org.apache.flink.table.api.dataview

Class ListView<T>

java.lang.Object

org.apache.flink.table.api.dataview.ListView<T>

Type Parameters:

T - element type

All Implemented Interfaces:

DataView

@TypeInfo(value=ListViewTypeInfoFactory.class)
 @PublicEvolving
public class ListView<T>
extends Object
implements DataView

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

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

Note: Elements of a ListView must not be null. 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 DataType of the view's elements is reflectively extracted from the accumulator definition. This includes the generic argument T 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 ListView:

  public class MyAccumulator {

    public ListView<String> list = new ListView<>();

    // or explicit:
    // {@literal @}DataTypeHint("ARRAY<STRING>")
    // public ListView<String> list = new ListView<>();

    public long count = 0L;
  }

  public class MyAggregateFunction extends AggregateFunction<String, MyAccumulator> {

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

   public void accumulate(MyAccumulator accumulator, String id) {
     accumulator.list.add(id);
     accumulator.count++;
   }

   {@literal @}Override
   public String getValue(MyAccumulator accumulator) {
     // return the count and the joined elements
     return count + ": " + String.join("|", acc.list.get());
   }
 }

 

Field Summary

Fields

Modifier and Type	Field and Description
org.apache.flink.api.common.typeinfo.TypeInformation<?>	elementType Deprecated.

Constructor Summary

Constructors

Constructor and Description
ListView() Creates a list view.
ListView(org.apache.flink.api.common.typeinfo.TypeInformation<?> elementType) 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	add(T value) Adds the given value to the list.
void	addAll(List<T> list) Adds all of the elements of the specified list to this list view.
void	clear() Removes all of the elements from this list view.
boolean	equals(Object o)
Iterable<T>	get() Returns an iterable of the list view.
List<T>	getList() Returns the entire view's content as an instance of List.
int	hashCode()
static DataType	newListViewDataType(DataType elementDataType) Utility method for creating a DataType of ListView explicitly.
boolean	remove(T value) Removes the given value from the list.
void	setList(List<T> list) Replaces the entire view's content with the content of the given List.

Methods inherited from class java.lang.Object

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

Field Detail

elementType

@Deprecated
public transient org.apache.flink.api.common.typeinfo.TypeInformation<?> elementType

Deprecated.

Constructor Detail

ListView

public ListView()

Creates a list view.

The DataType of the contained elements is reflectively extracted.

ListView

@Deprecated
public ListView(org.apache.flink.api.common.typeinfo.TypeInformation<?> elementType)

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

Creates a ListView for elements of the specified type.

Parameters:

elementType - The type of the list view elements.

Method Detail

getList

public List<T> getList()

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

setList

public void setList(List<T> list)

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

get

public Iterable<T> get()
                throws Exception

Returns an iterable of the list view.

Returns:

The iterable of the list.

Throws:

Exception - Thrown if the system cannot get data.

add

public void add(T value)
         throws Exception

Adds the given value to the list.

Parameters:

value - The element to be appended to this list view.

Throws:

Exception - Thrown if the system cannot add data.

addAll

public void addAll(List<T> list)
            throws Exception

Adds all of the elements of the specified list to this list view.

Parameters:

list - The list with the elements that will be stored in this list view.

Throws:

Exception - Thrown if the system cannot add all data.

remove

public boolean remove(T value)
               throws Exception

Removes the given value from the list.

Parameters:

value - The element to be removed from this list view.

Throws:

Exception

clear

public void clear()

Removes all of the elements from this list view.

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

newListViewDataType

public static DataType newListViewDataType(DataType elementDataType)

Utility method for creating a DataType of ListView explicitly.