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Java > Open Source Codes > org > archive > util > PatternMatcherRecycler


1 /* PatternMatcherRecycler
2 *
3 * $Id: PatternMatcherRecycler.java,v 1.1.20.1 2007/01/13 01:31:40 stack-sf Exp $
4 *
5 * Created on Dec 21, 2004
6 *
7 * Copyright (C) 2004 Internet Archive.
8 *
9 * This file is part of the Heritrix web crawler (crawler.archive.org).
10 *
11 * Heritrix is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU Lesser Public License as published by
13 * the Free Software Foundation; either version 2.1 of the License, or
14 * any later version.
15 *
16 * Heritrix is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU Lesser Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser Public License
22 * along with Heritrix; if not, write to the Free Software
23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 */
25 package org.archive.util;
26
27 import java.util.EmptyStackException JavaDoc;
28 import java.util.Stack JavaDoc;
29 import java.util.regex.Matcher JavaDoc;
30 import java.util.regex.Pattern JavaDoc;
31
32 /**
33  * Utility class to retain a compiled Pattern and multiple corresponding
34  * Matcher instances for reuse.
35  *
36  * @author gojomo
37  */
38 public class PatternMatcherRecycler {
39     /**
40      * Upper-bound on Matcher Stacks.
41      * Profiling has the size of these Stacks tending upward over
42      * the life of a crawl. TODO: do something better than an
43      * a coarse upperbound; do something that can get GC'd in
44      * low-memory conditions.
45      */
46     private final static int MAXIMUM_STACK_SIZE = 10;
47     
48     private Pattern JavaDoc pattern;
49     private Stack JavaDoc<Matcher JavaDoc> matchers;
50
51     public PatternMatcherRecycler(Pattern JavaDoc p) {
52         this.pattern = p;
53         this.matchers = new Stack JavaDoc<Matcher JavaDoc>();
54     }
55
56     public Pattern JavaDoc getPattern() {
57         return this.pattern;
58     }
59
60     /**
61      * Get a Matcher for the internal Pattern, against the given
62      * input sequence. Reuse an old Matcher if possible, otherwise
63      * create a new one.
64      *
65      * @param input CharSequence to match
66      * @return Matcher set against the the input sequence
67      */
68     public Matcher JavaDoc getMatcher(CharSequence JavaDoc input) {
69         if (input == null) {
70             throw new IllegalArgumentException JavaDoc("CharSequence 'input' must not be null");
71         }
72         try {
73             return ((Matcher JavaDoc)matchers.pop()).reset(input);
74         } catch (EmptyStackException JavaDoc e) {
75             return this.pattern.matcher(input);
76         }
77     }
78     
79     /**
80      * Return the given Matcher to the reuse stack, if stack is
81      * not already at its maximum size.
82      *
83      * @param m the Matcher to save for reuse
84      */
85     public void freeMatcher(Matcher JavaDoc m) {
86         if(this.matchers.size() < MAXIMUM_STACK_SIZE) {
87             matchers.push(m);
88         }
89     }
90 }
91
92
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