Allow custom repackage task to be used without a global main class

Closes gh-5956

spring-boot-integration-tests/spring-boot-gradle-tests/src/test/java/org/springframework/boot/gradle/RepackagingTests.java

@@ -159,6 +159,17 @@ public class RepackagingTests {
 		assertFalse(isDevToolsJarIncluded(repackageFile));
 	}
 
+	@Test
+	public void customRepackagingTaskWithOwnMainClassNameAnNoGlobalMainClassName() {
+		project.newBuild().forTasks("clean", "customRepackagedJarWithOwnMainClass")
+				.withArguments("-PbootVersion=" + BOOT_VERSION, "-Prepackage=true",
+						"-PexcludeDevtools=false", "-PnoMainClass=true")
+				.run();
+		File buildLibs = new File("target/repackage/build/libs");
+		assertTrue(new File(buildLibs, "custom.jar").exists());
+		assertTrue(new File(buildLibs, "custom.jar.original").exists());
+	}
+
 	private boolean isDevToolsJarIncluded(File repackageFile) throws IOException {
 		JarFile jarFile = new JarFile(repackageFile);
 		try {

spring-boot-integration-tests/spring-boot-gradle-tests/src/test/resources/repackage.gradle

@@ -23,7 +23,9 @@ dependencies {
 }
 
 springBoot {
+	if (!project.hasProperty("noMainClass")) {
 		mainClass = 'foo.bar.Baz'
+	}
 	excludeDevtools = Boolean.valueOf(project.excludeDevtools)
 }
 
@@ -50,3 +52,8 @@ task customRepackagedJar(type: BootRepackage, dependsOn: customJar) {
 task customRepackagedJarWithStringReference(type: BootRepackage, dependsOn: customJar) {
 	withJarTask = 'customJar'
 }
+
+task customRepackagedJarWithOwnMainClass(type: BootRepackage, dependsOn: customJar) {
+	withJarTask = customJar
+	mainClass = 'foo.bar.Baz'
+}

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/repackage/RepackageTask.java

@@ -240,15 +240,17 @@ public class RepackageTask extends DefaultTask {
 		}
 
 		private void setMainClass(Repackager repackager) {
-			String mainClass;
+			String mainClass = null;
 			if (getProject().hasProperty("mainClassName")) {
 				mainClass = (String) getProject().property("mainClassName");
 			}
 			else {
 				ExtraPropertiesExtension extraProperties = (ExtraPropertiesExtension) getProject()
 						.getExtensions().getByName("ext");
+				if (extraProperties.has("mainClassName")) {
 					mainClass = (String) extraProperties.get("mainClassName");
 				}
+			}
 			if (RepackageTask.this.mainClass != null) {
 				mainClass = RepackageTask.this.mainClass;
 			}
@@ -262,9 +264,14 @@ public class RepackageTask extends DefaultTask {
 							.property("main");
 				}
 			}
+			if (mainClass != null) {
 				getLogger().info("Setting mainClass: " + mainClass);
 				repackager.setMainClass(mainClass);
 			}
+			else {
+				getLogger().info("No mainClass configured");
+			}
+		}
 
 		private LaunchScript getLaunchScript() throws IOException {
 			if (isExecutable() || getEmbeddedLaunchScript() != null) {