Add ObjectToJsonConverter interface specifying a contract for converting an Object to JSON.

Resolves gh-67.

spring-geode/src/main/java/org/springframework/geode/data/json/converter/ObjectToJsonConverter.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2020 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
+ *
+ *     https://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 org.springframework.geode.data.json.converter;
+
+import org.springframework.core.convert.converter.Converter;
+
+/**
+ * A Spring {@link Converter} interface extension defining a contract to convert
+ * from an {@link Object} into a {@literal JSON} {@link String}.
+ *
+ * @author John Blum
+ * @see java.lang.FunctionalInterface
+ * @see java.lang.Object
+ * @see java.lang.String
+ * @see org.springframework.core.convert.converter.Converter
+ * @since 1.3.0
+ */
+@FunctionalInterface
+public interface ObjectToJsonConverter extends Converter<Object, String> {
+
+}