Java tutorial
/* Copyright 2012 Google Inc. * * 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.google.wireless.speed.speedometer.util; import com.google.myjson.FieldNamingPolicy; import com.google.myjson.Gson; import com.google.myjson.GsonBuilder; import com.google.myjson.JsonDeserializationContext; import com.google.myjson.JsonDeserializer; import com.google.myjson.JsonElement; import com.google.myjson.JsonParseException; import com.google.myjson.JsonPrimitive; import com.google.myjson.JsonSerializationContext; import com.google.myjson.JsonSerializer; import com.google.wireless.speed.speedometer.MeasurementDesc; import com.google.wireless.speed.speedometer.MeasurementTask; import com.google.wireless.speed.speedometer.SpeedometerApp; import android.content.Context; import android.util.Log; import org.json.JSONException; import org.json.JSONObject; import java.lang.reflect.Constructor; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.lang.reflect.Type; import java.text.DateFormat; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Date; import java.util.TimeZone; /** * Utility class that use the gson library to provide bidirectional conversion between * measurement objects (descriptions, tasks, and results, etc.) and JSON objects. * New types of MeasurementDesc should be registered in the static HashMap initialization * section. * @author wenjiezeng@google.com (Steve Zeng) * */ @SuppressWarnings("rawtypes") public class MeasurementJsonConvertor { /* 1. Automatically perform bidirectional translations for fields in java 'lowerCaseCamel' style * to JSON 'lower_case_with_underscores' style. * 2. Serialize and de-serialize UTC format date string * 3. It also serializes all null fields to 'null' */ public static Gson gson = new GsonBuilder().serializeNulls() .registerTypeAdapter(Date.class, new DateTypeConverter()) .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES).create(); private static final DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"); static { dateFormat.setTimeZone(TimeZone.getTimeZone("GMT")); } @SuppressWarnings("unchecked") public static MeasurementTask makeMeasurementTaskFromJson(JSONObject json, Context context) throws IllegalArgumentException { try { String type = String.valueOf(json.getString("type")); Class taskClass = MeasurementTask.getTaskClassForMeasurement(type); Method getDescMethod = taskClass.getMethod("getDescClass"); // The getDescClassForMeasurement() is static and takes no arguments Class descClass = (Class) getDescMethod.invoke(null, (Object[]) null); MeasurementDesc measurementDesc = gson.fromJson(json.toString(), descClass); Object[] cstParams = { measurementDesc, context }; Constructor<MeasurementTask> constructor = taskClass.getConstructor(MeasurementDesc.class, Context.class); return constructor.newInstance(cstParams); } catch (JSONException e) { throw new IllegalArgumentException(e); } catch (SecurityException e) { Log.w(SpeedometerApp.TAG, e.getMessage()); throw new IllegalArgumentException(e); } catch (NoSuchMethodException e) { Log.w(SpeedometerApp.TAG, e.getMessage()); throw new IllegalArgumentException(e); } catch (IllegalArgumentException e) { Log.w(SpeedometerApp.TAG, e.getMessage()); throw new IllegalArgumentException(e); } catch (InstantiationException e) { Log.w(SpeedometerApp.TAG, e.getMessage()); throw new IllegalArgumentException(e); } catch (IllegalAccessException e) { Log.w(SpeedometerApp.TAG, e.getMessage()); throw new IllegalArgumentException(e); } catch (InvocationTargetException e) { Log.w(SpeedometerApp.TAG, e.toString()); throw new IllegalArgumentException(e); } } public static JSONObject encodeToJson(Object obj) throws JSONException { String str = gson.toJson(obj); return new JSONObject(str); } public static String toJsonString(Object obj) { return gson.toJson(obj); } public static Gson getGsonInstance() { return gson; } private static class DateTypeConverter implements JsonSerializer<Date>, JsonDeserializer<Date> { @Override public JsonElement serialize(Date src, Type srcType, JsonSerializationContext context) { return new JsonPrimitive(formatDate(src)); } @Override public Date deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException { try { return parseDate(json.getAsString()); } catch (NumberFormatException e) { throw new JsonParseException("Cannot convert time string: " + json.toString()); } catch (IllegalArgumentException e) { Log.e(SpeedometerApp.TAG, "Cannot convert time string:" + json.toString()); throw new JsonParseException("Cannot convert time string: " + json.toString()); } catch (ParseException e) { throw new JsonParseException("Cannot convert UTC time string: " + json.toString()); } } } private static Date parseDate(String dateString) throws ParseException { return dateFormat.parse(dateString); } private static String formatDate(Date date) { return dateFormat.format(date); } }