org.apache.flink.table.api.dataview

Class MapView<K,V>

java.lang.Object

org.apache.flink.table.api.dataview.MapView<K,V>

Type Parameters:

K - key type

V - value type

All Implemented Interfaces:

DataView

Direct Known Subclasses:

StateMapView

@TypeInfo(value=MapViewTypeInfoFactory.class)
 @PublicEvolving
public class MapView<K,V>
extends Object
implements DataView

A DataView that provides Map-like functionality in the accumulator of an AggregateFunction or TableAggregateFunction when large amounts of data are expected.

A MapView can be backed by a Java HashMap or can leverage Flink's state backends depending on the context in which the aggregate function is used. In many unbounded data scenarios, the MapView delegates all calls to a MapState instead of the HashMap.

Note: Keys of a MapView must not be null. Nulls in values are supported. For heap-based state backends, hashCode/equals of the original (i.e. external) class are used. However, the serialization format will use internal data structures.

The DataTypes of the view's keys and values are reflectively extracted from the accumulator definition. This includes the generic argument K and V of this class. If reflective extraction is not successful, it is possible to use a DataTypeHint on top the accumulator field. It will be mapped to the underlying collection.

The following examples show how to specify an AggregateFunction with a MapView:

 public class MyAccumulator {

   public MapView<String, Integer> map = new MapView<>();

   // or explicit:
   // {@literal @}DataTypeHint("MAP<STRING, INT>")
   // public MapView<String, Integer> map = new MapView<>();

   public long count;
 }

 public class MyAggregateFunction extends AggregateFunction<Long, MyAccumulator> {

  {@literal @}Override
  public MyAccumulator createAccumulator() {
    return new MyAccumulator();
  }

   public void accumulate(MyAccumulator accumulator, String id) {
     if (!accumulator.map.contains(id)) {
       accumulator.map.put(id, 1);
       accumulator.count++;
     }
   }

  {@literal @}Override
   public Long getValue(MyAccumulator accumulator) {
     return accumulator.count;
   }
 }

 

Field Summary

Fields

Modifier and Type	Field and Description
TypeInformation<?>	keyType Deprecated.
TypeInformation<?>	valueType Deprecated.

Constructor Summary

Constructors

Constructor and Description
MapView() Creates a map view.
MapView(TypeInformation<?> keyType, TypeInformation<?> valueType) Deprecated. This method uses the old type system. Please use a DataTypeHint instead if the reflective type extraction is not successful.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all entries of this map.
boolean	contains(K key) Checks if the map view contains a value for a given key.
Iterable<Map.Entry<K,V>>	entries() Returns all entries of the map view.
boolean	equals(Object o)
V	get(K key) Return the value for the specified key or null if the key is not in the map view.
Map<K,V>	getMap() Returns the entire view's content as an instance of Map.
int	hashCode()
boolean	isEmpty() Returns true if the map view contains no key-value mappings, otherwise false.
Iterator<Map.Entry<K,V>>	iterator() Returns an iterator over all entries of the map view.
Iterable<K>	keys() Returns all the keys in the map view.
static DataType	newMapViewDataType(DataType keyDataType, DataType valueDataType) Utility method for creating a DataType of MapView explicitly.
void	put(K key, V value) Inserts a value for the given key into the map view.
void	putAll(Map<K,V> map) Inserts all mappings from the specified map to this map view.
void	remove(K key) Deletes the value for the given key.
void	setMap(Map<K,V> map) Replaces the entire view's content with the content of the given Map.
Iterable<V>	values() Returns all the values in the map view.

Methods inherited from class java.lang.Object

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

Field Detail

keyType

@Deprecated
public transient TypeInformation<?> keyType

Deprecated.

valueType

@Deprecated
public transient TypeInformation<?> valueType

Deprecated.

Constructor Detail

MapView

public MapView()

Creates a map view.

The DataType of keys and values is reflectively extracted.

MapView

@Deprecated
public MapView(TypeInformation<?> keyType,
                           TypeInformation<?> valueType)

Deprecated. This method uses the old type system. Please use a DataTypeHint instead if the reflective type extraction is not successful.

Creates a MapView with the specified key and value types.

Parameters:

keyType - The type of keys of the map view.

valueType - The type of values of the map view.

Method Detail

getMap

public Map<K,V> getMap()

Returns the entire view's content as an instance of Map.

setMap

public void setMap(Map<K,V> map)

Replaces the entire view's content with the content of the given Map.

get

public V get(K key)
      throws Exception

Return the value for the specified key or null if the key is not in the map view.

Parameters:

key - The look up key.

Returns:

The value for the specified key.

Throws:

Exception - Thrown if the system cannot get data.

put

public void put(K key,
                V value)
         throws Exception

Inserts a value for the given key into the map view. If the map view already contains a value for the key, the existing value is overwritten.

Parameters:

key - The key for which the value is inserted.

value - The value that is inserted for the key.

Throws:

Exception - Thrown if the system cannot put data.

putAll

public void putAll(Map<K,V> map)
            throws Exception

Inserts all mappings from the specified map to this map view.

Parameters:

map - The map whose entries are inserted into this map view.

Throws:

Exception - Thrown if the system cannot access the map.

remove

public void remove(K key)
            throws Exception

Deletes the value for the given key.

Parameters:

key - The key for which the value is deleted.

Throws:

Exception - Thrown if the system cannot access the map.

contains

public boolean contains(K key)
                 throws Exception

Checks if the map view contains a value for a given key.

Parameters:

key - The key to check.

Returns:

True if there exists a value for the given key, false otherwise.

Throws:

Exception - Thrown if the system cannot access the map.

entries

public Iterable<Map.Entry<K,V>> entries()
                                 throws Exception

Returns all entries of the map view.

Returns:

An iterable of all the key-value pairs in the map view.

Throws:

Exception - Thrown if the system cannot access the map.

keys

public Iterable<K> keys()
                 throws Exception

Returns all the keys in the map view.

Returns:

An iterable of all the keys in the map.

Throws:

Exception - Thrown if the system cannot access the map.

values

public Iterable<V> values()
                   throws Exception

Returns all the values in the map view.

Returns:

An iterable of all the values in the map.

Throws:

Exception - Thrown if the system cannot access the map.

iterator

public Iterator<Map.Entry<K,V>> iterator()
                                  throws Exception

Returns an iterator over all entries of the map view.

Returns:

An iterator over all the mappings in the map.

Throws:

Exception - Thrown if the system cannot access the map.

isEmpty

public boolean isEmpty()
                throws Exception

Returns true if the map view contains no key-value mappings, otherwise false.

Returns:

True if the map view contains no key-value mappings, otherwise false.

Throws:

Exception - Thrown if the system cannot access the state.

clear

public void clear()

Removes all entries of this map.

Specified by:

clear in interface DataView

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

newMapViewDataType

public static DataType newMapViewDataType(DataType keyDataType,
                                          DataType valueDataType)

Utility method for creating a DataType of MapView explicitly.