1   package org.apache.bcel.classfile;
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",
34   *    "Apache BCEL", nor may "Apache" appear in their name, without
35   *    prior written permission of the Apache Software Foundation.
36   *
37   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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39   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
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43   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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45   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48   * SUCH DAMAGE.
49   * ====================================================================
50   *
51   * This software consists of voluntary contributions made by many
52   * individuals on behalf of the Apache Software Foundation.  For more
53   * information on the Apache Software Foundation, please see
54   * <http://www.apache.org/>.
55   */
56  
57  import org.apache.bcel.Constants;
58  import java.io.*;
59  import java.util.HashMap;
60  
61  /***
62   * Abstract super class for <em>Attribute</em> objects. Currently the
63   * <em>ConstantValue</em>, <em>SourceFile</em>, <em>Code</em>,
64   * <em>Exceptiontable</em>, <em>LineNumberTable</em>, 
65   * <em>LocalVariableTable</em>, <em>InnerClasses</em> and
66   * <em>Synthetic</em> attributes are supported. The
67   * <em>Unknown</em> attribute stands for non-standard-attributes.
68   *
69   * @version $Id: Attribute.java,v 1.8 2002/07/11 19:39:04 mdahm Exp $
70   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
71   * @see     ConstantValue
72   * @see     SourceFile
73   * @see     Code
74   * @see     Unknown
75   * @see     ExceptionTable
76   * @see     LineNumberTable
77   * @see     LocalVariableTable 
78   * @see     InnerClasses
79   * @see     Synthetic
80   * @see     Deprecated
81   * @see     Signature
82  */
83  public abstract class Attribute implements Cloneable, Node, Serializable {
84    protected int          name_index; // Points to attribute name in constant pool
85    protected int          length;     // Content length of attribute field
86    protected byte         tag;        // Tag to distiguish subclasses
87    protected ConstantPool constant_pool;
88  
89    protected Attribute(byte tag, int name_index, int length,
90  		      ConstantPool constant_pool) {
91      this.tag           = tag;
92      this.name_index    = name_index;
93      this.length        = length;
94      this.constant_pool = constant_pool;
95    }
96  
97    /***
98     * Called by objects that are traversing the nodes of the tree implicitely
99     * defined by the contents of a Java class. I.e., the hierarchy of methods,
100    * fields, attributes, etc. spawns a tree of objects.
101    *
102    * @param v Visitor object
103    */
104   public abstract void accept(Visitor v);    
105 
106   /***
107    * Dump attribute to file stream in binary format.
108    *
109    * @param file Output file stream
110    * @throws IOException
111    */
112   public void dump(DataOutputStream file) throws IOException
113   {
114     file.writeShort(name_index);
115     file.writeInt(length);
116   }
117 
118   private static HashMap readers = new HashMap();
119 
120   /*** Add an Attribute reader capable of parsing (user-defined) attributes
121    * named "name". You should not add readers for the standard attributes
122    * such as "LineNumberTable", because those are handled internally.
123    *
124    * @param name the name of the attribute as stored in the class file
125    * @param r the reader object
126    */ 
127   public static void addAttributeReader(String name, AttributeReader r) {
128     readers.put(name, r);
129   }
130 
131   /*** Remove attribute reader
132    *
133    * @param name the name of the attribute as stored in the class file
134    */
135   public static void removeAttributeReader(String name) {
136     readers.remove(name);
137   }
138 
139   /* Class method reads one attribute from the input data stream.
140    * This method must not be accessible from the outside.  It is
141    * called by the Field and Method constructor methods.
142    *
143    * @see    Field
144    * @see    Method
145    * @param  file Input stream
146    * @param  constant_pool Array of constants
147    * @return Attribute
148    * @throws  IOException
149    * @throws  ClassFormatException
150    */
151   public static final Attribute readAttribute(DataInputStream file,
152 					      ConstantPool constant_pool)
153     throws IOException, ClassFormatException
154   {
155     ConstantUtf8 c;
156     String       name;
157     int          name_index;
158     int          length;
159     byte         tag = Constants.ATTR_UNKNOWN; // Unknown attribute
160 
161     // Get class name from constant pool via `name_index' indirection
162     name_index = (int)file.readUnsignedShort();
163     c          = (ConstantUtf8)constant_pool.getConstant(name_index, 
164 							 Constants.CONSTANT_Utf8);
165     name       = c.getBytes();
166 
167     // Length of data in bytes
168     length = file.readInt();
169 
170     // Compare strings to find known attribute
171     for(byte i=0; i < Constants.KNOWN_ATTRIBUTES; i++) {
172       if(name.equals(Constants.ATTRIBUTE_NAMES[i])) {
173 	tag = i; // found!
174 	break;
175       }
176     }
177 
178     // Call proper constructor, depending on `tag'
179     switch(tag) {
180     case Constants.ATTR_UNKNOWN:
181       AttributeReader r = (AttributeReader)readers.get(name);
182 
183       if(r != null)
184 	return r.createAttribute(name_index, length, file, constant_pool);
185       else
186 	return new Unknown(name_index, length, file, constant_pool);
187 
188     case Constants.ATTR_CONSTANT_VALUE:
189       return new ConstantValue(name_index, length, file, constant_pool);
190 
191     case Constants.ATTR_SOURCE_FILE:
192       return new SourceFile(name_index, length, file, constant_pool);
193 	  
194     case Constants.ATTR_CODE:
195       return new Code(name_index, length, file, constant_pool);
196 	  
197     case Constants.ATTR_EXCEPTIONS:
198       return new ExceptionTable(name_index, length, file, constant_pool);
199 	  
200     case Constants.ATTR_LINE_NUMBER_TABLE:
201       return new LineNumberTable(name_index, length, file, constant_pool);
202 	  
203     case Constants.ATTR_LOCAL_VARIABLE_TABLE:
204       return new LocalVariableTable(name_index, length, file, constant_pool);
205 
206     case Constants.ATTR_INNER_CLASSES:
207       return new InnerClasses(name_index, length, file, constant_pool);
208 
209     case Constants.ATTR_SYNTHETIC:
210       return new Synthetic(name_index, length, file, constant_pool);
211 
212     case Constants.ATTR_DEPRECATED:
213       return new Deprecated(name_index, length, file, constant_pool);
214 
215     case Constants.ATTR_PMG:
216       return new PMGClass(name_index, length, file, constant_pool);
217 
218     case Constants.ATTR_SIGNATURE:
219       return new Signature(name_index, length, file, constant_pool);
220 
221     case Constants.ATTR_STACK_MAP:
222       return new StackMap(name_index, length, file, constant_pool);
223 
224     default: // Never reached
225       throw new IllegalStateException("Ooops! default case reached.");
226     }
227   }    
228 
229   /***
230    * @return Length of attribute field in bytes.
231    */  
232   public final int   getLength()    { return length; }    
233 
234   /***
235    * @param Attribute length in bytes.
236    */
237   public final void setLength(int length) {
238     this.length = length;
239   }    
240 
241   /***
242    * @param name_index of attribute.
243    */
244   public final void setNameIndex(int name_index) {
245     this.name_index = name_index;
246   }    
247 
248   /***
249    * @return Name index in constant pool of attribute name.
250    */  
251   public final int getNameIndex() { return name_index; }    
252 
253   /***
254    * @return Tag of attribute, i.e., its type. Value may not be altered, thus
255    * there is no setTag() method.
256    */
257   public final byte  getTag()       { return tag; }    
258 
259   /***
260    * @return Constant pool used by this object.
261    * @see ConstantPool
262    */   
263   public final ConstantPool getConstantPool() { return constant_pool; }    
264 
265   /***
266    * @param constant_pool Constant pool to be used for this object.
267    * @see ConstantPool
268    */   
269   public final void setConstantPool(ConstantPool constant_pool) {
270     this.constant_pool = constant_pool;
271   }
272   
273   /***
274    * Use copy() if you want to have a deep copy(), i.e., with all references
275    * copied correctly.
276    *
277    * @return shallow copy of this attribute
278    */
279   public Object clone() {
280     Object o = null;
281 
282     try {
283       o = super.clone();
284     } catch(CloneNotSupportedException e) {
285       e.printStackTrace(); // Never occurs
286     }
287 
288     return o;
289   }
290 
291   /***
292    * @return deep copy of this attribute
293    */
294   public abstract Attribute copy(ConstantPool constant_pool);
295 
296   /***
297    * @return attribute name.
298    */ 
299   public String toString() {
300     return Constants.ATTRIBUTE_NAMES[tag];
301   }
302 }
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