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com.tangosol.util.extractor
Class KeyExtractor

java.lang.Object
com.tangosol.util.Base
com.tangosol.util.BitHelper
com.tangosol.util.ExternalizableHelper
com.tangosol.util.extractor.AbstractExtractor
com.tangosol.util.extractor.KeyExtractor

All Implemented Interfaces:

ExternalizableLite, PortableObject, QueryMapComparator, ValueExtractor, java.io.Serializable, java.util.Comparator

public class KeyExtractor

extends AbstractExtractor

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 mechanism described above is recommended.

Since:

Coherence 3.2

Author:

gg 2006.06.12

Field Summary

protected ValueExtractor

m_extractor The underlying ValueExtractor.

Fields inherited from class com.tangosol.util.extractor.AbstractExtractor

KEY, m_nTarget, VALUE

Constructor Summary

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

KeyExtractor(java.lang.String sMethod)
Construct a KeyExtractor for a specified method name.

KeyExtractor(ValueExtractor extractor)
Construct a KeyExtractor based on a specified ValueExtractor.

Method Summary

boolean	equals(java.lang.Object o) Compare the KeyExtractor with another object to determine equality.
java.lang.Object	extract(java.lang.Object oTarget) Extract the value from the passed object.
ValueExtractor	getExtractor() Obtain the underlying ValueExtractor.
int	hashCode() Determine a hash value for the KeyExtractor object according to the general Object.hashCode() contract.
void	readExternal(java.io.DataInput in) Restore the contents of this object by loading the object's state from the passed DataInput object.
void	readExternal(PofReader in) Restore the contents of a user type instance by reading its state using the specified PofReader object.
java.lang.String	toString() Return a human-readable description for this KeyExtractor.
void	writeExternal(java.io.DataOutput out) Save the contents of this object by storing the object's state into the passed DataOutput object.
void	writeExternal(PofWriter out) Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

Methods inherited from class com.tangosol.util.extractor.AbstractExtractor

compare, compareEntries, extractFromEntry, extractOriginalFromEntry

Methods inherited from class com.tangosol.util.BitHelper

countBits, countBits, countBits, indexOfLSB, indexOfLSB, indexOfLSB, indexOfMSB, indexOfMSB, indexOfMSB, rotateLeft, rotateLeft, rotateLeft, rotateRight, rotateRight, rotateRight, toBitString, toBitString, toBitString, toBytes, toBytes, toBytes, toBytes, toInt, toInt, toLong, toLong

Field Detail

m_extractor

protected ValueExtractor m_extractor

The underlying ValueExtractor.

Constructor Detail

KeyExtractor

public KeyExtractor()

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

KeyExtractor

public KeyExtractor(ValueExtractor extractor)

Construct a KeyExtractor based on a specified ValueExtractor.

Parameters:

extractor - the underlying ValueExtractor

KeyExtractor

public KeyExtractor(java.lang.String sMethod)

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 Detail

extract

public java.lang.Object extract(java.lang.Object 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

Overrides:

extract in class AbstractExtractor

Parameters:

oTarget - an Object to retrieve the value from

Returns:

the extracted value as an Object; null is an acceptable value

getExtractor

public ValueExtractor getExtractor()

Obtain the underlying ValueExtractor.

Returns:

the ValueExtractor

equals

public boolean equals(java.lang.Object o)

Compare the KeyExtractor with another object to determine equality. Two KeyExtractor objects are considered equal iff their underlying ValueExtractors are equal.

Specified by:

equals in interface ValueExtractor

Specified by:

equals in interface java.util.Comparator

Parameters:

o - the reference object with which to compare

Returns:

true iff this KeyExtractor and the passed object are equivalent

hashCode

public int hashCode()

Determine a hash value for the KeyExtractor object according to the general Object.hashCode() contract.

Specified by:

hashCode in interface ValueExtractor

Returns:

an integer hash value for this KeyExtractor object

toString

public java.lang.String toString()

Return a human-readable description for this KeyExtractor.

Specified by:

toString in interface ValueExtractor

Returns:

a String description of the KeyExtractor

readExternal

public void readExternal(java.io.DataInput in)
                  throws java.io.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:

java.io.IOException - if an I/O exception occurs

java.io.NotActiveException - if the object is not in its initial state, and therefore cannot be deserialized into

writeExternal

public void writeExternal(java.io.DataOutput out)
                   throws java.io.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:

java.io.IOException - if an I/O exception occurs

readExternal

public void readExternal(PofReader in)
                  throws java.io.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:

java.io.IOException - if an I/O error occurs

writeExternal

public void writeExternal(PofWriter out)
                   throws java.io.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:

java.io.IOException - if an I/O error occurs

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