ImmutableTimeStampedCache.java
/* Contributed in the public domain.
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS 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.orekit.utils;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.stream.Stream;
import org.hipparchus.exception.LocalizedCoreFormats;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitIllegalArgumentException;
import org.orekit.errors.OrekitIllegalStateException;
import org.orekit.errors.OrekitMessages;
import org.orekit.errors.TimeStampedCacheException;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.ChronologicalComparator;
import org.orekit.time.TimeStamped;
/**
* A cache of {@link TimeStamped} data that provides concurrency through
* immutability. This strategy is suitable when all of the cached data is stored
* in memory. (For example, {@link org.orekit.time.UTCScale UTCScale}) This
* class then provides convenient methods for accessing the data.
*
* @author Evan Ward
* @param <T> the type of data
*/
public class ImmutableTimeStampedCache<T extends TimeStamped>
implements TimeStampedCache<T> {
/**
* An empty immutable cache that always throws an exception on attempted
* access.
*/
@SuppressWarnings("rawtypes")
private static final ImmutableTimeStampedCache EMPTY_CACHE =
new EmptyTimeStampedCache<>();
/**
* the cached data. Be careful not to modify it after the constructor, or
* return a reference that allows mutating this list.
*/
private final List<T> data;
/**
* the maximum size list to return from {@link #getNeighbors(AbsoluteDate, int)}.
* @since 12.0
*/
private final int maxNeighborsSize;
/**
* Create a new cache with the given neighbors size and data.
*
* @param maxNeighborsSize the maximum size of the list returned from
* {@link #getNeighbors(AbsoluteDate, int)}. Must be less than or equal to
* {@code data.size()}.
* @param data the backing data for this cache. The list will be copied to
* ensure immutability. To guarantee immutability the entries in
* {@code data} must be immutable themselves. There must be more data
* than {@code maxNeighborsSize}.
* @throws IllegalArgumentException if {@code neightborsSize > data.size()}
* or if {@code neighborsSize} is negative
*/
public ImmutableTimeStampedCache(final int maxNeighborsSize,
final Collection<? extends T> data) {
// parameter check
if (maxNeighborsSize > data.size()) {
throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_CACHED_NEIGHBORS,
data.size(), maxNeighborsSize);
}
if (maxNeighborsSize < 1) {
throw new OrekitIllegalArgumentException(LocalizedCoreFormats.NUMBER_TOO_SMALL,
maxNeighborsSize, 1);
}
// assign instance variables
this.maxNeighborsSize = maxNeighborsSize;
// sort and copy data first
this.data = new ArrayList<>(data);
this.data.sort(new ChronologicalComparator());
}
/**
* private constructor for {@link #EMPTY_CACHE}.
*/
private ImmutableTimeStampedCache() {
this.data = null;
this.maxNeighborsSize = 0;
}
/** {@inheritDoc} */
public Stream<T> getNeighbors(final AbsoluteDate central, final int n) {
if (n > maxNeighborsSize) {
throw new OrekitException(OrekitMessages.NOT_ENOUGH_DATA, maxNeighborsSize);
}
return new SortedListTrimmer(n).getNeighborsSubList(central, data).stream();
}
/** {@inheritDoc} */
public int getMaxNeighborsSize() {
return maxNeighborsSize;
}
/** {@inheritDoc} */
public T getEarliest() {
return this.data.get(0);
}
/** {@inheritDoc} */
public T getLatest() {
return this.data.get(this.data.size() - 1);
}
/**
* Get all of the data in this cache.
*
* @return a sorted collection of all data passed in the
* {@link #ImmutableTimeStampedCache(int, Collection) constructor}.
*/
public List<T> getAll() {
return Collections.unmodifiableList(this.data);
}
/** {@inheritDoc} */
@Override
public String toString() {
return "Immutable cache with " + this.data.size() + " entries";
}
/**
* An empty immutable cache that always throws an exception on attempted
* access.
*/
private static class EmptyTimeStampedCache<T extends TimeStamped> extends ImmutableTimeStampedCache<T> {
/** {@inheritDoc} */
@Override
public Stream<T> getNeighbors(final AbsoluteDate central) {
throw new TimeStampedCacheException(OrekitMessages.NO_CACHED_ENTRIES);
}
/** {@inheritDoc} */
@Override
public int getMaxNeighborsSize() {
return 0;
}
/** {@inheritDoc} */
@Override
public T getEarliest() {
throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
}
/** {@inheritDoc} */
@Override
public T getLatest() {
throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
}
/** {@inheritDoc} */
@Override
public List<T> getAll() {
return Collections.emptyList();
}
/** {@inheritDoc} */
@Override
public String toString() {
return "Empty immutable cache";
}
}
/**
* Get an empty immutable cache, cast to the correct type.
* @param <TS> the type of data
* @return an empty {@link ImmutableTimeStampedCache}.
*/
@SuppressWarnings("unchecked")
public static <TS extends TimeStamped> ImmutableTimeStampedCache<TS> emptyCache() {
return (ImmutableTimeStampedCache<TS>) EMPTY_CACHE;
}
}