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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   *  Unless required by applicable law or agreed to in writing, software
12   *  distributed under the License is distributed on an "AS IS" BASIS,
13   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   *  See the License for the specific language governing permissions and
15   *  limitations under the License.
16   *
17   */
18  package org.apache.bcel.classfile;
19  
20  import java.io.DataInput;
21  import java.io.DataOutputStream;
22  import java.io.IOException;
23  
24  import org.apache.bcel.Const;
25  
26  /**
27   * This class represents the constant pool, i.e., a table of constants, of
28   * a parsed classfile. It may contain null references, due to the JVM
29   * specification that skips an entry after an 8-byte constant (double,
30   * long) entry.  Those interested in generating constant pools
31   * programatically should see <a href="../generic/ConstantPoolGen.html">
32   * ConstantPoolGen</a>.
33  
34   * @version $Id: ConstantPool.html 1018313 2017-09-18 09:03:04Z britter $
35   * @see     Constant
36   * @see     org.apache.bcel.generic.ConstantPoolGen
37   */
38  public class ConstantPool implements Cloneable, Node {
39  
40      private Constant[] constant_pool;
41  
42  
43      /**
44       * @param constant_pool Array of constants
45       */
46      public ConstantPool(final Constant[] constant_pool) {
47          this.constant_pool = constant_pool;
48      }
49  
50  
51      /**
52       * Read constants from given input stream.
53       *
54       * @param input Input stream
55       * @throws IOException
56       * @throws ClassFormatException
57       */
58      public ConstantPool(final DataInput input) throws IOException, ClassFormatException {
59          byte tag;
60          final int constant_pool_count = input.readUnsignedShort();
61          constant_pool = new Constant[constant_pool_count];
62          /* constant_pool[0] is unused by the compiler and may be used freely
63           * by the implementation.
64           */
65          for (int i = 1; i < constant_pool_count; i++) {
66              constant_pool[i] = Constant.readConstant(input);
67              /* Quote from the JVM specification:
68               * "All eight byte constants take up two spots in the constant pool.
69               * If this is the n'th byte in the constant pool, then the next item
70               * will be numbered n+2"
71               *
72               * Thus we have to increment the index counter.
73               */
74              tag = constant_pool[i].getTag();
75              if ((tag == Const.CONSTANT_Double) || (tag == Const.CONSTANT_Long)) {
76                  i++;
77              }
78          }
79      }
80  
81  
82      /**
83       * Called by objects that are traversing the nodes of the tree implicitely
84       * defined by the contents of a Java class. I.e., the hierarchy of methods,
85       * fields, attributes, etc. spawns a tree of objects.
86       *
87       * @param v Visitor object
88       */
89      @Override
90      public void accept( final Visitor v ) {
91          v.visitConstantPool(this);
92      }
93  
94  
95      /**
96       * Resolve constant to a string representation.
97       *
98       * @param  c Constant to be printed
99       * @return String representation
100      */
101     public String constantToString( Constant c ) throws ClassFormatException {
102         String str;
103         int i;
104         final byte tag = c.getTag();
105         switch (tag) {
106             case Const.CONSTANT_Class:
107                 i = ((ConstantClass) c).getNameIndex();
108                 c = getConstant(i, Const.CONSTANT_Utf8);
109                 str = Utility.compactClassName(((ConstantUtf8) c).getBytes(), false);
110                 break;
111             case Const.CONSTANT_String:
112                 i = ((ConstantString) c).getStringIndex();
113                 c = getConstant(i, Const.CONSTANT_Utf8);
114                 str = "\"" + escape(((ConstantUtf8) c).getBytes()) + "\"";
115                 break;
116             case Const.CONSTANT_Utf8:
117                 str = ((ConstantUtf8) c).getBytes();
118                 break;
119             case Const.CONSTANT_Double:
120                 str = String.valueOf(((ConstantDouble) c).getBytes());
121                 break;
122             case Const.CONSTANT_Float:
123                 str = String.valueOf(((ConstantFloat) c).getBytes());
124                 break;
125             case Const.CONSTANT_Long:
126                 str = String.valueOf(((ConstantLong) c).getBytes());
127                 break;
128             case Const.CONSTANT_Integer:
129                 str = String.valueOf(((ConstantInteger) c).getBytes());
130                 break;
131             case Const.CONSTANT_NameAndType:
132                 str = constantToString(((ConstantNameAndType) c).getNameIndex(),
133                         Const.CONSTANT_Utf8)
134                         + " " + constantToString(((ConstantNameAndType) c).getSignatureIndex(),
135                         Const.CONSTANT_Utf8);
136                 break;
137             case Const.CONSTANT_InterfaceMethodref:
138             case Const.CONSTANT_Methodref:
139             case Const.CONSTANT_Fieldref:
140                 str = constantToString(((ConstantCP) c).getClassIndex(), Const.CONSTANT_Class)
141                         + "." + constantToString(((ConstantCP) c).getNameAndTypeIndex(),
142                         Const.CONSTANT_NameAndType);
143                 break;
144             case Const.CONSTANT_MethodHandle:
145                 // Note that the ReferenceIndex may point to a Fieldref, Methodref or
146                 // InterfaceMethodref - so we need to peek ahead to get the actual type.
147                 final ConstantMethodHandle cmh = (ConstantMethodHandle) c;
148                 str = Const.getMethodHandleName(cmh.getReferenceKind())
149                         + " " + constantToString(cmh.getReferenceIndex(),
150                         getConstant(cmh.getReferenceIndex()).getTag());
151                 break;
152             case Const.CONSTANT_MethodType:
153                 final ConstantMethodType cmt = (ConstantMethodType) c;
154                 str = constantToString(cmt.getDescriptorIndex(), Const.CONSTANT_Utf8);
155                 break;
156             case Const.CONSTANT_InvokeDynamic:
157                 final ConstantInvokeDynamic cid = (ConstantInvokeDynamic) c;
158                 str = cid.getBootstrapMethodAttrIndex()
159                         + ":" + constantToString(cid.getNameAndTypeIndex(),
160                         Const.CONSTANT_NameAndType);
161                 break;
162             default: // Never reached
163                 throw new RuntimeException("Unknown constant type " + tag);
164         }
165         return str;
166     }
167 
168 
169     private static String escape( final String str ) {
170         final int len = str.length();
171         final StringBuilder buf = new StringBuilder(len + 5);
172         final char[] ch = str.toCharArray();
173         for (int i = 0; i < len; i++) {
174             switch (ch[i]) {
175                 case '\n':
176                     buf.append("\\n");
177                     break;
178                 case '\r':
179                     buf.append("\\r");
180                     break;
181                 case '\t':
182                     buf.append("\\t");
183                     break;
184                 case '\b':
185                     buf.append("\\b");
186                     break;
187                 case '"':
188                     buf.append("\\\"");
189                     break;
190                 default:
191                     buf.append(ch[i]);
192             }
193         }
194         return buf.toString();
195     }
196 
197 
198     /**
199      * Retrieve constant at `index' from constant pool and resolve it to
200      * a string representation.
201      *
202      * @param  index of constant in constant pool
203      * @param  tag expected type
204      * @return String representation
205      */
206     public String constantToString( final int index, final byte tag ) throws ClassFormatException {
207         final Constant c = getConstant(index, tag);
208         return constantToString(c);
209     }
210 
211 
212     /**
213      * Dump constant pool to file stream in binary format.
214      *
215      * @param file Output file stream
216      * @throws IOException
217      */
218     public void dump( final DataOutputStream file ) throws IOException {
219         file.writeShort(constant_pool.length);
220         for (int i = 1; i < constant_pool.length; i++) {
221             if (constant_pool[i] != null) {
222                 constant_pool[i].dump(file);
223             }
224         }
225     }
226 
227 
228     /**
229      * Get constant from constant pool.
230      *
231      * @param  index Index in constant pool
232      * @return Constant value
233      * @see    Constant
234      */
235     public Constant getConstant( final int index ) {
236         if (index >= constant_pool.length || index < 0) {
237             throw new ClassFormatException("Invalid constant pool reference: " + index
238                     + ". Constant pool size is: " + constant_pool.length);
239         }
240         return constant_pool[index];
241     }
242 
243 
244     /**
245      * Get constant from constant pool and check whether it has the
246      * expected type.
247      *
248      * @param  index Index in constant pool
249      * @param  tag Tag of expected constant, i.e., its type
250      * @return Constant value
251      * @see    Constant
252      * @throws  ClassFormatException
253      */
254     public Constant getConstant( final int index, final byte tag ) throws ClassFormatException {
255         Constant c;
256         c = getConstant(index);
257         if (c == null) {
258             throw new ClassFormatException("Constant pool at index " + index + " is null.");
259         }
260         if (c.getTag() != tag) {
261             throw new ClassFormatException("Expected class `" + Const.getConstantName(tag)
262                     + "' at index " + index + " and got " + c);
263         }
264         return c;
265     }
266 
267 
268     /**
269      * @return Array of constants.
270      * @see    Constant
271      */
272     public Constant[] getConstantPool() {
273         return constant_pool;
274     }
275 
276 
277     /**
278      * Get string from constant pool and bypass the indirection of
279      * `ConstantClass' and `ConstantString' objects. I.e. these classes have
280      * an index field that points to another entry of the constant pool of
281      * type `ConstantUtf8' which contains the real data.
282      *
283      * @param  index Index in constant pool
284      * @param  tag Tag of expected constant, either ConstantClass or ConstantString
285      * @return Contents of string reference
286      * @see    ConstantClass
287      * @see    ConstantString
288      * @throws  ClassFormatException
289      */
290     public String getConstantString( final int index, final byte tag ) throws ClassFormatException {
291         Constant c;
292         int i;
293         c = getConstant(index, tag);
294         /* This switch() is not that elegant, since the two classes have the
295          * same contents, they just differ in the name of the index
296          * field variable.
297          * But we want to stick to the JVM naming conventions closely though
298          * we could have solved these more elegantly by using the same
299          * variable name or by subclassing.
300          */
301         switch (tag) {
302             case Const.CONSTANT_Class:
303                 i = ((ConstantClass) c).getNameIndex();
304                 break;
305             case Const.CONSTANT_String:
306                 i = ((ConstantString) c).getStringIndex();
307                 break;
308             default:
309                 throw new RuntimeException("getConstantString called with illegal tag " + tag);
310         }
311         // Finally get the string from the constant pool
312         c = getConstant(i, Const.CONSTANT_Utf8);
313         return ((ConstantUtf8) c).getBytes();
314     }
315 
316 
317     /**
318      * @return Length of constant pool.
319      */
320     public int getLength() {
321         return constant_pool == null ? 0 : constant_pool.length;
322     }
323 
324 
325     /**
326      * @param constant Constant to set
327      */
328     public void setConstant( final int index, final Constant constant ) {
329         constant_pool[index] = constant;
330     }
331 
332 
333     /**
334      * @param constant_pool
335      */
336     public void setConstantPool( final Constant[] constant_pool ) {
337         this.constant_pool = constant_pool;
338     }
339 
340 
341     /**
342      * @return String representation.
343      */
344     @Override
345     public String toString() {
346         final StringBuilder buf = new StringBuilder();
347         for (int i = 1; i < constant_pool.length; i++) {
348             buf.append(i).append(")").append(constant_pool[i]).append("\n");
349         }
350         return buf.toString();
351     }
352 
353 
354     /**
355      * @return deep copy of this constant pool
356      */
357     public ConstantPool copy() {
358         ConstantPool c = null;
359         try {
360             c = (ConstantPool) clone();
361             c.constant_pool = new Constant[constant_pool.length];
362             for (int i = 1; i < constant_pool.length; i++) {
363                 if (constant_pool[i] != null) {
364                     c.constant_pool[i] = constant_pool[i].copy();
365                 }
366             }
367         } catch (final CloneNotSupportedException e) {
368             // TODO should this throw?
369         }
370         return c;
371     }
372 }