GH-130 - Fall back to annotated class' name as system name.

spring-modulith-core/src/main/java/org/springframework/modulith/core/AnnotationModulithMetadata.java

@@ -120,6 +120,7 @@ class AnnotationModulithMetadata implements ModulithMetadata {
 	public Optional<String> getSystemName() {
 
 		return Optional.of(annotation.systemName()) //
-				.filter(StringUtils::hasText);
+				.filter(StringUtils::hasText) //
+				.or(() -> Optional.of(modulithType.getSimpleName()));
 	}
 }

spring-modulith-core/src/main/java/org/springframework/modulith/core/ModulithMetadata.java

@@ -45,7 +45,7 @@ public interface ModulithMetadata {
 				String.format(ANNOTATION_MISSING, annotated.getSimpleName(), Modulith.class.getSimpleName(),
 						Modulithic.class.getSimpleName(), SpringTypes.AT_SPRING_BOOT_APPLICATION));
 
-		Supplier<ModulithMetadata> withDefaults = () -> DefaultModulithMetadata.of(annotated).orElseThrow(exception);
+		Supplier<ModulithMetadata> withDefaults = () -> SpringBootModulithMetadata.of(annotated).orElseThrow(exception);
 
 		return AnnotationModulithMetadata.of(annotated).orElseGet(withDefaults);
 	}
@@ -57,7 +57,7 @@ public interface ModulithMetadata {
 	 * @return will never be {@literal null}.
 	 */
 	public static ModulithMetadata of(String javaPackage) {
-		return DefaultModulithMetadata.of(javaPackage);
+		return SpringBootModulithMetadata.of(javaPackage);
 	}
 
 	/**

spring-modulith-core/src/main/java/org/springframework/modulith/core/SpringBootModulithMetadata.java

@@ -21,6 +21,7 @@ import java.util.List;
 import java.util.Optional;
 import java.util.stream.Stream;
 
+import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.lang.NonNull;
 import org.springframework.modulith.Modulith;
@@ -34,31 +35,33 @@ import org.springframework.util.Assert;
  *
  * @author Oliver Drotbohm
  */
-class DefaultModulithMetadata implements ModulithMetadata {
+class SpringBootModulithMetadata implements ModulithMetadata {
 
 	private static final Class<? extends Annotation> AT_SPRING_BOOT_APPLICATION = Types
 			.loadIfPresent(SpringTypes.AT_SPRING_BOOT_APPLICATION);
 
 	private final @NonNull Object source;
+	private final String systemName;
 
 	/**
-	 * Creates a new {@link DefaultModulithMetadata} for the given source.
+	 * Creates a new {@link SpringBootModulithMetadata} for the given source.
 	 *
 	 * @param source must not be {@literal null}.
 	 */
-	private DefaultModulithMetadata(Object source) {
+	private SpringBootModulithMetadata(Object source, String systemName) {
 
 		Assert.notNull(source, "Source must not be null!");
 
 		this.source = source;
+		this.systemName = systemName;
 	}
 
 	/**
-	 * Creates a new {@link ModulithMetadata} representing the defaults of a class annotated but not customized with
-	 * {@link Modulithic} or {@link Modulith}.
+	 * Creates a new {@link ModulithMetadata} representing the defaults of a class annotated with
+	 * {@link SpringBootApplication} but not customized with {@link Modulithic} or {@link Modulith}.
 	 *
 	 * @param annotated must not be {@literal null}.
-	 * @return
+	 * @return will never be {@literal null}.
 	 */
 	public static Optional<ModulithMetadata> of(Class<?> annotated) {
 
@@ -66,7 +69,7 @@ class DefaultModulithMetadata implements ModulithMetadata {
 
 		return Optional.ofNullable(AT_SPRING_BOOT_APPLICATION) //
 				.filter(it -> AnnotatedElementUtils.hasAnnotation(annotated, it)) //
-				.map(__ -> new DefaultModulithMetadata(annotated));
+				.map(__ -> new SpringBootModulithMetadata(annotated, annotated.getSimpleName()));
 	}
 
 	/**
@@ -79,7 +82,7 @@ class DefaultModulithMetadata implements ModulithMetadata {
 
 		Assert.hasText(javaPackage, "Package name must not be null or empty!");
 
-		return new DefaultModulithMetadata(javaPackage);
+		return new SpringBootModulithMetadata(javaPackage, null);
 	}
 
 	/*
@@ -133,6 +136,6 @@ class DefaultModulithMetadata implements ModulithMetadata {
 	 */
 	@Override
 	public Optional<String> getSystemName() {
-		return Optional.empty();
+		return Optional.ofNullable(systemName);
 	}
 }

spring-modulith-core/src/test/java/org/springframework/modulith/core/AnnotationModulithMetadataUnitTest.java

@@ -22,7 +22,6 @@ import java.lang.annotation.RetentionPolicy;
 
 import org.junit.jupiter.api.Test;
 import org.springframework.modulith.Modulithic;
-import org.springframework.modulith.core.AnnotationModulithMetadata;
 
 /**
  * Unit tests for {@link AnnotationModulithMetadata}.
@@ -47,6 +46,14 @@ class AnnotationModulithMetadataUnitTest {
 		});
 	}
 
+	@Test // #130
+	void usesSimpleClassNameAsDefaultSystemName() {
+
+		assertThat(AnnotationModulithMetadata.of(Sample.class)).hasValueSatisfying(it -> {
+			assertThat(it.getSystemName()).hasValue(Sample.class.getSimpleName());
+		});
+	}
+
 	@Modulithic(useFullyQualifiedModuleNames = true)
 	static class Sample {}
 
@@ -55,6 +62,5 @@ class AnnotationModulithMetadataUnitTest {
 
 	@Retention(RetentionPolicy.RUNTIME)
 	@Modulithic(useFullyQualifiedModuleNames = true)
-	@interface Intermediate {
-	}
+	@interface Intermediate {}
 }

spring-modulith-core/src/test/java/org/springframework/modulith/core/ModulithMetadataUnitTest.java

@@ -23,7 +23,6 @@ import org.junit.jupiter.api.Test;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.modulith.Modulith;
 import org.springframework.modulith.Modulithic;
-import org.springframework.modulith.core.ModulithMetadata;
 
 /**
  * Unit tests for {@link ModulithMetadata}.
@@ -53,7 +52,7 @@ class ModulithMetadataUnitTest {
 
 		assertThat(metadata.getAdditionalPackages()).isEmpty();
 		assertThat(metadata.getSharedModuleNames()).isEmpty();
-		assertThat(metadata.getSystemName()).isEmpty();
+		assertThat(metadata.getSystemName()).hasValue(SpringBootApplicationAnnotated.class.getSimpleName());
 		assertThat(metadata.useFullyQualifiedModuleNames()).isFalse();
 	}
 

spring-modulith-core/src/test/java/org/springframework/modulith/core/SpringBootModulithMetadataUnitTest.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.modulith.core;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * Unit tests for {@link SpringBootModulithMetadata}.
+ *
+ * @author Oliver Drotbohm
+ */
+class SpringBootModulithMetadataUnitTest {
+
+	@Test // #130
+	void usesClassNameAsSystemNameDefault() {
+
+		var metadata = SpringBootModulithMetadata.of(SpringBootApp.class);
+
+		assertThat(metadata).hasValueSatisfying(it -> {
+			assertThat(it.getSystemName()).hasValue(SpringBootApp.class.getSimpleName());
+		});
+	}
+
+	@Test // #130
+	void doesNotExposeASystemNameForPackageBasedMetadata() {
+		assertThat(SpringBootModulithMetadata.of("com.acme").getSystemName()).isEmpty();
+	}
+
+	@SpringBootApplication
+	private static class SpringBootApp {}
+}