Package org.apache.druid.frame.field

Class StringFieldReader

java.lang.Object

org.apache.druid.frame.field.StringFieldReader

All Implemented Interfaces:

FieldReader

Direct Known Subclasses:

StringArrayFieldReader

public class StringFieldReader
extends Object
implements FieldReader

Reads fields written by StringFieldWriter or StringArrayFieldWriter.

Strings are written in UTF8 and terminated by StringFieldWriter.VALUE_TERMINATOR. Note that this byte appears in valid UTF8 encodings if and only if the string contains a NUL (char 0). Therefore, this field writer cannot write out strings containing NUL characters.

All rows are terminated by StringFieldWriter.ROW_TERMINATOR.

Empty rows are represented in one byte: solely that StringFieldWriter.ROW_TERMINATOR. Rows that are null themselves (i.e., a null array) are represented as a StringFieldWriter.NULL_ROW followed by a StringFieldWriter.ROW_TERMINATOR. This encoding for null arrays is decoded by older readers as an empty array; null arrays are a feature that did not exist in earlier versions of the code.

Null strings are stored as StringFieldWriter.NULL_BYTE. All other strings are prepended by StringFieldWriter.NOT_NULL_BYTE byte to differentiate them from nulls.

This encoding allows the encoded data to be compared as bytes in a way that matches the behavior of StringDimensionHandler.DIMENSION_SELECTOR_COMPARATOR, except null and empty list are not considered equal.

Field Summary

Fields

Modifier and Type	Field	Description
static final byte[]	EXPECTED_BYTES_FOR_NULL

Constructor Summary

Constructors

Modifier	Constructor	Description
	StringFieldReader()
protected	StringFieldReader(boolean asArray)	Create a string reader.

Method Summary

Modifier and Type	Method	Description
boolean	isNull(org.apache.datasketches.memory.Memory memory, long position)	Whether the provided memory position points to a null value.
ColumnValueSelector<?>	makeColumnValueSelector(org.apache.datasketches.memory.Memory memory, ReadableFieldPointer fieldPointer)	Create a ColumnValueSelector backed by some memory and a moveable pointer.
DimensionSelector	makeDimensionSelector(org.apache.datasketches.memory.Memory memory, ReadableFieldPointer fieldPointer, ExtractionFn extractionFn)	Create a DimensionSelector backed by some memory and a moveable pointer.
Column	makeRACColumn(Frame frame, RowSignature signature, String columnName)	Create a Column which provides accses to the rows in the frame, via the Column.toAccessor().

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

EXPECTED_BYTES_FOR_NULL

public static final byte[] EXPECTED_BYTES_FOR_NULL

Constructor Details

StringFieldReader

public StringFieldReader()

StringFieldReader

protected StringFieldReader(boolean asArray)

Create a string reader.

Parameters:

asArray - if false, selectors from makeColumnValueSelector(org.apache.datasketches.memory.Memory, org.apache.druid.frame.field.ReadableFieldPointer) behave like ValueType.STRING selectors (potentially multi-value ones). If true, selectors from makeColumnValueSelector(org.apache.datasketches.memory.Memory, org.apache.druid.frame.field.ReadableFieldPointer) behave like string array selectors.

Method Details

makeColumnValueSelector

public ColumnValueSelector<?> makeColumnValueSelector(org.apache.datasketches.memory.Memory memory,
 ReadableFieldPointer fieldPointer)

Description copied from interface: FieldReader

Create a ColumnValueSelector backed by some memory and a moveable pointer.

Specified by:

makeColumnValueSelector in interface FieldReader

makeDimensionSelector

public DimensionSelector makeDimensionSelector(org.apache.datasketches.memory.Memory memory,
 ReadableFieldPointer fieldPointer,
 @Nullable
 ExtractionFn extractionFn)

Description copied from interface: FieldReader

Create a DimensionSelector backed by some memory and a moveable pointer.

Specified by:

makeDimensionSelector in interface FieldReader

isNull

public boolean isNull(org.apache.datasketches.memory.Memory memory,
 long position)

Description copied from interface: FieldReader

Whether the provided memory position points to a null value.

Specified by:

isNull in interface FieldReader

makeRACColumn

public Column makeRACColumn(Frame frame,
 RowSignature signature,
 String columnName)

Description copied from interface: FieldReader

Create a Column which provides accses to the rows in the frame, via the Column.toAccessor().

Specified by:

makeRACColumn in interface FieldReader