PdxInstance (GemFire Java API Documentation)

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GemFire 6.6.2

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com.gemstone.gemfire.pdx
Interface PdxInstance

All Superinterfaces:: Serializable

All Known Subinterfaces:: WritablePdxInstance

public interface PdxInstance
extends Serializable
extends Serializable

PdxInstance provides run time access to the fields of a PDX without deserializing the PDX. Preventing deserialization saves time and memory and does not require the domain class. This interface is implemented by GemFire. The PdxInstance implementation is a light weight wrapper that simply refers to the raw bytes of the PDX that are kept in the cache. Applications can choose to access PdxInstances instead of Java objects by configuring the Cache to prefer PDX instances during deserialization. This can be done in cache.xml by setting the attribute read-serialized to true on the pdx element. Or it can be done programmatically using either the setPdxReadSerialized or client setPdxReadSerialized method. Once this preference is configured, then any time deserialization of a PDX is done it will deserialize into a PdxInstance.

PdxInstances are immutable. If you want to change one call createWriter().

A PdxInstance's fields will always be those of the version it represents. So if you add a field to your domain class you can end up with a PdxInstance for version 1 (that does not have the field) and a PdxInstance for version 2. The PdxInstance for version 1 will not have the added field and the PdxInstance for version 2 will have the field. This differs from deserialization of a pdx back to a domain class. In that case if version 2 is deserializing version 1 PdxReader will return a default value for the added field even though version 1 has no knowledge of it.

Since:: 6.6

Method Summary
`WritablePdxInstance`	`createWriter()` Creates and returns a `WritablePdxInstance` whose initial values are those of this PdxInstance.
`boolean`	`equals(Object other)` Returns true if the given object is equals to this instance.
`String`	`getClassName()` Return the full name of the class that this pdx instance represents.
`Object`	`getField(String fieldName)` Reads the named field and returns its value.
`List<String>`	`getFieldNames()` Return an unmodifiable list of the field names on this PdxInstance.
`Object`	`getObject()` Deserializes and returns the domain object that this instance represents.
`boolean`	`hasField(String fieldName)` Checks if the named field exists and returns the result.
`int`	`hashCode()` Generates a hashCode based on the identity fields of this PdxInstance.
`boolean`	`isEnum()` Returns true if this instance represents an enum.
`boolean`	`isIdentityField(String fieldName)` Checks if the named field was `marked` as an identity field.
`String`	`toString()` Prints out all of the identity fields of this PdxInstance.

Method Detail

getClassName

String getClassName()

Return the full name of the class that this pdx instance represents.

Returns:: the name of the class that this pdx instance represents.
Since:: 6.6.2

isEnum

boolean isEnum()

Returns true if this instance represents an enum. Enum's have a String field named "name" and an int field named "ordinal". It is ok to cast a PdxInstance that represents an enum to Comparable. PdxInstances representing enums are not writable.

Returns:: true if this instance represents an enum.

getObject

Object getObject()

Deserializes and returns the domain object that this instance represents.

Returns:: the deserialized domain object.
Throws:: PdxSerializationException - if the instance could not be deserialized

hasField

boolean hasField(String fieldName)

Checks if the named field exists and returns the result.

This can be useful when writing code that handles more than one version of a PDX class.

Parameters:: fieldName - the name of the field to check
Returns:: true if the named field exists; otherwise false

getFieldNames

List<String> getFieldNames()

Return an unmodifiable list of the field names on this PdxInstance.

Returns:: an unmodifiable list of the field names on this PdxInstance

isIdentityField

boolean isIdentityField(String fieldName)

Checks if the named field was marked as an identity field.

Note that if no fields have been marked then all the fields are used as identity fields even though this method will return false since none of them have been marked.

Parameters:: fieldName - the name of the field to check
Returns:: true if the named field exists and was marked as an identify field; otherwise false

getField

Object getField(String fieldName)

Reads the named field and returns its value. If the field does not exist null is returned.

A null result indicates that the field does not exist or that it exists and its value is currently null. The hasField method can be used to figure out which if these two cases is true.

If an Object[] is deserialized by this call then that array's component type will be Object.class instead of the original class that the array had when it was serialized. This is done so that PdxInstance objects can be added to the array.

Parameters:: fieldName - name of the field to read
Returns:: If this instance has the named field then the field's value is returned, otherwise null is returned.
Throws:: PdxSerializationException - if the field could not be deserialized

equals

boolean equals(Object other)

Returns true if the given object is equals to this instance.

If other is not a PdxInstance then it is not equal to this instance. NOTE: Even if other is the result of calling getObject() it will not be equal to this instance.

Otherwise equality of two PdxInstances is determined as follows:

The domain class name must be equal for both PdxInstances
Each identity field must be equal.

If one of the instances does not have a field that the other one does then equals will assume it has the field with a default value. If a PdxInstance has marked identity fields using markIdentityField then only the marked identity fields are its identity fields. Otherwise all its fields are identity fields.

An identity field is equal if all the following are true:

The field name is equal.
The field type is equal.
The field value is equal.

If a field's type is OBJECT then its value must be deserialized to determine if it is equals. If the deserialized object is an array then deepEquals is used to determine equality. Otherwise equals is used.

If a field's type is OBJECT[] then its value must be deserialized and deepEquals is used to determine equality.

For all other field types then the value does not need to be deserialized. Instead the serialized raw bytes are compared and used to determine equality.

Note that any fields that have objects that do not override equals will cause equals to return false when you might have expected it to return true. The only exceptions to this are those that call deepEquals as noted above. You should either override equals and hashCode in these cases or mark other fields as your identity fields.

Overrides:: equals in class Object

Parameters:: other - the other instance to compare to this.
Returns:: true if this instance is equal to other.

hashCode

int hashCode()

Generates a hashCode based on the identity fields of this PdxInstance.

If a PdxInstance has marked identity fields using markIdentityField then only the marked identity fields are its identity fields. Otherwise all its fields are identity fields.

If an identity field is of type OBJECT then it is deserialized. If the deserialized object is an array then deepHashCode is used. Otherwise hashCode is used.

If an identity field is of type OBJECT[] this it is deserialized and deepHashCode is used.

Otherwise the field is not deserialized and the raw bytes of its value are used to compute the hash code.

Overrides:: hashCode in class Object

toString

String toString()

Prints out all of the identity fields of this PdxInstance.