Add support for Docker Compose

This commit adds the necessary infrastructure to design and contribute
a compose file to the project. ComposeHelpDocumentCustomizer can be
used to write out a section into the help file containing a table
listing all the services with their images and tags.

See gh-1417

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeFile.java

@@ -0,0 +1,70 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.io.PrintWriter;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * A Docker Compose file.
+ *
+ * @author Moritz Halbritter
+ */
+public class DockerComposeFile {
+
+	// TreeMap to sort services by name
+	private final Map<String, DockerComposeService> services = new TreeMap<>();
+
+	/**
+	 * Adds a {@link DockerComposeService service} to the file. If a service with the same
+	 * {@link DockerComposeService#getName() name} already exists, it is replaced.
+	 * @param service the service to add
+	 * @return {@code this}
+	 */
+	public DockerComposeFile addService(DockerComposeService service) {
+		this.services.put(service.getName(), service);
+		return this;
+	}
+
+	/**
+	 * Returns the service with the given name.
+	 * @param name the name
+	 * @return the service or {@code null} if no service with the given name exists
+	 */
+	public DockerComposeService getService(String name) {
+		return this.services.get(name);
+	}
+
+	/**
+	 * Returns all services.
+	 * @return all services
+	 */
+	public Collection<DockerComposeService> getServices() {
+		return Collections.unmodifiableCollection(this.services.values());
+	}
+
+	void write(PrintWriter writer) {
+		writer.println("services:");
+		for (DockerComposeService service : this.services.values()) {
+			service.write(writer, 1);
+		}
+	}
+
+}

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeFileCustomizer.java

@@ -0,0 +1,42 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import org.springframework.core.Ordered;
+
+/**
+ * Callback for customizing a project's {@link DockerComposeFile}. Invoked with an
+ * {@link Ordered order} of {@code 0} by default, considering overriding
+ * {@link #getOrder()} to customize this behaviour.
+ *
+ * @author Moritz Halbritter
+ */
+@FunctionalInterface
+public interface DockerComposeFileCustomizer extends Ordered {
+
+	/**
+	 * Customizes the given {@link DockerComposeFile}.
+	 * @param composeFile the compose file to customize
+	 */
+	void customize(DockerComposeFile composeFile);
+
+	@Override
+	default int getOrder() {
+		return 0;
+	}
+
+}

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeHelpDocumentCustomizer.java

@@ -0,0 +1,62 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+
+import io.spring.initializr.generator.spring.container.dockercompose.Markdown.MarkdownTable;
+import io.spring.initializr.generator.spring.documentation.HelpDocument;
+import io.spring.initializr.generator.spring.documentation.HelpDocumentCustomizer;
+
+/**
+ * Provide additional information in the {@link HelpDocument} if the
+ * {@link DockerComposeFile} isn't empty.
+ *
+ * @author Moritz Halbritter
+ */
+class DockerComposeHelpDocumentCustomizer implements HelpDocumentCustomizer {
+
+	private final DockerComposeFile composeFile;
+
+	DockerComposeHelpDocumentCustomizer(DockerComposeFile composeFile) {
+		this.composeFile = composeFile;
+	}
+
+	@Override
+	public void customize(HelpDocument document) {
+		Collection<DockerComposeService> services = this.composeFile.getServices();
+		Map<String, Object> model = new HashMap<>();
+		if (services.isEmpty()) {
+			model.put("serviceTable", null);
+			document.getWarnings()
+				.addItem(
+						"No Docker Compose services found. As of now, the application won't start! Please add at least one service to the `compose.yaml` file.");
+		}
+		else {
+			MarkdownTable serviceTable = Markdown.table("Service name", "Image", "Tag", "Website");
+			for (DockerComposeService service : services) {
+				serviceTable.addRow(service.getName(), Markdown.code(service.getImage()),
+						Markdown.code(service.getImageTag()), Markdown.link("Website", service.getImageWebsite()));
+			}
+			model.put("serviceTable", serviceTable.toMarkdown());
+		}
+		document.addSection("documentation/docker-compose", model);
+	}
+
+}

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeProjectContributor.java

@@ -0,0 +1,48 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import io.spring.initializr.generator.project.contributor.ProjectContributor;
+
+/**
+ * A {@link ProjectContributor} which contributes a 'compose.yaml' file through a
+ * {@link DockerComposeFile}.
+ *
+ * @author Moritz Halbritter
+ */
+class DockerComposeProjectContributor implements ProjectContributor {
+
+	private final DockerComposeFile composeFile;
+
+	DockerComposeProjectContributor(DockerComposeFile composeFile) {
+		this.composeFile = composeFile;
+	}
+
+	@Override
+	public void contribute(Path projectRoot) throws IOException {
+		Path file = Files.createFile(projectRoot.resolve("compose.yaml"));
+		try (PrintWriter writer = new PrintWriter(Files.newBufferedWriter(file))) {
+			this.composeFile.write(writer);
+		}
+	}
+
+}

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeProjectGenerationConfiguration.java

@@ -0,0 +1,49 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import io.spring.initializr.generator.project.ProjectGenerationConfiguration;
+
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.context.annotation.Bean;
+
+/**
+ * Configuration for contributions specific to the Docker Compose parts of a project.
+ *
+ * @author Moritz Halbritter
+ */
+@ProjectGenerationConfiguration
+public class DockerComposeProjectGenerationConfiguration {
+
+	@Bean
+	DockerComposeFile composeFile(ObjectProvider<DockerComposeFileCustomizer> composeFileCustomizers) {
+		DockerComposeFile composeFile = new DockerComposeFile();
+		composeFileCustomizers.orderedStream().forEach((customizer) -> customizer.customize(composeFile));
+		return composeFile;
+	}
+
+	@Bean
+	DockerComposeProjectContributor dockerComposeProjectContributor(DockerComposeFile composeFile) {
+		return new DockerComposeProjectContributor(composeFile);
+	}
+
+	@Bean
+	DockerComposeHelpDocumentCustomizer dockerComposeHelpDocumentCustomizer(DockerComposeFile composeFile) {
+		return new DockerComposeHelpDocumentCustomizer(composeFile);
+	}
+
+}

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeService.java

@@ -0,0 +1,254 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.io.PrintWriter;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.TreeSet;
+
+/**
+ * A Docker Compose service.
+ *
+ * @author Moritz Halbritter
+ */
+public final class DockerComposeService {
+
+	private static final String INDENT = "  ";
+
+	private final String name;
+
+	private final String image;
+
+	private final String imageTag;
+
+	private final String imageWebsite;
+
+	private final Map<String, String> environment;
+
+	private final Set<Integer> ports;
+
+	private DockerComposeService(Builder builder) {
+		this.name = builder.name;
+		this.image = builder.image;
+		this.imageTag = builder.imageTag;
+		this.imageWebsite = builder.imageWebsite;
+		this.environment = builder.environment;
+		this.ports = builder.ports;
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+	public String getImage() {
+		return this.image;
+	}
+
+	public String getImageTag() {
+		return this.imageTag;
+	}
+
+	public String getImageWebsite() {
+		return this.imageWebsite;
+	}
+
+	public Map<String, String> getEnvironment() {
+		return Collections.unmodifiableMap(this.environment);
+	}
+
+	public Set<Integer> getPorts() {
+		return Collections.unmodifiableSet(this.ports);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) {
+			return true;
+		}
+		if (o == null || getClass() != o.getClass()) {
+			return false;
+		}
+		DockerComposeService service = (DockerComposeService) o;
+		return Objects.equals(this.name, service.name) && Objects.equals(this.image, service.image)
+				&& Objects.equals(this.imageTag, service.imageTag)
+				&& Objects.equals(this.imageWebsite, service.imageWebsite)
+				&& Objects.equals(this.environment, service.environment) && Objects.equals(this.ports, service.ports);
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(this.name, this.image, this.imageTag, this.imageWebsite, this.environment, this.ports);
+	}
+
+	@Override
+	public String toString() {
+		return "DockerComposeService{" + "name='" + this.name + '\'' + ", image='" + this.image + '\'' + ", imageTag='"
+				+ this.imageTag + '\'' + ", imageWebsite='" + this.imageWebsite + '\'' + ", environment="
+				+ this.environment + ", ports=" + this.ports + '}';
+	}
+
+	void write(PrintWriter writer, int indentation) {
+		int currentIndent = indentation;
+		println(writer, this.name + ":", currentIndent);
+		currentIndent++;
+		println(writer, "image: '%s:%s'".formatted(this.image, this.imageTag), currentIndent);
+		if (!this.environment.isEmpty()) {
+			writeEnvironment(writer, currentIndent);
+		}
+		if (!this.ports.isEmpty()) {
+			writePorts(writer, currentIndent);
+		}
+	}
+
+	private void writePorts(PrintWriter writer, int currentIndent) {
+		println(writer, "ports:", currentIndent);
+		for (Integer port : this.ports) {
+			println(writer, "- '%d'".formatted(port), currentIndent + 1);
+		}
+	}
+
+	private void writeEnvironment(PrintWriter writer, int currentIndent) {
+		println(writer, "environment:", currentIndent);
+		for (Map.Entry<String, String> env : this.environment.entrySet()) {
+			println(writer, "- '%s=%s'".formatted(env.getKey(), env.getValue()), currentIndent + 1);
+		}
+	}
+
+	private void println(PrintWriter writer, String value, int indentation) {
+		writer.write(INDENT.repeat(indentation));
+		writer.println(value);
+	}
+
+	/**
+	 * Initialize a new {@link Builder} with the given image. The name is automatically
+	 * deduced.
+	 * @param image the image
+	 * @param tag the image tag
+	 * @return a new builder
+	 */
+	public static Builder withImage(String image, String tag) {
+		// See https://github.com/docker/compose/pull/1624
+		String name = image.replaceAll("[^a-zA-Z0-9._\\-]", "_");
+		return new Builder(name, image, tag);
+	}
+
+	/**
+	 * Initialize a new {@link Builder} with the given image. The name is automatically
+	 * deduced.
+	 * @param imageAndTag the image and tag in the format {@code image:tag}
+	 * @return a new builder
+	 */
+	public static Builder withImage(String imageAndTag) {
+		String[] split = imageAndTag.split(":", 2);
+		if (split.length == 1) {
+			return withImage(split[0], "latest");
+		}
+		else {
+			return withImage(split[0], split[1]);
+		}
+	}
+
+	/**
+	 * Initialize a {@link Builder} with the given service.
+	 * @param service the service to initialize from
+	 * @return a new builder
+	 */
+	public static Builder from(DockerComposeService service) {
+		return new Builder(service.name, service.image, service.imageTag).imageWebsite(service.imageWebsite)
+			.environment(service.environment)
+			.ports(service.ports);
+	}
+
+	/**
+	 * Builder for {@link DockerComposeService}.
+	 */
+	public static final class Builder {
+
+		private String name;
+
+		private String image;
+
+		private String imageTag;
+
+		private String imageWebsite;
+
+		private final Map<String, String> environment = new TreeMap<>();
+
+		private final Set<Integer> ports = new TreeSet<>();
+
+		private Builder(String name, String image, String imageTag) {
+			this.name = name;
+			this.image = image;
+			this.imageTag = imageTag;
+		}
+
+		public Builder name(String name) {
+			this.name = name;
+			return this;
+		}
+
+		public Builder image(String image) {
+			this.image = image;
+			return this;
+		}
+
+		public Builder imageTag(String imageTag) {
+			this.imageTag = imageTag;
+			return this;
+		}
+
+		public Builder imageWebsite(String imageWebsite) {
+			this.imageWebsite = imageWebsite;
+			return this;
+		}
+
+		public Builder environment(String key, String value) {
+			this.environment.put(key, value);
+			return this;
+		}
+
+		public Builder environment(Map<String, String> environment) {
+			this.environment.putAll(environment);
+			return this;
+		}
+
+		public Builder ports(Collection<Integer> ports) {
+			this.ports.addAll(ports);
+			return this;
+		}
+
+		public Builder ports(int... ports) {
+			return ports(Arrays.stream(ports).boxed().toList());
+		}
+
+		/**
+		 * Builds the {@link DockerComposeService} instance.
+		 * @return the built instance
+		 */
+		public DockerComposeService build() {
+			return new DockerComposeService(this);
+		}
+
+	}
+
+}

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/Markdown.java

@@ -0,0 +1,158 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Helper class for Markdown.
+ *
+ * @author Moritz Halbritter
+ */
+final class Markdown {
+
+	private Markdown() {
+		// Static class
+	}
+
+	/**
+	 * Formats the given string as code.
+	 * @param code the input string
+	 * @return string formatted as code
+	 */
+	static String code(String code) {
+		return "`%s`".formatted(code);
+	}
+
+	/**
+	 * Creates a Markdown link.
+	 * @param text text of the link
+	 * @param url url of the link
+	 * @return the formatted link in Markdown
+	 */
+	static String link(String text, String url) {
+		return "[%s](%s)".formatted(text, url);
+	}
+
+	/**
+	 * Creates a Markdown table.
+	 * @param headerCaptions captions of the header
+	 * @return the Markdown table
+	 */
+	static MarkdownTable table(String... headerCaptions) {
+		return new MarkdownTable(headerCaptions);
+	}
+
+	/**
+	 * A Markdown table.
+	 * <p>
+	 * The formatted table is pretty-printed, all the columns are padded with spaces to
+	 * have a consistent look.
+	 *
+	 * @author Moritz Halbritter
+	 */
+	static class MarkdownTable {
+
+		private final List<String> headerCaptions;
+
+		private final List<List<String>> rows;
+
+		/**
+		 * Creates a new table with the given header captions.
+		 * @param headerCaptions the header captions
+		 */
+		MarkdownTable(String... headerCaptions) {
+			this.headerCaptions = List.of(headerCaptions);
+			this.rows = new ArrayList<>();
+		}
+
+		/**
+		 * Adds a new row with the given cells.
+		 * @param cells the cells to add
+		 * @throws IllegalArgumentException if the cell size doesn't match the number of
+		 * header captions
+		 */
+		void addRow(String... cells) {
+			if (cells.length != this.headerCaptions.size()) {
+				throw new IllegalArgumentException(
+						"Expected %d cells, got %d".formatted(this.headerCaptions.size(), cells.length));
+			}
+			this.rows.add(List.of(cells));
+		}
+
+		/**
+		 * Formats the whole table as Markdown.
+		 * @return the table formatted as Markdown.
+		 */
+		String toMarkdown() {
+			int[] columnMaxLengths = calculateMaxColumnLengths();
+			StringBuilder result = new StringBuilder();
+			writeHeader(result, columnMaxLengths);
+			writeHeaderSeparator(result, columnMaxLengths);
+			writeRows(result, columnMaxLengths);
+			return result.toString();
+		}
+
+		private void writeHeader(StringBuilder result, int[] columnMaxLengths) {
+			for (int i = 0; i < this.headerCaptions.size(); i++) {
+				result.append((i > 0) ? " " : "| ")
+					.append(pad(this.headerCaptions.get(i), columnMaxLengths[i]))
+					.append(" |");
+			}
+			result.append(System.lineSeparator());
+		}
+
+		private void writeHeaderSeparator(StringBuilder result, int[] columnMaxLengths) {
+			for (int i = 0; i < this.headerCaptions.size(); i++) {
+				result.append((i > 0) ? " " : "| ").append("-".repeat(columnMaxLengths[i])).append(" |");
+			}
+			result.append(System.lineSeparator());
+		}
+
+		private void writeRows(StringBuilder result, int[] columnMaxLengths) {
+			for (List<String> row : this.rows) {
+				for (int i = 0; i < row.size(); i++) {
+					result.append((i > 0) ? " " : "| ").append(pad(row.get(i), columnMaxLengths[i])).append(" |");
+				}
+				result.append(System.lineSeparator());
+			}
+		}
+
+		private int[] calculateMaxColumnLengths() {
+			int[] columnMaxLengths = new int[this.headerCaptions.size()];
+			for (int i = 0; i < this.headerCaptions.size(); i++) {
+				columnMaxLengths[i] = this.headerCaptions.get(i).length();
+			}
+			for (List<String> row : this.rows) {
+				for (int i = 0; i < row.size(); i++) {
+					String cell = row.get(i);
+					if (cell.length() > columnMaxLengths[i]) {
+						columnMaxLengths[i] = cell.length();
+					}
+				}
+			}
+			return columnMaxLengths;
+		}
+
+		private String pad(String input, int length) {
+			return input + " ".repeat(length - input.length());
+		}
+
+	}
+
+}

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/container/dockercompose/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * 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.
+ */
+
+/**
+ * Support for Docker Compose.
+ */
+package io.spring.initializr.generator.spring.container.dockercompose;

initializr-generator-spring/src/main/resources/templates/documentation/docker-compose.mustache

@@ -0,0 +1,16 @@
+### Docker Compose support
+
+This project contains a Docker Compose file named `compose.yaml`.
+
+{{#serviceTable}}
+In this file, the following services have been defined:
+
+{{serviceTable}}
+
+Please review the tags of the used images and set them to the same as you're running in production.
+{{/serviceTable}}
+{{^serviceTable}}
+However, no services were found. As of now, the application won't start!
+
+Please make sure to add at least one service in the `compose.yaml` file.
+{{/serviceTable}}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeFileTests.java

@@ -0,0 +1,58 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DockerComposeFile}.
+ *
+ * @author Moritz Halbritter
+ */
+class DockerComposeFileTests {
+
+	@Test
+	void write() {
+		DockerComposeFile file = new DockerComposeFile();
+		file.addService(DockerComposeServiceHelper.service(1));
+		file.addService(DockerComposeServiceHelper.service(2));
+		StringWriter writer = new StringWriter();
+		file.write(new PrintWriter(writer));
+		assertThat(writer.toString()).isEqualToIgnoringNewLines("""
+				services:
+				  service-1:
+				    image: 'image-1:image-tag-1'
+				  service-2:
+				    image: 'image-2:image-tag-2'
+				""");
+	}
+
+	@Test
+	void servicesAreOrderedByName() {
+		DockerComposeFile file = new DockerComposeFile();
+		file.addService(DockerComposeServiceHelper.service(2));
+		file.addService(DockerComposeServiceHelper.service(1));
+		assertThat(file.getServices()).containsExactly(DockerComposeServiceHelper.service(1),
+				DockerComposeServiceHelper.service(2));
+	}
+
+}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeHelpDocumentCustomizerTests.java

@@ -0,0 +1,102 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+import io.spring.initializr.generator.io.template.MustacheTemplateRenderer;
+import io.spring.initializr.generator.io.text.MustacheSection;
+import io.spring.initializr.generator.io.text.Section;
+import io.spring.initializr.generator.spring.documentation.HelpDocument;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DockerComposeHelpDocumentCustomizer}.
+ *
+ * @author Moritz Halbritter
+ */
+class DockerComposeHelpDocumentCustomizerTests {
+
+	private DockerComposeHelpDocumentCustomizer customizer;
+
+	private DockerComposeFile dockerComposeFile;
+
+	@BeforeEach
+	void setUp() {
+		this.dockerComposeFile = new DockerComposeFile();
+		this.customizer = new DockerComposeHelpDocumentCustomizer(this.dockerComposeFile);
+	}
+
+	@Test
+	void addsDockerComposeSection() throws IOException {
+		this.dockerComposeFile.addService(DockerComposeServiceHelper.service());
+		HelpDocument helpDocument = helpDocument();
+		this.customizer.customize(helpDocument);
+		assertThat(helpDocument.getSections()).hasSize(1);
+		Section section = helpDocument.getSections().get(0);
+		assertThat(section).isInstanceOf(MustacheSection.class);
+		StringWriter stringWriter = new StringWriter();
+		helpDocument.write(new PrintWriter(stringWriter));
+		assertThat(stringWriter.toString()).isEqualToIgnoringNewLines("""
+				### Docker Compose support
+
+				This project contains a Docker Compose file named `compose.yaml`.
+
+				In this file, the following services have been defined:
+
+				| Service name | Image     | Tag           | Website                           |
+				| ------------ | --------- | ------------- | --------------------------------- |
+				| service-1    | `image-1` | `image-tag-1` | [Website](https://service-1.org/) |
+
+
+				Please review the tags of the used images and set them to the same as you're running in production.""");
+	}
+
+	@Test
+	void addsWarningIfNoServicesAreDefined() throws IOException {
+		HelpDocument helpDocument = helpDocument();
+		this.customizer.customize(helpDocument);
+		assertThat(helpDocument.getWarnings().getItems()).containsExactly(
+				"No Docker Compose services found. As of now, the application won't start! Please add at least one service to the `compose.yaml` file.");
+		StringWriter stringWriter = new StringWriter();
+		helpDocument.write(new PrintWriter(stringWriter));
+		assertThat(stringWriter.toString()).isEqualToIgnoringNewLines(
+				"""
+						# Read Me First
+						The following was discovered as part of building this project:
+
+						* No Docker Compose services found. As of now, the application won't start! Please add at least one service to the `compose.yaml` file.
+
+						### Docker Compose support
+
+						This project contains a Docker Compose file named `compose.yaml`.
+
+						However, no services were found. As of now, the application won't start!
+
+						Please make sure to add at least one service in the `compose.yaml` file.""");
+	}
+
+	private static HelpDocument helpDocument() {
+		return new HelpDocument(new MustacheTemplateRenderer("/templates"));
+	}
+
+}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeProjectContributorTests.java

@@ -0,0 +1,53 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DockerComposeProjectContributor}.
+ *
+ * @author Moritz Halbritter
+ */
+class DockerComposeProjectContributorTests {
+
+	private DockerComposeProjectContributor contributor;
+
+	private DockerComposeFile dockerComposeFile;
+
+	@BeforeEach
+	void setUp() {
+		this.dockerComposeFile = new DockerComposeFile();
+		this.contributor = new DockerComposeProjectContributor(this.dockerComposeFile);
+	}
+
+	@Test
+	void writesComposeYamlFile(@TempDir Path tempDir) throws IOException {
+		this.dockerComposeFile.addService(DockerComposeServiceHelper.service());
+		this.contributor.contribute(tempDir);
+		assertThat(tempDir.resolve("compose.yaml")).content(StandardCharsets.UTF_8).startsWith("services:");
+	}
+
+}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeProjectGenerationConfigurationTests.java

@@ -0,0 +1,71 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DockerComposeProjectGenerationConfiguration}.
+ *
+ * @author Moritz Halbritter
+ */
+class DockerComposeProjectGenerationConfigurationTests {
+
+	private final ApplicationContextRunner runner = new ApplicationContextRunner()
+		.withUserConfiguration(DockerComposeProjectGenerationConfiguration.class);
+
+	@Test
+	void providesBeans() {
+		this.runner.run((context) -> {
+			assertThat(context).hasSingleBean(DockerComposeFile.class);
+			assertThat(context).hasSingleBean(DockerComposeProjectContributor.class);
+			assertThat(context).hasSingleBean(DockerComposeHelpDocumentCustomizer.class);
+		});
+	}
+
+	@Test
+	void callsCustomizers() {
+		DockerComposeService service = DockerComposeServiceHelper.service(3);
+		DockerComposeFileCustomizer customizer = (composeFile) -> composeFile.addService(service);
+		this.runner.withBean(DockerComposeFileCustomizer.class, () -> customizer).run((context) -> {
+			DockerComposeFile composeFile = context.getBean(DockerComposeFile.class);
+			assertThat(composeFile.getServices()).containsExactly(service);
+		});
+	}
+
+	@Configuration
+	static class Services {
+
+		@Bean
+		DockerComposeService service1() {
+			return DockerComposeServiceHelper.service(1);
+		}
+
+		@Bean
+		DockerComposeService service2() {
+			return DockerComposeServiceHelper.service(2);
+		}
+
+	}
+
+}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeServiceHelper.java

@@ -0,0 +1,49 @@
+/*
+ * 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.spring.container.dockercompose;
+
+/**
+ * Helper class for {@link DockerComposeService}.
+ *
+ * @author Moritz Halbritter
+ */
+final class DockerComposeServiceHelper {
+
+	private DockerComposeServiceHelper() {
+	}
+
+	/**
+	 * Creates a new {@link DockerComposeService}.
+	 * @return a new {@link DockerComposeService}
+	 */
+	static DockerComposeService service() {
+		return service(1);
+	}
+
+	/**
+	 * Creates a new {@link DockerComposeService} with the given suffix.
+	 * @param suffix the suffix
+	 * @return a new {@link DockerComposeService}
+	 */
+	static DockerComposeService service(int suffix) {
+		return DockerComposeService.withImage("image-" + suffix, "image-tag-" + suffix)
+			.name("service-" + suffix)
+			.imageWebsite("https://service-" + suffix + ".org/")
+			.build();
+	}
+
+}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeServiceTests.java

@@ -0,0 +1,116 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
+
+/**
+ * Tests for {@link DockerComposeService}.
+ *
+ * @author Moritz Halbritter
+ */
+class DockerComposeServiceTests {
+
+	@Test
+	void shouldWriteToPrinter() {
+		StringWriter stringWriter = new StringWriter();
+		DockerComposeService service = DockerComposeService.withImage("elasticsearch:8.6.1")
+			.imageWebsite("https://www.docker.elastic.co/r/elasticsearch")
+			.environment("ELASTIC_PASSWORD", "secret")
+			.environment("discovery.type", "single-node")
+			.ports(9200, 9300)
+			.build();
+		service.write(new PrintWriter(stringWriter), 0);
+		String content = stringWriter.toString();
+		assertThat(content).isEqualToIgnoringNewLines("""
+				elasticsearch:
+				  image: 'elasticsearch:8.6.1'
+				  environment:
+				    - 'ELASTIC_PASSWORD=secret'
+				    - 'discovery.type=single-node'
+				  ports:
+				    - '9200'
+				    - '9300'
+				""");
+	}
+
+	@Test
+	void nameIsDeduced() {
+		DockerComposeService service = DockerComposeService.withImage("elasticsearch:8.6.1").build();
+		assertThat(service.getName()).isEqualTo("elasticsearch");
+	}
+
+	@Test
+	void tagIsSetToLatestIfNotGiven() {
+		DockerComposeService service = DockerComposeService.withImage("redis").build();
+		assertThat(service.getImage()).isEqualTo("redis");
+		assertThat(service.getImageTag()).isEqualTo("latest");
+	}
+
+	@Test
+	void removesIllegalCharsFromDecudedName() {
+		DockerComposeService service = DockerComposeService.withImage("SOME._-name<>;|\uD83C\uDF31").build();
+		assertThat(service.getName()).isEqualTo("SOME._-name_____");
+	}
+
+	@Test
+	void portsAreSorted() {
+		DockerComposeService service = DockerComposeService.withImage("redis").ports(5, 3, 4, 2, 1).build();
+		assertThat(service.getPorts()).containsExactly(1, 2, 3, 4, 5);
+	}
+
+	@Test
+	void environmentIsSorted() {
+		DockerComposeService service = DockerComposeService.withImage("redis")
+			.environment("z", "zz")
+			.environment("a", "aa")
+			.build();
+		assertThat(service.getEnvironment()).containsExactly(entry("a", "aa"), entry("z", "zz"));
+	}
+
+	@Test
+	void builderFrom() {
+		DockerComposeService service = DockerComposeService.withImage("elasticsearch", "8.6.1")
+			.imageWebsite("https://hub.docker.com/_/redis")
+			.environment(Map.of("some", "value"))
+			.ports(6379)
+			.build();
+		DockerComposeService service2 = DockerComposeService.from(service).build();
+		assertThat(service).isEqualTo(service2);
+	}
+
+	@Test
+	void equalsAndHashcode() {
+		DockerComposeService service1 = DockerComposeService.withImage("redis").build();
+		DockerComposeService service2 = DockerComposeService.withImage("elasticsearch:8.6.1").build();
+		DockerComposeService service3 = DockerComposeService.withImage("redis").build();
+		assertThat(service1).isEqualTo(service3);
+		assertThat(service1).hasSameHashCodeAs(service3);
+		assertThat(service3).isEqualTo(service1);
+		assertThat(service3).hasSameHashCodeAs(service1);
+		assertThat(service1).isNotEqualTo(service2);
+		assertThat(service2).isNotEqualTo(service1);
+	}
+
+}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/MarkdownTableTests.java

@@ -0,0 +1,67 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import io.spring.initializr.generator.spring.container.dockercompose.Markdown.MarkdownTable;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+/**
+ * Tests for {@link MarkdownTable}.
+ *
+ * @author Moritz Halbritter
+ */
+class MarkdownTableTests {
+
+	@Test
+	void shouldFormatCorrectly() {
+		MarkdownTable table = new MarkdownTable("a", "b1", "c22", "d333");
+		table.addRow("0", "1", "2", "3");
+		table.addRow("4", "5", "6", "7");
+		String markdown = table.toMarkdown();
+		assertThat(markdown).isEqualToIgnoringNewLines("""
+				| a | b1 | c22 | d333 |
+				| - | -- | --- | ---- |
+				| 0 | 1  | 2   | 3    |
+				| 4 | 5  | 6   | 7    |
+				""");
+	}
+
+	@Test
+	void rowIsBiggerThanHeading() {
+		MarkdownTable table = new MarkdownTable("a", "b", "c", "d");
+		table.addRow("0.0", "1.1", "2.2", "3.3");
+		table.addRow("4.4", "5.5", "6.6", "7.7");
+		String markdown = table.toMarkdown();
+		assertThat(markdown).isEqualToIgnoringNewLines("""
+				| a   | b   | c   | d   |
+				| --- | --- | --- | --- |
+				| 0.0 | 1.1 | 2.2 | 3.3 |
+				| 4.4 | 5.5 | 6.6 | 7.7 |
+				""");
+	}
+
+	@Test
+	void throwsIfCellsDifferFromHeader() {
+		MarkdownTable table = new MarkdownTable("a", "b", "c", "d");
+		assertThatThrownBy(() -> table.addRow("1")).isInstanceOf(IllegalArgumentException.class)
+			.hasMessage("Expected 4 cells, got 1");
+	}
+
+}

initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/MarkdownTests.java

@@ -0,0 +1,42 @@
+/*
+ * 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.spring.container.dockercompose;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link Markdown}.
+ *
+ * @author Moritz Halbritter
+ */
+class MarkdownTests {
+
+	@Test
+	void shouldFormatCode() {
+		String code = Markdown.code("c = a + b");
+		assertThat(code).isEqualTo("`c = a + b`");
+	}
+
+	@Test
+	void shouldFormatLink() {
+		String link = Markdown.link("Spring Website", "https://spring.io/");
+		assertThat(link).isEqualTo("[Spring Website](https://spring.io/)");
+	}
+
+}

src/checkstyle/checkstyle-suppressions.xml

@@ -6,4 +6,6 @@
 	<suppress files=".+Application\.java" checks="HideUtilityClassConstructor"/>
 	<suppress files="[\\/]initializr-service-sample[\\/]" checks="JavadocType"/>
 	<suppress files="[\\/]initializr-service-sample[\\/]" checks="ImportControl"/>
+	<suppress files="initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeServiceTests.java" checks="SpringLeadingWhitespace"/>
+	<suppress files="initializr-generator-spring/src/test/java/io/spring/initializr/generator/spring/container/dockercompose/DockerComposeFileTests." checks="SpringLeadingWhitespace"/>
 </suppressions>