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/main/asciidoc/packaging.adoc

@@ -93,8 +93,16 @@ property:
 include::../gradle/packaging/boot-jar-main-class.gradle[tags=main-class]
 ----
 
-Alternatively, if the {application-plugin}[`application` plugin] has been applied
-its `mainClassName` project property can be used:
+Alternatively, the main class name can be configured project-wide using the
+`mainClassName` property of the Spring Boot DSL:
+
+[source,groovy,indent=0,subs="verbatim"]
+----
+include::../gradle/packaging/spring-boot-dsl-main-class.gradle[tags=main-class]
+----
+
+If the {application-plugin}[`application` plugin] has been applied its `mainClassName`
+project property can be used for the same purpose:
 
 [source,groovy,indent=0,subs="verbatim"]
 ----

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/asciidoc/running.adoc

@@ -19,8 +19,16 @@ classpath. The main class can also be configured explicitly using the task's
 include::../gradle/running/boot-run-main.gradle[tags=main]
 ----
 
-Alternatively, if the {application-plugin}[`application` plugin] has been applied
-its `mainClassName` project property can be used:
+Alternatively, the main class name can be configured project-wide using the
+`mainClassName` property of the Spring Boot DSL:
+
+[source,groovy,indent=0,subs="verbatim"]
+----
+include::../gradle/running/spring-boot-dsl-main-class-name.gradle[tags=main-class]
+----
+
+If the {application-plugin}[`application` plugin] has been applied its `mainClassName`
+project property can be used for the same purpose:
 
 [source,groovy,indent=0,subs="verbatim"]
 ----

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/packaging/spring-boot-dsl-main-class.gradle

@@ -0,0 +1,14 @@
+buildscript {
+	dependencies {
+		classpath files(pluginClasspath.split(','))
+	}
+}
+
+apply plugin: 'org.springframework.boot'
+apply plugin: 'java'
+
+// tag::main-class[]
+springBoot {
+	mainClassName = 'com.example.ExampleApplication'
+}
+// end::main-class[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/gradle/running/spring-boot-dsl-main-class-name.gradle

@@ -0,0 +1,21 @@
+buildscript {
+	dependencies {
+		classpath files(pluginClasspath.split(','))
+	}
+}
+
+apply plugin: 'org.springframework.boot'
+apply plugin: 'java'
+apply plugin: 'application'
+
+// tag::main-class[]
+springBoot {
+	mainClassName = 'com.example.ExampleApplication'
+}
+// end::main-class[]
+
+task configuredMainClass {
+	doLast {
+		println bootRun.mainClassName
+	}
+}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/dsl/SpringBootExtension.java

@@ -39,6 +39,8 @@ public class SpringBootExtension {
 
 	private final Project project;
 
+	private String mainClassName;
+
 	/**
 	 * Creates a new {@code SpringBootPluginExtension} that is associated with the given
 	 * {@code project}.
@@ -49,6 +51,24 @@ public class SpringBootExtension {
 		this.project = project;
 	}
 
+	/**
+	 * Returns the main class name of the application.
+	 *
+	 * @return the name of the application's main class
+	 */
+	public String getMainClassName() {
+		return this.mainClassName;
+	}
+
+	/**
+	 * Sets the main class name of the application.
+	 *
+	 * @param mainClassName the name of the application's main class
+	 */
+	public void setMainClassName(String mainClassName) {
+		this.mainClassName = mainClassName;
+	}
+
 	/**
 	 * Creates a new {@link BuildInfo} task named {@code bootBuildInfo} and configures the
 	 * Java plugin's {@code classes} task to depend upon it.

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/MainClassConvention.java

@@ -25,6 +25,7 @@ import java.util.function.Supplier;
 import org.gradle.api.Project;
 import org.gradle.api.file.FileCollection;
 
+import org.springframework.boot.gradle.dsl.SpringBootExtension;
 import org.springframework.boot.loader.tools.MainClassFinder;
 
 /**
@@ -47,6 +48,12 @@ final class MainClassConvention implements Callable<String> {
 
 	@Override
 	public String call() throws Exception {
+		SpringBootExtension springBootExtension = this.project.getExtensions()
+				.findByType(SpringBootExtension.class);
+		if (springBootExtension != null
+				&& springBootExtension.getMainClassName() != null) {
+			return springBootExtension.getMainClassName();
+		}
 		if (this.project.hasProperty("mainClassName")) {
 			Object mainClassName = this.project.property("mainClassName");
 			if (mainClassName != null) {

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");

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/bundling/BootJarIntegrationTests-springBootExtensionMainClassNameIsUsed.gradle

@@ -0,0 +1,13 @@
+buildscript {
+	dependencies {
+		classpath files(pluginClasspath.split(','))
+	}
+}
+
+apply plugin: 'java'
+apply plugin: 'org.springframework.boot'
+apply plugin: 'application'
+
+springBoot {
+	mainClassName = 'com.example.CustomMain'
+}

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/bundling/BootWarIntegrationTests-springBootExtensionMainClassNameIsUsed.gradle

@@ -0,0 +1,13 @@
+buildscript {
+	dependencies {
+		classpath files(pluginClasspath.split(','))
+	}
+}
+
+apply plugin: 'war'
+apply plugin: 'org.springframework.boot'
+apply plugin: 'application'
+
+springBoot {
+	mainClassName = 'com.example.CustomMain'
+}

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

@@ -0,0 +1,16 @@
+buildscript {
+	dependencies {
+		classpath files(pluginClasspath.split(','))
+	}
+}
+
+apply plugin: 'application'
+apply plugin: 'org.springframework.boot'
+
+springBoot {
+	mainClassName = 'com.example.CustomMainClass'
+}
+
+task echoMainClassName {
+	println 'Main class name = ' + bootRun.mainClassName
+}