Implement shared email notification orchestration (Thymeleaf renderer, per-type builders)

pom.xml

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+<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>
+
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>3.3.2</version>
+        <relativePath/>
+    </parent>
+
+    <groupId>com.example</groupId>
+    <artifactId>email-notification-service</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>email-notification-service</name>
+    <description>Pattern example for email notification orchestration</description>
+
+    <properties>
+        <java.version>21</java.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-thymeleaf</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-configuration-processor</artifactId>
+            <optional>true</optional>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+</project>

src/main/java/com/example/notification/NotificationApplication.java

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+package com.example.notification;
+
+import com.example.notification.config.NotificationProperties;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+
+@SpringBootApplication
+@EnableConfigurationProperties(NotificationProperties.class)
+public class NotificationApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(NotificationApplication.class, args);
+    }
+}

src/main/java/com/example/notification/builder/HoldListCreatedModelBuilder.java

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+package com.example.notification.builder;
+
+import com.example.notification.domain.HoldListCreatedPayload;
+import com.example.notification.model.NotificationType;
+import com.example.notification.orchestration.NotificationModelBuilder;
+import org.springframework.stereotype.Component;
+
+import java.util.Map;
+
+@Component
+public class HoldListCreatedModelBuilder implements NotificationModelBuilder<HoldListCreatedPayload> {
+
+    @Override
+    public NotificationType type() {
+        return NotificationType.HOLD_LIST_CREATED;
+    }
+
+    @Override
+    public Class<HoldListCreatedPayload> payloadClass() {
+        return HoldListCreatedPayload.class;
+    }
+
+    @Override
+    public Map<String, Object> buildModel(HoldListCreatedPayload payload) {
+        return Map.of(
+                "holdListName", payload.holdListName(),
+                "createdBy", payload.createdBy(),
+                "itemCount", payload.itemCount()
+        );
+    }
+}

src/main/java/com/example/notification/builder/HoldListRemovedModelBuilder.java

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+package com.example.notification.builder;
+
+import com.example.notification.domain.HoldListRemovedPayload;
+import com.example.notification.model.NotificationType;
+import com.example.notification.orchestration.NotificationModelBuilder;
+import org.springframework.stereotype.Component;
+
+import java.util.Map;
+
+@Component
+public class HoldListRemovedModelBuilder implements NotificationModelBuilder<HoldListRemovedPayload> {
+
+    @Override
+    public NotificationType type() {
+        return NotificationType.HOLD_LIST_REMOVED;
+    }
+
+    @Override
+    public Class<HoldListRemovedPayload> payloadClass() {
+        return HoldListRemovedPayload.class;
+    }
+
+    @Override
+    public Map<String, Object> buildModel(HoldListRemovedPayload payload) {
+        return Map.of(
+                "holdListName", payload.holdListName(),
+                "removedBy", payload.removedBy(),
+                "reason", payload.reason()
+        );
+    }
+}

src/main/java/com/example/notification/config/NotificationCatalog.java

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+package com.example.notification.config;
+
+import com.example.notification.model.NotificationType;
+import org.springframework.stereotype.Component;
+
+@Component
+public class NotificationCatalog {
+
+    private final NotificationProperties properties;
+
+    public NotificationCatalog(NotificationProperties properties) {
+        this.properties = properties;
+    }
+
+    public NotificationDefinition getRequired(NotificationType type) {
+        NotificationDefinition definition = properties.getEmail().get(type);
+        if (definition == null) {
+            throw new IllegalArgumentException("No notification config found for type: " + type);
+        }
+        return definition;
+    }
+}

src/main/java/com/example/notification/config/NotificationDefinition.java

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+package com.example.notification.config;
+
+import java.util.List;
+
+public record NotificationDefinition(
+        List<String> recipients,
+        String template,
+        String subject,
+        Boolean enabled
+) {
+    public boolean isEnabled() {
+        return enabled == null || enabled;
+    }
+}

src/main/java/com/example/notification/config/NotificationProperties.java

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+package com.example.notification.config;
+
+import com.example.notification.model.NotificationType;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+import java.util.EnumMap;
+import java.util.Map;
+
+@ConfigurationProperties(prefix = "notifications")
+public class NotificationProperties {
+
+    private Map<NotificationType, NotificationDefinition> email = new EnumMap<>(NotificationType.class);
+
+    public Map<NotificationType, NotificationDefinition> getEmail() {
+        return email;
+    }
+
+    public void setEmail(Map<NotificationType, NotificationDefinition> email) {
+        this.email = email;
+    }
+}

src/main/java/com/example/notification/domain/HoldListCreatedPayload.java

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+package com.example.notification.domain;
+
+public record HoldListCreatedPayload(
+        String holdListName,
+        String createdBy,
+        int itemCount
+) {
+}

src/main/java/com/example/notification/domain/HoldListDomainService.java

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+package com.example.notification.domain;
+
+import com.example.notification.model.NotificationType;
+import com.example.notification.orchestration.EmailNotificationOrchestrator;
+import org.springframework.stereotype.Service;
+
+@Service
+public class HoldListDomainService {
+
+    private final EmailNotificationOrchestrator notificationOrchestrator;
+
+    public HoldListDomainService(EmailNotificationOrchestrator notificationOrchestrator) {
+        this.notificationOrchestrator = notificationOrchestrator;
+    }
+
+    public void createHoldList(String holdListName, String actor, int itemCount) {
+        HoldListCreatedPayload payload = new HoldListCreatedPayload(holdListName, actor, itemCount);
+        notificationOrchestrator.notify(NotificationType.HOLD_LIST_CREATED, payload);
+    }
+
+    public void removeHoldList(String holdListName, String actor, String reason) {
+        HoldListRemovedPayload payload = new HoldListRemovedPayload(holdListName, actor, reason);
+        notificationOrchestrator.notify(NotificationType.HOLD_LIST_REMOVED, payload);
+    }
+}

src/main/java/com/example/notification/domain/HoldListRemovedPayload.java

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+package com.example.notification.domain;
+
+public record HoldListRemovedPayload(
+        String holdListName,
+        String removedBy,
+        String reason
+) {
+}

src/main/java/com/example/notification/model/NotificationType.java

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+package com.example.notification.model;
+
+public enum NotificationType {
+    HOLD_LIST_CREATED,
+    HOLD_LIST_REMOVED
+}

src/main/java/com/example/notification/orchestration/EmailNotificationOrchestrator.java

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+package com.example.notification.orchestration;
+
+import com.example.notification.config.NotificationCatalog;
+import com.example.notification.config.NotificationDefinition;
+import com.example.notification.model.NotificationType;
+import com.example.notification.publish.EmailPublicationPublisher;
+import com.example.notification.publish.EmailPublicationRequest;
+import com.example.notification.rendering.TemplateRenderer;
+import org.springframework.stereotype.Service;
+
+import java.util.EnumMap;
+import java.util.List;
+import java.util.Map;
+
+@Service
+public class EmailNotificationOrchestrator {
+
+    private final NotificationCatalog catalog;
+    private final TemplateRenderer renderer;
+    private final EmailPublicationPublisher publisher;
+    private final Map<NotificationType, NotificationModelBuilder<?>> buildersByType;
+
+    public EmailNotificationOrchestrator(
+            NotificationCatalog catalog,
+            TemplateRenderer renderer,
+            EmailPublicationPublisher publisher,
+            List<NotificationModelBuilder<?>> builders
+    ) {
+        this.catalog = catalog;
+        this.renderer = renderer;
+        this.publisher = publisher;
+        this.buildersByType = new EnumMap<>(NotificationType.class);
+
+        for (NotificationModelBuilder<?> builder : builders) {
+            this.buildersByType.put(builder.type(), builder);
+        }
+    }
+
+    public <T> void notify(NotificationType type, T payload) {
+        NotificationDefinition definition = catalog.getRequired(type);
+        if (!definition.isEnabled()) {
+            return;
+        }
+
+        NotificationModelBuilder<T> builder = resolveBuilder(type, payload);
+        Map<String, Object> model = builder.buildModel(payload);
+        String renderedBody = renderer.render(definition.template(), model);
+
+        EmailPublicationRequest request = new EmailPublicationRequest(
+                type,
+                definition.recipients(),
+                definition.subject(),
+                renderedBody
+        );
+        publisher.publish(request);
+    }
+
+    @SuppressWarnings("unchecked")
+    private <T> NotificationModelBuilder<T> resolveBuilder(NotificationType type, T payload) {
+        NotificationModelBuilder<?> rawBuilder = buildersByType.get(type);
+        if (rawBuilder == null) {
+            throw new IllegalArgumentException("No NotificationModelBuilder registered for type: " + type);
+        }
+
+        if (!rawBuilder.payloadClass().isInstance(payload)) {
+            throw new IllegalArgumentException("Payload type mismatch for %s. Expected %s but got %s"
+                    .formatted(type, rawBuilder.payloadClass().getSimpleName(), payload.getClass().getSimpleName()));
+        }
+
+        return (NotificationModelBuilder<T>) rawBuilder;
+    }
+}

src/main/java/com/example/notification/orchestration/NotificationModelBuilder.java

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+package com.example.notification.orchestration;
+
+import com.example.notification.model.NotificationType;
+
+import java.util.Map;
+
+public interface NotificationModelBuilder<T> {
+
+    NotificationType type();
+
+    Class<T> payloadClass();
+
+    Map<String, Object> buildModel(T payload);
+}

src/main/java/com/example/notification/publish/EmailPublicationPublisher.java

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+package com.example.notification.publish;
+
+public interface EmailPublicationPublisher {
+    void publish(EmailPublicationRequest request);
+}

src/main/java/com/example/notification/publish/EmailPublicationRequest.java

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+package com.example.notification.publish;
+
+import com.example.notification.model.NotificationType;
+
+import java.util.List;
+
+public record EmailPublicationRequest(
+        NotificationType notificationType,
+        List<String> recipients,
+        String subject,
+        String body
+) {
+}

src/main/java/com/example/notification/rendering/TemplateRenderer.java

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+package com.example.notification.rendering;
+
+import java.util.Map;
+
+public interface TemplateRenderer {
+    String render(String templatePath, Map<String, Object> model);
+}

src/main/java/com/example/notification/rendering/ThymeleafTemplateRenderer.java

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+package com.example.notification.rendering;
+
+import org.springframework.stereotype.Component;
+import org.thymeleaf.TemplateEngine;
+import org.thymeleaf.context.Context;
+
+import java.util.Locale;
+import java.util.Map;
+
+@Component
+public class ThymeleafTemplateRenderer implements TemplateRenderer {
+
+    private final TemplateEngine templateEngine;
+
+    public ThymeleafTemplateRenderer(TemplateEngine templateEngine) {
+        this.templateEngine = templateEngine;
+    }
+
+    @Override
+    public String render(String templatePath, Map<String, Object> model) {
+        Context context = new Context(Locale.getDefault(), model);
+        return templateEngine.process(templatePath, context);
+    }
+}