Add mainClassName to springBoot DSL in Gradle plugin

This commit introduces a new mainClassName property on the springBoot
DSL provided by the Gradle plugin. It can be used to explicitly
configure the mainClassName of the default bootRun, bootJar, and
bootWar tasks in a single place. Previously, the only mechanism
provided to do so was the mainClassName property that's only available
when the application plugin has been applied.

Closes gh-10623

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/docs/PackagingDocumentationTests.java

@@ -89,6 +89,20 @@ public class PackagingDocumentationTests {
 		}
 	}
 
+	@Test
+	public void springBootDslMainClass() throws IOException {
+		this.gradleBuild
+		.script("src/main/gradle/packaging/spring-boot-dsl-main-class.gradle")
+		.build("bootJar");
+		File file = new File(this.gradleBuild.getProjectDir(),
+				"build/libs/" + this.gradleBuild.getProjectDir().getName() + ".jar");
+		assertThat(file).isFile();
+		try (JarFile jar = new JarFile(file)) {
+			assertThat(jar.getManifest().getMainAttributes().getValue("Start-Class"))
+			.isEqualTo("com.example.ExampleApplication");
+		}
+	}
+
 	@Test
 	public void bootWarIncludeDevtools() throws IOException {
 		new File(this.gradleBuild.getProjectDir(),

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/docs/RunningDocumentationTests.java

@@ -51,6 +51,14 @@ public class RunningDocumentationTests {
 						.contains("com.example.ExampleApplication");
 	}
 
+	@Test
+	public void springBootDslMainClassName() throws IOException {
+		assertThat(this.gradleBuild
+				.script("src/main/gradle/running/spring-boot-dsl-main-class-name.gradle")
+				.build("configuredMainClass").getOutput())
+		.contains("com.example.ExampleApplication");
+	}
+
 	@Test
 	public void bootRunSourceResources() throws IOException {
 		assertThat(this.gradleBuild

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/MainClassConventionTests.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2012-2017 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
+ *
+ *      http://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 org.springframework.boot.gradle.plugin;
+
+import java.io.IOException;
+
+import org.gradle.api.Project;
+import org.gradle.api.plugins.ExtraPropertiesExtension;
+import org.gradle.internal.impldep.org.junit.Before;
+import org.gradle.internal.impldep.org.junit.Rule;
+import org.gradle.internal.impldep.org.junit.Test;
+import org.gradle.internal.impldep.org.junit.rules.TemporaryFolder;
+import org.gradle.testfixtures.ProjectBuilder;
+
+import org.springframework.boot.gradle.dsl.SpringBootExtension;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class MainClassConventionTests {
+
+	@Rule
+	public final TemporaryFolder temp = new TemporaryFolder();
+
+	private Project project;
+
+	private MainClassConvention convention;
+
+	@Before
+	public void createConvention() throws IOException {
+		this.project = ProjectBuilder.builder().withProjectDir(this.temp.newFolder())
+				.build();
+		this.convention = new MainClassConvention(this.project, () -> null);
+	}
+
+	@Test
+	public void mainClassNameProjectPropertyIsUsed() throws Exception {
+		this.project.getExtensions().getByType(ExtraPropertiesExtension.class)
+				.set("mainClassName", "com.example.MainClass");
+		assertThat(this.convention.call()).isEqualTo("com.example.MainClass");
+	}
+
+	@Test
+	public void springBootExtensionMainClassNameIsUsed() throws Exception {
+		SpringBootExtension extension = this.project.getExtensions().create("springBoot",
+				SpringBootExtension.class, this.project);
+		extension.setMainClassName("com.example.MainClass");
+		assertThat(this.convention.call()).isEqualTo("com.example.MainClass");
+	}
+
+	@Test
+	public void springBootExtensionMainClassNameIsUsedInPreferenceToMainClassNameProjectProperty()
+			throws Exception {
+		this.project.getExtensions().getByType(ExtraPropertiesExtension.class)
+				.set("mainClassName", "com.example.ProjectPropertyMainClass");
+		SpringBootExtension extension = this.project.getExtensions().create("springBoot",
+				SpringBootExtension.class, this.project);
+		extension.setMainClassName("com.example.SpringBootExtensionMainClass");
+		assertThat(this.convention.call())
+				.isEqualTo("com.example.SpringBootExtensionMainClass");
+	}
+
+}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/AbstractBootArchiveIntegrationTests.java

@@ -112,7 +112,18 @@ public abstract class AbstractBootArchiveIntegrationTests {
 			assertThat(jarFile.getManifest().getMainAttributes().getValue("Start-Class"))
 					.isEqualTo("com.example.CustomMain");
 		}
+	}
 
+	@Test
+	public void springBootExtensionMainClassNameIsUsed() throws IOException {
+		assertThat(this.gradleBuild.build(this.taskName).task(":" + this.taskName)
+				.getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+		try (JarFile jarFile = new JarFile(
+				new File(this.gradleBuild.getProjectDir(), "build/libs")
+				.listFiles()[0])) {
+			assertThat(jarFile.getManifest().getMainAttributes().getValue("Start-Class"))
+			.isEqualTo("com.example.CustomMain");
+		}
 	}
 
 	@Test

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/run/BootRunIntegrationTests.java

@@ -96,6 +96,15 @@ public class BootRunIntegrationTests {
 				.doesNotContain(canonicalPathOf("build/resources/main"));
 	}
 
+	@Test
+	public void springBootExtensionMainClassNameIsUsed() throws IOException {
+		BuildResult result = this.gradleBuild.build("echoMainClassName");
+		assertThat(result.task(":echoMainClassName").getOutcome())
+				.isEqualTo(TaskOutcome.UP_TO_DATE);
+		assertThat(result.getOutput())
+				.contains("Main class name = com.example.CustomMainClass");
+	}
+
 	@Test
 	public void applicationPluginMainClassNameIsUsed() throws IOException {
 		BuildResult result = this.gradleBuild.build("echoMainClassName");