com.appenginefan.toolkit.persistence
Class MapBasedPersistence<T>

java.lang.Object
  com.appenginefan.toolkit.persistence.MapBasedPersistence<T>

All Implemented Interfaces:

Persistence<T>

public class MapBasedPersistence<T>
extends Object
implements Persistence<T>

A simple, map-based store that holds data in memory. Should only be used for unit tests, mostly for two reasons. First of all, this persistence does not do any defensive copies of its content, so nasty side effects can occur. Second, since all is in memory, nothing is really getting persisted beyond the lifetime of the virtual machine.

Constructor Summary

MapBasedPersistence()

Method Summary

T	get(String key) Gets an entry from the store.
List<String>	keyScan(String start, String end, int max) Finds zero or more entries that are within a given range.
List<String>	keyScanReverse(String start, String end, int max) Finds zero or more entries that are within a given range, but orders in the opposite direction.
T	mutate(String key, Function<? super T,? extends T> mutator) Modifies an entry in the store.
static <T> MapBasedPersistence<T>	newInstance() Factory method
List<Map.Entry<String,T>>	scan(String start, String end, int max) Finds zero or more entries that are within a given range
List<Map.Entry<String,T>>	scanReverse(String start, String end, int max) Finds zero or more entries that are within a given range, but orders in the opposite direction.

Methods inherited from class java.lang.Object

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

Constructor Detail

MapBasedPersistence

public MapBasedPersistence()

Method Detail

newInstance

public static <T> MapBasedPersistence<T> newInstance()

Factory method

get

public T get(String key)

Description copied from interface: Persistence

Gets an entry from the store.

Specified by:

get in interface Persistence<T>

Parameters:

key - the key to look up the data from

Returns:

the data or null, if the store does not contain data

mutate

public T mutate(String key,
                Function<? super T,? extends T> mutator)

Description copied from interface: Persistence

Modifies an entry in the store.

Specified by:

mutate in interface Persistence<T>

Parameters:

key - the key to modify

mutator - a function that applies a change to the data and stores the new result. If the data does not exist in the store yet, null will be passed in. If the data should be deleted from the store, the function will return null.

Returns:

the data that was stored

scan

public List<Map.Entry<String,T>> scan(String start,
                                      String end,
                                      int max)

Description copied from interface: Persistence

Finds zero or more entries that are within a given range

Specified by:

scan in interface Persistence<T>

Parameters:

start - a lower bound of the range of keys to look in (inclusive)

end - an upper bound of the range of keys to look in (exclusive)

max - a maximum amount of elements to return. The implementation of the store may choose to return less (for example, if a store can only fetch 10 elements per query, then setting a max of 1000 will still only return 10), but never more.

Returns:

a list of up to max key/value pairs, ordered by key

scanReverse

public List<Map.Entry<String,T>> scanReverse(String start,
                                             String end,
                                             int max)

Description copied from interface: Persistence

Finds zero or more entries that are within a given range, but orders in the opposite direction. Useful for pagination to jump to the end of a range and get the "last ten" entries

Specified by:

scanReverse in interface Persistence<T>

Parameters:

start - a lower bound of the range of keys to look in (inclusive)

end - an upper bound of the range of keys to look in (exclusive)

max - a maximum amount of elements to return. The implementation of the store may choose to return less (for example, if a store can only fetch 10 elements per query, then setting a max of 1000 will still only return 10), but never more.

Returns:

a list of up to max key/value pairs, ordered by key in descending order

keyScan

public List<String> keyScan(String start,
                            String end,
                            int max)

Description copied from interface: Persistence

Finds zero or more entries that are within a given range. Only returns the keys.

Specified by:

keyScan in interface Persistence<T>

Parameters:

start - a lower bound of the range of keys to look in (inclusive)

end - an upper bound of the range of keys to look in (exclusive)

max - a maximum amount of elements to return. The implementation of the store may choose to return less (for example, if a store can only fetch 10 elements per query, then setting a max of 1000 will still only return 10), but never more.

Returns:

a list of up to max key/value pairs, ordered by key

keyScanReverse

public List<String> keyScanReverse(String start,
                                   String end,
                                   int max)

Description copied from interface: Persistence

Finds zero or more entries that are within a given range, but orders in the opposite direction. Only returns the keys.

Specified by:

keyScanReverse in interface Persistence<T>

Parameters:

start - a lower bound of the range of keys to look in (inclusive)

end - an upper bound of the range of keys to look in (exclusive)

max - a maximum amount of elements to return. The implementation of the store may choose to return less (for example, if a store can only fetch 10 elements per query, then setting a max of 1000 will still only return 10), but never more.

Returns:

a list of up to max key/value pairs, ordered by key in descending order