Package org.apache.druid.query.lookup

Class LookupExtractor

java.lang.Object

org.apache.druid.query.lookup.LookupExtractor

Direct Known Subclasses:

ImmutableLookupMap.ImmutableLookupExtractor, MapLookupExtractor

public abstract class LookupExtractor
extends Object

Constructor Summary

Constructors

Constructor	Description
LookupExtractor()

Method Summary

Modifier and Type	Method	Description
abstract String	apply(String key)	Apply a particular lookup methodology to the input string
Map<String,String>	applyAll(Iterable<String> keys)
abstract Map<String,String>	asMap()	Returns a Map view of this lookup extractor.
long	estimateHeapFootprint()	Estimated heap footprint of this object.
abstract byte[]	getCacheKey()	Create a cache key for use in results caching
boolean	isOneToOne()
abstract boolean	supportsAsMap()	Returns whether this lookup extractor's asMap() will return a valid map.
protected abstract List<String>	unapply(String value)	Reverse lookup from a given value.
Iterator<String>	unapplyAll(Set<String> values)	Reverse lookup from a given set of values.

Methods inherited from class java.lang.Object

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

Constructor Detail

LookupExtractor

public LookupExtractor()

Method Detail

apply

@Nullable
public abstract String apply(@Nullable
                             String key)

Apply a particular lookup methodology to the input string

Parameters:

key - The value to apply the lookup to.

Returns:

The value for this key, or null when key is `null` or when key cannot have the lookup applied to it and should be treated as missing.

applyAll

public Map<String,String> applyAll(Iterable<String> keys)

Parameters:

keys - set of keys to apply lookup for each element

Returns:

Returns Map whose keys are the contents of keys and whose values are computed on demand using lookup function unapply(String) or empty map if values is `null` User can override this method if there is a better way to perform bulk lookup

unapply

protected abstract List<String> unapply(@Nullable
                                        String value)

Reverse lookup from a given value. Used by the default implementation of unapplyAll(Set). Otherwise unused. Implementations that override unapplyAll(Set) may throw UnsupportedOperationException from this method.

Parameters:

value - the value to apply the reverse lookup.

Returns:

the list of keys that maps to the provided value. In SQL-compatible null handling mode, null keys are omitted.

unapplyAll

@Nullable
public Iterator<String> unapplyAll(Set<String> values)

Reverse lookup from a given set of values.

Parameters:

values - set of values to reverse lookup.

Returns:

iterator of keys that map to to the provided set of values. May contain duplicate keys. Returns null if this lookup instance does not support reverse lookups. In SQL-compatible null handling mode, null keys are omitted.

supportsAsMap

public abstract boolean supportsAsMap()

Returns whether this lookup extractor's asMap() will return a valid map.

asMap

public abstract Map<String,String> asMap()

Returns a Map view of this lookup extractor. The map may change along with the underlying lookup data.

Throws:

UnsupportedOperationException - if supportsAsMap() returns false.

getCacheKey

public abstract byte[] getCacheKey()

Create a cache key for use in results caching

Returns:

A byte array that can be used to uniquely identify if results of a prior lookup can use the cached values

isOneToOne

public boolean isOneToOne()

estimateHeapFootprint

public long estimateHeapFootprint()

Estimated heap footprint of this object. Not guaranteed to be accurate. For example, some implementations return zero even though they do use on-heap structures. However, the most common classes, MapLookupExtractor and ImmutableLookupMap, do have reasonable implementations. This API is provided for best-effort memory management and monitoring.