Add AbstractHttpSessionApplicationInitializer

This reduces the boilerplate code required to register Spring Session with
the servlet container.

Fixes gh-43

samples/web/src/main/java/Initializer.java

@@ -15,31 +15,14 @@
  */
 
 
-import org.springframework.web.context.AbstractContextLoaderInitializer;
-import org.springframework.web.context.WebApplicationContext;
-import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;
-import org.springframework.web.filter.DelegatingFilterProxy;
-
-import javax.servlet.DispatcherType;
-import javax.servlet.ServletContext;
-import javax.servlet.ServletException;
-import java.util.EnumSet;
+import org.springframework.session.web.context.AbstractHttpSessionApplicationInitializer;
 
 /**
  * @author Rob Winch
  */
-public class Initializer extends AbstractContextLoaderInitializer {
-    @Override
-    public void onStartup(ServletContext servletContext) throws ServletException {
-        super.onStartup(servletContext);
-        servletContext.addFilter("springSessionRepositoryFilter", DelegatingFilterProxy.class)
-                .addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), false, "/*");
-    }
+public class Initializer extends AbstractHttpSessionApplicationInitializer {
 
-    @Override
-    protected WebApplicationContext createRootApplicationContext() {
-        AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
-        context.register(Config.class);
-        return context;
+    public Initializer() {
+        super(Config.class);
     }
 }