Send email from Spring Boot

package com.acme.email;

import java.util.List;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestClient;
import org.springframework.web.client.RestClientResponseException;

@ConfigurationProperties(prefix = "emailssh")
record EmailsshProperties(String apiKey, String from, String baseUrl) {}

@Configuration
@EnableAsync
class EmailConfig {

    @Bean
    RestClient emailsshClient(RestClient.Builder builder, EmailsshProperties props) {
        return builder
                .baseUrl(props.baseUrl())
                .defaultHeader(HttpHeaders.AUTHORIZATION, "Bearer " + props.apiKey())
                .defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
                .build();
    }
}

@Service
public class EmailService {

    private static final Logger log = LoggerFactory.getLogger(EmailService.class);

    private final RestClient client;
    private final EmailsshProperties props;

    public EmailService(RestClient emailsshClient, EmailsshProperties props) {
        this.client = emailsshClient;
        this.props = props;
    }

    /** Runs on the async executor, so the controller thread is free immediately. */
    @Async
    public void sendWelcome(String to, String name) {
        Map<String, Object> body = Map.of(
                "from", props.from(),
                "to", List.of(to),
                "subject", "Welcome to Acme",
                "html", "<p>Hi " + escape(name) + ", your Acme account is ready.</p>",
                "text", "Hi " + name + ", your Acme account is ready.",
                "idempotency_key", "welcome:" + to.toLowerCase());

        try {
            Map<?, ?> response = client.post()
                    .uri("/emails")
                    .body(body)
                    .retrieve()
                    .body(Map.class);

            log.info("emails.sh queued {}", response == null ? "unknown" : response.get("id"));
        } catch (RestClientResponseException error) {
            // The response body is prose and says what to do next, so keep it.
            log.error("emails.sh {}: {}", error.getStatusCode(), error.getResponseBodyAsString());
        }
    }

    private static String escape(String value) {
        return value.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;");
    }
}

package com.acme.email;

import jakarta.validation.Valid;
import jakarta.validation.constraints.Email;
import jakarta.validation.constraints.NotBlank;

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class SignupController {

    private final EmailService email;

    public SignupController(EmailService email) {
        this.email = email;
    }

    record SignupRequest(@NotBlank @Email String email, String name) {}

    @PostMapping("/signup")
    public ResponseEntity<Void> signup(@Valid @RequestBody SignupRequest request) {
        email.sendWelcome(request.email(), request.name() == null ? "there" : request.name());
        return ResponseEntity.accepted().build();
    }
}

package com.acme;

import com.acme.email.EmailsshProperties;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;

@SpringBootApplication
@EnableConfigurationProperties(EmailsshProperties.class)
public class AcmeApplication {

    public static void main(String[] args) {
        SpringApplication.run(AcmeApplication.class, args);
    }
}