How to write and read the byte array to DataInput and DataOutput Stream

Question

Hbase acts as a source and sink for my Map reduce job. I have written my custom writable class called (vector writable) and it has two fields in it.

private DoubleVector vector; // It is a Double Array
private byte[] rowKey;       // The row key of the Hbase 

My mapper emits this as its value, hence I have implemented write and read methods in my vectorWritable class

  @Override
   public final void write(DataOutput out) throws IOException {
   writeVectorCluster(this.vector, this.rowKey, out);       
   }

   @Override
   public final void readFields(DataInput in) throws IOException {
   this.vector = readVector(in);
   this.rowKey = readRowKey(in);
   } 

public static void writeVectorCluster(DoubleVector vector, byte[] rowkey, DataOutput out)
            throws IOException {
        out.writeInt(vector.getLength());
            for (int i = 0; i < vector.getDimension(); i++) {
                out.writeDouble(vector.get(i));
            }
            int length = rowkey.length;
            out.writeInt(length);

           //Is this the right way ?
            out.write(rowkey);
        }


public static DoubleVector readVector(DataInput in) throws IOException {
        int length = in.readInt();
        DoubleVector vector = null;
            vector = new DenseDoubleVector(length);
            for (int i = 0; i < length; i++) {
                vector.set(i, in.readDouble());
            }
        return vector;
    }

   @SuppressWarnings("null")
    public static byte[] readRowKey(DataInput in) throws IOException {
        int length = in.readInt();
        byte [] test = null;
            for (int i = 0; i < length; i++) {
                // getting null pointer exception here
                test[i] = in.readByte();
            }
        return test;
    }

I get a NullPointerException when I try to read the rowKey from the input stream. The readVector method works fine though and I am getting the right value.

How can I write the byte array in the DataInput Stream so that I could retrive it in my Output streams

UPDATE : SOLVED This is the update of my rowKey method which works fine. Thanks @Perception

public static byte[] readRowKey(DataInput in) throws IOException {  
        int length = in.readInt();
        byte[] theBytes = new byte[length];
        in.readFully(theBytes); 
        return theBytes;
    }

Answer 1

You didn't initialize your byte array:

byte [] test = null;

Should be:

byte [] test = new byte[length];