Send Emails with Spring Boot and Google Cloud: Complete Guide with SendGrid Integration

Workflow of sending an email in a Spring Boot application integrated with Google Cloud's SendGrid service

Explanation of the Diagram

1. User Interaction: A user sends an HTTP request to the Spring Boot application to trigger the email-sending process.
2. Application Processing: The Spring Boot app validates the input and prepares the email request.
3. API Integration: The app sends the email request to the SendGrid API.
4. SendGrid Processing: SendGrid processes the email request and sends the email to the recipient.
5. Response Handling: SendGrid returns the status, and the Spring Boot app relays this back to the user.

Here’s an end-to-end example of how to send emails in a Spring Boot application using Google Cloud services, specifically integrating with SendGrid, which is a recommended solution for transactional email in Google Cloud.

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1. Set Up SendGrid on Google Cloud

1. Enable SendGrid:

   • Go to the Google Cloud Marketplace - SendGrid.
   • Click "Subscribe" and choose a pricing plan.

2. Create an API Key:

   • Log in to the SendGrid Dashboard.
   • Navigate to Settings > API Keys.
   • Click "Create API Key", provide a name, and assign permissions (e.g., Full Access).
   • Copy the API key (you’ll need it later).

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2. Spring Boot Project Setup

2.1 Add Dependencies

Add the following dependencies to your pom.xml:

<dependencies>
    <!-- Spring Boot Starter Web -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <!-- SendGrid Java Library -->
    <dependency>
        <groupId>com.sendgrid</groupId>
        <artifactId>sendgrid-java</artifactId>
        <version>4.9.3</version>
    </dependency>
</dependencies>

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2.2 Configure SendGrid API Key

Add the API key to your application.properties or application.yml:

application.properties:

sendgrid.api.key=YOUR_SENDGRID_API_KEY

application.yml:

sendgrid:
  api:
    key: YOUR_SENDGRID_API_KEY

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3. Create Email Service

Create a service to handle email sending:

import com.sendgrid.*;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

import java.io.IOException;

@Service
public class EmailService {

    @Value("${sendgrid.api.key}")
    private String sendGridApiKey;

    public String sendEmail(String toEmail, String subject, String body) {
        Email from = new Email("your-email@example.com"); // Replace with your verified SendGrid email
        Email to = new Email(toEmail);
        Content content = new Content("text/plain", body);
        Mail mail = new Mail(from, subject, to, content);

        SendGrid sg = new SendGrid(sendGridApiKey);
        Request request = new Request();

        try {
            request.setMethod(Method.POST);
            request.setEndpoint("mail/send");
            request.setBody(mail.build());
            Response response = sg.api(request);
            return "Email sent with status code: " + response.getStatusCode();
        } catch (IOException ex) {
            return "Error sending email: " + ex.getMessage();
        }
    }
}

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4. Create a REST Controller

Create a controller to expose an API for sending emails:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api/emails")
public class EmailController {

    @Autowired
    private EmailService emailService;

    @PostMapping("/send")
    public String sendEmail(@RequestParam String to, @RequestParam String subject, @RequestParam String body) {
        return emailService.sendEmail(to, subject, body);
    }
}

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5. Test the Application

1. Start your Spring Boot application.
2. Use a tool like Postman or curl to test the API:

Request:

POST http://localhost:8080/api/emails/send
Content-Type: application/x-www-form-urlencoded

to=recipient@example.com
subject=Hello from Spring Boot
body=This is a test email sent via Google Cloud and SendGrid!

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6. Deploy to Google Cloud (Optional)

6.1 Dockerize Your Application

Create a Dockerfile:

FROM openjdk:17-jdk-slim
VOLUME /tmp
COPY target/*.jar app.jar
ENTRYPOINT ["java", "-jar", "/app.jar"]

Build the Docker image:

mvn clean package
docker build -t spring-boot-email-app .

6.2 Deploy to Google Cloud Run

1. Push the Docker image to Google Container Registry (GCR) or Artifact Registry.
2. Deploy to Google Cloud Run.

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7. Monitor Email Logs

Log in to the SendGrid Dashboard to monitor email delivery, bounces, or errors.