MapView (Flink : Table : Common 1.12.5 API)

java.lang.Object
- org.apache.flink.table.api.dataview.MapView<K,V>

类型参数:

K - key type

V - value type

所有已实现的接口:

DataView
```
@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;
   }
 }

 
```

字段概要

字段
限定符和类型	字段和说明
`org.apache.flink.api.common.typeinfo.TypeInformation<?>`	`keyType` 已过时。
`org.apache.flink.api.common.typeinfo.TypeInformation<?>`	`valueType` 已过时。

构造器概要

构造器
构造器和说明
`MapView()` Creates a map view.
`MapView(org.apache.flink.api.common.typeinfo.TypeInformation<?> keyType, org.apache.flink.api.common.typeinfo.TypeInformation<?> valueType)` 已过时。 This method uses the old type system. Please use a `DataTypeHint` instead if the reflective type extraction is not successful.

方法概要

所有方法静态方法实例方法具体方法
限定符和类型	方法和说明
`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.

从类继承的方法 java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

- 字段详细资料
  - keyType
```
@Deprecated
public transient org.apache.flink.api.common.typeinfo.TypeInformation<?> keyType
```
    已过时。
  - valueType
```
@Deprecated
public transient org.apache.flink.api.common.typeinfo.TypeInformation<?> valueType
```
    已过时。
- 构造器详细资料
  - MapView
```
public MapView()
```
    Creates a map view.
    The DataType of keys and values is reflectively extracted.
  - MapView
```
@Deprecated
public MapView(org.apache.flink.api.common.typeinfo.TypeInformation<?> keyType,
                           org.apache.flink.api.common.typeinfo.TypeInformation<?> valueType)
```
    已过时。 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.
    
    参数:
    
    keyType - The type of keys of the map view.
    
    valueType - The type of values of the map view.
- 方法详细资料
  - 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.
    
    参数:
    
    key - The look up key.
    
    返回:
    
    The value for the specified key.
    
    抛出:
    
    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.
    
    参数:
    
    key - The key for which the value is inserted.
    
    value - The value that is inserted for the key.
    
    抛出:
    
    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.
    
    参数:
    
    map - The map whose entries are inserted into this map view.
    
    抛出:
    
    Exception - Thrown if the system cannot access the map.
  - remove
```
public void remove(K key)
            throws Exception
```
    Deletes the value for the given key.
    
    参数:
    
    key - The key for which the value is deleted.
    
    抛出:
    
    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.
    
    参数:
    
    key - The key to check.
    
    返回:
    
    True if there exists a value for the given key, false otherwise.
    
    抛出:
    
    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.
    
    返回:
    
    An iterable of all the key-value pairs in the map view.
    
    抛出:
    
    Exception - Thrown if the system cannot access the map.
  - keys
```
public Iterable<K> keys()
                 throws Exception
```
    Returns all the keys in the map view.
    
    返回:
    
    An iterable of all the keys in the map.
    
    抛出:
    
    Exception - Thrown if the system cannot access the map.
  - values
```
public Iterable<V> values()
                   throws Exception
```
    Returns all the values in the map view.
    
    返回:
    
    An iterable of all the values in the map.
    
    抛出:
    
    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.
    
    返回:
    
    An iterator over all the mappings in the map.
    
    抛出:
    
    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.
    
    返回:
    
    True if the map view contains no key-value mappings, otherwise false.
    
    抛出:
    
    Exception - Thrown if the system cannot access the state.
  - clear
```
public void clear()
```
    Removes all entries of this map.
    
    指定者:
    
    clear 在接口中 DataView
  - equals
```
public boolean equals(Object o)
```
    覆盖:
    
    equals 在类中 Object
  - hashCode
```
public int hashCode()
```
    覆盖:
    
    hashCode 在类中 Object
  - newMapViewDataType
```
public static DataType newMapViewDataType(DataType keyDataType,
                                          DataType valueDataType)
```
    Utility method for creating a DataType of MapView explicitly.

类 MapView<K,V>

字段概要

构造器概要

方法概要

从类继承的方法 java.lang.Object

字段详细资料

keyType

valueType

构造器详细资料

MapView

MapView

方法详细资料

getMap

setMap

get

put

putAll

remove

contains

entries

keys

values

iterator

isEmpty

clear

equals

hashCode

newMapViewDataType