Add InitializrMetadataCustomizer callback

initializr/src/main/groovy/io/spring/initializr/InitializrMetadata.groovy

@@ -26,6 +26,7 @@ import io.spring.initializr.mapper.InitializrMetadataV2JsonMapper
 import io.spring.initializr.support.InvalidVersionException
 import io.spring.initializr.support.VersionRange
 
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.context.properties.ConfigurationProperties
 
 /**
@@ -65,6 +66,9 @@ class InitializrMetadata {
 	final Env env = new Env()
 
 	private final Map<String, Dependency> indexedDependencies = [:]
+	
+	@Autowired
+	List<InitializrMetadataCustomizer> customizers = []
 
 	/**
 	 * Return the {@link Dependency} with the specified id or {@code null} if
@@ -170,7 +174,12 @@ class InitializrMetadata {
 	 */
 	@PostConstruct
 	void validate() {
-		for (DependencyGroup group : dependencies) {
+
+		customizers.each { customizer ->
+			customizer.customize(this)
+		}
+
+		dependencies.each { group ->
 			group.content.each { dependency ->
 				validateDependency(dependency)
 				indexDependency(dependency.id, dependency)

initializr/src/main/groovy/io/spring/initializr/InitializrMetadataCustomizer.groovy

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2014-2015 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 io.spring.initializr
+
+/**
+ * @author Dave Syer
+ *
+ */
+interface InitializrMetadataCustomizer {
+	void customize(InitializrMetadata metadata)
+}

initializr/src/test/groovy/io/spring/initializr/InitializrMetadataTests.groovy

@@ -139,6 +139,21 @@ class InitializrMetadataTests {
 		dependency.generateId()
 	}
 
+	@Test
+	void addDependencyInCustomizer() {
+		def group = new InitializrMetadata.DependencyGroup()
+		group.name = 'Extra'
+		def dependency = createDependency('com.foo:foo:1.0.0')
+		group.content.add(dependency)
+		metadata.setCustomizers([new InitializrMetadataCustomizer() {
+			void customize(InitializrMetadata metadata) {
+				metadata.dependencies.add(group)
+			}
+		}])
+		metadata.validate()
+		assertEquals 1, metadata.dependencies.size()
+	}
+
 	@Test
 	void indexedDependencies() {
 		def dependency = createDependency('first')