Package com.tangosol.util.extractor

Class KeyExtractor<T,E>

java.lang.Object
com.tangosol.util.Base
com.tangosol.util.BitHelper
com.tangosol.util.ExternalizableHelper
com.tangosol.util.extractor.AbstractExtractor<T,E>
com.tangosol.util.extractor.KeyExtractor<T,E>
All Implemented Interfaces:
CanonicallyNamed, ExternalizableLite, PortableObject, QueryMapComparator, Remote.Function<T,E>, Remote.ToDoubleFunction<T>, Remote.ToIntFunction<T>, Remote.ToLongFunction<T>, ValueExtractor<T,E>, Serializable, Comparator, Function<T,E>, ToDoubleFunction<T>, ToIntFunction<T>, ToLongFunction<T>
public class KeyExtractor<T,E> extends AbstractExtractor<T,E> implements ExternalizableLite, PortableObject
The KeyExtractor is a special purpose ValueExtractor implementation that serves as an indicator that a query should be run against the key objects rather than the values. The major difference between the KeyExtractor and a standard ReflectionExtractor is that when used in various EntryFilter implementations it forces the evaluation of entry keys rather than entry values.

For example, consider a key object that consists of two properties: "FirstName" and "LastName". To retrieve all keys that have a value of the "LastName" property equal to "Smith", the following query could be used: 

 ValueExtractor extractor = new KeyExtractor("getLastName");
 Set setKeys = cache.keySet(new EqualsFilter(extractor, "Smith"));
As of Coherence 3.5, the same effect can be achieved for subclasses of the AbstractExtractor, for example: 
 ValueExtractor extractor = new ReflectionExtractor("getLastName", null,
      AbstractExtractor.KEY);
 Set setKeys = cache.keySet(new EqualsFilter(extractor, "Smith"));
Note: This class does not function with PofExtractor and the recommendation is to create a PofExtractor with the target set to AbstractExtractor.KEY or create a PofExtractor and call the ValueExtractor.fromKey() method on it.

Since:
Coherence 3.2
Author:
gg 2006.06.12
See Also:

  • Field Details

    • m_extractor

      protected ValueExtractor<? super T,? extends E> m_extractor
      The underlying ValueExtractor.

  • Constructor Details

    • KeyExtractor

      public KeyExtractor()
      Default constructor (necessary for the ExternalizableLite and PortableObject interfaces).

    • KeyExtractor

      public KeyExtractor(ValueExtractor<? super T,? extends E> extractor)
      Construct a KeyExtractor based on a specified ValueExtractor.
      Parameters:
      extractor - the underlying ValueExtractor

    • KeyExtractor

      public KeyExtractor(String sMethod)
      Deprecated.
      use Extractors.key(String...) instead.
      Construct a KeyExtractor for a specified method name.
      Parameters:
      sMethod - a method name to construct an underlying ReflectionExtractor for; this parameter can also be a dot-delimited sequence of method names which would result in a KeyExtractor based on the ChainedExtractor that is based on an array of corresponding ReflectionExtractor objects

  • Method Details

    • extract

      public E extract(T oTarget)
      Extract the value from the passed object. The returned value may be null. For intrinsic types, the returned value is expected to be a standard wrapper type in the same manner that reflection works; for example, int would be returned as a java.lang.Integer.
      Specified by:
      extract in interface ValueExtractor<T,E>
      Overrides:
      extract in class AbstractExtractor<T,E>
      Parameters:
      oTarget - the object to extract the value from
      Returns:
      the extracted value; null is an acceptable value

    • getCanonicalName

      public String getCanonicalName()
      Description copied from interface: ValueExtractor
      Return the canonical name for this extractor.

      A canonical name uniquely identifies what is to be extracted, but not how it is to be extracted. Thus two different extractor implementations with the same non-null canonical name are considered to be equal, and should reflect this in their implementations of hashCode and equals.

      Canonical names for properties are designated by their property name in camel case, for instance a Java Bean with method getFooBar would have a property named fooBar, and would have fooBar as its canonical name.

      Canonical names for zero-arg method invocations are the method name followed by ().

      Dots in a canonical name delimit one or more property/method accesses represented by a chaining ValueExtractor such as ChainedExtractor or PofExtractor(Class, PofNavigator, String).

      There is currently no canonical name format for methods which take parameters and as such they must return a canonical name of null.

      Specified by:
      getCanonicalName in interface CanonicallyNamed
      Specified by:
      getCanonicalName in interface ValueExtractor<T,E>
      Overrides:
      getCanonicalName in class AbstractExtractor<T,E>
      Returns:
      the extractor's canonical name, or null

    • getExtractor

      public ValueExtractor<? super T,? extends E> getExtractor()
      Obtain the underlying ValueExtractor.
      Returns:
      the ValueExtractor

    • of

      public static <T, E> ValueExtractor<T,E> of(ValueExtractor<T,E> extractor)
      Factory method for key extractor.
      Type Parameters:
      T - the type of the value to extract from
      E - the type of value that will be extracted
      Parameters:
      extractor - an extractor to convert to key extractor
      Returns:
      key extractor based on the specified extractor

    • equals

      public boolean equals(Object o)
      Description copied from class: AbstractExtractor
      Equivalence by canonical name and target.

      When precondition AbstractExtractor.isCanonicallyEquatable(Object) is false, fall back to implementation specific equals implementation.

      Specified by:
      equals in interface Comparator<T>
      Specified by:
      equals in interface ValueExtractor<T,E>
      Overrides:
      equals in class AbstractExtractor<T,E>
      Parameters:
      o - the reference object with which to compare
      Returns:
      true if canonical name match and no target mismatch

    • hashCode

      public int hashCode()
      Compute hashCode from underlying ValueExtractor.
      Specified by:
      hashCode in interface ValueExtractor<T,E>
      Overrides:
      hashCode in class AbstractExtractor<T,E>
      Returns:
      an integer hash value for this KeyExtractor object

    • toString

      public String toString()
      Return a human-readable description for this KeyExtractor.
      Overrides:
      toString in class Object
      Returns:
      a String description of the KeyExtractor

    • readExternal

      public void readExternal(DataInput in) throws IOException
      Restore the contents of this object by loading the object's state from the passed DataInput object.
      Specified by:
      readExternal in interface ExternalizableLite
      Parameters:
      in - the DataInput stream to read data from in order to restore the state of this object
      Throws:
      IOException - if an I/O exception occurs

    • writeExternal

      public void writeExternal(DataOutput out) throws IOException
      Save the contents of this object by storing the object's state into the passed DataOutput object.
      Specified by:
      writeExternal in interface ExternalizableLite
      Parameters:
      out - the DataOutput stream to write the state of this object to
      Throws:
      IOException - if an I/O exception occurs

    • readExternal

      public void readExternal(PofReader in) throws IOException
      Restore the contents of a user type instance by reading its state using the specified PofReader object.
      Specified by:
      readExternal in interface PortableObject
      Parameters:
      in - the PofReader from which to read the object's state
      Throws:
      IOException - if an I/O error occurs

    • writeExternal

      public void writeExternal(PofWriter out) throws IOException
      Save the contents of a POF user type instance by writing its state using the specified PofWriter object.
      Specified by:
      writeExternal in interface PortableObject
      Parameters:
      out - the PofWriter to which to write the object's state
      Throws:
      IOException - if an I/O error occurs