Add custom LayoutFactory sample

Add a sample that shows how a custom LayoutFactory can be used with
both Maven and Gradle.

Closes gh-7263

spring-boot-samples/spring-boot-sample-custom-layout/src/main/java/sample/layout/SampleLayout.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2012-2016 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 sample.layout;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+
+import org.springframework.boot.loader.tools.CustomLoaderLayout;
+import org.springframework.boot.loader.tools.Layouts;
+import org.springframework.boot.loader.tools.LoaderClassesWriter;
+
+/**
+ * @author pwebb
+ */
+public class SampleLayout extends Layouts.Jar implements CustomLoaderLayout {
+
+	private String name;
+
+	public SampleLayout(String name) {
+		this.name = name;
+	}
+
+	@Override
+	public void writeLoadedClasses(LoaderClassesWriter writer) throws IOException {
+		writer.writeEntry(this.name, new ByteArrayInputStream("test".getBytes()));
+	}
+
+}

spring-boot-samples/spring-boot-sample-custom-layout/src/main/java/sample/layout/SampleLayoutFactory.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2012-2016 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 sample.layout;
+
+import java.io.File;
+
+import org.springframework.boot.loader.tools.Layout;
+import org.springframework.boot.loader.tools.LayoutFactory;
+
+public class SampleLayoutFactory implements LayoutFactory {
+
+	private String name = "sample";
+
+	public SampleLayoutFactory() {
+	}
+
+	public SampleLayoutFactory(String name) {
+		this.name = name;
+	}
+
+	public void setName(String name) {
+		this.name = name;
+	}
+
+	public String getName() {
+		return this.name;
+	}
+
+	@Override
+	public Layout getLayout(File source) {
+		return new SampleLayout(this.name);
+	}
+
+}