Allow gradle builds without version numbers

Add a gradle `ResolutionStrategy` that resolves missing version numbers
using the `spring-boot-dependencies` POM.

This commit also introduces a new `spring-boot-dependency-tools` module
that provides programmatic access to the `dependencyManagement` section
of the dependencies POM.

Fixed gh-262

spring-boot-tools/spring-boot-gradle-plugin/README.md

@@ -1,6 +1,7 @@
 # Spring Boot - Gradle Plugin
 The Spring Boot Gradle Plugin provides Spring Boot support in Gradle, allowing you to
-package executable jar or war archives.
+package executable jar or war archives, run Spring Boot applications and remove version
+information from your `build.gradle` file.
 
 ## Including the plugin
 To use the Spring Boot Gradle Plugin simply include a `buildscript` dependency and apply
@@ -27,6 +28,23 @@ buildscript {
 }
 ```
 
+## Declaring dependencies without versions
+The `spring-boot` plugin will register a custom Gradle `ResolutionStrategy` with your
+build that allows you to omit version numbers when declaring dependencies to known
+artifacts. All artifacts with a `org.springframework.boot` group ID, and any of the
+artifacts declared in the `managementDependencies` section of the `spring-dependencies`
+POM can have their version number resolved automatically.
+
+Simply declare dependencies in the usual way, but leave the version number empty:
+
+```groovy
+dependencies {
+    compile("org.springframework.boot:spring-boot-starter-web")
+    compile("org.thymeleaf:thymeleaf-spring4")
+    compile("nz.net.ultraq.thymeleaf:thymeleaf-layout-dialect")
+}
+```
+
 ## Packaging executable jar and war files
 Once the `spring-boot` plugin has been applied to your project it will automatically
 attempt to rewrite archives to make them executable using the `bootRepackage` task. You
@@ -45,7 +63,6 @@ $ java -jar build/libs/mymodule-0.0.1-SNAPSHOT.jar
 ```
 
 ### Running a Project in Place
-
 To run a project in place without building a jar first you can use the "bootRun" task:
 
 ```

spring-boot-tools/spring-boot-gradle-plugin/pom.xml

@@ -18,6 +18,11 @@
 			<artifactId>spring-boot-loader-tools</artifactId>
 			<version>${project.version}</version>
 		</dependency>
+		<dependency>
+            <groupId>${project.groupId}</groupId>
+            <artifactId>spring-boot-dependency-tools</artifactId>
+            <version>${project.version}</version>
+		</dependency>
 		<!-- Provided -->
 		<dependency>
 			<groupId>org.codehaus.groovy</groupId>

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/SpringBootPlugin.java

@@ -16,8 +16,10 @@
 
 package org.springframework.boot.gradle;
 
+import org.gradle.api.Action;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
+import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.artifacts.Dependency;
 import org.gradle.api.plugins.ApplicationPlugin;
 import org.gradle.api.plugins.BasePlugin;
@@ -26,8 +28,8 @@ import org.springframework.boot.gradle.task.Repackage;
 import org.springframework.boot.gradle.task.RunApp;
 
 /**
- * Gradle 'Spring Boot' {@link Plugin}. Provides 2 tasks (bootRepackge and bootRun).
- * 
+ * Gradle 'Spring Boot' {@link Plugin}.
+ *
  * @author Phillip Webb
  * @author Dave Syer
  */
@@ -44,19 +46,31 @@ public class SpringBootPlugin implements Plugin<Project> {
 		project.getPlugins().apply(ApplicationPlugin.class);
 		project.getExtensions().create("springBoot", SpringBootPluginExtension.class);
 
-		// register BootRepackage so that we can use
-		// task foo(type: BootRepackage) {}
-		project.getExtensions().getExtraProperties().set("BootRepackage", Repackage.class);
-		Repackage packageTask = addRepackageTask(project);
-		ensureTaskRunsOnAssembly(project, packageTask);
-		addRunAppTask(project);
+		applyRepackage(project);
+		applyRun(project);
+		applyResolutionStrategy(project);
 	}
 
-	private void addRunAppTask(Project project) {
-		RunApp runJarTask = project.getTasks().create(RUN_APP_TASK_NAME, RunApp.class);
-		runJarTask.setDescription("Run the project with support for auto-detecting main class and reloading static resources");
-		runJarTask.setGroup("Execution");
-		runJarTask.dependsOn("assemble");
+	private void applyRepackage(Project project) {
+		Repackage packageTask = addRepackageTask(project);
+		ensureTaskRunsOnAssembly(project, packageTask);
+	}
+
+	private void applyRun(Project project) {
+		addRunAppTask(project);
+		// register BootRepackage so that we can use task foo(type: BootRepackage) {}
+		project.getExtensions().getExtraProperties().set("BootRepackage", Repackage.class);
+	}
+
+	private void applyResolutionStrategy(Project project) {
+		project.getConfigurations().all(new Action<Configuration>() {
+
+			@Override
+			public void execute(Configuration configuration) {
+				SpringBootResolutionStrategy.apply(configuration.getResolutionStrategy());
+			}
+
+		});
 	}
 
 	private Repackage addRepackageTask(Project project) {
@@ -71,6 +85,13 @@ public class SpringBootPlugin implements Plugin<Project> {
 		return packageTask;
 	}
 
+	private void addRunAppTask(Project project) {
+		RunApp runJarTask = project.getTasks().create(RUN_APP_TASK_NAME, RunApp.class);
+		runJarTask.setDescription("Run the project with support for auto-detecting main class and reloading static resources");
+		runJarTask.setGroup("Execution");
+		runJarTask.dependsOn("assemble");
+	}
+
 	private void ensureTaskRunsOnAssembly(Project project, Repackage task) {
 		project.getTasks().getByName(BasePlugin.ASSEMBLE_TASK_NAME).dependsOn(task);
 	}

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/SpringBootPluginExtension.groovy

@@ -39,8 +39,19 @@ import org.springframework.boot.loader.tools.Layouts
 public class SpringBootPluginExtension {
 
 	static enum LayoutType {
-		JAR(new Layouts.Jar()), WAR(new Layouts.War()), ZIP(new Layouts.Expanded()), DIR(new Layouts.Expanded()), NONE(new Layouts.None());
+
+		JAR(new Layouts.Jar()),
+
+		WAR(new Layouts.War()),
+
+		ZIP(new Layouts.Expanded()),
+
+		DIR(new Layouts.Expanded()),
+
+		NONE(new Layouts.None());
+
 		Layout layout;
+
 		private LayoutType(Layout layout) {
 			this.layout = layout;
 		}
@@ -85,6 +96,6 @@ public class SpringBootPluginExtension {
 	 * @return the Layout to use or null if not explicitly set
 	 */
 	Layout convertLayout() {
-		layout==null ? null : layout.layout
+		(layout == null ? null : layout.layout)
 	}
 }

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/SpringBootResolutionStrategy.java

@@ -0,0 +1,51 @@
+
+package org.springframework.boot.gradle;
+
+import org.gradle.api.Action;
+import org.gradle.api.artifacts.DependencyResolveDetails;
+import org.gradle.api.artifacts.ModuleVersionSelector;
+import org.gradle.api.artifacts.ResolutionStrategy;
+import org.springframework.boot.dependency.tools.Dependency;
+import org.springframework.boot.dependency.tools.ManagedDependencies;
+
+/**
+ * A resolution strategy to resolve missing version numbers using the
+ * 'spring-boot-dependencies' POM.
+ *
+ * @author Phillip Webb
+ */
+public class SpringBootResolutionStrategy {
+
+	private static final String SPRING_BOOT_GROUP = "org.springframework.boot";
+
+	public static void apply(ResolutionStrategy resolutionStrategy) {
+		resolutionStrategy.eachDependency(new Action<DependencyResolveDetails>() {
+
+			@Override
+			public void execute(DependencyResolveDetails resolveDetails) {
+				String version = resolveDetails.getTarget().getVersion();
+				if (version == null || version.trim().length() == 0) {
+					resolve(resolveDetails);
+				}
+			}
+
+		});
+	}
+
+	protected static void resolve(DependencyResolveDetails resolveDetails) {
+
+		ManagedDependencies dependencies = ManagedDependencies.get();
+		ModuleVersionSelector target = resolveDetails.getTarget();
+
+		if (SPRING_BOOT_GROUP.equals(target.getGroup())) {
+			resolveDetails.useVersion(dependencies.getVersion());
+			return;
+		}
+
+		Dependency dependency = dependencies.find(target.getGroup(), target.getName());
+		if (dependency != null) {
+			resolveDetails.useVersion(dependency.getVersion());
+		}
+	}
+
+}

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/task/RunApp.java

@@ -36,7 +36,7 @@ import org.springframework.boot.loader.tools.MainClassFinder;
 
 /**
  * Run the project from Gradle.
- * 
+ *
  * @author Dave Syer
  */
 public class RunApp extends DefaultTask {
@@ -57,6 +57,7 @@ public class RunApp extends DefaultTask {
 					main = set;
 				}
 			};
+
 		});
 
 		final Set<File> allResources = new LinkedHashSet<File>();