Support image building with Maven and war packaging

This commit updates the Maven image building goal to support building
images from executable and non-executable war files.

Fixes gh-23823

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/docs/asciidoc/packaging-oci-image.adoc

 [[build-image]]
 == Packaging OCI Images
-The plugin can create an https://github.com/opencontainers/image-spec[OCI image] from an executable jar file using https://buildpacks.io/[Cloud Native Buildpacks] (CNB).
+The plugin can create an https://github.com/opencontainers/image-spec[OCI image] from a jar or war file using https://buildpacks.io/[Cloud Native Buildpacks] (CNB).
 Images can be built using the `build-image` goal.
 
 NOTE: For security reasons, images build and run as non-root users.
 See the {buildpacks-reference}/reference/spec/platform-api/#users[CNB specification] for more details.
 
-NOTE: The `build-image` goal is not supported with projects using <<repackage, war packaging>>.
-
 The easiest way to get started is to invoke `mvn spring-boot:build-image` on a project.
 It is possible to automate the creation of an image whenever the `package` phase is invoked, as shown in the following example:
 

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/java/org/springframework/boot/maven/BuildImageTests.java

@@ -68,6 +68,30 @@ public class BuildImageTests extends AbstractArchiveIntegrationTests {
 				});
 	}
 
+	@TestTemplate
+	void whenBuildImageIsInvokedWithWarPackaging(MavenBuild mavenBuild) {
+		mavenBuild.project("build-image-war-packaging").goals("package")
+				.systemProperty("spring-boot.build-image.pullPolicy", "IF_NOT_PRESENT")
+				.prepare(this::writeLongNameResource).execute((project) -> {
+					File war = new File(project, "target/build-image-war-packaging-0.0.1.BUILD-SNAPSHOT.war");
+					assertThat(war).isFile();
+					File original = new File(project,
+							"target/build-image-war-packaging-0.0.1.BUILD-SNAPSHOT.war.original");
+					assertThat(original).doesNotExist();
+					assertThat(buildLog(project)).contains("Building image")
+							.contains("docker.io/library/build-image-war-packaging:0.0.1.BUILD-SNAPSHOT")
+							.contains("Successfully built image");
+					ImageReference imageReference = ImageReference.of(ImageName.of("build-image-war-packaging"),
+							"0.0.1.BUILD-SNAPSHOT");
+					try (GenericContainer<?> container = new GenericContainer<>(imageReference.toString())) {
+						container.waitingFor(Wait.forLogMessage("Launched\\n", 1)).start();
+					}
+					finally {
+						removeImage(imageReference);
+					}
+				});
+	}
+
 	@TestTemplate
 	void whenBuildImageIsInvokedWithCustomImageName(MavenBuild mavenBuild) {
 		mavenBuild.project("build-image-custom-name").goals("package")
@@ -191,12 +215,6 @@ public class BuildImageTests extends AbstractArchiveIntegrationTests {
 						.containsPattern("Builder lifecycle '.*' failed with status code"));
 	}
 
-	@TestTemplate
-	void failsWithWarPackaging(MavenBuild mavenBuild) {
-		mavenBuild.project("build-image-war-packaging").goals("package").executeAndFail(
-				(project) -> assertThat(buildLog(project)).contains("Executable jar file required for building image"));
-	}
-
 	@TestTemplate
 	void failsWithBuildpackNotInBuilder(MavenBuild mavenBuild) {
 		mavenBuild.project("build-image-bad-buildpack").goals("package")

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/projects/build-image-war-packaging/pom.xml

@@ -3,7 +3,7 @@
 	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 	<modelVersion>4.0.0</modelVersion>
 	<groupId>org.springframework.boot.maven.it</groupId>
-	<artifactId>build-image-war</artifactId>
+	<artifactId>build-image-war-packaging</artifactId>
 	<version>0.0.1.BUILD-SNAPSHOT</version>
 	<packaging>war</packaging>
 	<properties>

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/intTest/projects/build-image-war-packaging/src/main/java/org/test/SampleApplication.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -19,6 +19,10 @@ package org.test;
 public class SampleApplication {
 
 	public static void main(String[] args) throws Exception {
+		System.out.println("Launched");
+		synchronized(args) {
+			args.wait(); // Prevent exit"
+		}
 	}
 
 }

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/BuildImageMojo.java

@@ -218,23 +218,26 @@ public class BuildImageMojo extends AbstractPackagerMojo {
 	}
 
 	private TarArchive getApplicationContent(Owner owner, Libraries libraries) {
-		ImagePackager packager = getConfiguredPackager(() -> new ImagePackager(getJarFile()));
+		ImagePackager packager = getConfiguredPackager(() -> new ImagePackager(getArchiveFile()));
 		return new PackagedTarArchive(owner, libraries, packager);
 	}
 
-	private File getJarFile() {
+	private File getArchiveFile() {
 		// We can use 'project.getArtifact().getFile()' because that was done in a
 		// forked lifecycle and is now null
 		StringBuilder name = new StringBuilder(this.finalName);
 		if (StringUtils.hasText(this.classifier)) {
 			name.append("-").append(this.classifier);
 		}
-		name.append(".jar");
-		File jarFile = new File(this.sourceDirectory, name.toString());
-		if (!jarFile.exists()) {
-			throw new IllegalStateException("Executable jar file required for building image");
+		File archiveFile = new File(this.sourceDirectory, name.toString() + ".jar");
+		if (archiveFile.exists()) {
+			return archiveFile;
 		}
-		return jarFile;
+		archiveFile = new File(this.sourceDirectory, name.toString() + ".war");
+		if (archiveFile.exists()) {
+			return archiveFile;
+		}
+		throw new IllegalStateException("A jar or war file is required for building image");
 	}
 
 	private BuildRequest customize(BuildRequest request) {