classfornamechecker.java

ProGuard 是一个免费的 Java类文件的压缩

/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2007 Eric Lafortune ([e-mail])
 *
 * This program 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.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.classfile.util;

import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.AttributeVisitor;
import proguard.classfile.attribute.annotation.*;
import proguard.classfile.constant.*;
import proguard.classfile.constant.visitor.ConstantVisitor;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.visitor.*;


/**
 * This class can check whether method references point to <code>Class.forName</code>
 * or <code>.class</code>.
 *
 * @author Eric Lafortune
 */
class      ClassForNameChecker
extends    SimplifiedVisitor
implements ConstantVisitor,
           MemberVisitor,
           AttributeVisitor,
           InstructionVisitor
{
    // These fields acts as a return variables and status variables for the visitors.
    private boolean isClassForNameInvocation;
    private boolean insideDotClassMethod;
    private boolean firstInstructionOk;


    /**
     * Creates a new ClassForNameChecker.
     */
    public ClassForNameChecker()
    {
    }


    /**
     * Checks whether the specified method reference points to
     * <code>Class.forName</code> or <code>.class</code>.
     * @param clazz              the class in which the method reference
     *                               is located.
     * @param methodrefConstantIndex the index of the method reference in the
     *                               constant pool.
     * @return a boolean that indicates whether the reference points to either
     *         method.
     */
    public boolean check(Clazz clazz, int methodrefConstantIndex)
    {
        isClassForNameInvocation = false;

        clazz.constantPoolEntryAccept(methodrefConstantIndex, this);

        return isClassForNameInvocation;
    }


    // Implementations for ConstantVisitor.

    /**
     * Checks whether the given method reference points to
     * <code>Class.forName</code> or <code>.class</code>.
     */
    public void visitMethodrefConstant(Clazz clazz, MethodrefConstant methodrefConstant)
    {
        String className  = methodrefConstant.getClassName(clazz);
        String methodName = methodrefConstant.getName(clazz);
        String methodType = methodrefConstant.getType(clazz);

        // Is it a reference to "Class Class.forName(String)"?
        isClassForNameInvocation =
            className .equals(ClassConstants.INTERNAL_CLASS_NAME_JAVA_LANG_CLASS) &&
            methodName.equals(ClassConstants.INTERNAL_METHOD_NAME_CLASS_FOR_NAME) &&
            methodType.equals(ClassConstants.INTERNAL_METHOD_TYPE_CLASS_FOR_NAME);

        if (isClassForNameInvocation || insideDotClassMethod)
        {
            return;
        }

        // Is it a reference to .class? This construct is typically implemented
        // as (static) "Class class$(String)" or "Class class$(String, boolean)".
        // First check the type, which has to be right to start with.
        isClassForNameInvocation =
            methodType.equals(ClassConstants.INTERNAL_METHOD_TYPE_DOT_CLASS_JAVAC) ||
            methodType.equals(ClassConstants.INTERNAL_METHOD_TYPE_DOT_CLASS_JIKES);

        if (!isClassForNameInvocation)
        {
            return;
        }

        // Then check if the method perhaps still has its original "class$" name.
        isClassForNameInvocation =
            methodName.equals(ClassConstants.INTERNAL_METHOD_NAME_DOT_CLASS);

        if (isClassForNameInvocation)
        {
            return;
        }

        // We're still not sure it's not a reference to .class, since the
        // method name may have been changed or obfuscated.
        // Perform a more detailed analysis by looking at the referenced method
        // itself. Make sure we don't do this recursively.
        insideDotClassMethod   = true;
        methodrefConstant.referencedMemberAccept(this);
        insideDotClassMethod   = false;
    }


    // Implementations for MemberVisitor.

    /**
     * Checks whether the given method is a .class implementation.
     */
    public void visitProgramMethod(ProgramClass programClass, ProgramMethod programMethod)
    {
        programMethod.attributesAccept(programClass, this);
    }


    // Implementations for AttributeVisitor.

    /**
     * Checks whether the given code is an implementation of class$(String) or
     * class$(String, boolean).
     */
    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
    {
        // Check whether the first instruction recalls the first argument of
        // this method.
        firstInstructionOk = false;
        codeAttribute.instructionAccept(clazz, method, 0, this);

        // Continue checking whether the second instruction invokes
        // Class.forName.
        if (firstInstructionOk)
        {
            codeAttribute.instructionAccept(clazz, method, 1, this);
        }
    }


    // Implementations for InstructionVisitor.

    /**
     * Checks whether this is a valid first instruction for a .class implementation.
     */
    public void visitVariableInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, VariableInstruction variableInstruction)
    {
        firstInstructionOk = variableInstruction.opcode == InstructionConstants.OP_ALOAD_0;
    }

    /**
     * Checks whether this is a valid second instruction for a .class implementation.
     */
    public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
    {
        if (firstInstructionOk &&
            constantInstruction.opcode == InstructionConstants.OP_INVOKESTATIC)
        {
            clazz.constantPoolEntryAccept(constantInstruction.constantIndex, this);
        }
    }
}