/* Copyright (c) 2009 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.wave.api.event;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonElement;
import com.google.gson.JsonNull;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonSerializationContext;
import com.google.wave.api.Wavelet;
import com.google.wave.api.JsonRpcConstant.ParamsProperty;
import com.google.wave.api.impl.EventMessageBundle;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.util.HashMap;
import java.util.Map;
/**
* Object that is responsible for serializing and deserializing implementors
* of {@link Event} to and from {@link JsonObject}.
*/
public class EventSerializer {
/**
* An interface for map key conversion.
*
* @param <T> the generic type of the resulting key.
*/
private static interface KeyConverter<T> {
/**
* Converts the given string key into an instance of {@code T}.
*
* @param key the key to be converted.
* @return an instance of {@code T} that represents the given string key.
*/
T convert(String key);
}
/** Constants for accessing the properties of the given JSON object. */
private static final String TYPE = "type";
private static final String MODIFIED_BY = "modifiedBy";
private static final String TIMESTAMP = "timestamp";
private static final String BLIP_ID = "blipId";
private static final String WAVELET = "wavelet";
private static final String PROPERTIES = "properties";
private static final String BUNDLE = "bundle";
/**
* Serializes the given {@link Event} into a {@link JsonObject}.
*
* @param event the {@link Event} to be serialized.
* @param context the serialization context.
* @return an instance of {@link JsonObject}, that is the JSON representation
* of the given {@link Event}.
*/
public static JsonObject serialize(Event event, JsonSerializationContext context)
throws EventSerializationException {
JsonObject result = new JsonObject();
// Serialize basic properties from Event.
result.addProperty(TYPE, event.getType().name());
result.addProperty(MODIFIED_BY, event.getModifiedBy());
result.addProperty(TIMESTAMP, event.getTimestamp());
result.addProperty(TIMESTAMP, event.getTimestamp());
// Construct a properties object.
JsonObject properties = new JsonObject();
try {
// Serialize the blip id.
Field blipIdField = AbstractEvent.class.getDeclaredField(BLIP_ID);
blipIdField.setAccessible(true);
properties.addProperty(BLIP_ID, (String) blipIdField.get(event));
// Serialize event specific properties.
for (Field field : event.getClass().getDeclaredFields()) {
field.setAccessible(true);
properties.add(field.getName(), context.serialize(field.get(event)));
}
} catch (IllegalArgumentException e) {
throw new EventSerializationException("Unable to serialize event: " + BLIP_ID +
" in " + event.getClass() + " is not accessible.");
} catch (IllegalAccessException e) {
throw new EventSerializationException("Unable to serialize event: " + BLIP_ID +
" in " + event.getClass() + " is not accessible.");
} catch (NoSuchFieldException e) {
throw new EventSerializationException("Unable to serialize event: " + BLIP_ID +
" in " + event.getClass() + " is not accessible.");
}
result.add(PROPERTIES, properties);
return result;
}
/**
* Deserializes the given {@link JsonObject} into an {@link Event}, and
* assign the given {@link Wavelet} to the {@link Event}.
*
* @param wavelet the wavelet where the event occurred.
* @param json the JSON representation of {@link Event}.
* @param context the deserialization context.
* @return an instance of {@link Event}.
*
* @throw {@link EventSerializationException} if there is a problem
* deserializing the event JSON.
*/
public static Event deserialize(Wavelet wavelet, EventMessageBundle bundle, JsonObject json,
JsonDeserializationContext context) throws EventSerializationException {
// Construct the event object.
String eventTypeString = json.get(TYPE).getAsString();
EventType type = EventType.valueOfIgnoreCase(eventTypeString);
if (type == EventType.UNKNOWN) {
throw new EventSerializationException("Trying to deserialize event JSON with unknown " +
"type: " + json, json);
}
// Parse the generic parameters.
String modifiedBy = json.get(MODIFIED_BY).getAsString();
Long timestamp = json.get(TIMESTAMP).getAsLong();
// Construct the event object.
Class<? extends Event> clazz = type.getClazz();
Constructor<? extends Event> ctor;
try {
ctor = clazz.getDeclaredConstructor();
ctor.setAccessible(true);
Event event = ctor.newInstance();
// Set the default fields from AbstractEvent.
Class<?> rootClass = AbstractEvent.class;
setField(event, rootClass.getDeclaredField(WAVELET), wavelet);
setField(event, rootClass.getDeclaredField(MODIFIED_BY), modifiedBy);
setField(event, rootClass.getDeclaredField(TIMESTAMP), timestamp);
setField(event, rootClass.getDeclaredField(TYPE), type);
setField(event, rootClass.getDeclaredField(BUNDLE), bundle);
JsonObject properties = json.get(PROPERTIES).getAsJsonObject();
// Set the blip id field, that can be null for certain events, such as
// OPERATION_ERROR.
JsonElement blipId = properties.get(BLIP_ID);
if (blipId != null && !(blipId instanceof JsonNull)) {
setField(event, rootClass.getDeclaredField(BLIP_ID), blipId.getAsString());
}
// Set the additional fields.
for (Field field : clazz.getDeclaredFields()) {
String fieldName = field.getName();
if (properties.has(fieldName)) {
setField(event, field, context.deserialize(properties.get(fieldName),
field.getGenericType()));
}
}
return event;
} catch (NoSuchMethodException e) {
throw new EventSerializationException("Unable to deserialize event JSON: " + json, json);
} catch (NoSuchFieldException e) {
throw new EventSerializationException("Unable to deserialize event JSON: " + json, json);
} catch (InstantiationException e) {
throw new EventSerializationException("Unable to deserialize event JSON: " + json, json);
} catch (IllegalAccessException e) {
throw new EventSerializationException("Unable to deserialize event JSON: " + json, json);
} catch (InvocationTargetException e) {
throw new EventSerializationException("Unable to deserialize event JSON: " + json, json);
} catch (JsonParseException e) {
throw new EventSerializationException("Unable to deserialize event JSON: " + json, json);
}
}
/**
* Extracts event specific properties into a map. This method will not include
* the basic properties from {@link AbstractEvent}, except for blip id, in the
* resulting map.
*
* @param event the event whose properties will be extracted.
* @return a map of {@link ParamsProperty} to {@link Object} of properties.
*
* @throws EventSerializationException if there is a problem accessing the
* event's fields.
*/
public static Map<ParamsProperty, Object> extractPropertiesToParamsPropertyMap(Event event)
throws EventSerializationException {
return extractProperties(event, new KeyConverter<ParamsProperty>() {
@Override
public ParamsProperty convert(String key) {
return ParamsProperty.fromKey(key);
}
});
}
/**
* Extracts event specific properties into a map. This method will not include
* the basic properties from {@link AbstractEvent}, except for blip id, in the
* resulting map.
*
* @param event the event whose properties will be extracted.
* @return a map of {@link String} to {@link Object} of properties.
*
* @throws EventSerializationException if there is a problem accessing the
* event's fields.
*/
public static Map<String, Object> extractPropertiesToStringMap(Event event)
throws EventSerializationException {
return extractProperties(event, new KeyConverter<String>() {
@Override
public String convert(String key) {
return key;
}
});
}
/**
* Extracts event specific properties into a map. This method will not include
* the basic properties from {@link AbstractEvent}, except for blip id, in the
* resulting map.
*
* @param event the event whose properties will be extracted.
* @param keyConverter the converter to convert the event property name into
* a proper key object for the resulting map.
* @return a map of {@code T} to {@link Object} of properties.
*
* @throws EventSerializationException if there is a problem accessing the
* event's fields.
*/
private static <T> Map<T, Object> extractProperties(Event event, KeyConverter<T> keyConverter)
throws EventSerializationException {
Field[] fields = event.getClass().getDeclaredFields();
Map<T, Object> data = new HashMap<T, Object>(fields.length + 1);
try {
for (Field field : fields) {
field.setAccessible(true);
data.put(keyConverter.convert(field.getName()), field.get(event));
}
Field field = AbstractEvent.class.getDeclaredField(BLIP_ID);
field.setAccessible(true);
data.put(keyConverter.convert(BLIP_ID), field.get(event));
} catch (IllegalArgumentException e) {
throw new EventSerializationException(e.getMessage());
} catch (IllegalAccessException e) {
throw new EventSerializationException(e.getMessage());
} catch (NoSuchFieldException e) {
throw new EventSerializationException(e.getMessage());
}
return data;
}
/**
* Sets the field of the given {@link Event} object.
*
* @param event the {@link Event} object whose field will be set.
* @param field the {@link Field} object that represents the field.
* @param value the value to be set to the field.
*
* @throws IllegalAccessException if the field is not accessible.
*/
private static void setField(Event event, Field field, Object value)
throws IllegalAccessException {
field.setAccessible(true);
field.set(event, value);
}
}