Merge pull request #44330 from nosan

* pr/44330:
  Polish ClasspathBuilder

Closes gh-44330

Author: philwebb

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

@@ -51,27 +51,30 @@ protected ClasspathBuilder(List<URL> urls) {
 	}
 
 	/**
-	 * Builds a classpath string or an argument file representing the classpath, depending
-	 * on the operating system.
-	 * @param urls an array of {@link URL} representing the elements of the classpath
-	 * @return the classpath; on Windows, the path to an argument file is returned,
-	 * prefixed with '@'
+	 * Creates a ClasspathBuilder instance using the specified list of URLs.
+	 * @param urls a list of {@link URL} objects representing the elements of the
+	 * classpath
+	 * @return a new instance of {@code ClasspathBuilder}
 	 */
 	static ClasspathBuilder forURLs(List<URL> urls) {
 		return new ClasspathBuilder(new ArrayList<>(urls));
 	}
 
 	/**
-	 * Builds a classpath string or an argument file representing the classpath, depending
-	 * on the operating system.
-	 * @param urls an array of {@link URL} representing the elements of the classpath
-	 * @return the classpath; on Windows, the path to an argument file is returned,
-	 * prefixed with '@'
+	 * Creates a ClasspathBuilder instance using the specified array of URLs.
+	 * @param urls an array of {@link URL} objects representing the elements of the
+	 * classpath
+	 * @return a new instance of {@code ClasspathBuilder}
 	 */
 	static ClasspathBuilder forURLs(URL... urls) {
 		return new ClasspathBuilder(Arrays.asList(urls));
 	}
 
+	/**
+	 * Builds {@link Classpath} that containing a classpath argument and its corresponding
+	 * classpath elements.
+	 * @return a {@code Classpath}
+	 */
 	Classpath build() {
 		if (ObjectUtils.isEmpty(this.urls)) {
 			return new Classpath("", Collections.emptyList());
@@ -88,6 +91,13 @@ Classpath build() {
 		return new Classpath(argument, files);
 	}
 
+	/**
+	 * Determines if an argument file should be used for the classpath based on the
+	 * operating system. On Windows, argument files are used due to the command length
+	 * limitation.
+	 * @return {@code true} if an argument file is required for the classpath,
+	 * {@code false} otherwise
+	 */
 	protected boolean needsClasspathArgFile() {
 		String os = System.getProperty("os.name");
 		if (!StringUtils.hasText(os)) {
@@ -145,6 +155,9 @@ private static Path toFile(URL url) {
 		}
 	}
 
+	/**
+	 * Classpath consisting of a {@code -cp} argument and its associated elements.
+	 */
 	static final class Classpath {
 
 		private final String argument;
@@ -157,7 +170,8 @@ private Classpath(String argument, List<Path> elements) {
 		}
 
 		/**
-		 * Return the {@code -cp} argument value.
+		 * Return the {@code -cp} argument value; on Windows, the path to an argument file
+		 * is returned, prefixed with '@'.
 		 * @return the argument to use
 		 */
 		String argument() {

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/test/java/org/springframework/boot/maven/CommandLineBuilderTests.java

@@ -119,9 +119,12 @@ void buildWithClassPathOnWindows(@TempDir Path tempDir) throws Exception {
 
 	@Test
 	void buildAndRunWithLongClassPath() throws IOException, InterruptedException {
-		URL[] urls = Arrays.stream(ManagementFactory.getRuntimeMXBean().getClassPath().split(File.pathSeparator))
-			.map(this::toURL)
-			.toArray(URL[]::new);
+		StringBuilder classPath = new StringBuilder(ManagementFactory.getRuntimeMXBean().getClassPath());
+		// Simulates [CreateProcess error=206, The filename or extension is too long]
+		while (classPath.length() < 35000) {
+			classPath.append(File.pathSeparator).append(classPath);
+		}
+		URL[] urls = Arrays.stream(classPath.toString().split(File.pathSeparator)).map(this::toURL).toArray(URL[]::new);
 		List<String> command = CommandLineBuilder.forMainClass(ClassWithMainMethod.class.getName())
 			.withClasspath(urls)
 			.build();