Java tutorial
/******************************************************************************* * Copyright 2012 The Infinit.e Open Source Project * * 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 * * 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. ******************************************************************************/ package com.ikanow.infinit.e.data_model.store; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.util.Collection; import java.util.Date; import java.util.GregorianCalendar; import java.util.List; import java.util.SimpleTimeZone; import org.bson.types.ObjectId; import com.google.gson.GsonBuilder; import com.google.gson.JsonDeserializationContext; import com.google.gson.JsonDeserializer; import com.google.gson.JsonElement; import com.google.gson.JsonObject; import com.google.gson.JsonParseException; import com.google.gson.JsonSerializationContext; import com.google.gson.JsonSerializer; import com.google.gson.reflect.TypeToken; import com.ikanow.infinit.e.data_model.utils.ThreadSafeSimpleDateFormat; import com.mongodb.DBCursor; import com.mongodb.DBObject; public class BaseDbPojo { // Every Pojo should "override" this static function (stick the actual class in the 2x <>s) for readability static public <S> TypeToken<List<S>> listType() { return new TypeToken<List<S>>() { }; } // Override this function to perform custom serialization (see BasePojoApiMap) public GsonBuilder extendBuilder(GsonBuilder gp) { return extendBuilder_internal(gp); } // Allows API owner to enforce some custom serializations final public static GsonBuilder getDefaultBuilder() { return new GsonBuilder().registerTypeAdapter(ObjectId.class, new ObjectIdDeserializer()) .registerTypeAdapter(Date.class, new DateDeserializer()) .registerTypeAdapter(Long.class, new LongDeserializer()) .registerTypeAdapter(Integer.class, new IntegerDeserializer()) .registerTypeAdapter(ObjectId.class, new ObjectIdSerializer()) .registerTypeAdapter(Date.class, new DateSerializer()); } private static GsonBuilder extendBuilder_internal(GsonBuilder gp) { return gp; } //________________________________________________________________________________________________ // Won't normally override these (but can) // DB format conversion // For BaseDbPojos // 2 versions, 1 where you need dynamic mapping (eg runtime-specific) // (in both cases for single objects, you can use the nicer class<X> or // the nastier Google TypeToken, the latter has 2 advantages: // a. consisntency with list types, where you have to use the TypeToken // b. the class<X> doesn't work where X is generic) // // Note - the code is a bit unpleasant in places.... ///////////////////////////////////////////////////////////////////////////////////// // To the API JSON From a single Object public static <S extends BaseDbPojo> DBObject toDb(S s) { return toDb(s, null); } // (Nicer version of the static "toApi") public DBObject toDb() { return toDb(this); } public static <S extends BaseDbPojo> DBObject toDb(S s, BasePojoDbMap<S> dynamicMap) { GsonBuilder gb = s.extendBuilder(BaseDbPojo.getDefaultBuilder()); if (null != dynamicMap) { gb = dynamicMap.extendBuilder(gb); } return (DBObject) MongoDbUtil.encode(gb.create().toJsonTree(s).getAsJsonObject()); } ///////////////////////////////////////////////////////////////////////////////////// // From the API JSON To a single Object public static <S extends BaseDbPojo> S fromDb(DBObject s, Class<S> type) { return fromDb(s, type, null); } public static <S extends BaseDbPojo> S fromDb(DBObject s, TypeToken<S> type) { return fromDb(s, type, null); } public static <S extends BaseDbPojo> S fromDb(DBObject s, Class<S> type, BasePojoDbMap<S> dynamicMap) { if (null == s) return null; // Create a new instance of the class in order to override it GsonBuilder gb = null; try { gb = type.newInstance().extendBuilder(BaseDbPojo.getDefaultBuilder()); } catch (Exception e) { return null; } if (null != dynamicMap) { gb = dynamicMap.extendBuilder(gb); } return gb.create().fromJson(MongoDbUtil.encode(s), type); } @SuppressWarnings("unchecked") public static <S extends BaseDbPojo> S fromDb(DBObject s, TypeToken<S> type, BasePojoDbMap<S> dynamicMap) { if (null == s) return null; GsonBuilder gb = null; try { Class<S> clazz = (Class<S>) type.getType(); gb = ((S) clazz.newInstance()).extendBuilder(BaseDbPojo.getDefaultBuilder()); } catch (Exception e) { return null; } if (null != dynamicMap) { gb = dynamicMap.extendBuilder(gb); } return (S) gb.create().fromJson(MongoDbUtil.encode(s), type.getType()); } ///////////////////////////////////////////////////////////////////////////////////// // To the API JSON From a list of objects public static <S extends BaseDbPojo> DBObject listToDb(Collection<S> list, TypeToken<? extends Collection<S>> listType) { return listToDb(list, listType, null); } public static <S extends BaseDbPojo> DBObject listToDb(Collection<S> list, TypeToken<? extends Collection<S>> listType, BasePojoDbMap<S> dynamicMap) { GsonBuilder gb = null; try { if (!list.isEmpty()) { gb = list.iterator().next().extendBuilder(BaseDbPojo.getDefaultBuilder()); } } catch (Exception e) { return null; } return (DBObject) MongoDbUtil .encodeArray(gb.create().toJsonTree(list, listType.getType()).getAsJsonArray()); } ///////////////////////////////////////////////////////////////////////////////////// // From the API JSON to a list of objects public static <S extends BaseDbPojo, L extends Collection<S>> L listFromDb(DBCursor bson, TypeToken<? extends L> listType) { return listFromDb(bson, listType, null); } @SuppressWarnings("unchecked") public static <S extends BaseDbPojo, L extends Collection<S>> L listFromDb(DBCursor bson, TypeToken<? extends L> listType, BasePojoDbMap<S> dynamicMap) { GsonBuilder gb = null; try { Class<S> clazz = (Class<S>) ((ParameterizedType) listType.getType()).getActualTypeArguments()[0]; // (know this works because of construction of listType) gb = (clazz.newInstance()).extendBuilder(BaseDbPojo.getDefaultBuilder()); } catch (Exception e) { return null; } if (null != dynamicMap) { gb = dynamicMap.extendBuilder(gb); } return (L) gb.create().fromJson(MongoDbUtil.encode(bson), listType.getType()); } //___________________________________________________________________ // Default MongoDB serialization/deserialization rules: // 1. Object Ids protected static class ObjectIdSerializer implements JsonSerializer<ObjectId> { @Override public JsonElement serialize(ObjectId id, Type typeOfT, JsonSerializationContext context) { JsonObject jo = new JsonObject(); jo.addProperty("$oid", id.toStringMongod()); return jo; } } protected static class ObjectIdDeserializer implements JsonDeserializer<ObjectId> { @Override public ObjectId deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { if (json.isJsonPrimitive()) { return new ObjectId(json.getAsString()); } else { try { return new ObjectId(json.getAsJsonObject().get("$oid").getAsString()); } catch (Exception e) { return null; } } } } // Dates: protected static class DateDeserializer implements JsonDeserializer<Date> { private static ThreadSafeSimpleDateFormat _format = new ThreadSafeSimpleDateFormat( "yyyy-MM-dd'T'HH:mm:ss'Z'"); private static ThreadSafeSimpleDateFormat _format2 = new ThreadSafeSimpleDateFormat( "MMM d, yyyy hh:mm:ss a"); @Override public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { Date d = null; if (json.isJsonPrimitive()) { try { d = _format2.parse(json.getAsString()); } catch (Exception e) { try { d = _format.parse(json.getAsString()); } catch (Exception e2) { d = null; } } } else { try { d = _format.parse(json.getAsJsonObject().get("$date").getAsString()); } catch (Exception e) { d = null; } } return d; } } protected static class DateSerializer implements JsonSerializer<Date> { private static ThreadSafeSimpleDateFormat _format = null; @Override public JsonElement serialize(Date date, Type typeOfT, JsonSerializationContext context) { Date d = (Date) date; if (null == _format) { _format = new ThreadSafeSimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'"); _format.setCalendar(new GregorianCalendar(new SimpleTimeZone(0, "UTC"))); } JsonObject jo = new JsonObject(); jo.addProperty("$date", _format.format(d)); return jo; } } // OK MongoDB is very keen on turning Long/Integer into doubles (eg from the console) - these converts them back protected static class LongDeserializer implements JsonDeserializer<Long> { @Override public Long deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { try { return json.getAsLong(); } catch (Exception e) { return (long) json.getAsNumber().doubleValue(); } } } protected static class IntegerDeserializer implements JsonDeserializer<Integer> { @Override public Integer deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { try { return json.getAsInt(); } catch (Exception e) { return (int) json.getAsNumber().doubleValue(); } } } }