Add implementation of CacheDataImporter/Exporter to import/export JSON sourced data.

Resolves gh-67.

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

@@ -0,0 +1,127 @@
+/*
+ * 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;
+
+import static org.springframework.data.gemfire.util.RuntimeExceptionFactory.newIllegalStateException;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Optional;
+
+import org.apache.geode.cache.Region;
+import org.apache.geode.pdx.JSONFormatter;
+import org.apache.geode.pdx.PdxInstance;
+
+import org.springframework.core.io.Resource;
+import org.springframework.dao.DataAccessResourceFailureException;
+import org.springframework.data.gemfire.util.CollectionUtils;
+import org.springframework.geode.data.AbstractCacheDataImporterExporter;
+import org.springframework.geode.data.CacheDataExporter;
+import org.springframework.geode.data.CacheDataImporter;
+import org.springframework.lang.NonNull;
+import org.springframework.stereotype.Component;
+import org.springframework.util.Assert;
+
+/**
+ * The {@link JsonCacheDataImporterExporter} class is a {@link CacheDataImporter} and {@link CacheDataExporter}
+ * implementation that can export/import JSON data to/from a {@link Resource} given a target {@link Region}.
+ *
+ * @author John Blum
+ * @see org.apache.geode.cache.Region
+ * @see org.springframework.core.io.Resource
+ * @see org.springframework.geode.data.AbstractCacheDataImporterExporter
+ * @see org.springframework.geode.data.CacheDataExporter
+ * @see org.springframework.geode.data.CacheDataImporter
+ * @see org.springframework.stereotype.Component
+ * @since 1.3.0
+ */
+@Component
+@SuppressWarnings("rawtypes")
+public class JsonCacheDataImporterExporter extends AbstractCacheDataImporterExporter {
+
+	protected static final String RESOURCE_NAME_PATTERN = "data-%s.json";
+
+	@NonNull @Override
+	public Region doExportFrom(@NonNull Region region) {
+
+		Assert.notNull(region, "Region must not be null");
+
+		String regionName = region.getName();
+
+		return region;
+	}
+
+	@NonNull @Override @SuppressWarnings("unchecked")
+	public Region doImportInto(@NonNull Region region) {
+
+		Assert.notNull(region, "Region must not be null");
+
+		// TODO: handle a JSON array of objects and PdxInstances!!!
+		getResource(region)
+			.filter(Resource::exists)
+			.map(this::getContent)
+			.map(this::toPdxInstance)
+			.ifPresent(pdxInstance -> region.put(getIdentifier(pdxInstance), pdxInstance));
+
+		return region;
+	}
+
+	private @NonNull byte[] getContent(@NonNull Resource resource) {
+
+		try (InputStream in = resource.getInputStream()){
+
+			ByteArrayOutputStream out = new ByteArrayOutputStream(in.available());
+
+			byte[] buffer = new byte[32768];
+
+			for (int bytesRead = in.read(buffer); bytesRead != -1; bytesRead = in.read(buffer)) {
+				out.write(buffer, 0, bytesRead);
+				out.flush();
+			}
+
+			return out.toByteArray();
+		}
+		catch (IOException cause) {
+			throw new DataAccessResourceFailureException(String.format("Failed to read from Resource [%s]",
+				resource.getDescription()), cause);
+		}
+	}
+
+	private Optional<Resource> getResource(@NonNull Region region) {
+
+		String regionName = region.getName().toLowerCase();
+		String resourceName = String.format(RESOURCE_NAME_PATTERN, regionName);
+
+		return getApplicationContext()
+			.map(it -> it.getResource(String.format("classpath:%s", resourceName)));
+	}
+
+	protected @NonNull Object getIdentifier(@NonNull PdxInstance pdxInstance) {
+
+		String idField = CollectionUtils.nullSafeList(pdxInstance.getFieldNames()).stream()
+			.filter(pdxInstance::isIdentityField)
+			.findFirst()
+			.orElseThrow(() -> newIllegalStateException("PdxInstance for type [%s] has no declared identify field",
+				pdxInstance.getClassName()));
+
+		return pdxInstance.getField(idField);
+	}
+
+	protected PdxInstance toPdxInstance(byte[] json) {
+		return JSONFormatter.fromJSON(json);
+	}
+}