source: sample/hadoop-0.17/tw/org/nchc/tuple/ListWritable.java @ 20

/*
 * Cloud9: A MapReduce Library for Hadoop
 * 
 * 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 tw.org.nchc.tuple;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInput;
import java.io.DataInputStream;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

import org.apache.hadoop.io.WritableComparable;

/**
 * <p>
 * Class that represents a list in Hadoop's data type system. Elements in the
 * list must be homogeneous and must implement Hadoop's WritableComparable
 * interface. This class, combined with {@link Tuple}, allows the user to
 * define arbitrarily complex data structures.
 * </p>
 * 
 * @see Tuple
 * @param <E>
 *            type of list element
 */
public class ListWritable<E extends WritableComparable> implements WritableComparable, Iterable<E>, List<E> {

  private List<E> mList;

  private Class<?> listElementClass;

  /**
   * Creates a ListWritable object.
   */
  public ListWritable() {
    mList = new ArrayList<E>();
  }

  /**
   * Appends the specified element to the end of this list.
   * 
   * @param e
   *            element to be appended to this list
   */
  public boolean add(E e) {
    if (mList.size() == 0) 
      listElementClass = e.getClass();
    else if (!e.getClass().equals(listElementClass))
      throw new IllegalArgumentException("Cannot add element of type " + e.getClass().getCanonicalName() + " to list of type " + listElementClass.getCanonicalName());
    return mList.add(e);
  }

  /**
   * Returns the element at the specified position in this list
   * 
   * @param index
   *            index of the element to return
   * @return the element at the specified position in this list
   */
  public E get(int index) {
    if (index < 0 || index >= mList.size()) {
      throw new IndexOutOfBoundsException();
    }

    return mList.get(index);
  }

  /**
   * Removes all elements from this list.
   */
  public void clear() {
    mList.clear();
  }

  /**
   * Replaces the element at the specified position in this list with the
   * specified element.
   * 
   * @param index
   *            index of the element to replace
   * @param element
   *            element to be stored at the specified position
   */
  public E set(int index, E element) {
        if(mList.size() > 0 && !element.getClass().equals(listElementClass)) {
      throw new IllegalArgumentException("Cannot add element of type " + element.getClass().getCanonicalName() + " to list of type " + listElementClass.getCanonicalName());
        }
    return mList.set(index, element);
  }

  /**
   * Returns the number of elements in this list.
   * 
   * @return the number of elements in this list
   */
  public int size() {
    return mList.size();
  }

  /**
   * Deserializes the Tuple.
   * 
   * @param in
   *            source for raw byte representation
   */
  @SuppressWarnings("unchecked")
  public void readFields(DataInput in) throws IOException {

    mList.clear();

    int numFields = in.readInt();
    String className = in.readUTF();
    E obj;
    try {
      Class c = Class.forName(className);
      listElementClass = c;

      for (int i = 0; i < numFields; i++) {
        obj = (E) c.newInstance();
        int sz = in.readInt();
        byte[] bytes = new byte[sz];
        in.readFully(bytes);

        obj.readFields(new DataInputStream(new ByteArrayInputStream(bytes)));
        this.add(obj);
      }

    } catch (ClassNotFoundException e) {
      e.printStackTrace();
    } catch (IllegalAccessException e) {
      e.printStackTrace();
    } catch (InstantiationException e) {
      e.printStackTrace();
    }
  }

  /**
   * Serializes this Tuple.
   * 
   * @param out
   *            where to write the raw byte representation
   */
  public void write(DataOutput out) throws IOException {
    out.writeInt(mList.size());
    if (mList.size() > 0)
      out.writeUTF(listElementClass.getCanonicalName());
    else
      out.writeUTF(WritableComparable.class.getCanonicalName());

    for (int i = 0; i < mList.size(); i++) {
      if (mList.get(i) == null) {
        throw new IOException("Cannot serialize null fields!");
      }

      ByteArrayOutputStream bytesOut = new ByteArrayOutputStream();
      DataOutputStream dataOut = new DataOutputStream(bytesOut);

      mList.get(i).write(dataOut);

      out.writeInt(bytesOut.size());
      out.write(bytesOut.toByteArray());
    }
  }

  /**
   * Generates human-readable String representation of this Tuple.
   * 
   * @return human-readable String representation of this Tuple
   */
  public String toString() {
    StringBuffer sb = new StringBuffer();
    sb.append("[");
    for (int i = 0; i < this.size(); i++) {
      if (i != 0)
        sb.append(", ");
      sb.append(this.get(i));
    }
    sb.append("]");

    return sb.toString();
  }

  /**
   * <p>
   * Defines a natural sort order for the ListWritable class. Following
   * standard convention, this method returns a value less than zero, a value
   * greater than zero, or zero if this ListWritable should be sorted before,
   * sorted after, or is equal to <code>obj</code>. The sort order is
   * defined as follows:
   * </p>
   * 
   * <ul>
   * <li>Each element in the list is compared sequentially from first to
   * last.</li>
   * <li>Lists are sorted with respect to the natural order of the current
   * list element under consideration, by calling its <code>compareTo</code>
   * method.</li>
   * <li>If the current list elements are equal, the next set of elements are
   * considered.</li>
   * <li>If all compared elements are equal, but lists are different lengths,
   * the shorter list is sorted first.</li>
   * <li>If all list elements are equal and the lists are equal in length,
   * then the lists are considered equal</li>
   * </ul>
   * 
   * @return a value less than zero, a value greater than zero, or zero if
   *         this Tuple should be sorted before, sorted after, or is equal to
   *         <code>obj</code>.
   */
  public int compareTo(Object obj) {
    ListWritable<?> that = (ListWritable<?>) obj;

    // iterate through the fields
    for (int i = 0; i < this.size(); i++) {
      // sort shorter list first
      if (i >= that.size())
        return 1;

      @SuppressWarnings("unchecked")
      Comparable<Object> thisField = this.get(i);
      @SuppressWarnings("unchecked")
      Comparable<Object> thatField = that.get(i);

      if (thisField.equals(thatField)) {
        // if we're down to the last field, sort shorter list first
        if (i == this.size() - 1) {
          if (this.size() > that.size())
            return 1;

          if (this.size() < that.size())
            return -1;
        }
        // otherwise, move to next field
      } else {
        return thisField.compareTo(thatField);
      }
    }

    return 0;
  }

  /**
   * @return an iterator over the elements in this list in proper sequence.
   */
  public Iterator<E> iterator() {
    return this.mList.iterator();
  }

  /* (non-Javadoc)
   * @see java.util.List#add(int, java.lang.Object)
   */
  public void add(int pos, E element) {
    
        if(mList.size() > 0 && !element.getClass().equals(listElementClass)) {
      throw new IllegalArgumentException("Cannot add element of type " + element.getClass().getCanonicalName() + " to list of type " + listElementClass.getCanonicalName());
        }
    mList.add(pos, element);
  }

  /* (non-Javadoc)
   * @see java.util.List#addAll(java.util.Collection)
   */
  public boolean addAll(Collection<? extends E> elements) {
    boolean failure = false;
    Iterator<? extends E> it = elements.iterator();
    while (it.hasNext()) {
      E obj = it.next();
      if (mList.size() == 0) 
        listElementClass = obj.getClass();
      else if (!obj.getClass().equals(listElementClass))
        throw new IllegalArgumentException("Cannot add element of type " + obj.getClass().getCanonicalName() + " to list of type " + listElementClass.getCanonicalName());
      
      if (!mList.add(obj)) failure = true;
    }
    
    
    return !failure;
  }

  /* (non-Javadoc)
   * @see java.util.List#addAll(int, java.util.Collection)
   */
  public boolean addAll(int pos, Collection<? extends E> elements) {
    // TODO: Check the return type of this method.
    Iterator<? extends E> it = elements.iterator();
    int curPos = pos;
    while (it.hasNext()) {
      E obj = it.next();
      if (mList.size() == 0) 
        listElementClass = obj.getClass();
      else if (!obj.getClass().equals(listElementClass))
        throw new IllegalArgumentException("Cannot add element of type " + obj.getClass().getCanonicalName() + " to list of type " + listElementClass.getCanonicalName());
      
      mList.add(curPos, obj);
      ++curPos;
    }
    
    
    return true;
  }

  /* (non-Javadoc)
   * @see java.util.List#contains(java.lang.Object)
   */
  public boolean contains(Object element) {
    return mList.contains(element);
  }

  /* (non-Javadoc)
   * @see java.util.List#containsAll(java.util.Collection)
   */
  public boolean containsAll(Collection<?> elements) {
    return mList.containsAll(elements);
  }

  /* (non-Javadoc)
   * @see java.util.List#indexOf(java.lang.Object)
   */
  public int indexOf(Object element) {
    return mList.indexOf(element);
  }

  /* (non-Javadoc)
   * @see java.util.List#isEmpty()
   */
  public boolean isEmpty() {
    return mList.isEmpty();
  }

  /* (non-Javadoc)
   * @see java.util.List#lastIndexOf(java.lang.Object)
   */
  public int lastIndexOf(Object element) {
    return mList.lastIndexOf(element);
  }

  /* (non-Javadoc)
   * @see java.util.List#listIterator()
   */
  public ListIterator<E> listIterator() {
    return mList.listIterator();
  }

  /* (non-Javadoc)
   * @see java.util.List#listIterator(int)
   */
  public ListIterator<E> listIterator(int arg0) {
    return mList.listIterator(arg0);
  }

  /* (non-Javadoc)
   * @see java.util.List#remove(java.lang.Object)
   */
  public boolean remove(Object element) {
    return mList.remove(element);
  }

  /* (non-Javadoc)
   * @see java.util.List#remove(int)
   */
  public E remove(int pos) {
    return mList.remove(pos);
  }

  /* (non-Javadoc)
   * @see java.util.List#removeAll(java.util.Collection)
   */
  public boolean removeAll(Collection<?> elements) {
    return mList.removeAll(elements);
  }

  /* (non-Javadoc)
   * @see java.util.List#retainAll(java.util.Collection)
   */
  public boolean retainAll(Collection<?> elements) {
    return mList.retainAll(elements);
  }

  /* (non-Javadoc)
   * @see java.util.List#subList(int, int)
   */
  public List<E> subList(int arg0, int arg1) {
    // TODO Consider making this return a type of ListWritable rather than of ArrayList.
    return mList.subList(arg0, arg1);
  }

  /* (non-Javadoc)
   * @see java.util.List#toArray()
   */
  public Object[] toArray() {
    return mList.toArray();
  }

  /* (non-Javadoc)
   * @see java.util.List#toArray(T[])
   */
  public <T> T[] toArray(T[] arg0) {
    return mList.toArray(arg0);
  }

}