Use a convention mapping for resolving main class from the classpath

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/MainClassSupplier.java → spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/MainClassResolver.java

@@ -19,52 +19,40 @@ package org.springframework.boot.gradle;
 import java.io.File;
 import java.io.IOException;
 import java.util.Objects;
-import java.util.function.Supplier;
 
 import org.gradle.api.file.FileCollection;
 
 import org.springframework.boot.loader.tools.MainClassFinder;
 
 /**
- * Supplies the main class for an application by returning a configured main class if
- * available. If a main class is not available, directories in the application's classpath
- * are searched.
+ * Resolves the main class for an application.
  *
  * @author Andy Wilkinson
  */
-public class MainClassSupplier implements Supplier<String> {
+public class MainClassResolver {
 
 	private static final String SPRING_BOOT_APPLICATION_CLASS_NAME = "org.springframework.boot.autoconfigure.SpringBootApplication";
 
-	private final Supplier<FileCollection> classpathSupplier;
-
-	private String mainClass;
+	private final FileCollection classpath;
 
 	/**
-	 * Creates a new {@code MainClassSupplier} that will fall back to searching
-	 * directories in the classpath supplied by the given {@code classpathSupplier} for
+	 * Creates a new {@code MainClassResolver} that will search
+	 * directories in the given {@code classpath} for
 	 * the application's main class.
 	 *
-	 * @param classpathSupplier the supplier of the classpath
+	 * @param classpath the classpath
 	 */
-	public MainClassSupplier(Supplier<FileCollection> classpathSupplier) {
-		this.classpathSupplier = classpathSupplier;
-	}
-
-	@Override
-	public String get() {
-		if (this.mainClass == null) {
-			this.mainClass = findMainClass();
-		}
-		return this.mainClass;
+	public MainClassResolver(FileCollection classpath) {
+		this.classpath = classpath;
 	}
 
-	private String findMainClass() {
-		FileCollection classpath = this.classpathSupplier.get();
-		if (classpath == null) {
-			return null;
-		}
-		return classpath.filter(File::isDirectory).getFiles().stream()
+	/**
+	 * Resolves the main class.
+	 *
+	 * @return the main class or {@code null}
+	 */
+	public String resolveMainClass() {
+		return this.classpath.filter(File::isDirectory).getFiles().stream()
 				.map(this::findMainClass).filter(Objects::nonNull).findFirst()
 				.orElse(null);
 	}
@@ -80,13 +68,4 @@ public class MainClassSupplier implements Supplier<String> {
 		}
 	}
 
-	/**
-	 * Sets the {@code mainClass} that will be supplied.
-	 *
-	 * @param mainClass the main class to supply
-	 */
-	public void setMainClass(String mainClass) {
-		this.mainClass = mainClass;
-	}
-
 }

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/bundling/BootArchiveSupport.java

@@ -37,25 +37,21 @@ class BootArchiveSupport {
 
 	private final PatternSet requiresUnpack = new PatternSet();
 
-	private final MainClassSupplier mainClassSupplier;
-
 	private final Set<String> storedPathPrefixes;
 
 	private String loaderMainClass;
 
 	private LaunchScriptConfiguration launchScript = new LaunchScriptConfiguration();
 
-	BootArchiveSupport(MainClassSupplier mainClassSupplier,
-			String... storedPathPrefixes) {
-		this.mainClassSupplier = mainClassSupplier;
+	BootArchiveSupport(String... storedPathPrefixes) {
 		this.storedPathPrefixes = new HashSet<>(Arrays.asList(storedPathPrefixes));
 		this.requiresUnpack.include(Specs.satisfyNone());
 	}
 
-	void configureManifest(Jar jar) {
+	void configureManifest(Jar jar, String mainClass) {
 		Attributes attributes = jar.getManifest().getAttributes();
 		attributes.putIfAbsent("Main-Class", this.loaderMainClass);
-		attributes.putIfAbsent("Start-Class", this.mainClassSupplier.get());
+		attributes.putIfAbsent("Start-Class", mainClass);
 	}
 
 	CopyAction createCopyAction(Jar jar) {

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/bundling/BootJar.java

@@ -28,8 +28,6 @@ import org.gradle.api.internal.file.copy.CopyAction;
 import org.gradle.api.specs.Spec;
 import org.gradle.api.tasks.bundling.Jar;
 
-import org.springframework.boot.gradle.MainClassSupplier;
-
 /**
  * A custom {@link Jar} task that produces a Spring Boot executable jar.
  *
@@ -37,10 +35,7 @@ import org.springframework.boot.gradle.MainClassSupplier;
  */
 public class BootJar extends Jar implements BootArchive {
 
-	private final MainClassSupplier mainClassSupplier = new MainClassSupplier(
-			this::getClasspath);
-
-	private BootArchiveSupport support = new BootArchiveSupport(this.mainClassSupplier, "BOOT-INF/lib");
+	private BootArchiveSupport support = new BootArchiveSupport("BOOT-INF/lib");
 
 	private FileCollection classpath;
 
@@ -65,7 +60,7 @@ public class BootJar extends Jar implements BootArchive {
 
 	@Override
 	public void copy() {
-		this.support.configureManifest(this);
+		this.support.configureManifest(this, getMainClass());
 		super.copy();
 	}
 
@@ -82,7 +77,6 @@ public class BootJar extends Jar implements BootArchive {
 	@Override
 	public void setMainClass(String mainClass) {
 		this.mainClass = mainClass;
-		this.mainClassSupplier.setMainClass(mainClass);
 	}
 
 	@Override

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/bundling/BootWar.java

@@ -29,8 +29,6 @@ import org.gradle.api.specs.Spec;
 import org.gradle.api.tasks.Optional;
 import org.gradle.api.tasks.bundling.War;
 
-import org.springframework.boot.gradle.MainClassSupplier;
-
 /**
  * A custom {@link War} task that produces a Spring Boot executable war.
  *
@@ -38,11 +36,8 @@ import org.springframework.boot.gradle.MainClassSupplier;
  */
 public class BootWar extends War implements BootArchive {
 
-	private final MainClassSupplier mainClassSupplier = new MainClassSupplier(
-			this::getClasspath);
-
-	private final BootArchiveSupport support = new BootArchiveSupport(
-			this.mainClassSupplier, "WEB-INF/lib/", "WEB-INF/lib-provided");
+	private final BootArchiveSupport support = new BootArchiveSupport("WEB-INF/lib/",
+			"WEB-INF/lib-provided");
 
 	private String mainClass;
 
@@ -60,7 +55,7 @@ public class BootWar extends War implements BootArchive {
 
 	@Override
 	public void copy() {
-		this.support.configureManifest(this);
+		this.support.configureManifest(this, getMainClass());
 		super.copy();
 	}
 
@@ -77,7 +72,6 @@ public class BootWar extends War implements BootArchive {
 	@Override
 	public void setMainClass(String mainClass) {
 		this.mainClass = mainClass;
-		this.mainClassSupplier.setMainClass(mainClass);
 	}
 
 	@Override

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/bundling/BundlingPluginFeatures.java

@@ -37,6 +37,7 @@ import org.gradle.api.plugins.WarPlugin;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.Upload;
 
+import org.springframework.boot.gradle.MainClassResolver;
 import org.springframework.boot.gradle.PluginFeatures;
 
 /**
@@ -65,6 +66,9 @@ public class BundlingPluginFeatures implements PluginFeatures {
 		ArchivePublishArtifact artifact = new ArchivePublishArtifact(bootWar);
 		this.singlePublishedArtifact.addCandidate(artifact);
 		project.getComponents().add(new BootSoftwareComponent(artifact, "bootWeb"));
+		bootWar.conventionMapping("mainClass", () -> {
+			return new MainClassResolver(bootWar.getClasspath()).resolveMainClass();
+		});
 	}
 
 	private void configureBootJarTask(Project project) {
@@ -79,6 +83,9 @@ public class BundlingPluginFeatures implements PluginFeatures {
 		ArchivePublishArtifact artifact = new ArchivePublishArtifact(bootJar);
 		this.singlePublishedArtifact.addCandidate(artifact);
 		project.getComponents().add(new BootSoftwareComponent(artifact, "bootJava"));
+		bootJar.conventionMapping("mainClass", () -> {
+			return new MainClassResolver(bootJar.getClasspath()).resolveMainClass();
+		});
 	}
 
 	private void configureBootArchivesUpload(Project project) {

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/run/BootRunTask.java

@@ -26,7 +26,6 @@ import org.gradle.api.internal.file.collections.SimpleFileCollection;
 import org.gradle.api.tasks.JavaExec;
 import org.gradle.api.tasks.SourceSet;
 
-import org.springframework.boot.gradle.MainClassSupplier;
 import org.springframework.boot.loader.tools.FileUtils;
 
 /**
@@ -38,9 +37,6 @@ import org.springframework.boot.loader.tools.FileUtils;
  */
 public class BootRunTask extends JavaExec {
 
-	private final MainClassSupplier mainClassSupplier = new MainClassSupplier(
-			this::getClasspath);
-
 	/**
 	 * Whether or not resources (typically in {@code src/main/resources} are added
 	 * directly to the classpath. When enabled, this allows live in-place editing of
@@ -67,17 +63,6 @@ public class BootRunTask extends JavaExec {
 		super.exec();
 	}
 
-	@Override
-	public String getMain() {
-		return this.mainClassSupplier.get();
-	}
-
-	@Override
-	public JavaExec setMain(String mainClassName) {
-		this.mainClassSupplier.setMainClass(mainClassName);
-		return super.setMain(mainClassName);
-	}
-
 	private void addResourcesIfNecessary() {
 		if (this.addResources) {
 			SourceSet mainSourceSet = SourceSets.findMainSourceSet(getProject());

spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/run/RunPluginFeatures.java

@@ -23,6 +23,7 @@ import org.gradle.api.Project;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.plugins.JavaPluginConvention;
 
+import org.springframework.boot.gradle.MainClassResolver;
 import org.springframework.boot.gradle.PluginFeatures;
 
 /**
@@ -60,6 +61,9 @@ public class RunPluginFeatures implements PluginFeatures {
 				return Collections.emptyList();
 			}
 		});
+		run.conventionMapping("main", () -> {
+			return new MainClassResolver(run.getClasspath()).resolveMainClass();
+		});
 	}
 
 }