DateTypeAdapter.java

package org.apache.fulcrum.json.gson;

/*
 * 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.io.IOException;
import java.text.DateFormat;
import java.text.ParseException;
import java.util.Date;

import com.google.gson.Gson;
import com.google.gson.JsonSyntaxException;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;

/**
 * Adapter for Date. Although this class appears stateless, it is not.
 * DateFormat captures its time zone and locale when it is created, which gives
 * this class state. DateFormat isn't thread safe either, so this class has
 * to synchronize its read and write methods.
 */
public final class DateTypeAdapter extends TypeAdapter<Date> {
  public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
    @Override
    @SuppressWarnings("unchecked") // we use a runtime check to make sure the 'T's equal
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
      return typeToken.getRawType() == Date.class ? (TypeAdapter<T>) new DateTypeAdapter() : null;
    }
  };
  
  // default 
  private DateFormat customDateFormat = DateFormat.getDateTimeInstance(DateFormat.DEFAULT, DateFormat.DEFAULT);;
  
  public void setCustomDateFormat(DateFormat df) {
      this.customDateFormat = df;
  }
  
  public DateFormat getCustomDateFormat() {
      return customDateFormat;
  }


  @Override public Date read(JsonReader in) throws IOException {
    if (in.peek() == JsonToken.NULL) {
      in.nextNull();
      return null;
    }
    return deserializeToDate(in.nextString());
  }

  private synchronized Date deserializeToDate(String json) {
    try {
      return customDateFormat.parse(json);
    } catch (ParseException e) {
      throw new JsonSyntaxException(json, e);
    }
  }

  @Override public synchronized void write(JsonWriter out, Date value) throws IOException {
    if (value == null) {
      out.nullValue();
      return;
    }
    String dateFormatAsString = customDateFormat.format(value);
    out.value(dateFormatAsString);
  }

}