Java tutorial
package org.apache.tika.metadata.serialization; /* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 * * http://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. */ import java.lang.reflect.Type; import java.util.Arrays; import org.apache.tika.metadata.Metadata; import com.google.gson.JsonArray; import com.google.gson.JsonElement; import com.google.gson.JsonNull; import com.google.gson.JsonObject; import com.google.gson.JsonPrimitive; import com.google.gson.JsonSerializationContext; import com.google.gson.JsonSerializer; /** * Serializer for Metadata * * If overriding this, remember that this is called from a static context. * Share state only with great caution. * */ public class JsonMetadataSerializer implements JsonSerializer<Metadata> { /** * Serializes a Metadata object into effectively Map<String, String[]>. * * @param metadata object to serialize * @param type (ignored) * @param context (ignored) * @return JsonElement with key/value(s) pairs or JsonNull if metadata is null. */ @Override public JsonElement serialize(Metadata metadata, Type type, JsonSerializationContext context) { if (metadata == null) { return JsonNull.INSTANCE; } String[] names = getNames(metadata); if (names == null) { return JsonNull.INSTANCE; } JsonObject root = new JsonObject(); for (String n : names) { String[] vals = metadata.getValues(n); if (vals == null) { //silently skip continue; } if (vals.length == 1) { root.addProperty(n, vals[0]); } else { JsonArray jArr = new JsonArray(); for (int i = 0; i < vals.length; i++) { jArr.add(new JsonPrimitive(vals[i])); } root.add(n, jArr); } } return root; } /** * Override to get a custom sort order * or to filter names. * * @param metadata metadata from which to grab names * @return list of names in the order in which they should be serialized */ protected String[] getNames(Metadata metadata) { String[] names = metadata.names(); Arrays.sort(names); return names; } }