DATACMNS-483 - Support for wrapper types as return types for repository methods.

The repository method invocation mechanism now post-processes the result of the actual method invocation in case it's not type-compatible with the return type of the invoked method and invokes a conversion if applicable. This allows us to register custom converters for well-known wrapper types. We currently support Optional from both Google Guava and JDK 8.

Implementation notice

We use some JDK 8 type stubs from the Spring Data Build project to be able to compile using JDKs < 8. This is necessary as we need to remain compatible with Spring 3.2.x for the Dijkstra release train and our test executions still run into some issues with it a Java 8 runtime (mostly ASM related). These issues were reported in [0, 1] and we'll probably get off the hack for Dijkstra GA by upgrading to Spring 3.2.9.

[0] https://jira.spring.io/browse/SPR-11719
[1] https://jira.spring.io/browse/SPR-11718

pom.xml

@@ -2,7 +2,7 @@
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 
 	<modelVersion>4.0.0</modelVersion>
-	
+
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-commons</artifactId>
 	<version>1.8.0.BUILD-SNAPSHOT</version>
@@ -15,13 +15,14 @@
 		<version>1.4.0.BUILD-SNAPSHOT</version>
 		<relativePath>../spring-data-build/parent/pom.xml</relativePath>
 	</parent>
-	
+
 	<properties>
+		<guava>16.0.1</guava>
 		<jackson1>1.9.7</jackson1>
 		<springhateoas>0.10.0.RELEASE</springhateoas>
 		<dist.key>DATACMNS</dist.key>
 	</properties>
-	
+
 	<dependencies>
 		<dependency>
 			<groupId>org.springframework</groupId>
@@ -74,7 +75,7 @@
 			<artifactId>spring-web</artifactId>
 			<optional>true</optional>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>javax.servlet</groupId>
 			<artifactId>servlet-api</artifactId>
@@ -109,7 +110,7 @@
 			<version>${querydsl}</version>
 			<scope>provided</scope>
 		</dependency>
-		
+
 		<!-- EJB Transactions -->
 		<dependency>
 			<groupId>javax.ejb</groupId>
@@ -126,21 +127,35 @@
 			<scope>provided</scope>
 			<optional>true</optional>
 		</dependency>
-		
+
+		<dependency>
+			<groupId>com.google.guava</groupId>
+			<artifactId>guava</artifactId>
+			<version>${guava}</version>
+			<optional>true</optional>
+		</dependency>
+
+		<dependency>
+			<groupId>org.springframework.data.build</groupId>
+			<artifactId>spring-data-java8-stub</artifactId>
+			<version>1.4.0.BUILD-SNAPSHOT</version>
+			<scope>provided</scope>
+		</dependency>
+
 		<dependency>
 			<groupId>javax.el</groupId>
 			<artifactId>el-api</artifactId>
 			<version>${cdi}</version>
 			<scope>test</scope>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>org.apache.openwebbeans.test</groupId>
 			<artifactId>cditest-owb</artifactId>
 			<version>${webbeans}</version>
 			<scope>test</scope>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>org.springframework.hateoas</groupId>
 			<artifactId>spring-hateoas</artifactId>
@@ -152,14 +167,14 @@
 			<artifactId>spring-webmvc</artifactId>
 			<optional>true</optional>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>com.sun.xml.bind</groupId>
 			<artifactId>jaxb-impl</artifactId>
 			<version>2.2.3U1</version>
 			<scope>test</scope>
 		</dependency>
-		
+
 		<dependency>
 			<groupId>xmlunit</groupId>
 			<artifactId>xmlunit</artifactId>
@@ -175,9 +190,10 @@
 			<scope>test</scope>
 		</dependency>
 	</dependencies>
-	
+
 	<build>
 		<plugins>
+
 			<plugin>
 				<groupId>com.mysema.maven</groupId>
 				<artifactId>apt-maven-plugin</artifactId>
@@ -205,14 +221,14 @@
 			</plugin>
 		</plugins>
 	</build>
-	
+
 	<repositories>
 		<repository>
 			<id>spring-libs-snapshot</id>
 			<url>http://repo.spring.io/libs-snapshot</url>
 		</repository>
 	</repositories>
-	
+
 	<pluginRepositories>
 		<pluginRepository>
 			<id>spring-plugins-release</id>