com.gigaspaces.client.mutators

Class SpaceEntryMutator

java.lang.Object

com.gigaspaces.client.mutators.SpaceEntryMutator

All Implemented Interfaces:

ChangeOperation, Serializable

Direct Known Subclasses:

CustomChangeOperation, SpaceEntryPathMutator

public abstract class SpaceEntryMutator
extends Object
implements Serializable, ChangeOperation

Since:

9.1

Author:

Niv Ingberg

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
SpaceEntryMutator()

Method Summary

Modifier and Type	Method and Description
abstract Object	change(MutableServerEntry entry) Changes an entry.
ChangeOperationResult	getChangeOperationResult(Serializable result)

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.gigaspaces.sync.change.ChangeOperation

getName

Constructor Detail

SpaceEntryMutator

public SpaceEntryMutator()

Method Detail

change

public abstract Object change(MutableServerEntry entry)

Changes an entry. The provided MutableServerEntry is wrapping the actual object which is kept in space, therefore it is crucial to understand when a value is retrieved from the entry it points to the actual reference in the data structure of the space. The content of this reference should not be changed as it will affect directly the object in space and will break data integrity, transaction and visibility scoping (transaction abort will not restore the previous value). Changing a value should always be done via the MutableServerEntry.setPathValue(String, Object). Moreover, if you want to change a property within that value by invoking a method on that object (e.g. if the value is a list, adding an item to the list) first you must clone the fetched value first, and invoke the method on the cloned copy otherwise, for the reason explained before, you will change the existing data structure in the space without going the proper data update path and break data integrity.

Note that when using a replicated topology (e.g. backup space, gateway, mirror) the change operation itself is replicated (and *NOT* the modified entry). Hence, it is imperative that this method will always cause the exact same affect on the entry assuming the same entry was provided, for example it should not rely on variables that may change between executions, such as system time, random, machine name etc. If the operation is not structured that way, the state can be inconsistent in the different locations after being replicated When creating a custom change operation always have this in the back of your mind - "With great power comes great responsibility".

Following is an example that reads propertyA and set its value into propertyB and returns nothing.

 public Object change(MutableServerEntry entry)
 {
     Object value entry.getPathValue("propertyA");
     entry.setPathValue("propertyB", newValue);
     return null;
 }
 

Following is an example that adds the element 2 into an ArrayList that exists in the entry under a property named "listProperty", the result sent to client if requested is the size of the collection after the change, note that we clone the ArrayList before modifying it as explained before.

 public Object change(MutableServerEntry entry)
 {
     ArrayList oldValue = (ArrayList)entry.getPathValue("listPropery");
     if (oldValue == null)
         throw new IllegalStateException("No collection instance exists under the given path
 'listProperty', in order to add a value a collection instance must exist");
     Collection newValue = (ArrayList)oldValue.clone()
     newValue.add(2);
     int size = newValue.size();
     entry.setPathValue("listProperty", newValue);
     return size;
 }
 

Parameters:

entry - the entry to change.

Returns:

a result value of this change which will be sent to the client if the change operation was executed with ChangeModifiers.RETURN_DETAILED_RESULTS modifier.

getChangeOperationResult

public ChangeOperationResult getChangeOperationResult(Serializable result)