AttributeShrinker.java revision b9cc48a43ed984587c939d02fba5316bf5c0df6e 
1/*
2 * ProGuard -- shrinking, optimization, obfuscation, and preverification
3 *             of Java bytecode.
4 *
5 * Copyright (c) 2002-2013 Eric Lafortune (eric@graphics.cornell.edu)
6 *
7 * This program is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License as published by the Free
9 * Software Foundation; either version 2 of the License, or (at your option)
10 * any later version.
11 *
12 * This program is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
15 * more details.
16 *
17 * You should have received a copy of the GNU General Public License along
18 * with this program; if not, write to the Free Software Foundation, Inc.,
19 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
20 */
21package proguard.obfuscate;
22
23import proguard.classfile.*;
24import proguard.classfile.attribute.*;
25import proguard.classfile.attribute.visitor.AttributeVisitor;
26import proguard.classfile.util.SimplifiedVisitor;
27import proguard.classfile.visitor.*;
28
29import java.util.Arrays;
30
31/**
32 * This ClassVisitor removes attributes that are not marked as being used or
33 * required.
34 *
35 * @see AttributeUsageMarker
36 *
37 * @author Eric Lafortune
38 */
39public class AttributeShrinker
40extends      SimplifiedVisitor
41implements   ClassVisitor,
42             MemberVisitor,
43             AttributeVisitor
44{
45    // Implementations for ClassVisitor.
46
47    public void visitProgramClass(ProgramClass programClass)
48    {
49        // Compact the array for class attributes.
50        programClass.u2attributesCount =
51            shrinkArray(programClass.attributes,
52                        programClass.u2attributesCount);
53
54        // Compact the attributes in fields, methods, and class attributes,
55        programClass.fieldsAccept(this);
56        programClass.methodsAccept(this);
57        programClass.attributesAccept(this);
58    }
59
60
61    public void visitLibraryClass(LibraryClass libraryClass)
62    {
63        // Library classes are left unchanged.
64    }
65
66
67    // Implementations for MemberVisitor.
68
69    public void visitProgramMember(ProgramClass programClass, ProgramMember programMember)
70    {
71        // Compact the attributes array.
72        programMember.u2attributesCount =
73            shrinkArray(programMember.attributes,
74                        programMember.u2attributesCount);
75
76        // Compact any attributes of the remaining attributes.
77        programMember.attributesAccept(programClass, this);
78    }
79
80
81    // Implementations for AttributeVisitor.
82
83    public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
84
85
86    public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
87    {
88        // Compact the attributes array.
89        codeAttribute.u2attributesCount =
90            shrinkArray(codeAttribute.attributes,
91                        codeAttribute.u2attributesCount);
92    }
93
94
95    // Small utility methods.
96
97    /**
98     * Removes all VisitorAccepter objects that are not marked as being used
99     * from the given array.
100     * @return the new number of VisitorAccepter objects.
101     */
102    private static int shrinkArray(VisitorAccepter[] array, int length)
103    {
104        int counter = 0;
105
106        // Shift the used objects together.
107        for (int index = 0; index < length; index++)
108        {
109            if (AttributeUsageMarker.isUsed(array[index]))
110            {
111                array[counter++] = array[index];
112            }
113        }
114
115        // Clear the remaining array elements.
116        Arrays.fill(array, counter, length, null);
117
118        return counter;
119    }
120}
121