1   package org.apache.bcel.verifier;
2   
3   /* ====================================================================
4    * The Apache Software License, Version 1.1
5    *
6    * Copyright (c) 2001 The Apache Software Foundation.  All rights
7    * reserved.
8    *
9    * Redistribution and use in source and binary forms, with or without
10   * modification, are permitted provided that the following conditions
11   * are met:
12   *
13   * 1. Redistributions of source code must retain the above copyright
14   *    notice, this list of conditions and the following disclaimer.
15   *
16   * 2. Redistributions in binary form must reproduce the above copyright
17   *    notice, this list of conditions and the following disclaimer in
18   *    the documentation and/or other materials provided with the
19   *    distribution.
20   *
21   * 3. The end-user documentation included with the redistribution,
22   *    if any, must include the following acknowledgment:
23   *       "This product includes software developed by the
24   *        Apache Software Foundation (http://www.apache.org/)."
25   *    Alternately, this acknowledgment may appear in the software itself,
26   *    if and wherever such third-party acknowledgments normally appear.
27   *
28   * 4. The names "Apache" and "Apache Software Foundation" and
29   *    "Apache BCEL" must not be used to endorse or promote products
30   *    derived from this software without prior written permission. For
31   *    written permission, please contact apache@apache.org.
32   *
33   * 5. Products derived from this software may not be called "Apache",
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35   *    prior written permission of the Apache Software Foundation.
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50   *
51   * This software consists of voluntary contributions made by many
52   * individuals on behalf of the Apache Software Foundation.  For more
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55   */
56  
57  import java.util.ArrayList;
58  
59  /***
60   * A PassVerifier actually verifies a class file; it is instantiated
61   * by a Verifier.
62   * The verification should conform with a certain pass as described
63   * in The Java Virtual Machine Specification, 2nd edition.
64   * This book describes four passes. Pass one means loading the
65   * class and verifying a few static constraints. Pass two actually
66   * verifies some other constraints that could enforce loading in
67   * referenced class files. Pass three is the first pass that actually
68   * checks constraints in the code array of a method in the class file;
69   * it has two parts with the first verifying static constraints and
70   * the second part verifying structural constraints (where a data flow
71   * analysis is used for). The fourth pass, finally, performs checks
72   * that can only be done at run-time.
73   * JustIce does not have a run-time pass, but certain constraints that
74   * are usually delayed until run-time for performance reasons are also
75   * checked during the second part of pass three.
76   * PassVerifier instances perform caching.
77   * That means, if you really want a new verification run of a certain
78   * pass you must use a new instance of a given PassVerifier.
79   *
80   * @version $Id: PassVerifier.java,v 1.1.1.1 2001/10/29 20:00:31 jvanzyl Exp $
81   * @author <A HREF="http://www.inf.fu-berlin.de/~ehaase"/>Enver Haase</A>
82   * @see org.apache.bcel.verifier.Verifier
83   * @see #verify()
84   */
85  public abstract class PassVerifier{
86  
87  	/*** The (warning) messages. */
88  	private ArrayList messages = new ArrayList(); //Type of elements: String
89  	
90  	/*** The VerificationResult cache. */
91  	private VerificationResult verificationResult = null;
92  
93  	/***
94  	 * This method runs a verification pass conforming to the
95  	 * Java Virtual Machine Specification, 2nd edition, on a
96  	 * class file.
97  	 * PassVerifier instances perform caching;
98  	 * i.e. if the verify() method once determined a VerificationResult,
99  	 * then this result may be returned after every invocation of this
100 	 * method instead of running the verification pass anew; likewise with
101 	 * the result of getMessages().
102 	 *
103 	 * @see #getMessages()
104 	 * @see #addMessage(String)
105 	 */
106 	public VerificationResult verify(){
107 		if (verificationResult == null){
108 			verificationResult = do_verify();
109 		}
110 		return verificationResult;
111 	}
112 
113 	/*** Does the real verification work, uncached. */
114 	public abstract VerificationResult do_verify();
115 
116 	/***
117 	 * This method adds a (warning) message to the message pool of this
118 	 * PassVerifier. This method is normally only internally used by
119 	 * BCEL's class file verifier "JustIce" and should not be used from
120 	 * the outside. 
121 	 *
122 	 * @see #getMessages()
123 	 */
124 	public void addMessage(String message){
125 		messages.add(message);
126 	}
127 
128 	/***
129 	 * Returns the (warning) messages that this PassVerifier accumulated
130 	 * during its do_verify()ing work.
131 	 *
132 	 * @see #addMessage(String)
133 	 * @see #do_verify()
134 	 */
135 	public String[] getMessages(){
136 		verify(); // create messages if not already done (cached!)
137 		String[] ret = new String[messages.size()];
138 		for (int i=0; i<messages.size(); i++){
139 			ret[i] = (String) messages.get(i);
140 		}
141 		return ret;
142 	}
143 }
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