Add JsonToPdxConverter interface specifying a contract to convert JSON to PDX.

The JSON may be expressed as a byte[] or a String.

Resolves gh-67.

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

@@ -0,0 +1,47 @@
+/*
+ * 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.apache.geode.pdx.PdxInstance;
+
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.lang.NonNull;
+
+/**
+ * A Spring {@link Converter} interface extension defining a contract to convert
+ * from a {@literal JSON} {@link String} to a {@link PdxInstance}.
+ *
+ * @author John Blum
+ * @see java.lang.FunctionalInterface
+ * @see org.apache.geode.pdx.PdxInstance
+ * @see org.springframework.core.convert.converter.Converter
+ * @since 1.3.0
+ */
+@FunctionalInterface
+public interface JsonToPdxConverter extends Converter<String, PdxInstance> {
+
+	/**
+	 * Converts the array of {@link Byte#TYPE bytes} containing {@literal JSON} into a {@link PdxInstance}.
+	 *
+	 * @param json array of {@link Byte#TYPE bytes} containing {@literal JSON}
+	 * to convert into a {@link PdxInstance}; must not be {@literal null}.
+	 * @return a {@link PdxInstance} converted from the array of {@link Byte#TYPE bytes} containing {@literal JSON}.
+	 * @see #convert(Object)
+	 */
+	default @NonNull PdxInstance convert(@NonNull byte[] json) {
+		return convert(new String(json));
+	}
+}