classycle.classfile.Constant Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of classycle Show documentation
dependency analysis tool based on bytecode inspection
The newest version!
/*
 * Copyright (c) 2003-2008, Franz-Josef Elmer, All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are met:
 * 
 * - Redistributions of source code must retain the above copyright notice, 
 *   this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice, 
 *   this list of conditions and the following disclaimer in the documentation 
 *   and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR 
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */
package classycle.classfile;

import java.io.DataInputStream;
import java.io.IOException;

/**
 * Abstract super class of all type of constants in the constant pool of
 * a class file.
 * 
 * @author Franz-Josef Elmer
 */
public abstract class Constant {
  private static final int MAGIC = 0xcafebabe;
  private static final int CONSTANT_CLASS = 7,
                           CONSTANT_FIELDREF = 9,
                           CONSTANT_METHODREF = 10,
                           CONSTANT_INTERFACE_METHODREF = 11,
                           CONSTANT_STRING = 8,
                           CONSTANT_INTEGER = 3,
                           CONSTANT_FLOAT = 4,
                           CONSTANT_LONG = 5,
                           CONSTANT_DOUBLE = 6,
                           CONSTANT_NAME_AND_TYPE = 12,
                           CONSTANT_UTF8 = 1,
                           CONSTANT_METHOD_HANDLE=15,
                           CONSTANT_METHOD_TYPE=16,
                           CONSTANT_INVOKE_DYNAMIC=18;
  
  /**
   * Extracts the constant pool from the specified data stream of a class file.
   * @param stream Input stream of a class file starting at the first byte.
   * @return extracted array of constants.
   * @throws IOException in case of reading errors or invalid class file.
   */
  public static Constant[] extractConstantPool(DataInputStream stream)
                                                    throws IOException {
    Constant[] pool = null;
    if (stream.readInt() == MAGIC) {
      stream.readUnsignedShort();
      stream.readUnsignedShort();
      pool = new Constant[stream.readUnsignedShort()];
      for (int i = 1; i < pool.length; ) {
        boolean skipIndex = false;
        Constant c = null;
        int type = stream.readUnsignedByte();
        switch (type) {
        case CONSTANT_CLASS:
          c = new ClassConstant(pool, stream.readUnsignedShort());
          break;
        case CONSTANT_FIELDREF:
          c = new FieldRefConstant(pool, stream.readUnsignedShort(),
                                   stream.readUnsignedShort());
          break;
        case CONSTANT_METHODREF:
          c = new MethodRefConstant(pool, stream.readUnsignedShort(),
                                    stream.readUnsignedShort());
          break;
        case CONSTANT_INTERFACE_METHODREF:
          c = new InterfaceMethodRefConstant(pool,
                                             stream.readUnsignedShort(),
                                             stream.readUnsignedShort());
          break;
        case CONSTANT_STRING:
          c = new StringConstant(pool, stream.readUnsignedShort());
          break;
        case CONSTANT_INTEGER:
          c = new IntConstant(pool, stream.readInt());
          break;
        case CONSTANT_FLOAT:
          c = new FloatConstant(pool, stream.readFloat());
          break;
        case CONSTANT_LONG:
          c = new LongConstant(pool, stream.readLong());
          skipIndex = true;
          break;
        case CONSTANT_DOUBLE:
          c = new DoubleConstant(pool, stream.readDouble());
          skipIndex = true;
          break;
        case CONSTANT_NAME_AND_TYPE:
          c = new NameAndTypeConstant(pool, stream.readUnsignedShort(),
                                      stream.readUnsignedShort());
          break;
        case CONSTANT_UTF8:
          c = new UTF8Constant(pool, stream.readUTF());
          break;
        case CONSTANT_METHOD_HANDLE:
          c = new MethodHandleConstant(pool, stream.readUnsignedByte(), stream.readUnsignedShort());
          break;
        case CONSTANT_METHOD_TYPE:
          c = new MethodTypeConstant(pool, stream.readUnsignedShort());
          break;
        case CONSTANT_INVOKE_DYNAMIC:
          c = new InvokeDynamicConstant(pool, stream.readUnsignedShort(), stream.readUnsignedShort());
          break;
        }
        pool[i] = c;
        i += skipIndex ? 2 : 1; // double and long constants occupy two entries
      }
      return pool;
    }
    throw new IOException("Not a class file: Magic number missing.");
  }

  private Constant[] _pool;

  /**
   * Creates an instance.
   * @param pool The poole which will be needed to resolve references.
   */
  public Constant(Constant[] pool) {
    _pool = pool;
  }

  /**
   * Returns the specified constant from the pool.
   * @param index Index of requested constant.
   */
  public Constant getConstant(int index) {
    return _pool[index];
  }
} //class