Java tutorial
/* * 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.cassandra.db.lifecycle; import java.util.*; import com.google.common.base.Predicate; import com.google.common.collect.*; import org.apache.cassandra.io.sstable.format.SSTableReader; import static com.google.common.base.Predicates.*; import static com.google.common.collect.Iterables.any; import static com.google.common.collect.Iterables.concat; import static com.google.common.collect.Iterables.filter; import static com.google.common.collect.Iterables.getFirst; import static org.apache.cassandra.utils.Throwables.merge; class Helpers { /** * update the contents of a set with the provided sets, ensuring that the items to remove are * really present, and that the items to add are not (unless we're also removing them) * @return a new set with the contents of the provided one modified */ static <T> Set<T> replace(Set<T> original, Set<T> remove, Iterable<T> add) { return ImmutableSet.copyOf(replace(identityMap(original), remove, add).keySet()); } /** * update the contents of an "identity map" with the provided sets, ensuring that the items to remove are * really present, and that the items to add are not (unless we're also removing them) * @return a new identity map with the contents of the provided one modified */ static <T> Map<T, T> replace(Map<T, T> original, Set<T> remove, Iterable<T> add) { // ensure the ones being removed are the exact same ones present for (T reader : remove) assert original.get(reader) == reader; // ensure we don't already contain any we're adding, that we aren't also removing assert !any(add, and(not(in(remove)), in(original.keySet()))) : String .format("original:%s remove:%s add:%s", original.keySet(), remove, add); Map<T, T> result = identityMap(concat(add, filter(original.keySet(), not(in(remove))))); assert result.size() == original.size() - remove.size() + Iterables.size(add) : String.format( "Expecting new size of %d, got %d while replacing %s by %s in %s", original.size() - remove.size() + Iterables.size(add), result.size(), remove, add, original.keySet()); return result; } /** * A convenience method for encapsulating this action over multiple SSTableReader with exception-safety * @return accumulate if not null (with any thrown exception attached), or any thrown exception otherwise */ static Throwable setReplaced(Iterable<SSTableReader> readers, Throwable accumulate) { for (SSTableReader reader : readers) { try { reader.setReplaced(); } catch (Throwable t) { accumulate = merge(accumulate, t); } } return accumulate; } /** * A convenience method for encapsulating this action over multiple SSTableReader with exception-safety * @return accumulate if not null (with any thrown exception attached), or any thrown exception otherwise */ static void setupKeycache(Iterable<SSTableReader> readers) { for (SSTableReader reader : readers) reader.setupKeyCache(); } /** * assert that none of these readers have been replaced */ static void checkNotReplaced(Iterable<SSTableReader> readers) { for (SSTableReader reader : readers) assert !reader.isReplaced(); } /** * A convenience method for encapsulating this action over multiple SSTableReader with exception-safety * @return accumulate if not null (with any thrown exception attached), or any thrown exception otherwise */ static Throwable markObsolete(Tracker tracker, Iterable<SSTableReader> readers, Throwable accumulate) { for (SSTableReader reader : readers) { try { boolean firstToCompact = reader.markObsolete(tracker); assert firstToCompact : reader + " was already marked compacted"; } catch (Throwable t) { accumulate = merge(accumulate, t); } } return accumulate; } /** * @return the identity function, as a Map, with domain of the provided values */ static <T> Map<T, T> identityMap(Iterable<T> values) { ImmutableMap.Builder<T, T> builder = ImmutableMap.<T, T>builder(); for (T t : values) builder.put(t, t); return builder.build(); } /** * @return an Iterable of the union if the sets, with duplicates being represented by their first encountered instance * (as defined by the order of set provision) */ static <T> Iterable<T> concatUniq(Set<T>... sets) { List<Predicate<T>> notIn = new ArrayList<>(sets.length); for (Set<T> set : sets) notIn.add(not(in(set))); List<Iterable<T>> results = new ArrayList<>(sets.length); for (int i = 0; i < sets.length; i++) results.add(filter(sets[i], and(notIn.subList(0, i)))); return concat(results); } /** * @return a Predicate yielding true for an item present in NONE of the provided sets */ static <T> Predicate<T> notIn(Set<T>... sets) { return not(orIn(sets)); } /** * @return a Predicate yielding true for an item present in ANY of the provided sets */ static <T> Predicate<T> orIn(Collection<T>... sets) { Predicate<T>[] orIn = new Predicate[sets.length]; for (int i = 0; i < orIn.length; i++) orIn[i] = in(sets[i]); return or(orIn); } /** * filter out (i.e. remove) matching elements * @return filter, filtered to only those elements that *are not* present in *any* of the provided sets (are present in none) */ static <T> Iterable<T> filterOut(Iterable<T> filter, Set<T>... inNone) { return filter(filter, notIn(inNone)); } /** * filter in (i.e. retain) * * @return filter, filtered to only those elements that *are* present in *any* of the provided sets */ static <T> Iterable<T> filterIn(Iterable<T> filter, Set<T>... inAny) { return filter(filter, orIn(inAny)); } static Set<SSTableReader> emptySet() { return Collections.emptySet(); } static <T> T select(T t, Collection<T> col) { if (col instanceof Set && !col.contains(t)) return null; return getFirst(filter(col, equalTo(t)), null); } static <T> T selectFirst(T t, Collection<T>... sets) { for (Collection<T> set : sets) { T select = select(t, set); if (select != null) return select; } return null; } static <T> Predicate<T> idIn(Set<T> set) { return idIn(identityMap(set)); } static <T> Predicate<T> idIn(final Map<T, T> identityMap) { return new Predicate<T>() { public boolean apply(T t) { return identityMap.get(t) == t; } }; } }