DataBinder unwraps Optional objects and allows for proper handling of Optional.empty()

Issue: SPR-12241

spring-context/src/main/java/org/springframework/validation/DataBinder.java

@@ -24,6 +24,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -41,7 +42,9 @@ import org.springframework.beans.TypeConverter;
 import org.springframework.beans.TypeMismatchException;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.convert.ConversionService;
+import org.springframework.lang.UsesJava8;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.PatternMatchUtils;
 import org.springframework.util.StringUtils;
@@ -119,6 +122,19 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 	 */
 	protected static final Log logger = LogFactory.getLog(DataBinder.class);
 
+	private static Class<?> javaUtilOptionalClass = null;
+
+	static {
+		try {
+			javaUtilOptionalClass =
+					ClassUtils.forName("java.util.Optional", DataBinder.class.getClassLoader());
+		}
+		catch (ClassNotFoundException ex) {
+			// Java 8 not available - Optional references simply not supported then.
+		}
+	}
+
+
 	private final Object target;
 
 	private final String objectName;
@@ -165,7 +181,12 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 	 * @param objectName the name of the target object
 	 */
 	public DataBinder(Object target, String objectName) {
-		this.target = target;
+		if (target != null && target.getClass().equals(javaUtilOptionalClass)) {
+			this.target = OptionalUnwrapper.unwrap(target);
+		}
+		else {
+			this.target = target;
+		}
 		this.objectName = objectName;
 	}
 
@@ -779,4 +800,22 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 		return getBindingResult().getModel();
 	}
 
+
+	/**
+	 * Inner class to avoid a hard dependency on Java 8.
+	 */
+	@UsesJava8
+	private static class OptionalUnwrapper {
+
+		public static Object unwrap(Object optionalObject) {
+			Optional<?> optional = (Optional<?>) optionalObject;
+			if (!optional.isPresent()) {
+				return null;
+			}
+			Object result = optional.get();
+			Assert.isTrue(!(result instanceof Optional), "Multi-level Optional usage not supported");
+			return result;
+		}
+	}
+
 }