org.apache.commons.collections4.map.PassiveExpiringMap Maven / Gradle / Ivy
Show all versions of commons-collections4 Show documentation
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.collections4.map;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;
/**
* Decorates a Map to evict expired entries once their expiration
* time has been reached.
*
* When putting a key-value pair in the map this decorator uses a
* {@link ExpirationPolicy} to determine how long the entry should remain alive
* as defined by an expiration time value.
*
*
* When accessing the mapped value for a key, its expiration time is checked,
* and if it is a negative value or if it is greater than the current time, the
* mapped value is returned. Otherwise, the key is removed from the decorated
* map, and null is returned.
*
*
* When invoking methods that involve accessing the entire map contents (i.e
* {@link #containsKey(Object)}, {@link #entrySet()}, etc.) this decorator
* removes all expired entries prior to actually completing the invocation.
*
*
* Note that {@link PassiveExpiringMap} is not synchronized and is not
* thread-safe. If you wish to use this map from multiple threads
* concurrently, you must use appropriate synchronization. The simplest approach
* is to wrap this map using {@link java.util.Collections#synchronizedMap(Map)}.
* This class may throw exceptions when accessed by concurrent threads without
* synchronization.
*
*
* @param the type of the keys in this map
* @param the type of the values in this map
* @since 4.0
*/
public class PassiveExpiringMap
extends AbstractMapDecorator
implements Serializable {
/**
* A {@link org.apache.commons.collections4.map.PassiveExpiringMap.ExpirationPolicy ExpirationPolicy}
* that returns a expiration time that is a
* constant about of time in the future from the current time.
*
* @param the type of the keys in the map
* @param the type of the values in the map
* @since 4.0
*/
public static class ConstantTimeToLiveExpirationPolicy
implements ExpirationPolicy {
/** Serialization version */
private static final long serialVersionUID = 1L;
/** the constant time-to-live value measured in milliseconds. */
private final long timeToLiveMillis;
/**
* Default constructor. Constructs a policy using a negative
* time-to-live value that results in entries never expiring.
*/
public ConstantTimeToLiveExpirationPolicy() {
this(-1L);
}
/**
* Construct a policy with the given time-to-live constant measured in
* milliseconds. A negative time-to-live value indicates entries never
* expire. A zero time-to-live value indicates entries expire (nearly)
* immediately.
*
* @param timeToLiveMillis the constant amount of time (in milliseconds)
* an entry is available before it expires. A negative value
* results in entries that NEVER expire. A zero value results in
* entries that ALWAYS expire.
*/
public ConstantTimeToLiveExpirationPolicy(final long timeToLiveMillis) {
super();
this.timeToLiveMillis = timeToLiveMillis;
}
/**
* Construct a policy with the given time-to-live constant measured in
* the given time unit of measure.
*
* @param timeToLive the constant amount of time an entry is available
* before it expires. A negative value results in entries that
* NEVER expire. A zero value results in entries that ALWAYS
* expire.
* @param timeUnit the unit of time for the timeToLive
* parameter, must not be null.
* @throws NullPointerException if the time unit is null.
*/
public ConstantTimeToLiveExpirationPolicy(final long timeToLive,
final TimeUnit timeUnit) {
this(validateAndConvertToMillis(timeToLive, timeUnit));
}
/**
* Determine the expiration time for the given key-value entry.
*
* @param key the key for the entry (ignored).
* @param value the value for the entry (ignored).
* @return if {@link #timeToLiveMillis} ≥ 0, an expiration time of
* {@link #timeToLiveMillis} +
* {@link System#currentTimeMillis()} is returned. Otherwise, -1
* is returned indicating the entry never expires.
*/
@Override
public long expirationTime(final K key, final V value) {
if (timeToLiveMillis >= 0L) {
// avoid numerical overflow
final long now = System.currentTimeMillis();
if (now > Long.MAX_VALUE - timeToLiveMillis) {
// expiration would be greater than Long.MAX_VALUE
// never expire
return -1;
}
// timeToLiveMillis in the future
return now + timeToLiveMillis;
}
// never expire
return -1L;
}
}
/**
* A policy to determine the expiration time for key-value entries.
*
* @param the key object type.
* @param the value object type
* @since 4.0
*/
public interface ExpirationPolicy
extends Serializable {
/**
* Determine the expiration time for the given key-value entry.
*
* @param key the key for the entry.
* @param value the value for the entry.
* @return the expiration time value measured in milliseconds. A
* negative return value indicates the entry never expires.
*/
long expirationTime(K key, V value);
}
/** Serialization version */
private static final long serialVersionUID = 1L;
/**
* First validate the input parameters. If the parameters are valid, convert
* the given time measured in the given units to the same time measured in
* milliseconds.
*
* @param timeToLive the constant amount of time an entry is available
* before it expires. A negative value results in entries that NEVER
* expire. A zero value results in entries that ALWAYS expire.
* @param timeUnit the unit of time for the timeToLive
* parameter, must not be null.
* @throws NullPointerException if the time unit is null.
*/
private static long validateAndConvertToMillis(final long timeToLive,
final TimeUnit timeUnit) {
if (timeUnit == null) {
throw new NullPointerException("Time unit must not be null");
}
return TimeUnit.MILLISECONDS.convert(timeToLive, timeUnit);
}
/** map used to manage expiration times for the actual map entries. */
private final Map expirationMap = new HashMap<>();
/** the policy used to determine time-to-live values for map entries. */
private final ExpirationPolicy expiringPolicy;
/**
* Default constructor. Constructs a map decorator that results in entries
* NEVER expiring.
*/
public PassiveExpiringMap() {
this(-1L);
}
/**
* Construct a map decorator using the given expiration policy to determine
* expiration times.
*
* @param expiringPolicy the policy used to determine expiration times of
* entries as they are added.
* @throws NullPointerException if expiringPolicy is null
*/
public PassiveExpiringMap(final ExpirationPolicy expiringPolicy) {
this(expiringPolicy, new HashMap());
}
/**
* Construct a map decorator that decorates the given map and uses the given
* expiration policy to determine expiration times. If there are any
* elements already in the map being decorated, they will NEVER expire
* unless they are replaced.
*
* @param expiringPolicy the policy used to determine expiration times of
* entries as they are added.
* @param map the map to decorate, must not be null.
* @throws NullPointerException if the map or expiringPolicy is null.
*/
public PassiveExpiringMap(final ExpirationPolicy expiringPolicy,
final Map map) {
super(map);
if (expiringPolicy == null) {
throw new NullPointerException("Policy must not be null.");
}
this.expiringPolicy = expiringPolicy;
}
/**
* Construct a map decorator that decorates the given map using the given
* time-to-live value measured in milliseconds to create and use a
* {@link ConstantTimeToLiveExpirationPolicy} expiration policy.
*
* @param timeToLiveMillis the constant amount of time (in milliseconds) an
* entry is available before it expires. A negative value results in
* entries that NEVER expire. A zero value results in entries that
* ALWAYS expire.
*/
public PassiveExpiringMap(final long timeToLiveMillis) {
this(new ConstantTimeToLiveExpirationPolicy(timeToLiveMillis),
new HashMap());
}
/**
* Construct a map decorator using the given time-to-live value measured in
* milliseconds to create and use a
* {@link ConstantTimeToLiveExpirationPolicy} expiration policy. If there
* are any elements already in the map being decorated, they will NEVER
* expire unless they are replaced.
*
* @param timeToLiveMillis the constant amount of time (in milliseconds) an
* entry is available before it expires. A negative value results in
* entries that NEVER expire. A zero value results in entries that
* ALWAYS expire.
* @param map the map to decorate, must not be null.
* @throws NullPointerException if the map is null.
*/
public PassiveExpiringMap(final long timeToLiveMillis, final Map map) {
this(new ConstantTimeToLiveExpirationPolicy(timeToLiveMillis),
map);
}
/**
* Construct a map decorator using the given time-to-live value measured in
* the given time units of measure to create and use a
* {@link ConstantTimeToLiveExpirationPolicy} expiration policy.
*
* @param timeToLive the constant amount of time an entry is available
* before it expires. A negative value results in entries that NEVER
* expire. A zero value results in entries that ALWAYS expire.
* @param timeUnit the unit of time for the timeToLive
* parameter, must not be null.
* @throws NullPointerException if the time unit is null.
*/
public PassiveExpiringMap(final long timeToLive, final TimeUnit timeUnit) {
this(validateAndConvertToMillis(timeToLive, timeUnit));
}
/**
* Construct a map decorator that decorates the given map using the given
* time-to-live value measured in the given time units of measure to create
* {@link ConstantTimeToLiveExpirationPolicy} expiration policy. This policy
* is used to determine expiration times. If there are any elements already
* in the map being decorated, they will NEVER expire unless they are
* replaced.
*
* @param timeToLive the constant amount of time an entry is available
* before it expires. A negative value results in entries that NEVER
* expire. A zero value results in entries that ALWAYS expire.
* @param timeUnit the unit of time for the timeToLive
* parameter, must not be null.
* @param map the map to decorate, must not be null.
* @throws NullPointerException if the map or time unit is null.
*/
public PassiveExpiringMap(final long timeToLive, final TimeUnit timeUnit, final Map map) {
this(validateAndConvertToMillis(timeToLive, timeUnit), map);
}
/**
* Constructs a map decorator that decorates the given map and results in
* entries NEVER expiring. If there are any elements already in the map
* being decorated, they also will NEVER expire.
*
* @param map the map to decorate, must not be null.
* @throws NullPointerException if the map is null.
*/
public PassiveExpiringMap(final Map map) {
this(-1L, map);
}
/**
* Normal {@link Map#clear()} behavior with the addition of clearing all
* expiration entries as well.
*/
@Override
public void clear() {
super.clear();
expirationMap.clear();
}
/**
* All expired entries are removed from the map prior to determining the
* contains result.
* {@inheritDoc}
*/
@Override
public boolean containsKey(final Object key) {
removeIfExpired(key, now());
return super.containsKey(key);
}
/**
* All expired entries are removed from the map prior to determining the
* contains result.
* {@inheritDoc}
*/
@Override
public boolean containsValue(final Object value) {
removeAllExpired(now());
return super.containsValue(value);
}
/**
* All expired entries are removed from the map prior to returning the entry set.
* {@inheritDoc}
*/
@Override
public Set> entrySet() {
removeAllExpired(now());
return super.entrySet();
}
/**
* All expired entries are removed from the map prior to returning the entry value.
* {@inheritDoc}
*/
@Override
public V get(final Object key) {
removeIfExpired(key, now());
return super.get(key);
}
/**
* All expired entries are removed from the map prior to determining if it is empty.
* {@inheritDoc}
*/
@Override
public boolean isEmpty() {
removeAllExpired(now());
return super.isEmpty();
}
/**
* Determines if the given expiration time is less than now.
*
* @param now the time in milliseconds used to compare against the
* expiration time.
* @param expirationTimeObject the expiration time value retrieved from
* {@link #expirationMap}, can be null.
* @return true if expirationTimeObject is ≥ 0
* and expirationTimeObject < now.
* false otherwise.
*/
private boolean isExpired(final long now, final Long expirationTimeObject) {
if (expirationTimeObject != null) {
final long expirationTime = expirationTimeObject.longValue();
return expirationTime >= 0 && now >= expirationTime;
}
return false;
}
/**
* All expired entries are removed from the map prior to returning the key set.
* {@inheritDoc}
*/
@Override
public Set keySet() {
removeAllExpired(now());
return super.keySet();
}
/**
* The current time in milliseconds.
*/
private long now() {
return System.currentTimeMillis();
}
/**
* Add the given key-value pair to this map as well as recording the entry's expiration time based on
* the current time in milliseconds and this map's {@link #expiringPolicy}.
*
* {@inheritDoc}
*/
@Override
public V put(final K key, final V value) {
// record expiration time of new entry
final long expirationTime = expiringPolicy.expirationTime(key, value);
expirationMap.put(key, Long.valueOf(expirationTime));
return super.put(key, value);
}
@Override
public void putAll(final Map mapToCopy) {
for (final Map.Entry entry : mapToCopy.entrySet()) {
put(entry.getKey(), entry.getValue());
}
}
/**
* Normal {@link Map#remove(Object)} behavior with the addition of removing
* any expiration entry as well.
* {@inheritDoc}
*/
@Override
public V remove(final Object key) {
expirationMap.remove(key);
return super.remove(key);
}
/**
* Removes all entries in the map whose expiration time is less than
* now. The exceptions are entries with negative expiration
* times; those entries are never removed.
*
* @see #isExpired(long, Long)
*/
private void removeAllExpired(final long now) {
final Iterator> iter = expirationMap.entrySet().iterator();
while (iter.hasNext()) {
final Map.Entry expirationEntry = iter.next();
if (isExpired(now, expirationEntry.getValue())) {
// remove entry from collection
super.remove(expirationEntry.getKey());
// remove entry from expiration map
iter.remove();
}
}
}
/**
* Removes the entry with the given key if the entry's expiration time is
* less than now. If the entry has a negative expiration time,
* the entry is never removed.
*/
private void removeIfExpired(final Object key, final long now) {
final Long expirationTimeObject = expirationMap.get(key);
if (isExpired(now, expirationTimeObject)) {
remove(key);
}
}
/**
* All expired entries are removed from the map prior to returning the size.
* {@inheritDoc}
*/
@Override
public int size() {
removeAllExpired(now());
return super.size();
}
/**
* Read the map in using a custom routine.
*
* @param in the input stream
* @throws IOException if an error occurs while reading from the stream
* @throws ClassNotFoundException if an object read from the stream can not be loaded
*/
@SuppressWarnings("unchecked")
// (1) should only fail if input stream is incorrect
private void readObject(final ObjectInputStream in)
throws IOException, ClassNotFoundException {
in.defaultReadObject();
map = (Map) in.readObject(); // (1)
}
/**
* Write the map out using a custom routine.
*
* @param out the output stream
* @throws IOException if an error occurs while writing to the stream
*/
private void writeObject(final ObjectOutputStream out)
throws IOException {
out.defaultWriteObject();
out.writeObject(map);
}
/**
* All expired entries are removed from the map prior to returning the value collection.
* {@inheritDoc}
*/
@Override
public Collection values() {
removeAllExpired(now());
return super.values();
}
}