com.google.cloud.dataflow.sdk.coders.JAXBCoder Maven / Gradle / Ivy

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Google Cloud Dataflow Java SDK provides a simple, Java-based interface for processing virtually any size data using Google cloud resources. This artifact includes entire Dataflow Java SDK.
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/*
 * Copyright (C) 2015 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.cloud.dataflow.sdk.coders;

import com.google.cloud.dataflow.sdk.util.CloudObject;
import com.google.cloud.dataflow.sdk.util.Structs;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;

import java.io.FilterInputStream;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

/**
 * A coder for JAXB annotated objects. This coder uses JAXB marshalling/unmarshalling mechanisms
 * to encode/decode the objects. Users must provide the {@code Class} of the JAXB annotated object.
 *
 * @param  type of JAXB annotated objects that will be serialized.
 */
public class JAXBCoder extends AtomicCoder {

  private final Class jaxbClass;
  private transient volatile JAXBContext jaxbContext;

  public Class getJAXBClass() {
    return jaxbClass;
  }

  private JAXBCoder(Class jaxbClass) {
    this.jaxbClass = jaxbClass;
  }

  /**
   * Create a coder for a given type of JAXB annotated objects.
   *
   * @param jaxbClass the {@code Class} of the JAXB annotated objects.
   */
  public static  JAXBCoder of(Class jaxbClass) {
    return new JAXBCoder<>(jaxbClass);
  }

  @Override
  public void encode(T value, OutputStream outStream, Context context)
      throws CoderException, IOException {
    try {
      JAXBContext jaxbContext = getContext();
      // TODO: Consider caching in a ThreadLocal if this impacts performance
      Marshaller jaxbMarshaller = jaxbContext.createMarshaller();

      jaxbMarshaller.marshal(value, new FilterOutputStream(outStream) {
        // JAXB closes the underyling stream so we must filter out those calls.
        @Override
        public void close() throws IOException {
        }
      });
    } catch (JAXBException e) {
      throw new CoderException(e);
    }
  }

  @Override
  public T decode(InputStream inStream, Context context) throws CoderException, IOException {
    try {
      JAXBContext jaxbContext = getContext();
      // TODO: Consider caching in a ThreadLocal if this impacts performance
      Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

      @SuppressWarnings("unchecked")
      T obj = (T) jaxbUnmarshaller.unmarshal(new FilterInputStream(inStream) {
        // JAXB closes the underyling stream so we must filter out those calls.
        @Override
        public void close() throws IOException {
        }
      });
      return obj;
    } catch (JAXBException e) {
      throw new CoderException(e);
    }
  }

  private JAXBContext getContext() throws JAXBException {
    if (jaxbContext == null) {
      synchronized (this) {
        if (jaxbContext == null) {
          jaxbContext = JAXBContext.newInstance(jaxbClass);
        }
      }
    }
    return jaxbContext;
  }

  @Override
  public String getEncodingId() {
    return getJAXBClass().getName();
  }

  ////////////////////////////////////////////////////////////////////////////////////
  // JSON Serialization details below

  private static final String JAXB_CLASS = "jaxb_class";

  /**
   * Constructor for JSON deserialization only.
   */
  @JsonCreator
  public static  JAXBCoder of(
      @JsonProperty(JAXB_CLASS) String jaxbClassName) {
    try {
      @SuppressWarnings("unchecked")
      Class jaxbClass = (Class) Class.forName(jaxbClassName);
      return of(jaxbClass);
    } catch (ClassNotFoundException e) {
      throw new IllegalArgumentException(e);
    }
  }

  @Override
  public CloudObject asCloudObject() {
    CloudObject result = super.asCloudObject();
    Structs.addString(result, JAXB_CLASS, jaxbClass.getName());
    return result;
  }
}