code: /*
   * Copyright 2012-2018 Chronicle Map Contributors
   *
   * 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 net.openhft.chronicle.hash.serialization.impl;
  
  import net.openhft.chronicle.hash.Data;
  import net.openhft.chronicle.hash.serialization.DataAccess;
  import net.openhft.chronicle.wire.WireIn;
  import net.openhft.chronicle.wire.WireOut;
  import org.jetbrains.annotations.NotNull;
  import org.jetbrains.annotations.Nullable;
  
  import java.io.Externalizable;
  import java.io.IOException;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  
  import static net.openhft.chronicle.hash.serialization.impl.DefaultElasticBytes.DEFAULT_BYTES_CAPACITY;
  
  public class ExternalizableDataAccess<T extends Externalizable> extends SerializableDataAccess<T> {
  
      /**
       * Config field
       */
      private Class<T> tClass;
  
      public ExternalizableDataAccess(Class<T> tClass) {
          this(tClass, DEFAULT_BYTES_CAPACITY);
      }
  
      private ExternalizableDataAccess(Class<T> tClass, long bytesCapacity) {
          super(bytesCapacity);
          this.tClass = tClass;
      }
  
      protected Class<T> tClass() {
          return tClass;
      }
  
      protected T createInstance() {
          try {
              return tClass.newInstance();
          } catch (InstantiationException | IllegalAccessException e) {
              throw new RuntimeException(
                      "Externalizable " + tClass + " must have a public no-arg constructor", e);
          }
      }
  
      @Override
      public T getUsing(@Nullable T using) {
          if (using == null)
              using = createInstance();
          try {
              using.readExternal(new ObjectInputStream(in));
              bytes.readPosition(0);
              return using;
          } catch (IOException | ClassNotFoundException e) {
              throw new RuntimeException(e);
          }
      }
  
      @Override
      public Data<T> getData(@NotNull T instance) {
          this.instance = instance;
          bytes.clear();
          try {
              ObjectOutputStream out = new ObjectOutputStream(this.out);
              instance.writeExternal(out);
              out.flush();
              return this;
          } catch (IOException e) {
              throw new RuntimeException(e);
          }
      }
  
      @Override
      public DataAccess<T> copy() {
          return new ExternalizableDataAccess<>(tClass, bytes.realCapacity());
      }
  
      @Override
      public void readMarshallable(@NotNull WireIn wireIn) {
          tClass = wireIn.read(() -> "tClass").typeLiteral();
          initTransients(DEFAULT_BYTES_CAPACITY);
      }
  
      @Override
      public void writeMarshallable(@NotNull WireOut wireOut) {
          wireOut.write(() -> "tClass").typeLiteral(tClass);
      }
  }
  