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package com.techempower.cache;
import java.util.*;
import com.techempower.data.*;
import com.techempower.util.*;
/**
* A Pure-Memory Entity Group is a specialization of the standard CacheGroup
* that does away entirely with the persistence of Entities in a database.
* Instead, client code is expected to provide an Initializer reference that
* is capable of providing the initial Entities.
*
* The use case for a PureMemoryGroup is the maintenance of derived data
* structures, or any sort of application state that does not warrant
* persistence, while retaining EntityGroup / EntityStore semantics for
* put/get/etc. and listener notifications.
*/
public class PureMemoryGroup
extends CacheGroup
{
//
// Member variables.
//
private final GroupInitializer initializer;
//
// Constructors.
//
/**
* Constructor.
*/
protected PureMemoryGroup(EntityStore entityStore,
Class type,
EntityMaker maker,
Comparator comparator,
GroupInitializer initializer,
boolean readOnly)
{
super(entityStore, type, null, null, maker, comparator, null, null,
readOnly);
this.initializer = initializer;
}
//
// Builder methods.
//
/**
* Creates a new {@link Builder}, which is used to construct an
* {@link PureMemoryGroup}. Example usage:
*
*
* PureMemoryGroup<Foo> = PureMemoryGroup.of(Foo.class) // new Builder
* .build(entityStore); // new CacheGroup
*
*
* Note that a {@link EntityStore#register(EntityGroup.Builder)} method
* exists, so in the common case where you only want to register the group and
* don't care to retain your own reference to it, calling
* {@code .build(entityStore)} is unnecessary. For example:
*
*
* register(CacheGroup.of(Foo.class) // new Builder
* ); // the register method calls .build(entityStore) for us
*
*
* @param type The type of the entities.
* @return A new {@link Builder}.
*/
public static Builder of(Class type)
{
return new Builder<>(type);
}
//
// Member methods.
//
/**
* Specialization of CacheGroup.putPersistent to disable the persistence
* of entities.
*/
@Override
protected void putPersistent(T object)
{
// Does nothing.
}
/**
* Specialization of CacheGroup.putAllPersistent to disable the persistence
* of entities.
*/
@Override
protected void putAllPersistent(Collection objects)
{
// Does nothing.
}
/**
* Specialization of CacheGroup.removePersistent to disable the persistence
* of entities.
*/
@Override
protected void removePersistent(long id)
{
// Does nothing.
}
/**
* Specialization of CacheGroup.removeAllPersistent to disable the
* persistence of entities.
*/
@Override
protected void removeAllPersistent(Collection ids)
{
// Does nothing.
}
/**
* Fetches all persisted objects. Call the provided Initializer or return
* an empty list in the default case.
*/
@Override
protected List fetchAllPersistedObjects()
{
// We sort whatever the initializer gives us because there is no
// guarantee that it's in the right order.
List result = initializer.list();
Collections.sort(result, comparator());
return result;
}
/**
* The Refresh method does nothing for the PureMemoryGroup because once
* initialized, there is no other source from which to fetch objects.
*/
@Override
public void refresh(long... ids)
{
// Does nothing.
}
@Override
protected boolean isPersisted(Identifiable entity)
{
// We consider anything that the map contains to have been "persisted"
// for our purposes.
return containsRaw(entity);
}
//
// Inner classes.
//
/**
* Creates new instances of {@code PureMemoryGroup}.
*/
public static class Builder
extends CacheGroup.Builder
{
private static final String ERROR_NO_INITIALIZER = "CacheInitializer may not be null.";
private GroupInitializer initializer = new EmptyInitializer<>();
protected Builder(Class type)
{
super(type);
}
@Override
public PureMemoryGroup build(EntityStore entityStore)
{
return new PureMemoryGroup<>(
entityStore,
this.type,
this.maker,
this.comparator,
this.initializer,
this.readOnly);
}
/**
* Sets the GroupInitializer to pre-populate this group with a list of
* entities. If no initializer is specified, the group will be set to
* an empty list during initialization.
*/
public Builder initializer(GroupInitializer groupInitializer)
{
if (groupInitializer == null)
{
throw new IllegalArgumentException(ERROR_NO_INITIALIZER);
}
this.initializer = groupInitializer;
return this;
}
@Override
public Builder maker(EntityMaker entityMaker)
{
super.maker(entityMaker);
return this;
}
@Override
public Builder comparator(Comparator entityComparator)
{
super.comparator(entityComparator);
return this;
}
@Override
public Builder comparator(String methodName)
{
super.comparator(methodName);
return this;
}
@Override
public Builder constructorArgs(Object... arguments)
{
super.constructorArgs(arguments);
return this;
}
} // End Builder.
}