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1   /* DecideRule
2   *
3   * $Id: DecideRule.java 5010 2007-03-16 15:50:55Z Gojomo $
4   *
5   * Created on Mar 3, 2005
6   *
7   * Copyright (C) 2005 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.crawler.deciderules;
26  
27  import org.archive.crawler.framework.CrawlController;
28  import org.archive.crawler.settings.ModuleType;
29  
30  
31  /***
32   * Interface for rules which, given an object to evaluate,
33   * respond with a decision: {@link DecideRule#ACCEPT}, 
34   * {@link DecideRule#REJECT}, or 
35   * {@link DecideRule#PASS}.
36   * 
37   * Rules return {@link #PASS} by default.
38   *
39   * @author gojomo
40   * @see org.archive.crawler.deciderules.DecideRuleSequence
41   */
42  public class DecideRule extends ModuleType {
43  
44      private static final long serialVersionUID = 3437522810581532520L;
45      // enumeration of 'actions'
46      public static final String ACCEPT = "ACCEPT".intern();
47      public static final String REJECT = "REJECT".intern();
48      public static final String PASS = "PASS".intern();
49  
50      /***
51       * Constructor.
52       * @param name Name of this rule.
53       */
54      public DecideRule(String name) {
55          super(name);
56      }
57  
58      /***
59       * Make decision on passed <code>object</code>.
60       * @param object Object to rule on.
61       * @return {@link #ACCEPT}, {@link #REJECT}, or {@link #PASS}.
62       */
63      public Object decisionFor(Object object) {
64          return PASS;
65      }
66  
67      /***
68       * If this rule is "one-way" -- can only return a single
69       * possible decision other than PASS -- return that 
70       * decision. Otherwise return null. Most rules will be
71       * one-way. 
72       * @param object 
73       * 
74       * @return the one decision other than PASS this rule might
75       * return, if there is only one
76       */
77      public Object singlePossibleNonPassDecision(Object object) {
78          // by default, don't assume one-way
79          return null;
80      }
81      
82      /***
83       * Respond to a settings update, refreshing any internal settings-derived
84       * state.
85       * 
86       * This method gives implementors a chance to refresh internal state
87       * after a settings change. Normally new settings are picked up w/o
88       * the need of work on the part of settings' clients but some facilities
89       * -- for example, Surt classes need to sort submissions into
90       * common-prefix-coalesced collection of Surt prefixes, or,
91       * settings changes that alter external file or seeds/directives
92       * references -- need to be flagged so they can take
93       * compensatory action. 
94       */
95      public void kickUpdate() {
96          // by default do nothing
97      }
98      
99      /*** 
100      * Get the controller object.
101      *
102      * @return the controller object.
103      */
104     public CrawlController getController() {
105         return getSettingsHandler().getOrder().getController();
106     }
107 }