dependencies:

<dependency>
    <groupId>commons-codec</groupId>
    <artifactId>commons-codec</artifactId>
</dependency>

Java - Deploy Script

Execute deployment script when webhook is received.

private void runDeployScript() {
    try {
        ProcessBuilder pb = new ProcessBuilder(
            "/bin/bash", "/path/to/deploy.sh"
        );
        pb.start();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Java - Complete Example

Full working Spring Boot webhook handler.

import org.springframework.web.bind.annotation.*;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.codec.binary.Hex;
import org.apache.commons.codec.digest.HmacUtils;
import java.io.BufferedReader;
import java.io.IOException;

@RestController
public class GithubWebhookController {

    private static final String SECRET = "YOUR_WEBHOOK_SECRET";

    @PostMapping("/webhook")
    public String handleWebhook(HttpServletRequest request) throws IOException {

        // Read payload
        StringBuilder payload = new StringBuilder();
        try (BufferedReader reader = request.getReader()) {
            String line;
            while ((line = reader.readLine()) != null) {
                payload.append(line);
            }
        }

        // Verify signature (X-Hub-Signature-256)
        String signature = request.getHeader("X-Hub-Signature-256");
        if (!verifySignature(signature, payload.toString())) {
            return "Invalid signature";
        }

        String event = request.getHeader("X-GitHub-Event");

        if ("push".equals(event)) {
            // Execute deployment script or command
            runDeployScript();
        }

        return "OK";
    }

    private boolean verifySignature(String signature, String payload) {
        if (signature == null) return false;

        String expected = "sha256=" +
                Hex.encodeHexString(HmacUtils.hmacSha256(SECRET, payload));

        return expected.equals(signature);
    }

    private void runDeployScript() {
        try {
            ProcessBuilder pb = new ProcessBuilder(
                "/bin/bash", "/path/to/deploy.sh"
            );
            pb.start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Run Application

Run the Spring Boot application.

# Run via JAR
java -jar target/yourapp.jar

Production Options:

• Tomcat
• Docker
• systemd service

Maven Dependencies

Add required dependencies to pom.xml.

<dependencies>
    <!-- Spring Boot Web -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <!-- Apache Commons Codec for HMAC -->
    <dependency>
        <groupId>commons-codec</groupId>
        <artifactId>commons-codec</artifactId>
    </dependency>
</dependencies>

Application Properties

Configure server port in application.properties.

server.port=8080

Docker Deployment

Containerize the Spring Boot webhook handler.

FROM openjdk:17-slim
COPY target/webhook-handler.jar app.jar
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "/app.jar"]

Build and run:

docker build -t github-webhook .
docker run -p 8080:8080 -e SECRET=your_secret github-webhook

Systemd Service

Run as a systemd service on Linux.

Create /etc/systemd/system/github-webhook.service:

[Unit]
Description=GitHub Webhook Handler
After=network.target

[Service]
Type=simple
User=appuser
WorkingDirectory=/opt/webhook
ExecStart=/usr/bin/java -jar /opt/webhook/app.jar
Restart=on-failure

[Install]
WantedBy=multi-user.target

Enable and start:

sudo systemctl enable github-webhook
sudo systemctl start github-webhook