Top Description Inners Fields Constructors Methods
org.apache.tomcat.util.collections

public Class ManagedConcurrentWeakHashMap<K, V>

extends AbstractMap<K, V>
implements ConcurrentMap<K, V>
Class Inheritance
All Implemented Interfaces
java.util.concurrent.ConcurrentMap, java.util.Map
Type Parameters
<K>
The type of keys used with the Map instance
<V>
The type of values used with the Map instance
Imports
java.lang.ref.Reference, .ReferenceQueue, .WeakReference, java.util.AbstractMap, .AbstractSet, .Collection, .Iterator, .Map, .Objects, .Set, java.util.concurrent.ConcurrentHashMap, .ConcurrentMap
Concurrent hash map that holds its keys via weak references. Unlike WeakHashMap this class does not handle dead keys during common access operations, but expects you to call its maintain() method periodically. Both keys and values are expected to be not-null.

Nested and Inner Type Summary

Modifier and TypeClass and Description
private static class
ManagedConcurrentWeakHashMap.Key

Field Summary

Modifier and TypeField and Description
private final ConcurrentMap<ManagedConcurrentWeakHashMap.Key, V>
map

private final ReferenceQueue<Object>
queue

Constructor Summary

AccessConstructor and Description
public
ManagedConcurrentWeakHashMap()

Method Summary

Modifier and TypeMethod and Description
public void
clear()

Overrides java.util.AbstractMap.clear.

Implements java.util.Map.clear.

Removes all of the mappings from this map (optional operation).

public boolean
containsKey(Object
key whose presence in this map is to be tested
key)

Overrides java.util.AbstractMap.containsKey.

Implements java.util.Map.containsKey.

Returns true if this map contains a mapping for the specified key.

public boolean
containsValue(Object
value whose presence in this map is to be tested
value)

Overrides java.util.AbstractMap.containsValue.

Implements java.util.Map.containsValue.

Returns true if this map maps one or more keys to the specified value.

private ManagedConcurrentWeakHashMap.Key
createLookupKey(Object key)

Creates Key instance to be used only to lookup values in the map.

private ManagedConcurrentWeakHashMap.Key
createStoreKey(Object key)

Creates Key instance to be used to store values in the map.

public Set<Map.Entry<K, V>>
entrySet()

Implements abstract java.util.AbstractMap.entrySet.

Implements java.util.Map.entrySet.

Returns a Set view of the mappings contained in this map.

public V
get(Object
the key whose associated value is to be returned
key)

Overrides java.util.AbstractMap.get.

Implements java.util.Map.get.

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

public boolean
isEmpty()

Overrides java.util.AbstractMap.isEmpty.

Implements java.util.Map.isEmpty.

Returns true if this map contains no key-value mappings.

public void
maintain()

Method, that has to be invoked periodically to clean dead keys from the map.

public V
put(K
key with which the specified value is to be associated
key, V
value to be associated with the specified key
value)

Overrides java.util.AbstractMap.put.

Implements java.util.Map.put.

Associates the specified value with the specified key in this map (optional operation).

public V
putIfAbsent(K
key with which the specified value is to be associated
key, V
value to be associated with the specified key
value)

Overrides default java.util.Map.putIfAbsent.

Implements java.util.concurrent.ConcurrentMap.putIfAbsent.

If the specified key is not already associated with a value, associates it with the given value.

public V
remove(Object
key whose mapping is to be removed from the map
key)

Overrides java.util.AbstractMap.remove.

Implements java.util.Map.remove.

Removes the mapping for a key from this map if it is present (optional operation).

public boolean
remove(Object
key with which the specified value is associated
key, Object
value expected to be associated with the specified key
value)

Overrides default java.util.Map.remove.

Implements java.util.concurrent.ConcurrentMap.remove.

Removes the entry for a key only if currently mapped to a given value.

public boolean
replace(K
key with which the specified value is associated
key, V
value expected to be associated with the specified key
oldValue, V
value to be associated with the specified key
newValue)

Overrides default java.util.Map.replace.

Implements java.util.concurrent.ConcurrentMap.replace.

Replaces the entry for a key only if currently mapped to a given value.

public V
replace(K
key with which the specified value is associated
key, V
value to be associated with the specified key
value)

Overrides default java.util.Map.replace.

Implements java.util.concurrent.ConcurrentMap.replace.

Replaces the entry for a key only if currently mapped to some value.

public int
size()

Overrides java.util.AbstractMap.size.

Implements java.util.Map.size.

Returns the number of key-value mappings in this map.

public Collection<V>
values()

Overrides java.util.AbstractMap.values.

Implements java.util.Map.values.

Returns a Collection view of the values contained in this map.

Inherited from java.util.AbstractMap:
cloneequalshashCodekeySetputAlltoString

Field Detail

mapback to summary
private final ConcurrentMap<ManagedConcurrentWeakHashMap.Key, V> map
queueback to summary
private final ReferenceQueue<Object> queue

Constructor Detail

ManagedConcurrentWeakHashMapback to summary
public ManagedConcurrentWeakHashMap()

Method Detail

clearback to summary
public void clear()

Overrides java.util.AbstractMap.clear.

Implements java.util.Map.clear.

Doc from java.util.Map.clear.

Removes all of the mappings from this map (optional operation). The map will be empty after this call returns.

Annotations
@Override
containsKeyback to summary
public boolean containsKey(Object key)

Overrides java.util.AbstractMap.containsKey.

Implements java.util.Map.containsKey.

Doc from java.util.Map.containsKey.

Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that Objects.equals(key, k). (There can be at most one such mapping.)

Parameters
key:Object

key whose presence in this map is to be tested

Returns:boolean

true if this map contains a mapping for the specified key

Annotations
@Override
containsValueback to summary
public boolean containsValue(Object value)

Overrides java.util.AbstractMap.containsValue.

Implements java.util.Map.containsValue.

Doc from java.util.Map.containsValue.

Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that Objects.equals(value, v). This operation will probably require time linear in the map size for most implementations of the Map interface.

Parameters
value:Object

value whose presence in this map is to be tested

Returns:boolean

true if this map maps one or more keys to the specified value

Annotations
@Override
createLookupKeyback to summary
private ManagedConcurrentWeakHashMap.Key createLookupKey(Object key)

Creates Key instance to be used only to lookup values in the map. It is not registered with the ReferenceQueue.

createStoreKeyback to summary
private ManagedConcurrentWeakHashMap.Key createStoreKey(Object key)

Creates Key instance to be used to store values in the map. It is registered with the ReferenceQueue.

entrySetback to summary
public Set<Map.Entry<K, V>> entrySet()

Implements abstract java.util.AbstractMap.entrySet.

Implements java.util.Map.entrySet.

Doc from java.util.Map.entrySet.

Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation, or through the setValue operation on a map entry returned by the iterator) the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Returns:Set<Map.Entry<K, V>>

a set view of the mappings contained in this map

Annotations
@Override
getback to summary
public V get(Object key)

Overrides java.util.AbstractMap.get.

Implements java.util.Map.get.

Doc from java.util.Map.get.

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key k to a value v such that Objects.equals(key, k), then this method returns v; otherwise it returns null. (There can be at most one such mapping.)

If this map permits null values, then a return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Parameters
key:Object

the key whose associated value is to be returned

Returns:V

the value to which the specified key is mapped, or null if this map contains no mapping for the key

Annotations
@Override
isEmptyback to summary
public boolean isEmpty()

Overrides java.util.AbstractMap.isEmpty.

Implements java.util.Map.isEmpty.

Doc from java.util.Map.isEmpty.

Returns true if this map contains no key-value mappings.

Returns:boolean

true if this map contains no key-value mappings

Annotations
@Override
maintainback to summary
public void maintain()

Method, that has to be invoked periodically to clean dead keys from the map.

putback to summary
public V put(K key, V value)

Overrides java.util.AbstractMap.put.

Implements java.util.Map.put.

Doc from java.util.Map.put.

Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for the key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.)

Parameters
key:K

key with which the specified value is to be associated

value:V

value to be associated with the specified key

Returns:V

the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)

Annotations
@Override
putIfAbsentback to summary
public V putIfAbsent(K key, V value)

Overrides default java.util.Map.putIfAbsent.

Implements java.util.concurrent.ConcurrentMap.putIfAbsent.

Doc from java.util.concurrent.ConcurrentMap.putIfAbsent.

If the specified key is not already associated with a value, associates it with the given value. This is equivalent to, for this map: 

 if (!map.containsKey(key))
  return map.put(key, value);
else
  return map.get(key);
except that the action is performed atomically.
Parameters
key:K

key with which the specified value is to be associated

value:V

value to be associated with the specified key

Returns:V

the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)

Annotations
@Override
removeback to summary
public V remove(Object key)

Overrides java.util.AbstractMap.remove.

Implements java.util.Map.remove.

Doc from java.util.Map.remove.

Removes the mapping for a key from this map if it is present (optional operation). More formally, if this map contains a mapping from key k to value v such that Objects.equals(key, k), that mapping is removed. (The map can contain at most one such mapping.)

Returns the value to which this map previously associated the key, or null if the map contained no mapping for the key.

If this map permits null values, then a return value of null does not necessarily indicate that the map contained no mapping for the key; it's also possible that the map explicitly mapped the key to null.

The map will not contain a mapping for the specified key once the call returns.

Parameters
key:Object

key whose mapping is to be removed from the map

Returns:V

the previous value associated with key, or null if there was no mapping for key.

Annotations
@Override
removeback to summary
public boolean remove(Object key, Object value)

Overrides default java.util.Map.remove.

Implements java.util.concurrent.ConcurrentMap.remove.

Doc from java.util.concurrent.ConcurrentMap.remove.

Removes the entry for a key only if currently mapped to a given value. This is equivalent to, for this map: 

 if (map.containsKey(key)
    && Objects.equals(map.get(key), value)) {
  map.remove(key);
  return true;
} else {
  return false;
}
except that the action is performed atomically.
Parameters
key:Object

key with which the specified value is associated

value:Object

value expected to be associated with the specified key

Returns:boolean

true if the value was removed

Annotations
@Override
replaceback to summary
public boolean replace(K key, V oldValue, V newValue)

Overrides default java.util.Map.replace.

Implements java.util.concurrent.ConcurrentMap.replace.

Doc from java.util.concurrent.ConcurrentMap.replace.

Replaces the entry for a key only if currently mapped to a given value. This is equivalent to, for this map: 

 if (map.containsKey(key)
    && Objects.equals(map.get(key), oldValue)) {
  map.put(key, newValue);
  return true;
} else {
  return false;
}
except that the action is performed atomically.
Parameters
key:K

key with which the specified value is associated

oldValue:V

value expected to be associated with the specified key

newValue:V

value to be associated with the specified key

Returns:boolean

true if the value was replaced

Annotations
@Override
replaceback to summary
public V replace(K key, V value)

Overrides default java.util.Map.replace.

Implements java.util.concurrent.ConcurrentMap.replace.

Doc from java.util.concurrent.ConcurrentMap.replace.

Replaces the entry for a key only if currently mapped to some value. This is equivalent to, for this map: 

 if (map.containsKey(key))
  return map.put(key, value);
else
  return null;
except that the action is performed atomically.
Parameters
key:K

key with which the specified value is associated

value:V

value to be associated with the specified key

Returns:V

the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)

Annotations
@Override
sizeback to summary
public int size()

Overrides java.util.AbstractMap.size.

Implements java.util.Map.size.

Doc from java.util.Map.size.

Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Returns:int

the number of key-value mappings in this map

Annotations
@Override
valuesback to summary
public Collection<V> values()

Overrides java.util.AbstractMap.values.

Implements java.util.Map.values.

Doc from java.util.Map.values.

Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. If the map is modified while an iteration over the collection is in progress (except through the iterator's own remove operation), the results of the iteration are undefined. The collection supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Collection.remove, removeAll, retainAll and clear operations. It does not support the add or addAll operations.

Returns:Collection<V>

a collection view of the values contained in this map

Annotations
@Override
org.apache.tomcat.util.collections back to summary

private Class ManagedConcurrentWeakHashMap.Key

extends WeakReference<Object>
Class Inheritance

Field Summary

Modifier and TypeField and Description
private boolean
dead

private final int
hash

Constructor Summary

AccessConstructor and Description
pack-priv
Key(Object key, ReferenceQueue<Object> queue)

Method Summary

Modifier and TypeMethod and Description
public void
ackDeath()

public boolean
equals(Object
the reference object with which to compare.
obj)

Overrides java.lang.Object.equals.

Indicates whether some other object is "equal to" this one.

public int
hashCode()

Overrides java.lang.Object.hashCode.

Returns a hash code value for this object.

public boolean
isDead()

Field Detail

deadback to summary
private boolean dead
hashback to summary
private final int hash

Constructor Detail

Keyback to summary
pack-priv Key(Object key, ReferenceQueue<Object> queue)

Method Detail

ackDeathback to summary
public void ackDeath()
equalsback to summary
public boolean equals(Object obj)

Overrides java.lang.Object.equals.

Doc from java.lang.Object.equals.

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

  • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
  • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
  • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
  • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
  • For any non-null reference value x, x.equals(null) should return false.

An equivalence relation partitions the elements it operates on into equivalence classes; all the members of an equivalence class are equal to each other. Members of an equivalence class are substitutable for each other, at least for some purposes.

Parameters
obj:Object

the reference object with which to compare.

Returns:boolean

true if this object is the same as the obj argument; false otherwise.

Annotations
@Override
hashCodeback to summary
public int hashCode()

Overrides java.lang.Object.hashCode.

Doc from java.lang.Object.hashCode.

Returns a hash code value for this object. This method is supported for the benefit of hash tables such as those provided by java.util.HashMap.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
Returns:int

a hash code value for this object

Annotations
@Override
isDeadback to summary
public boolean isDead()