abstractstructure.java

Java Bytecode Editor 是一个 JAVA 的字节码反汇编和修改器。它可以很方便的修改已经编译成 Class 文件的 JAVA 文件。

/*
    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public
    License as published by the Free Software Foundation; either
    version 2 of the license, or (at your option) any later version.
*/

package org.gjt.jclasslib.structures;

import org.gjt.jclasslib.io.Log;

import java.io.*;
import java.lang.reflect.Array;

/**
 * Base class for all structures defined in the class file format. <p>
 * Provides common services such as reading, writing and debugging.
 *
 * @author <a href="mailto:[e-mail]">Ingo Kegel</a>, <a href="mailto:[e-mail]">Vitor Carreira</a>
 * @version $Revision: 1.1 $ $Date: 2005/11/01 13:18:24 $
 */
public abstract class AbstractStructure {

    /**
     * Set this JVM System property to true to switch on debugging for
     * reading and writing class files.
     */
    public static final String SYSTEM_PROPERTY_DEBUG = "jclasslib.io.debug";

    /**
     * Parent class file for this structure. <tt>Null</tt> for a <tt>ClassFile</tt>
     * structure.
     */
    protected ClassFile classFile;

    /**
     * Flag for debugging while reading and writing class files.
     */
    protected boolean debug;

    /**
     * Constructor.
     */
    protected AbstractStructure() {
        debug = Boolean.getBoolean(SYSTEM_PROPERTY_DEBUG);
    }

    /**
     * Get parent class file.
     *
     * @return the class file
     */
    public ClassFile getClassFile() {
        return classFile;
    }

    /**
     * Set parent class file. <p>
     * <p/>
     * Has to be called at least once on a structure.
     *
     * @param classFile the new parent class file
     */
    public void setClassFile(ClassFile classFile) {
        this.classFile = classFile;
    }

    /**
     * Read this structure from the given <tt>DataInput</tt>. <p>
     * <p/>
     * Excpects <tt>DataInput</tt> to be in JVM class file format and just
     * before a structure of this kind. No look ahead parsing since
     * the class file format is deterministic.
     *
     * @param in the <tt>DataInput</tt> from which to read
     * @throws InvalidByteCodeException if the byte code is invalid
     * @throws IOException              if an exception occurs with the <tt>DataInput</tt>
     */
    public void read(DataInput in)
            throws InvalidByteCodeException, IOException {
    }

    /**
     * Write this structure to the given <tt>DataOutput</tt>. <p>
     * <p/>
     * The written bytes are in JVM class file format.
     *
     * @param out the <tt>DataOutput</tt> to which to write
     * @throws InvalidByteCodeException if the structure is internally inconsistent
     * @throws IOException              if an exception occurs with the <tt>DataOutput</tt>
     */
    public void write(DataOutput out)
            throws InvalidByteCodeException, IOException {
    }

    /**
     * Get the debug mode for this structure.
     *
     * @return whether debug is on or not
     */
    public boolean getDebug() {
        return debug;
    }

    /**
     * Set the debug mode for this structure.
     *
     * @param debug the new debug mode
     */
    public void setDebug(boolean debug) {
        this.debug = debug;
    }

    /**
     * Utility method for derived structures. Get the
     * length of an arbitrary array which may hold
     * primitive types or reference types or may be null.
     *
     * @param array the array for which the length is requested
     * @return the length
     */
    protected int getLength(Object array) {
        if (array == null || !array.getClass().isArray()) {
            return 0;
        } else {
            return Array.getLength(array);
        }
    }

    /**
     * Utility method for derived structures. Dump a specific debug message.
     *
     * @param message the debug message
     */
    protected void debug(String message) {
        if (debug) {
            Log.debug(message);
        }
    }

    /**
     * Utility method for derived structures. Print an int value as a hex string.
     *
     * @param bytes the int value to print as a hex string
     * @return the hex string
     */
    protected String printBytes(int bytes) {
        return padHexString(Integer.toHexString(bytes), 8);
    }

    /**
     * Utility method for derived structures. Print an access flag or an
     * unsigned short value as a hex string.
     *
     * @param accessFlags the unsigned short value to print as a hex string
     * @return the hex string
     */
    protected String printAccessFlags(int accessFlags) {
        return padHexString(Integer.toHexString(accessFlags), 4);
    }

    private String padHexString(String hexString, int length) {
        StringBuffer buffer = new StringBuffer("0x");

        for (int i = hexString.length(); i < length; i++) {
            buffer.append('0');
        }
        buffer.append(hexString);

        return buffer.toString();
    }

    /**
     * Utility method for derived structures. Print an access flag as
     * a space separated list of verbose java access modifiers.
     *
     * @param accessFlags the unsigned short value to print as a hex string
     * @return the hex string
     */
    abstract protected String printAccessFlagsVerbose(int accessFlags);

    /**
     * Utility method for derived structures. Print an access flag as
     * a space separated list of verbose java access modifiers.
     *
     * @param availableAccessFlags        array with the access flags available
     *                                    for the derived structure
     * @param availableAccessFlagsVerbose array with verbose description
     *                                    of the access flags available for the derived structure
     * @param accessFlags                 the unsigned short value to print as a hex string
     * @return the access flags verbose description
     */
    protected String printAccessFlagsVerbose(int[] availableAccessFlags, String[] availableAccessFlagsVerbose,
                                             int accessFlags) {
        StringBuffer accessFlagsVerbose = new StringBuffer();


        int all = 0;
        for (int i = 0; i < availableAccessFlags.length; i++) {
            all |= availableAccessFlags[i];
            if ((accessFlags & availableAccessFlags[i]) != 0) {
                accessFlagsVerbose.append(availableAccessFlagsVerbose[i]).append(' ');
            }
        }
        
        // Check if every possible flag has been processed
        if ((all | accessFlags) != all) {
            accessFlagsVerbose.append("? ");
        }
        if (accessFlagsVerbose.length() > 0) {
            accessFlagsVerbose.setLength(accessFlagsVerbose.length() - 1);
        }
        return accessFlagsVerbose.toString();
    }

}