org.apache.nutch.util.PrefixStringMatcher Maven / Gradle / Ivy
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* 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.nutch.util;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
/**
* A class for efficiently matching Strings against a set of
* prefixes.
*/
public class PrefixStringMatcher extends TrieStringMatcher {
/**
* Creates a new PrefixStringMatcher which will match
* Strings with any prefix in the supplied array. Zero-length
* Strings are ignored.
*/
public PrefixStringMatcher(String[] prefixes) {
super();
for (int i = 0; i < prefixes.length; i++)
addPatternForward(prefixes[i]);
}
/**
* Creates a new PrefixStringMatcher which will match
* Strings with any prefix in the supplied
* Collection.
*
* @throws ClassCastException
* if any Objects in the collection are not
* Strings
*/
public PrefixStringMatcher(Collection prefixes) {
super();
Iterator iter = prefixes.iterator();
while (iter.hasNext())
addPatternForward(iter.next());
}
/**
* Returns true if the given String is matched by a prefix in the
* trie
*/
public boolean matches(String input) {
TrieNode node = root;
for (int i = 0; i < input.length(); i++) {
node = node.getChild(input.charAt(i));
if (node == null)
return false;
if (node.isTerminal())
return true;
}
return false;
}
/**
* Returns the shortest prefix of input that is matched,
* or null if no match exists.
*/
public String shortestMatch(String input) {
TrieNode node = root;
for (int i = 0; i < input.length(); i++) {
node = node.getChild(input.charAt(i));
if (node == null)
return null;
if (node.isTerminal())
return input.substring(0, i + 1);
}
return null;
}
/**
* Returns the longest prefix of input that is matched,
* or null if no match exists.
*/
public String longestMatch(String input) {
TrieNode node = root;
String result = null;
for (int i = 0; i < input.length(); i++) {
node = node.getChild(input.charAt(i));
if (node == null)
break;
if (node.isTerminal())
result = input.substring(0, i + 1);
}
return result;
}
public static final void main(String[] argv) {
String[] prefixes = new String[] { "abcd", "abc", "aac", "baz", "foo",
"foobar" };
PrefixStringMatcher matcher = new PrefixStringMatcher(prefixes);
String[] tests = { "a", "ab", "abc", "abcdefg", "apple", "aa", "aac",
"aaccca", "abaz", "baz", "bazooka", "fo", "foobar", "kite", };
for (int i = 0; i < tests.length; i++) {
System.out.println("testing: " + tests[i]);
System.out.println(" matches: " + matcher.matches(tests[i]));
System.out.println(" shortest: " + matcher.shortestMatch(tests[i]));
System.out.println(" longest: " + matcher.longestMatch(tests[i]));
}
int iterations = 1000;
System.out.println("Testing thread-safety (NUTCH-2585) with " + iterations
+ " iterations:");
List testsList = Arrays.asList(tests);
for (int i = 0; i < iterations; i++) {
matcher = new PrefixStringMatcher(prefixes);
Collections.shuffle(testsList);
try {
long count = testsList.parallelStream().filter(matcher::matches).count();
System.out.print(String.format("Cycle %4d : %d matches\r", i, count));
} catch (Exception e) {
// flush output
System.out.println("");
throw e;
}
}
System.out.println("");
}
}