Advantages of using NullWritable in Hadoop

Question

What are the advantages of using NullWritable for null keys/values over using null texts (i.e. new Text(null)). I see the fol

Answer 1

You can always wrap your string in your own Writable class and have a boolean indicating it has blank strings or not:

@Override
public void readFields(DataInput in) throws IOException { 
    ...
    boolean hasWord = in.readBoolean();
    if( hasWord ) {
        word = in.readUTF();
    }
    ...
}

and

@Override
public void write(DataOutput out) throws IOException {
    ...
    boolean hasWord = StringUtils.isNotBlank(word);
    out.writeBoolean(hasWord);
    if(hasWord) {
        out.writeUTF(word);
    }
    ...
}