Merge pull request #1290 from herder

* pr/1290:
  Polish "Add support for Maven extensions"
  Add support for Maven extensions

Closes gh-1290

initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/maven/MavenBuild.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2023 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.
@@ -26,6 +26,7 @@ import io.spring.initializr.generator.buildsystem.maven.MavenBuildSettings.Build
  *
  * @author Andy Wilkinson
  * @author Stephane Nicoll
+ * @author Niklas Herder
  */
 public class MavenBuild extends Build {
 
@@ -37,6 +38,8 @@ public class MavenBuild extends Build {
 
 	private final MavenPluginContainer plugins = new MavenPluginContainer();
 
+	private final MavenExtensionContainer extensions = new MavenExtensionContainer();
+
 	private final MavenDistributionManagement.Builder distributionManagement = new MavenDistributionManagement.Builder();
 
 	private final MavenProfileContainer profiles;
@@ -105,6 +108,15 @@ public class MavenBuild extends Build {
 		return this.plugins;
 	}
 
+	/**
+	 * Return the {@linkplain MavenExtensionContainer extension container} to use to
+	 * configure extensions.
+	 * @return the {@link MavenExtensionContainer}
+	 */
+	public MavenExtensionContainer extensions() {
+		return this.extensions;
+	}
+
 	/**
 	 * Return the {@linkplain MavenProfileContainer profile container} to use to configure
 	 * profiles.

initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/maven/MavenBuildWriter.java

@@ -59,6 +59,7 @@ import org.springframework.util.StringUtils;
  * @author Olga Maciaszek-Sharma
  * @author Jafer Khan Shamshad
  * @author Joachim Pasquali
+ * @author Niklas Herder
  */
 public class MavenBuildWriter {
 
@@ -315,7 +316,8 @@ public class MavenBuildWriter {
 		MavenBuildSettings settings = build.getSettings();
 		if (settings.getDefaultGoal() == null && settings.getFinalName() == null
 				&& settings.getSourceDirectory() == null && settings.getTestSourceDirectory() == null
-				&& build.resources().isEmpty() && build.testResources().isEmpty() && build.plugins().isEmpty()) {
+				&& build.resources().isEmpty() && build.testResources().isEmpty() && build.plugins().isEmpty()
+				&& build.extensions().isEmpty()) {
 			return;
 		}
 		writer.println();
@@ -326,6 +328,7 @@ public class MavenBuildWriter {
 			writeSingleElement(writer, "testSourceDirectory", settings.getTestSourceDirectory());
 			writeResources(writer, build.resources(), build.testResources());
 			writeCollectionElement(writer, "plugins", build.plugins().values(), this::writePlugin);
+			writeCollectionElement(writer, "extensions", build.extensions().values(), this::writeExtension);
 		});
 	}
 
@@ -495,6 +498,14 @@ public class MavenBuildWriter {
 		}
 	}
 
+	private void writeExtension(IndentingWriter writer, MavenExtension extension) {
+		writeElement(writer, "extension", () -> {
+			writeSingleElement(writer, "groupId", extension.getGroupId());
+			writeSingleElement(writer, "artifactId", extension.getArtifactId());
+			writeSingleElement(writer, "version", extension.getVersion());
+		});
+	}
+
 	private void writeProfiles(IndentingWriter writer, MavenBuild build) {
 		MavenProfileContainer profiles = build.profiles();
 		if (profiles.isEmpty()) {

initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/maven/MavenExtension.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2012-2023 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 io.spring.initializr.generator.buildsystem.maven;
+
+/**
+ * A build extension in a @{@link MavenBuild}.
+ *
+ * @author Niklas Herder
+ * @author Stephane Nicoll
+ */
+public class MavenExtension {
+
+	private final String groupId;
+
+	private final String artifactId;
+
+	private final String version;
+
+	protected MavenExtension(Builder builder) {
+		this.groupId = builder.groupId;
+		this.artifactId = builder.artifactId;
+		this.version = builder.version;
+	}
+
+	/**
+	 * Return the group ID of the extension.
+	 * @return the group id
+	 */
+	public String getGroupId() {
+		return this.groupId;
+	}
+
+	/**
+	 * Return the artifact ID of the extension.
+	 * @return the artifact id
+	 */
+	public String getArtifactId() {
+		return this.artifactId;
+	}
+
+	/**
+	 * Return the version of the extension.
+	 * @return the artifact id
+	 */
+	public String getVersion() {
+		return this.version;
+	}
+
+	public static class Builder {
+
+		private final String groupId;
+
+		private final String artifactId;
+
+		private String version;
+
+		protected Builder(String groupId, String artifactId) {
+			this.groupId = groupId;
+			this.artifactId = artifactId;
+		}
+
+		/**
+		 * Set the version of the extension.
+		 * @param version the version of the extension
+		 * @return this for method chaining
+		 */
+		public Builder version(String version) {
+			this.version = version;
+			return this;
+		}
+
+		/**
+		 * Build a {@link MavenExtension} with the current state of this builder.
+		 * @return a {@link MavenExtension}
+		 */
+		public MavenExtension build() {
+			return new MavenExtension(this);
+		}
+
+	}
+
+}

initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/maven/MavenExtensionContainer.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2012-2023 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 io.spring.initializr.generator.buildsystem.maven;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.function.Consumer;
+import java.util.stream.Stream;
+
+/**
+ * A container for {@link MavenExtension maven extensions}.
+ *
+ * @author Niklas Herder
+ * @author Stephane Nicoll
+ */
+public class MavenExtensionContainer {
+
+	private final Map<String, MavenExtension.Builder> extensions = new LinkedHashMap<>();
+
+	/**
+	 * Specify if this container is empty.
+	 * @return {@code true} if no {@link MavenExtension} is added
+	 */
+	public boolean isEmpty() {
+		return this.extensions.isEmpty();
+	}
+
+	/**
+	 * Specify if this container has a extension with the specified {@code groupId} and
+	 * {@code artifactId}.
+	 * @param groupId the groupId of the extension
+	 * @param artifactId the artifactId of the extension
+	 * @return {@code true} if an item with the specified {@code groupId} and
+	 * {@code artifactId} exists
+	 */
+	public boolean has(String groupId, String artifactId) {
+		return this.extensions.containsKey(extensionKey(groupId, artifactId));
+	}
+
+	/**
+	 * Returns a {@link Stream} of registered {@link MavenExtension}s.
+	 * @return a stream of {@link MavenExtension}s
+	 */
+	public Stream<MavenExtension> values() {
+		return this.extensions.values().stream().map(MavenExtension.Builder::build);
+	}
+
+	/**
+	 * Add a {@link MavenExtension} with the specified {@code groupId},
+	 * {@code artifactId}, and {@code version}. If the extension has already been added,
+	 * only update the version if necessary.
+	 * @param groupId the groupId of the extension
+	 * @param artifactId the artifactId of the extension
+	 * @param version the version of the extension
+	 * @see #add(String, String, Consumer)
+	 */
+	public void add(String groupId, String artifactId, String version) {
+		add(groupId, artifactId, (extension) -> extension.version(version));
+	}
+
+	/**
+	 * Add a {@link MavenExtension} with the specified {@code groupId} and
+	 * {@code artifactId} and {@link Consumer} to customize the extension. If the
+	 * extension has already been added, the consumer can be used to further tune the
+	 * existing extension configuration.
+	 * @param groupId the groupId of the extension
+	 * @param artifactId the artifactId of the extension
+	 * @param extension a {@link Consumer} to customize the {@link MavenExtension}
+	 */
+	public void add(String groupId, String artifactId, Consumer<MavenExtension.Builder> extension) {
+		extension.accept(addExtension(groupId, artifactId));
+	}
+
+	private MavenExtension.Builder addExtension(String groupId, String artifactId) {
+		return this.extensions.computeIfAbsent(extensionKey(groupId, artifactId),
+				(extensionId) -> new MavenExtension.Builder(groupId, artifactId));
+	}
+
+	/**
+	 * Remove the extension with the specified {@code groupId} and {@code artifactId}.
+	 * @param groupId the groupId of the extension to remove
+	 * @param artifactId the artifactId of the extension to remove
+	 * @return {@code true} if such a extension was registered, {@code false} otherwise
+	 */
+	public boolean remove(String groupId, String artifactId) {
+		return this.extensions.remove(extensionKey(groupId, artifactId)) != null;
+	}
+
+	private String extensionKey(String groupId, String artifactId) {
+		return String.format("%s:%s", groupId, artifactId);
+	}
+
+}

initializr-generator/src/test/java/io/spring/initializr/generator/buildsystem/maven/MavenBuildWriterTests.java

@@ -700,6 +700,23 @@ class MavenBuildWriterTests {
 		});
 	}
 
+	@Test
+	void pomWithoutExtensions() {
+		MavenBuild build = new MavenBuild();
+		generatePom(build, (pom) -> assertThat(pom).nodeAtPath("/project/build/extensions").isNull());
+	}
+
+	@Test
+	void pomWithExtension() {
+		MavenBuild build = new MavenBuild();
+		build.extensions().add("com.example", "testExtension", "1.6.1");
+		generatePom(build, (pom) -> {
+			assertThat(pom).textAtPath("/project/build/extensions/extension/groupId").isEqualTo("com.example");
+			assertThat(pom).textAtPath("/project/build/extensions/extension/artifactId").isEqualTo("testExtension");
+			assertThat(pom).textAtPath("/project/build/extensions/extension/version").isEqualTo("1.6.1");
+		});
+	}
+
 	@Test
 	void pomWithEmptyBuild() {
 		MavenBuild build = new MavenBuild();