suffixstringmatcher.java

nutch0.8源码

/**
 * Copyright 2005 The Apache Software Foundation
 *
 * Licensed 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.Collection;
import java.util.Iterator;

/**
 * A class for efficiently matching <code>String</code>s against a set
 * of suffixes.  Zero-length <code>Strings</code> are ignored.
 */
public class SuffixStringMatcher extends TrieStringMatcher {

  /**
   * Creates a new <code>PrefixStringMatcher</code> which will match
   * <code>String</code>s with any suffix in the supplied array.
   */
  public SuffixStringMatcher(String[] suffixes) {
    super();
    for (int i= 0; i < suffixes.length; i++)
      addPatternBackward(suffixes[i]);
  }

  /**
   * Creates a new <code>PrefixStringMatcher</code> which will match
   * <code>String</code>s with any suffix in the supplied
   * <code>Collection</code>
   */
  public SuffixStringMatcher(Collection suffixes) {
    super();
    Iterator iter= suffixes.iterator();
    while (iter.hasNext())
      addPatternBackward((String)iter.next());
  }

  /**
   * Returns true if the given <code>String</code> is matched by a
   * suffix in the trie
   */
  public boolean matches(String input) {
    TrieNode node= root;
    for (int i= input.length() - 1; i >= 0; i--) {
      node= node.getChild(input.charAt(i));
      if (node == null) 
        return false;
      if (node.isTerminal())
        return true;
    }
    return false;
  }


  /**
   * Returns the shortest suffix of <code>input<code> that is matched,
   * or <code>null<code> if no match exists.
   */
  public String shortestMatch(String input) {
    TrieNode node= root;
    for (int i= input.length() - 1; i >= 0; i--) {
      node= node.getChild(input.charAt(i));
      if (node == null) 
        return null;
      if (node.isTerminal())
        return input.substring(i);
    }
    return null;
  }

  /**
   * Returns the longest suffix of <code>input<code> that is matched,
   * or <code>null<code> if no match exists.
   */
  public String longestMatch(String input) {
    TrieNode node= root;
    String result= null;
    for (int i= input.length() - 1; i >= 0; i--) {
      node= node.getChild(input.charAt(i));
      if (node == null) 
        break;
      if (node.isTerminal())
        result= input.substring(i);
    }
    return result;
  }

  public static final void main(String[] argv) {
    SuffixStringMatcher matcher= 
      new SuffixStringMatcher( 
        new String[] 
        {"a", "abcd", "bcd", "bcdefg", "defg", "aac", "baz", "foo", "foobar"} );

    String[] tests= {"a", "ac", "abcd", "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]));
    }
  }
}