UDF for Pig to choose a field by the value of another field

ChooseByFieldName.java

    // Enable multiple languages by specifying the model path. See http://text.sourceforge.net/models-1.5/
    public Tuple exec(Tuple input) throws IOException
    {
        if(input.size() < 2) {
            throw new IOException();
        }

        String fieldName = input.get(0).toString();
        if(fieldName == null || fieldName == "") {
            return null;
        }
        System.err.println("fieldName: " + fieldName);

        Tuple outTuple = tf.newTuple(fieldName);
        Schema inputSchema = getInputSchema();
        int i = 0;
        for(FieldSchema fieldSchema : inputSchema.getFields())
        {
            if(fieldSchema.alias == fieldName) {
                outTuple.append(input.get(i));
                System.err.println("Matched fieldname " + fieldName + " with value: " + input.get(i).toString());
            }
        }

        return outTuple;
    }