org.archive.util.PrefixSet Maven / Gradle / Ivy
/*
* This file is part of the Heritrix web crawler (crawler.archive.org).
*
* Licensed to the Internet Archive (IA) by one or more individual
* contributors.
*
* The IA 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.archive.util;
import java.util.SortedSet;
import java.util.concurrent.ConcurrentSkipListSet;
/**
* Utility class for maintaining sorted set of string prefixes.
* Redundant prefixes are coalesced into the shorter prefix.
*/
public class PrefixSet extends ConcurrentSkipListSet {
private static final long serialVersionUID = -6054697706348411992L;
public PrefixSet() {
super();
}
/**
* Test whether the given String is prefixed by one
* of this set's entries.
*
* @param s
* @return True if contains prefix.
*/
public boolean containsPrefixOf(String s) {
SortedSet sub = headSet(s);
// because redundant prefixes have been eliminated,
// only a test against last item in headSet is necessary
if (!sub.isEmpty() && s.startsWith((String)sub.last())) {
return true; // prefix substring exists
} // else: might still exist exactly (headSet does not contain boundary)
return contains(s); // exact string exists, or no prefix is there
}
/**
* Maintains additional invariant: if one entry is a
* prefix of another, keep only the prefix.
*
* @see java.util.Collection#add(java.lang.Object)
*/
public boolean add(String s) {
SortedSet sub = headSet(s);
if (!sub.isEmpty() && s.startsWith((String)sub.last())) {
// no need to add; prefix is already present
return false;
}
boolean retVal = super.add(s);
sub = tailSet(s+"\0");
while(!sub.isEmpty() && ((String)sub.first()).startsWith(s)) {
// remove redundant entries
sub.remove(sub.first());
}
return retVal;
}
}