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 Details

    • LookupExtractor

      public LookupExtractor()

  • Method Details

    • 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.