Handling NULL values

Your UDxs must be prepared to handle NULL values. These values usually must be handled separately from regular values.

Reading NULL values

Your UDx reads data from instances of the the BlockReader or PartitionReader classes. If the value of a column is NULL, the methods you use to get data (such as getLong) return a Java null reference. If you attempt to use the value without checking for NULL, the Java runtime will throw a null pointer exception.

You can test for null values before reading columns by using the data-type-specific methods (such as isLongNull, isDoubleNull, and isBooleanNull). For example, to test whether the INTEGER first column of your UDx's input is a NULL, you would use the statement:

// See if the Long value in column 0 is a NULL
if (inputReader.isLongNull(0)) {
    // value is null
    . . .

Writing NULL values

You output NULL values using type-specific methods on the BlockWriter and PartitionWriter classes (such as setLongNull and setStringNull). These methods take the column number to receive the NULL value. In addition, the PartitionWriter class has data-type specific set value methods (such as setLongValue and setStringValue). If you pass these methods a value, they set the output column to that value. If you pass them a Java null reference, they set the output column to NULL.