classreader.java

asm的源码包 并且包含英文的文档

/***
 * ASM: a very small and fast Java bytecode manipulation framework
 * Copyright (c) 2000-2005 INRIA, France Telecom
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * 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 org.objectweb.asm;

import java.io.InputStream;
import java.io.IOException;

/**
 * A Java class parser to make a {@link ClassVisitor} visit an existing class.
 * This class parses a byte array conforming to the Java class file format and
 * calls the appropriate visit methods of a given class visitor for each field,
 * method and bytecode instruction encountered.
 * 
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class ClassReader {

    /**
     * Flag to skip method code. If this class is set <code>CODE</code>
     * attribute won't be visited. This can be used, for example, to retrieve
     * annotations for methods and method parameters.
     */
    public final static int SKIP_CODE = 1;

    /**
     * Flag to skip the debug information in the class. If this flag is set the
     * debug information of the class is not visited, i.e. the
     * {@link MethodVisitor#visitLocalVariable visitLocalVariable} and
     * {@link MethodVisitor#visitLineNumber visitLineNumber} methods will not be
     * called.
     */
    public final static int SKIP_DEBUG = 2;

    /**
     * Flag to skip the stack map frames in the class. If this flag is set the
     * stack map frames of the class is not visited, i.e. the
     * {@link MethodVisitor#visitFrame visitFrame} method will not be called.
     * This flag is useful when the {@link ClassWriter#COMPUTE_FRAMES} option is
     * used: it avoids visiting frames that will be ignored and recomputed from
     * scratch in the class writer.
     */
    public final static int SKIP_FRAMES = 4;

    /**
     * Flag to expand the stack map frames. By default stack map frames are
     * visited in their original format (i.e. "expanded" for classes whose
     * version is less than V1_6, and "compressed" for the other classes). If
     * this flag is set, stack map frames are always visited in expanded format
     * (this option adds a decompression/recompression step in ClassReader and
     * ClassWriter which degrades performances quite a lot).
     */
    public final static int EXPAND_FRAMES = 8;

    /**
     * The class to be parsed. <i>The content of this array must not be
     * modified. This field is intended for {@link Attribute} sub classes, and
     * is normally not needed by class generators or adapters.</i>
     */
    public final byte[] b;

    /**
     * The start index of each constant pool item in {@link #b b}, plus one.
     * The one byte offset skips the constant pool item tag that indicates its
     * type.
     */
    private final int[] items;

    /**
     * The String objects corresponding to the CONSTANT_Utf8 items. This cache
     * avoids multiple parsing of a given CONSTANT_Utf8 constant pool item,
     * which GREATLY improves performances (by a factor 2 to 3). This caching
     * strategy could be extended to all constant pool items, but its benefit
     * would not be so great for these items (because they are much less
     * expensive to parse than CONSTANT_Utf8 items).
     */
    private final String[] strings;

    /**
     * Maximum length of the strings contained in the constant pool of the
     * class.
     */
    private final int maxStringLength;

    /**
     * Start index of the class header information (access, name...) in
     * {@link #b b}.
     */
    public final int header;

    // ------------------------------------------------------------------------
    // Constructors
    // ------------------------------------------------------------------------

    /**
     * Constructs a new {@link ClassReader} object.
     * 
     * @param b the bytecode of the class to be read.
     */
    public ClassReader(final byte[] b) {
        this(b, 0, b.length);
    }

    /**
     * Constructs a new {@link ClassReader} object.
     * 
     * @param b the bytecode of the class to be read.
     * @param off the start offset of the class data.
     * @param len the length of the class data.
     */
    public ClassReader(final byte[] b, final int off, final int len) {
        this.b = b;
        // parses the constant pool
        items = new int[readUnsignedShort(off + 8)];
        int n = items.length;
        strings = new String[n];
        int max = 0;
        int index = off + 10;
        for (int i = 1; i < n; ++i) {
            items[i] = index + 1;
            int size;
            switch (b[index]) {
                case ClassWriter.FIELD:
                case ClassWriter.METH:
                case ClassWriter.IMETH:
                case ClassWriter.INT:
                case ClassWriter.FLOAT:
                case ClassWriter.NAME_TYPE:
                    size = 5;
                    break;
                case ClassWriter.LONG:
                case ClassWriter.DOUBLE:
                    size = 9;
                    ++i;
                    break;
                case ClassWriter.UTF8:
                    size = 3 + readUnsignedShort(index + 1);
                    if (size > max) {
                        max = size;
                    }
                    break;
                // case ClassWriter.CLASS:
                // case ClassWriter.STR:
                default:
                    size = 3;
                    break;
            }
            index += size;
        }
        maxStringLength = max;
        // the class header information starts just after the constant pool
        header = index;
    }

    /**
     * Returns the class's access flags (see {@link Opcodes}). This value may
     * not reflect Deprecated and Synthetic flags when bytecode is before 1.5
     * and those flags are represented by attributes.
     * 
     * @return the class access flags
     * 
     * @see ClassVisitor#visit(int, int, String, String, String, String[])
     */
    public int getAccess() {
        return readUnsignedShort(header);
    }

    /**
     * Returns the internal name of the class (see
     * {@link Type#getInternalName() getInternalName}).
     * 
     * @return the internal class name
     * 
     * @see ClassVisitor#visit(int, int, String, String, String, String[])
     */
    public String getClassName() {
        return readClass(header + 2, new char[maxStringLength]);
    }

    /**
     * Returns the internal of name of the super class (see
     * {@link Type#getInternalName() getInternalName}). For interfaces, the
     * super class is {@link Object}.
     * 
     * @return the internal name of super class, or <tt>null</tt> for
     *         {@link Object} class.
     * 
     * @see ClassVisitor#visit(int, int, String, String, String, String[])
     */
    public String getSuperName() {
        int n = items[readUnsignedShort(header + 4)];
        return n == 0 ? null : readUTF8(n, new char[maxStringLength]);
    }

    /**
     * Returns the internal names of the class's interfaces (see
     * {@link Type#getInternalName() getInternalName}).
     * 
     * @return the array of internal names for all implemented interfaces or
     *         <tt>null</tt>.
     * 
     * @see ClassVisitor#visit(int, int, String, String, String, String[])
     */
    public String[] getInterfaces() {
        int index = header + 6;
        int n = readUnsignedShort(index);
        String[] interfaces = new String[n];
        if (n > 0) {
            char[] buf = new char[maxStringLength];
            for (int i = 0; i < n; ++i) {
                index += 2;
                interfaces[i] = readClass(index, buf);
            }
        }
        return interfaces;
    }

    /**
     * Copies the constant pool data into the given {@link ClassWriter}. Should
     * be called before the {@link #accept(ClassVisitor,int)} method.
     * 
     * @param classWriter the {@link ClassWriter} to copy constant pool into.
     */
    void copyPool(final ClassWriter classWriter) {
        char[] buf = new char[maxStringLength];
        int ll = items.length;
        Item[] items2 = new Item[ll];
        for (int i = 1; i < ll; i++) {
            int index = items[i];
            int tag = b[index - 1];
            Item item = new Item(i);
            int nameType;
            switch (tag) {
                case ClassWriter.FIELD:
                case ClassWriter.METH:
                case ClassWriter.IMETH:
                    nameType = items[readUnsignedShort(index + 2)];
                    item.set(tag,
                            readClass(index, buf),
                            readUTF8(nameType, buf),
                            readUTF8(nameType + 2, buf));
                    break;

                case ClassWriter.INT:
                    item.set(readInt(index));
                    break;

                case ClassWriter.FLOAT:
                    item.set(Float.intBitsToFloat(readInt(index)));
                    break;

                case ClassWriter.NAME_TYPE:
                    item.set(tag,
                            readUTF8(index, buf),
                            readUTF8(index + 2, buf),
                            null);
                    break;

                case ClassWriter.LONG:
                    item.set(readLong(index));
                    ++i;
                    break;

                case ClassWriter.DOUBLE:
                    item.set(Double.longBitsToDouble(readLong(index)));
                    ++i;
                    break;

                case ClassWriter.UTF8: {
                    String s = strings[i];
                    if (s == null) {
                        index = items[i];
                        s = strings[i] = readUTF(index + 2,
                                readUnsignedShort(index),
                                buf);
                    }
                    item.set(tag, s, null, null);
                }
                    break;