library/src/main/java/org/apache/apex/malhar/lib/appdata/query/serde/MessageDeserializerFactory.java

/**
 * 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.
 */
package org.apache.apex.malhar.lib.appdata.query.serde;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.util.Map;
import java.util.Set;

import org.codehaus.jettison.json.JSONException;
import org.codehaus.jettison.json.JSONObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.apex.malhar.lib.appdata.schemas.Message;

import com.google.common.base.Preconditions;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;

/**
 * This is a utility class which simplifies deserializing AppData messages. The factory is configured by specifying the {@link Message} Classes
 * that messages will be deserialized into. The {@link MessageDeserializerFactory} knows the correct type of a Message, its deserializer, and its
 * validator by looking up annotations specified on the {@link Message} class. An example of a {@link Message} class that can be deserialized by
 * {@link MessageDeserializerFactory} is below.
 * <br/>
 * <br/>
 * <pre>
 * <code>
 *  {@literal @}MessageType(type="MyMessageType")
 *  {@literal @}MessageDeserializerInfo(clazz=MyAppDataMessageDeserializer.class)
 *  {@literal @}MessageValidatorInfo(clazz=MyAppDataMessageValidator.class)
 *  public class MyAppDataMessage extends Message
 *  {
 *    ...
 *  }
 * </code>
 * </pre>
 * @since 3.0.0
 */
public class MessageDeserializerFactory
{
  /**
   * A map from message type to the corresponding class.
   */
  private final Map<String, Class<? extends Message>> typeToClass = Maps.newHashMap();
  /**
   * A map from query types to their corresponding deserializers.
   */
  private final Map<String, CustomMessageDeserializer> typeToCustomQueryBuilder = Maps.newHashMap();
  /**
   * A map from query types to their corresponding validators.
   */
  private final Map<String, CustomMessageValidator> typeToCustomQueryValidator = Maps.newHashMap();
  /**
   * A map from Message classes to their corresponding contexts.
   */
  private final Map<Class<? extends Message>, Object> deserializationContext = Maps.newHashMap();

  /**
   * Creates a {@link MessageDeserializerFactory} to deserialize the messages corresponding to the specified classes.
   * @param schemas The classes to deserialize Messages into.
   */
  public MessageDeserializerFactory(Class<? extends Message>... schemas)
  {
    setClasses(schemas);
  }

  /**
   * This sets the context object to use when deserializing the specified class of messages.
   * @param clazz The Class of messages that a context a being set for.
   * @param context The context to use when deserializing messages corresponding to the specified class.
   */
  public void setContext(Class<? extends Message> clazz, Object context)
  {
    deserializationContext.put(clazz, context);
  }

  /**
   * This is a helper method which validates setting the desired class that data will be deserialized into.
   * @param schemas The classes that data will be deserialized into.
   */
  private void setClasses(Class<? extends Message>[] schemas)
  {
    Preconditions.checkArgument(schemas.length != 0, "No schemas provided.");

    Set<Class<? extends Message>> clazzes = Sets.newHashSet();

    for (Class<? extends Message> schema : schemas) {
      Preconditions.checkNotNull(schema, "Provided schema cannot be null");
      Preconditions.checkArgument(!clazzes.contains(schema), "Schema %s was passed twice.", schema);
      clazzes.add(schema);

      Annotation[] ans = schema.getAnnotations();

      String schemaType = null;
      Class<? extends CustomMessageDeserializer> cqd = null;
      Class<? extends CustomMessageValidator> cqv = null;

      for (Annotation an : ans) {
        if (an instanceof MessageType) {
          if (schemaType != null) {
            throw new IllegalArgumentException("Cannot specify the " + MessageType.class +
                " annotation twice on the class: " + schema);
          }

          schemaType = ((MessageType)an).type();

          LOG.debug("Detected schemaType for {} is {}", schema, schemaType);
        } else if (an instanceof MessageDeserializerInfo) {
          if (cqd != null) {
            throw new IllegalArgumentException("Cannot specify the " + MessageDeserializerInfo.class +
                " annotation twice on the class: " + schema);
          }

          cqd = ((MessageDeserializerInfo)an).clazz();
        } else if (an instanceof MessageValidatorInfo) {
          if (cqv != null) {
            throw new IllegalArgumentException("Cannot specify the " + MessageValidatorInfo.class +
                " annotation twice on the class: ");
          }

          cqv = ((MessageValidatorInfo)an).clazz();
        }
      }

      if (schemaType == null) {
        throw new IllegalArgumentException("No " + MessageType.class + " annotation found on class: " + schema);
      }

      if (cqd == null) {
        throw new IllegalArgumentException("No " + MessageDeserializerInfo.class + " annotation found on class: " +
            schema);
      }

      if (cqv == null) {
        throw new IllegalArgumentException(
            "No " + MessageValidatorInfo.class + " annotation found on class: " + schema);
      }

      Class<? extends Message> prevSchema = typeToClass.put(schemaType, schema);
      LOG.debug("prevSchema {}:", prevSchema);

      if (prevSchema != null) {
        throw new IllegalArgumentException("Cannot have the " +
            schemaType + " schemaType defined on multiple classes: " + schema + ", " + prevSchema);
      }

      try {
        CustomMessageDeserializer cqdI = cqd.newInstance();
        CustomMessageValidator cqvI = cqv.newInstance();
        typeToCustomQueryBuilder.put(schemaType, cqdI);
        typeToCustomQueryValidator.put(schemaType, cqvI);
      } catch (InstantiationException | IllegalAccessException ex) {
        throw new RuntimeException(ex);
      }
    }
  }

  /**
   * This is the method that is called to deserialize a given json string into a Message object of
   * the appropriate type.
   * @param json The json to deserialize.
   * @return The deserialized Message.
   * @throws IOException
   */
  public Message deserialize(String json) throws IOException
  {
    String type;

    try {
      JSONObject jsonObject = new JSONObject(json);
      type = jsonObject.getString(Message.FIELD_TYPE);
    } catch (JSONException e) {
      throw new IOException(e);
    }

    CustomMessageDeserializer cqb = typeToCustomQueryBuilder.get(type);

    if (cqb == null) {
      throw new IOException("The query type " +
          type +
          " does not have a corresponding deserializer.");
    }

    CustomMessageValidator cqv = typeToCustomQueryValidator.get(type);
    Object context = deserializationContext.get(typeToClass.get(type));
    Message data = cqb.deserialize(json, typeToClass.get(type), context);

    LOG.debug("{}", data);

    if (data == null || !(cqv != null && cqv.validate(data, context))) {
      return null;
    }

    data.setType(type);
    return data;
  }

  private static final Logger LOG = LoggerFactory.getLogger(MessageDeserializerFactory.class);
}