Introduce builder API for AOT processor Settings

Closes gh-29341

Author: sbrannen

Diff for: spring-context/src/main/java/org/springframework/context/aot/AbstractAotProcessor.java

@@ -24,6 +24,7 @@
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.nativex.FileNativeConfigurationWriter;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.FileSystemUtils;
 
 /**
@@ -49,6 +50,7 @@ public abstract class AbstractAotProcessor {
 
 	/**
 	 * Create a new processor instance with the supplied {@linkplain Settings settings}.
+	 * @see Settings#builder()
 	 */
 	protected AbstractAotProcessor(Settings settings) {
 		this.settings = settings;
@@ -102,114 +104,163 @@ protected void writeHints(RuntimeHints hints) {
 	/**
 	 * Common settings for AOT processors.
 	 */
-	public static class Settings {
+	public static final class Settings {
 
-		@Nullable
-		private Path sourceOutput;
+		private final Path sourceOutput;
 
-		@Nullable
-		private Path resourceOutput;
+		private final Path resourceOutput;
 
-		@Nullable
-		private Path classOutput;
+		private final Path classOutput;
 
-		@Nullable
-		private String groupId;
+		private final String groupId;
 
-		@Nullable
-		private String artifactId;
+		private final String artifactId;
 
 
-		/**
-		 * Set the output directory for generated sources.
-		 * @param sourceOutput the location of generated sources
-		 * @return this settings object for method chaining
-		 */
-		public Settings setSourceOutput(Path sourceOutput) {
+		private Settings(Path sourceOutput, Path resourceOutput, Path classOutput, String groupId, String artifactId) {
 			this.sourceOutput = sourceOutput;
-			return this;
+			this.resourceOutput = resourceOutput;
+			this.classOutput = classOutput;
+			this.groupId = groupId;
+			this.artifactId = artifactId;
 		}
 
+
 		/**
-		 * Get the output directory for generated sources.
+		 * Create a new {@link Builder} for {@link Settings}.
 		 */
-		@Nullable
-		public Path getSourceOutput() {
-			return this.sourceOutput;
+		public static Builder builder() {
+			return new Builder();
 		}
 
+
 		/**
-		 * Set the output directory for generated resources.
-		 * @param resourceOutput the location of generated resources
-		 * @return this settings object for method chaining
+		 * Get the output directory for generated sources.
 		 */
-		public Settings setResourceOutput(Path resourceOutput) {
-			this.resourceOutput = resourceOutput;
-			return this;
+		public Path getSourceOutput() {
+			return this.sourceOutput;
 		}
 
 		/**
 		 * Get the output directory for generated resources.
 		 */
-		@Nullable
 		public Path getResourceOutput() {
 			return this.resourceOutput;
 		}
 
-		/**
-		 * Set the output directory for generated classes.
-		 * @param classOutput the location of generated classes
-		 * @return this settings object for method chaining
-		 */
-		public Settings setClassOutput(Path classOutput) {
-			this.classOutput = classOutput;
-			return this;
-		}
-
 		/**
 		 * Get the output directory for generated classes.
 		 */
-		@Nullable
 		public Path getClassOutput() {
 			return this.classOutput;
 		}
 
-		/**
-		 * Set the group ID of the application.
-		 * @param groupId the group ID of the application, used to locate
-		 * {@code native-image.properties}
-		 * @return this settings object for method chaining
-		 */
-		public Settings setGroupId(String groupId) {
-			this.groupId = groupId;
-			return this;
-		}
-
 		/**
 		 * Get the group ID of the application.
 		 */
-		@Nullable
 		public String getGroupId() {
 			return this.groupId;
 		}
 
 		/**
-		 * Set the artifact ID of the application.
-		 * @param artifactId the artifact ID of the application, used to locate
-		 * {@code native-image.properties}
-		 * @return this settings object for method chaining
+		 * Get the artifact ID of the application.
 		 */
-		public Settings setArtifactId(String artifactId) {
-			this.artifactId = artifactId;
-			return this;
+		public String getArtifactId() {
+			return this.artifactId;
 		}
 
+
 		/**
-		 * Get the artifact ID of the application.
+		 * Fluent builder API for {@link Settings}.
 		 */
-		@Nullable
-		public String getArtifactId() {
-			return this.artifactId;
+		public static final class Builder {
+
+			@Nullable
+			private Path sourceOutput;
+
+			@Nullable
+			private Path resourceOutput;
+
+			@Nullable
+			private Path classOutput;
+
+			@Nullable
+			private String groupId;
+
+			@Nullable
+			private String artifactId;
+
+
+			private Builder() {
+				// internal constructor
+			}
+
+
+			/**
+			 * Set the output directory for generated sources.
+			 * @param sourceOutput the location of generated sources
+			 * @return this builder for method chaining
+			 */
+			public Builder sourceOutput(Path sourceOutput) {
+				this.sourceOutput = sourceOutput;
+				return this;
+			}
+
+			/**
+			 * Set the output directory for generated resources.
+			 * @param resourceOutput the location of generated resources
+			 * @return this builder for method chaining
+			 */
+			public Builder resourceOutput(Path resourceOutput) {
+				this.resourceOutput = resourceOutput;
+				return this;
+			}
+
+			/**
+			 * Set the output directory for generated classes.
+			 * @param classOutput the location of generated classes
+			 * @return this builder for method chaining
+			 */
+			public Builder classOutput(Path classOutput) {
+				this.classOutput = classOutput;
+				return this;
+			}
+
+			/**
+			 * Set the group ID of the application.
+			 * @param groupId the group ID of the application, used to locate
+			 * {@code native-image.properties}
+			 * @return this builder for method chaining
+			 */
+			public Builder groupId(String groupId) {
+				this.groupId = groupId;
+				return this;
+			}
+
+			/**
+			 * Set the artifact ID of the application.
+			 * @param artifactId the artifact ID of the application, used to locate
+			 * {@code native-image.properties}
+			 * @return this builder for method chaining
+			 */
+			public Builder artifactId(String artifactId) {
+				this.artifactId = artifactId;
+				return this;
+			}
+
+			/**
+			 * Build the {@link Settings} configured in this {@code Builder}.
+			 */
+			public Settings build() {
+				Assert.notNull(this.sourceOutput, "'sourceOutput' must not be null");
+				Assert.notNull(this.resourceOutput, "'resourceOutput' must not be null");
+				Assert.notNull(this.classOutput, "'classOutput' must not be null");
+				Assert.hasText(this.groupId, "'groupId' must not be null or empty");
+				Assert.hasText(this.artifactId, "'artifactId' must not be null or empty");
+				return new Settings(this.sourceOutput, this.resourceOutput, this.classOutput,
+						this.groupId, this.artifactId);
+			}
+
 		}
 
 	}

Diff for: spring-context/src/test/java/org/springframework/context/aot/AotProcessorTests.java

@@ -0,0 +1,126 @@
+/*
+ * Copyright 2002-2022 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.context.aot;
+
+import java.nio.file.Path;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import org.springframework.context.aot.AbstractAotProcessor.Settings;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link AbstractAotProcessor}, settings, and builder.
+ *
+ * @author Sam Brannen
+ * @since 6.0
+ */
+class AotProcessorTests {
+
+	@Test
+	void builderRejectsMissingSourceOutput() {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Settings.builder().build())
+			.withMessageContaining("'sourceOutput'");
+	}
+
+	@Test
+	void builderRejectsMissingResourceOutput(@TempDir Path tempDir) {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Settings.builder().sourceOutput(tempDir).build())
+			.withMessageContaining("'resourceOutput'");
+	}
+
+	@Test
+	void builderRejectsMissingClassOutput(@TempDir Path tempDir) {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Settings.builder()
+				.sourceOutput(tempDir)
+				.resourceOutput(tempDir)
+				.build())
+			.withMessageContaining("'classOutput'");
+	}
+
+	@Test
+	void builderRejectsMissingGroupdId(@TempDir Path tempDir) {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Settings.builder()
+				.sourceOutput(tempDir)
+				.resourceOutput(tempDir)
+				.classOutput(tempDir)
+				.build())
+			.withMessageContaining("'groupId'");
+	}
+
+	@Test
+	void builderRejectsEmptyGroupdId(@TempDir Path tempDir) {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Settings.builder()
+				.sourceOutput(tempDir)
+				.resourceOutput(tempDir)
+				.classOutput(tempDir)
+				.groupId("           ")
+				.build())
+			.withMessageContaining("'groupId'");
+	}
+
+	@Test
+	void builderRejectsMissingArtifactId(@TempDir Path tempDir) {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Settings.builder()
+				.sourceOutput(tempDir)
+				.resourceOutput(tempDir)
+				.classOutput(tempDir)
+				.groupId("my-group")
+				.build())
+			.withMessageContaining("'artifactId'");
+	}
+
+	@Test
+	void builderRejectsEmptyArtifactId(@TempDir Path tempDir) {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> Settings.builder()
+				.sourceOutput(tempDir)
+				.resourceOutput(tempDir)
+				.classOutput(tempDir)
+				.groupId("my-group")
+				.artifactId("           ")
+				.build())
+			.withMessageContaining("'artifactId'");
+	}
+
+	@Test
+	void builderAcceptsRequiredSettings(@TempDir Path tempDir) {
+		Settings settings = Settings.builder()
+				.sourceOutput(tempDir)
+				.resourceOutput(tempDir)
+				.classOutput(tempDir)
+				.groupId("my-group")
+				.artifactId("my-artifact")
+				.build();
+		assertThat(settings).isNotNull();
+		assertThat(settings.getSourceOutput()).isEqualTo(tempDir);
+		assertThat(settings.getResourceOutput()).isEqualTo(tempDir);
+		assertThat(settings.getClassOutput()).isEqualTo(tempDir);
+		assertThat(settings.getGroupId()).isEqualTo("my-group");
+		assertThat(settings.getArtifactId()).isEqualTo("my-artifact");
+	}
+
+}

Diff for: spring-context/src/test/java/org/springframework/context/aot/ContextAotProcessorTests.java

@@ -128,12 +128,13 @@ private static class DemoContextAotProcessor extends ContextAotProcessor {
 
 		private static Settings createSettings(Path sourceOutput, Path resourceOutput,
 				Path classOutput, String groupId, String artifactId) {
-			return new Settings()
-					.setSourceOutput(sourceOutput)
-					.setResourceOutput(resourceOutput)
-					.setClassOutput(classOutput)
-					.setArtifactId(artifactId)
-					.setGroupId(groupId);
+			return Settings.builder()
+					.sourceOutput(sourceOutput)
+					.resourceOutput(resourceOutput)
+					.classOutput(classOutput)
+					.artifactId(artifactId)
+					.groupId(groupId)
+					.build();
 		}
 
 		@Override