Merge pull request #16182 from Hendrig Sellik

* gh-16182:
  Polish "Determine Spring Boot version correctly when using module path"
  Determine Spring Boot version correctly when using module path

Closes gh-16182

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringBootVersion.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -16,16 +16,29 @@
 
 package org.springframework.boot;
 
+import java.io.File;
+import java.io.IOException;
+import java.net.JarURLConnection;
+import java.net.URL;
+import java.net.URLConnection;
+import java.util.jar.Attributes;
+import java.util.jar.Attributes.Name;
+import java.util.jar.JarFile;
+
 /**
- * Class that exposes the Spring Boot version. Fetches the "Implementation-Version"
- * manifest attribute from the jar file.
+ * Class that exposes the Spring Boot version. Fetches the
+ * {@link Name#IMPLEMENTATION_VERSION Implementation-Version} manifest attribute from the
+ * jar file via {@link Package#getImplementationVersion()}, falling back to locating the
+ * jar file that contains this class and reading the {@code Implementation-Version}
+ * attribute from its manifest.
  * <p>
- * Note that some ClassLoaders do not expose the package metadata, hence this class might
- * not be able to determine the Spring Boot version in all environments. Consider using a
- * reflection-based check instead: For example, checking for the presence of a specific
- * Spring Boot method that you intend to call.
+ * This class might not be able to determine the Spring Boot version in all environments.
+ * Consider using a reflection-based check instead: For example, checking for the presence
+ * of a specific Spring Boot method that you intend to call.
  *
  * @author Drummond Dawson
+ * @author Hendrig Sellik
+ * @author Andy Wilkinson
  * @since 1.3.0
  */
 public final class SpringBootVersion {
@@ -40,8 +53,35 @@ public final class SpringBootVersion {
 	 * @see Package#getImplementationVersion()
 	 */
 	public static String getVersion() {
-		Package pkg = SpringBootVersion.class.getPackage();
-		return (pkg != null) ? pkg.getImplementationVersion() : null;
+		return determineSpringBootVersion();
+	}
+
+	private static String determineSpringBootVersion() {
+		String implementationVersion = SpringBootVersion.class.getPackage()
+				.getImplementationVersion();
+		if (implementationVersion != null) {
+			return implementationVersion;
+		}
+		URL codeSourceLocation = SpringBootVersion.class.getProtectionDomain()
+				.getCodeSource().getLocation();
+		try {
+			URLConnection connection = codeSourceLocation.openConnection();
+			if (connection instanceof JarURLConnection) {
+				return getImplementationVersion(
+						((JarURLConnection) connection).getJarFile());
+			}
+			try (JarFile jarFile = new JarFile(new File(codeSourceLocation.toURI()))) {
+				return getImplementationVersion(jarFile);
+			}
+		}
+		catch (Exception ex) {
+			return null;
+		}
+	}
+
+	private static String getImplementationVersion(JarFile jarFile) throws IOException {
+		return jarFile.getManifest().getMainAttributes()
+				.getValue(Attributes.Name.IMPLEMENTATION_VERSION);
 	}
 
 }