org.apache.beam.sdk.state

Interface MapState<K,V>

Type Parameters:

K - the type of keys maintained by this map

V - the type of mapped values

All Superinterfaces:

State

@Experimental(value=STATE)
public interface MapState<K,V>
extends State

A ReadableState cell mapping keys to values.

Implementations of this form of state are expected to implement map operations efficiently as supported by some associated backing key-value store.

Method Summary

Modifier and Type	Method and Description
ReadableState<V>	computeIfAbsent(K key, java.util.function.Function<? super K,? extends V> mappingFunction) A deferred read-followed-by-write.
ReadableState<java.lang.Iterable<java.util.Map.Entry<K,V>>>	entries() Returns an Iterable over the key-value pairs contained in this map.
ReadableState<V>	get(K key) A deferred lookup, using null values if the item is not found.
ReadableState<V>	getOrDefault(K key, V defaultValue) A deferred lookup.
ReadableState<java.lang.Boolean>	isEmpty() Returns a ReadableState whose ReadableState.read() method will return true if this state is empty at the point when that ReadableState.read() call returns.
ReadableState<java.lang.Iterable<K>>	keys() Returns an Iterable over the keys contained in this map.
void	put(K key, V value) Associates the specified value with the specified key in this state.
default ReadableState<V>	putIfAbsent(K key, V value) A deferred read-followed-by-write.
void	remove(K key) Remove the mapping for a key from this map if it is present.
ReadableState<java.lang.Iterable<V>>	values() Returns an Iterable over the values contained in this map.

Methods inherited from interface org.apache.beam.sdk.state.State

clear

Method Detail

put

void put(K key,
         V value)

Associates the specified value with the specified key in this state.

Changes will not be reflected in the results returned by previous calls to ReadableState.read() on the results any of the reading methods (get(K), keys(), values(), and entries()).

putIfAbsent

default ReadableState<V> putIfAbsent(K key,
                                     V value)

A deferred read-followed-by-write.

When read() is called on the result or state is committed, it forces a read of the map and reconciliation with any pending modifications.

If the specified key is not already associated with a value (or is mapped to null) associates it with the given value and returns null, else returns the current value.

Changes will not be reflected in the results returned by previous calls to ReadableState.read() on the results any of the reading methods (get(K), keys(), values(), and entries()).

Since the condition is not evaluated until ReadableState.read() is called, a call to putIfAbsent(K, V) followed by a call to remove(K) followed by a read on the putIfAbsent return will result in the item being written to the map. Similarly, if there are multiple calls to putIfAbsent(K, V) for the same key, precedence will be given to the first one on which read is called.

computeIfAbsent

ReadableState<V> computeIfAbsent(K key,
                                 java.util.function.Function<? super K,? extends V> mappingFunction)

A deferred read-followed-by-write.

When read() is called on the result or state is committed, it forces a read of the map and reconciliation with any pending modifications.

If the specified key is not already associated with a value (or is mapped to null) associates it with the computed and returns null, else returns the current value.

Changes will not be reflected in the results returned by previous calls to ReadableState.read() on the results any of the reading methods (get(K), keys(), values(), and entries()).

Since the condition is not evaluated until ReadableState.read() is called, a call to putIfAbsent(K, V) followed by a call to remove(K) followed by a read on the putIfAbsent return will result in the item being written to the map. Similarly, if there are multiple calls to putIfAbsent(K, V) for the same key, precedence will be given to the first one on which read is called.

remove

void remove(K key)

Remove the mapping for a key from this map if it is present.

Changes will not be reflected in the results returned by previous calls to ReadableState.read() on the results any of the reading methods (get(K), keys(), values(), and entries()).

get

ReadableState<V> get(K key)

A deferred lookup, using null values if the item is not found.

A user is encouraged to call get for all relevant keys and call readLater() on the results.

When read() is called, a particular state implementation is encouraged to perform all pending reads in a single batch.

getOrDefault

ReadableState<V> getOrDefault(K key,
                              @Nullable
                              V defaultValue)

A deferred lookup.

A user is encouraged to call get for all relevant keys and call readLater() on the results.

When read() is called, a particular state implementation is encouraged to perform all pending reads in a single batch.

keys

ReadableState<java.lang.Iterable<K>> keys()

Returns an Iterable over the keys contained in this map.

values

ReadableState<java.lang.Iterable<V>> values()

Returns an Iterable over the values contained in this map.

entries

ReadableState<java.lang.Iterable<java.util.Map.Entry<K,V>>> entries()

Returns an Iterable over the key-value pairs contained in this map.

isEmpty

ReadableState<java.lang.Boolean> isEmpty()

Returns a ReadableState whose ReadableState.read() method will return true if this state is empty at the point when that ReadableState.read() call returns.