Make Optional annotation repeatable

src/com/esotericsoftware/kryo/serializers/CachedFields.java

@@ -127,8 +127,11 @@ private void addField (Field field, boolean asm, ArrayList<CachedField> fields,
 			}
 		}
 
-		Optional optional = field.getAnnotation(Optional.class);
-		if (optional != null && !serializer.kryo.getContext().containsKey(optional.value())) return;
+		Optional[] optionals = field.getAnnotationsByType(Optional.class);
+		if (optionals.length > 0 && Arrays.stream(optionals).noneMatch(
+				optional -> serializer.kryo.getContext().containsKey(optional.value()))) {
+			return;
+		}
 
 		if (removedFields.contains(field)) return;
 

src/com/esotericsoftware/kryo/serializers/FieldSerializer.java

@@ -34,6 +34,7 @@
 import com.esotericsoftware.reflectasm.FieldAccess;
 
 import java.lang.annotation.ElementType;
+import java.lang.annotation.Repeatable;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
@@ -350,15 +351,25 @@ public String toString () {
 
 	}
 
+	/** Indicates a field should be ignored when its declaring class is registered unless the {@link Kryo#getContext() context} has
+	 * a value set for a key specified by at least one of the {@link Optional} annotations. */
+	@Retention(RetentionPolicy.RUNTIME)
+	@Target(ElementType.FIELD)
+	public @interface Optionals {
+		Optional[] value();
+	}
+
 	/** Indicates a field should be ignored when its declaring class is registered unless the {@link Kryo#getContext() context} has
 	 * a value set for the specified key. This can be useful when a field must be serialized for one purpose, but not for another.
 	 * Eg, a class for a networked application could have a field that should not be serialized and sent to clients, but should be
 	 * serialized when stored on the server.
+	 * If a field has multiple of this annotation, then the field is serialized if at least one of the keys is present in the context.
 	 * @author Nathan Sweet */
 	@Retention(RetentionPolicy.RUNTIME)
 	@Target(ElementType.FIELD)
+	@Repeatable(Optionals.class)
 	public @interface Optional {
-		public String value();
+		String value();
 	}
 
 	/** Used to annotate fields with a specific Kryo serializer.

test/com/esotericsoftware/kryo/serializers/FieldSerializerTest.java

@@ -364,10 +364,35 @@ void testOptionalAnnotation () {
 		kryo.setRegistrationRequired(false);
 		kryo.setReferences(true);
 		roundTrip(82, new HasOptionalAnnotation());
+
+		kryo = new Kryo();
+		kryo.setRegistrationRequired(false);
+		kryo.setReferences(true);
+		kryo.getContext().put("smurf", null);
+		roundTrip(83, new HasOptionalAnnotation());
+
+		// To verify that more than one matching key is fine
+		kryo = new Kryo();
+		kryo.setRegistrationRequired(false);
+		kryo.setReferences(true);
+		kryo.getContext().put("smurf", null);
+		kryo.getContext().put("another smurf", null);
+		roundTrip(83, new HasOptionalAnnotation());
+
+		// To verify that additional keys do not matter
 		kryo = new Kryo();
 		kryo.setRegistrationRequired(false);
 		kryo.setReferences(true);
 		kryo.getContext().put("smurf", null);
+		kryo.getContext().put("another smurf", null);
+		kryo.getContext().put("has nothing to do with it", null);
+		roundTrip(83, new HasOptionalAnnotation());
+
+		// To verify that the order of Optional annotations does not matter
+		kryo = new Kryo();
+		kryo.setRegistrationRequired(false);
+		kryo.setReferences(true);
+		kryo.getContext().put("another smurf", null);
 		roundTrip(83, new HasOptionalAnnotation());
 	}
 
@@ -1026,7 +1051,7 @@ public boolean equals (Object obj) {
 	}
 
 	public static class HasOptionalAnnotation {
-		@Optional("smurf") int moo;
+		@Optional("smurf") @Optional("another smurf") int moo;
 
 		public boolean equals (Object obj) {
 			if (this == obj) return true;