library/src/main/java/org/apache/apex/malhar/lib/appdata/query/serde/MessageSerializerFactory.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 com.datatorrent.lib.appdata.query.serde;

import java.lang.annotation.Annotation;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

import com.datatorrent.lib.appdata.schemas.Result;
import com.datatorrent.lib.appdata.schemas.ResultFormatter;

/**
 * This class simplifies serializing Messages. This is done by placing an annotation on the Message
 * class which specifies the serializer for the class. Also another annotation is placed on the Message
 * class to specify its type. An example is below:
 * <br/>
 * <br/>
 * <pre>
 * <code>
 *  {@literal @}MessageType(type=DataQueryDimensional.TYPE)
 *  {@literal @}MessageSerializerInfo(clazz=DataResultDimensionalSerializer.class)
 *  public class MyResultClass
 *  {
 *    ...
 *  }
 * </code>
 * </pre>
 * Then this class can be deserialized by doing the following:
 * <br/>
 * <br/>
 * <pre>
 * <code>
 *  {@literal @}MyResultClass result;
 *  {@literal @}MessageSerializerFactory serializerFactory = new MessageSerializerFactory(new ResultFormatter());
 *  ...
 *  String json = serializerFactory.serialize(result);
 * }
 * </code>
 * </pre>
 * @since 3.0.0
 */
public class MessageSerializerFactory
{
  private final Map<Class<? extends Result>, CustomMessageSerializer> clazzToCustomResultBuilder = Maps.newHashMap();
  private final Map<Class<? extends Result>, String> clazzToType = Maps.newHashMap();

  private ResultFormatter resultFormatter = new ResultFormatter();

  public MessageSerializerFactory(ResultFormatter resultFormatter)
  {
    setResultFormatter(resultFormatter);
  }

  private void setResultFormatter(ResultFormatter resultFormatter)
  {
    this.resultFormatter = Preconditions.checkNotNull(resultFormatter);
  }

  public ResultFormatter getResultFormatter()
  {
    return resultFormatter;
  }

  public String serialize(Result result)
  {
    CustomMessageSerializer mcrs = clazzToCustomResultBuilder.get(result.getClass());
    Class<? extends Result> schema = result.getClass();

    if (mcrs == null) {
      Annotation[] ans = schema.getAnnotations();

      Class<? extends CustomMessageSerializer> crs = null;
      String type = null;

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

          crs = ((MessageSerializerInfo)an).clazz();
        } else if (an instanceof MessageType) {
          if (type != null) {
            throw new UnsupportedOperationException("Cannot specify the " + MessageType.class +
                " annotation twice on the class: " + schema);
          }

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

      if (crs == null) {
        throw new UnsupportedOperationException("No " + MessageSerializerInfo.class + " annotation found on class: "
            + schema);
      }

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

      try {
        mcrs = crs.newInstance();
      } catch (InstantiationException | IllegalAccessException ex) {
        throw new RuntimeException(ex);
      }

      clazzToCustomResultBuilder.put(schema, mcrs);
      clazzToType.put(schema, type);
    }

    result.setType(clazzToType.get(schema));

    return mcrs.serialize(result, resultFormatter);
  }

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