Support for custom layout types to change loader classes

A layout can
also optionally change the loader jar that is unpacked in the root
of the repackaged archive by implementing a new method in Layout.

spring-boot-docs/src/main/asciidoc/build-tool-plugins.adoc

@@ -493,7 +493,7 @@ The following configuration options are available:
 
 
 [[build-tool-plugins-gradle-configuration-layouts]]
-==== Available layouts
+==== Available built-in layouts
 
 The `layout` attribute configures the format of the archive and whether the bootstrap
 loader should be included or not. The following layouts are available:
@@ -530,6 +530,37 @@ loader should be included or not. The following layouts are available:
 
 
 
+[[build-tool-plugins-gradle-configuration-custom-layout]]
+==== Using a custom layout
+If you have custom requirements for how to arrange the dependencies and loader classes
+inside the repackaged jar, you can use a custom layout in addition to the built-in values.
+Any library which defines one or more `LayoutFactory` implementations and
+lists them in `META-INF/spring.factories` can be added to the build script dependencies
+and then the layout type becomes available in the `springBoot` configuration. For example
+
+[source,groovy,indent=0,subs="verbatim,attributes"]
+----
+buildscript {
+	ext {
+		springBootVersion = '1.5.0.BUILD-SNAPSHOT'
+		customVersion = '0.0.1.BUILD-SNAPSHOT'
+	}
+	repositories {
+		mavenLocal()
+		mavenCentral()
+	}
+	dependencies {
+		classpath("com.example:custom-layout:${customVersion}")
+		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
+	}
+}
+
+springBoot {
+	layout = 'CUSTOM'
+}
+----
+
+
 [[build-tool-plugins-understanding-the-gradle-plugin]]
 === Understanding how the Gradle plugin works
 When `spring-boot` is applied to your Gradle project a default task named `bootRepackage`

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

@@ -20,6 +20,8 @@ import java.io.File;
 import java.util.Map;
 import java.util.Set;
 
+import groovy.lang.Closure;
+
 import org.gradle.api.Project;
 import org.gradle.api.plugins.JavaPlugin;
 
@@ -27,8 +29,6 @@ import org.springframework.boot.gradle.buildinfo.BuildInfo;
 import org.springframework.boot.loader.tools.Layout;
 import org.springframework.boot.loader.tools.LayoutType;
 
-import groovy.lang.Closure;
-
 /**
  * Gradle DSL Extension for 'Spring Boot'. Most of the time Spring Boot can guess the
  * settings in this extension, but occasionally you might need to explicitly set one or

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/JarWriter.java

@@ -53,8 +53,6 @@ import org.springframework.lang.UsesJava7;
  */
 public class JarWriter {
 
-	private static final String NESTED_LOADER_JAR = "META-INF/loader/spring-boot-loader.jar";
-
 	private static final int BUFFER_SIZE = 32 * 1024;
 
 	private final JarOutputStream jarOutput;
@@ -206,9 +204,20 @@ public class JarWriter {
 	/**
 	 * Write the required spring-boot-loader classes to the JAR.
 	 * @throws IOException if the classes cannot be written
+	 * @deprecated us {@link #writeLoaderClasses(String)} instead
 	 */
+	@Deprecated
 	public void writeLoaderClasses() throws IOException {
-		URL loaderJar = getClass().getClassLoader().getResource(NESTED_LOADER_JAR);
+		writeLoaderClasses(Layouts.DEFAULT_LOADER_JAR);
+	}
+
+	/**
+	 * Write the required spring-boot-loader classes to the JAR.
+	 * @param loaderJarPath the path to the loader jar (in the classpath)
+	 * @throws IOException if the classes cannot be written
+	 */
+	public void writeLoaderClasses(String loaderJarPath) throws IOException {
+		URL loaderJar = getClass().getClassLoader().getResource(loaderJarPath);
 		JarInputStream inputStream = new JarInputStream(
 				new BufferedInputStream(loaderJar.openStream()));
 		JarEntry entry;

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Layout.java

@@ -40,15 +40,25 @@ public interface Layout {
 	String getLibraryDestination(String libraryName, LibraryScope scope);
 
 	/**
-	 * Returns the location of classes within the archive.
+	 * Returns the location of classes within the archive. Empty if the location is the
+	 * root path, otherwise ends with a slash ('/').
 	 * @return the classes location
 	 */
 	String getClassesLocation();
 
 	/**
-	 * Returns if loader classes should be included to make the archive executable.
+	 * Returns if loader classes should be included to make the archive executable. If
+	 * true, then {@link #getLoaderJarPath()} should point to a valid jar file that
+	 * contains the loader classes.
 	 * @return if the layout is executable
 	 */
 	boolean isExecutable();
 
+	/**
+	 * Returns the path to a nested jar that contains the loader, and which will be
+	 * unpacked into the root of the repackaged jar.
+	 * @return the path to a nested jar that contains the loader
+	 */
+	String getLoaderJarPath();
+
 }

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/LayoutType.java

@@ -24,6 +24,8 @@ import org.springframework.core.io.support.SpringFactoriesLoader;
 
 /**
  * Archive layout types.
+ *
+ * @author Dave Syer
  */
 public enum LayoutType {
 

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Layouts.java

@@ -33,6 +33,11 @@ import java.util.Set;
  */
 public final class Layouts {
 
+	/**
+	 * Default value for {@link #getLoaderJarPath()}.
+	 */
+	public static final String DEFAULT_LOADER_JAR = "META-INF/loader/spring-boot-loader.jar";
+
 	private Layouts() {
 	}
 
@@ -87,6 +92,11 @@ public final class Layouts {
 			return true;
 		}
 
+		@Override
+		public String getLoaderJarPath() {
+			return DEFAULT_LOADER_JAR;
+		}
+
 	}
 
 	/**
@@ -116,6 +126,11 @@ public final class Layouts {
 			return false;
 		}
 
+		@Override
+		public String getLoaderJarPath() {
+			return DEFAULT_LOADER_JAR;
+		}
+
 	}
 
 	/**
@@ -154,6 +169,11 @@ public final class Layouts {
 			return true;
 		}
 
+		@Override
+		public String getLoaderJarPath() {
+			return DEFAULT_LOADER_JAR;
+		}
+
 	}
 
 	/**
@@ -188,6 +208,11 @@ public final class Layouts {
 			return false;
 		}
 
+		@Override
+		public String getLoaderJarPath() {
+			return DEFAULT_LOADER_JAR;
+		}
+
 	}
 
 }

spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Repackager.java

@@ -217,7 +217,7 @@ public class Repackager {
 			}
 			writeNestedLibraries(standardLibraries, seen, writer);
 			if (this.layout.isExecutable()) {
-				writer.writeLoaderClasses();
+				writer.writeLoaderClasses(this.layout.getLoaderJarPath());
 			}
 		}
 		finally {

spring-boot-tools/spring-boot-loader-tools/src/test/java/org/springframework/boot/loader/tools/LayoutTypeTests.java

@@ -28,7 +28,8 @@ public class LayoutTypeTests {
 
 	@Test
 	public void standardType() {
-		assertThat(LayoutType.layout("DIR")).isEqualTo(LayoutType.valueOf("DIR").layout());
+		assertThat(LayoutType.layout("DIR"))
+				.isEqualTo(LayoutType.valueOf("DIR").layout());
 	}
 
 	@Test
@@ -46,6 +47,7 @@ public class LayoutTypeTests {
 		@Override
 		public String getName() {
 			return "CUSTOM";
-		}}
+		}
+	}
 
 }

spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/RepackageMojo.java

@@ -227,6 +227,7 @@ public class RepackageMojo extends AbstractDependencyFilterMojo {
 		repackager.setMainClass(this.mainClass);
 		if (this.layout != null) {
 			getLog().info("Layout: " + this.layout);
+			repackager.setLayout(LayoutType.layout(this.layout));
 		}
 		return repackager;
 	}

spring-boot-tools/spring-boot-maven-plugin/src/site/apt/examples/custom-layout.apt.vm

@@ -0,0 +1,57 @@
+ -----
+ Use a custom layout
+ -----
+ Dave Syer
+ -----
+ 2016-10-30
+ -----
+
+  Spring Boot repackages the jar file for this project using a custom
+  layout defined in the additional jar file, provided as a dependency
+  to the build plugin:
+
+---
+<project>
+  ...
+  <build>
+    ...
+    <plugins>
+      ...
+      <plugin>
+        <groupId>${project.groupId}</groupId>
+        <artifactId>${project.artifactId}</artifactId>
+        <version>${project.version}</version>
+        <executions>
+          <execution>
+            <goals>
+              <goal>repackage</goal>
+            </goals>
+            <configuration>
+              <layout>CUSTOM</layout>
+            </configuration>
+          </execution>
+        </executions>
+        <dependencies>
+          <dependency>
+            <groupId>com.example</groupid>
+            <artifactId>custom-layout</artifactId>
+            <version>0.0.1.BUILD-SNAPSHOT</version>
+          </dependency>
+        </dependencies>
+        ...
+      </plugin>
+      ...
+    </plugins>
+    ...
+  </build>
+  ...
+</project>
+---
+
+  The layout is provided as an implementation of <<LayoutFactory>>
+  (from spring-boot-loader-tools) listed in
+  <<META-INF/spring-factories>> inside the <<custom-layout>> jar.
+
+
+
+

spring-boot-tools/spring-boot-maven-plugin/src/site/apt/index.apt

@@ -48,6 +48,8 @@ Spring Boot Maven Plugin
 
   * {{{./examples/repackage-disable-attach.html}Local repackaged artifact}}
 
+  * {{{./examples/custom-layout.html}Custom layout}}
+
   * {{{./examples/exclude-dependency.html}Exclude a dependency}}
 
   * {{{./examples/run-debug.html}Debug the application}}