Java tutorial
/* * Copyright (c) 2017, Kasra Faghihi, All rights reserved. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 3.0 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library. */ package com.offbynull.actors.gateways.servlet; import com.google.gson.Gson; import com.google.gson.GsonBuilder; import com.google.gson.JsonArray; 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.JsonPrimitive; import com.google.gson.JsonSerializationContext; import com.google.gson.JsonSerializer; import com.google.gson.JsonSyntaxException; import com.offbynull.actors.address.Address; import com.offbynull.actors.shuttle.Message; import java.lang.reflect.Type; import java.util.ArrayList; import java.util.List; import org.apache.commons.lang3.Validate; final class JsonConverter { private static final String SOURCE_PROPERTY = "source"; private static final String DESTINATION_PROPERTY = "destination"; private static final String TYPE_PROPERTY = "type"; private static final String DATA_PROPERTY = "data"; private static final String ID_PROPERTY = "id"; private static final String IN_QUEUE_PROPERTY = "inQueue"; private static final String IN_QUEUE_OFFSET_PROPERTY = "inQueueOffset"; private static final String OUT_QUEUE_PROPERTY = "outQueue"; private static final String OUT_QUEUE_OFFSET_PROPERTY = "outQueueOffset"; private final Gson gson; JsonConverter() { GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(Message.class, new MessageJsonDeserializer()); gsonBuilder.registerTypeAdapter(Message.class, new MessageJsonSerializer()); gsonBuilder.registerTypeAdapter(RequestBlock.class, new RequestBlockDeserializer()); gsonBuilder.registerTypeAdapter(ResponseBlock.class, new ResponseBlockSerializer()); gson = gsonBuilder.create(); } public String toJson(ResponseBlock response) { Validate.notNull(response); return gson.toJson(response, ResponseBlock.class); } public RequestBlock fromJson(String request) { Validate.notNull(request); try { return gson.fromJson(request, RequestBlock.class); } catch (NullPointerException | IllegalArgumentException | JsonSyntaxException e) { // these types are things that either gson or the serializer/deserializer we registered can throw -- it means the input was bad throw new IllegalArgumentException(e); } } private static final class MessageJsonDeserializer implements JsonDeserializer<Message> { @Override public Message deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { JsonObject jsonObject = json.getAsJsonObject(); String from = jsonObject.get(SOURCE_PROPERTY).getAsString(); Address fromAddress = Address.fromString(from); String to = jsonObject.get(DESTINATION_PROPERTY).getAsString(); Address toAddress = Address.fromString(to); JsonElement jsonType = jsonObject.get(TYPE_PROPERTY); String type = jsonType.getAsString(); Class<?> cls; try { cls = Class.forName(type, false, getClass().getClassLoader()); } catch (ClassNotFoundException cnfe) { throw new IllegalArgumentException(cnfe); } JsonElement jsonData = jsonObject.get(DATA_PROPERTY); Object obj = context.deserialize(jsonData, cls); return new Message(fromAddress, toAddress, obj); } } private static final class MessageJsonSerializer implements JsonSerializer<Message> { @Override public JsonElement serialize(Message src, Type typeOfSrc, JsonSerializationContext context) { JsonObject output = new JsonObject(); JsonElement payload = context.serialize(src.getMessage()); String from = src.getSourceAddress().toString(); String to = src.getDestinationAddress().toString(); Object obj = src.getMessage(); String type = obj.getClass().getName(); output.add(SOURCE_PROPERTY, new JsonPrimitive(from)); output.add(DESTINATION_PROPERTY, new JsonPrimitive(to)); output.add(TYPE_PROPERTY, new JsonPrimitive(type)); output.add(DATA_PROPERTY, payload); return output; } } private static final class ResponseBlockSerializer implements JsonSerializer<ResponseBlock> { @Override public JsonElement serialize(ResponseBlock src, Type typeOfSrc, JsonSerializationContext context) { JsonObject jsonObject = new JsonObject(); JsonArray jsonOutQueue = new JsonArray(); for (Message message : src.getOutQueue()) { JsonElement jsonMessage = context.serialize(message); jsonOutQueue.add(jsonMessage); } jsonObject.add(OUT_QUEUE_PROPERTY, jsonOutQueue); return jsonObject; } } private static final class RequestBlockDeserializer implements JsonDeserializer<RequestBlock> { @Override public RequestBlock deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { JsonObject jsonObject = json.getAsJsonObject(); String id = jsonObject.get(ID_PROPERTY).getAsString(); int outQueueOffset = jsonObject.get(OUT_QUEUE_OFFSET_PROPERTY).getAsInt(); int inQueueOffset = jsonObject.get(IN_QUEUE_OFFSET_PROPERTY).getAsInt(); JsonArray jsonInQueue = jsonObject.get(IN_QUEUE_PROPERTY).getAsJsonArray(); List<Message> inQueue = new ArrayList<>(jsonInQueue.size()); for (JsonElement jsonMessage : jsonInQueue) { Message message = context.deserialize(jsonMessage, Message.class); inQueue.add(message); } return new RequestBlock(id, outQueueOffset, inQueueOffset, inQueue); } } }