[jira] [Created] (HADOOP-9240) Making ArrayWritable typed

["David Parks (JIRA)" <ji...@apache.org>]

David Parks created HADOOP-9240:
-----------------------------------

             Summary: Making ArrayWritable typed
                 Key: HADOOP-9240
                 URL: https://issues.apache.org/jira/browse/HADOOP-9240
             Project: Hadoop Common
          Issue Type: Improvement
          Components: io
            Reporter: David Parks
            Priority: Minor


ArrayWritable is just painful to use in practice, it would be nice if we had a typed version of ArrayWritable that had all the features of an ArrayList.

It wasn't hard to write, and it doesn't cost more in terms of storage or CPU than an ArrayWritable. 

So I wonder why not include a more usable ArrayListWritable class with Hadoop? Code pasted below, unless there's a reason that this is a bad idea I'm happy to provide the unit test for it as well.


@SuppressWarnings("serial")
public class ArrayListWritable<E extends Writable> extends ArrayList<E> implements Writable {
	Class<E> type = null;
	
	public ArrayListWritable(Class<E> type){
		super();
		this.type = type;
	}
	
	public ArrayListWritable(){
		super();
	}
	
	public void setArrayClassType(Class<E> clazz){
		this.type = clazz;
	}

	
	@Override
	public void write(DataOutput out) throws IOException {
		if(type==null){ throw new IOException("Cannot write an " + getClass().getName() + " without the class type being set in the constructor or with setArrayClassType(...)"); };
		out.writeUTF(type.getCanonicalName());
		out.writeInt(size());
		for(E writable : this) writable.write(out);
	}
	
	@SuppressWarnings("unchecked")
	@Override
	public void readFields(DataInput in) throws IOException {
		clear();
		
		//Read the class name
		try {
			type = (Class<E>)Class.forName(in.readUTF());
		} catch (ClassNotFoundException e) {
			throw new IOException("Invalid connonical name read from input bytes", e);
		}
		//Read the size & set capacity of the arraylist
		int size = in.readInt();
		ensureCapacity(size);
		
		//Read in individual writables
		for (int i = 0; i < size; i++) {
			Writable value = WritableFactories.newInstance(type);
			value.readFields(in);                       // read a value
			add((E)value);								// add it to the ArrayList
		}
	}
}


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