Source code

    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 *  Unless required by applicable law or agreed to in writing, software
    012 *  distributed under the License is distributed on an "AS IS" BASIS,
    013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 *  See the License for the specific language governing permissions and
    015 *  limitations under the License.
    016 *
    017 */
    018package org.apache.bcel.util;
    019
    020import java.io.IOException;
    021import java.io.OutputStream;
    022import java.io.PrintWriter;
    023import java.util.Locale;
    024
    025import org.apache.bcel.Const;
    026import org.apache.bcel.Repository;
    027import org.apache.bcel.classfile.ClassParser;
    028import org.apache.bcel.classfile.ConstantValue;
    029import org.apache.bcel.classfile.Field;
    030import org.apache.bcel.classfile.JavaClass;
    031import org.apache.bcel.classfile.Method;
    032import org.apache.bcel.classfile.Utility;
    033import org.apache.bcel.generic.ArrayType;
    034import org.apache.bcel.generic.ConstantPoolGen;
    035import org.apache.bcel.generic.MethodGen;
    036import org.apache.bcel.generic.Type;
    037
    038/**
    039 * This class takes a given JavaClass object and converts it to a
    040 * Java program that creates that very class using BCEL. This
    041 * gives new users of BCEL a useful example showing how things
    042 * are done with BCEL. It does not cover all features of BCEL,
    043 * but tries to mimic hand-written code as close as possible.
    044 *
    045 */
    046public class BCELifier extends org.apache.bcel.classfile.EmptyVisitor {
    047
    048    /**
    049     * Enum corresponding to flag source.
    050     */
    051    public enum FLAGS {
    052        UNKNOWN,
    053        CLASS,
    054        METHOD,
    055    }
    056
    057    // The base package name for imports; assumes Const is at the top level
    058    // N.B we use the class so renames will be detected by the compiler/IDE
    059    private static final String BASE_PACKAGE = Const.class.getPackage().getName();
    060    private static final String CONSTANT_PREFIX = Const.class.getSimpleName()+".";
    061
    062    private final JavaClass _clazz;
    063    private final PrintWriter _out;
    064    private final ConstantPoolGen _cp;
    065
    066    /** @param clazz Java class to "decompile"
    067     * @param out where to output Java program
    068     */
    069    public BCELifier(final JavaClass clazz, final OutputStream out) {
    070        _clazz = clazz;
    071        _out = new PrintWriter(out);
    072        _cp = new ConstantPoolGen(_clazz.getConstantPool());
    073    }
    074
    075
    076    /** Start Java code generation
    077     */
    078    public void start() {
    079        visitJavaClass(_clazz);
    080        _out.flush();
    081    }
    082
    083
    084    @Override
    085    public void visitJavaClass( final JavaClass clazz ) {
    086        String class_name = clazz.getClassName();
    087        final String super_name = clazz.getSuperclassName();
    088        final String package_name = clazz.getPackageName();
    089        final String inter = Utility.printArray(clazz.getInterfaceNames(), false, true);
    090        if (!"".equals(package_name)) {
    091            class_name = class_name.substring(package_name.length() + 1);
    092            _out.println("package " + package_name + ";");
    093            _out.println();
    094        }
    095        _out.println("import " + BASE_PACKAGE + ".generic.*;");
    096        _out.println("import " + BASE_PACKAGE + ".classfile.*;");
    097        _out.println("import " + BASE_PACKAGE + ".*;");
    098        _out.println("import java.io.*;");
    099        _out.println();
    100        _out.println("public class " + class_name + "Creator {");
    101        _out.println("  private InstructionFactory _factory;");
    102        _out.println("  private ConstantPoolGen    _cp;");
    103        _out.println("  private ClassGen           _cg;");
    104        _out.println();
    105        _out.println("  public " + class_name + "Creator() {");
    106        _out.println("    _cg = new ClassGen(\""
    107                + (("".equals(package_name)) ? class_name : package_name + "." + class_name)
    108                + "\", \"" + super_name + "\", " + "\"" + clazz.getSourceFileName() + "\", "
    109                + printFlags(clazz.getAccessFlags(), FLAGS.CLASS) + ", "
    110                + "new String[] { " + inter + " });");
    111        _out.println("    _cg.setMajor(" + clazz.getMajor() +");");
    112        _out.println("    _cg.setMinor(" + clazz.getMinor() +");");
    113        _out.println();
    114        _out.println("    _cp = _cg.getConstantPool();");
    115        _out.println("    _factory = new InstructionFactory(_cg, _cp);");
    116        _out.println("  }");
    117        _out.println();
    118        printCreate();
    119        final Field[] fields = clazz.getFields();
    120        if (fields.length > 0) {
    121            _out.println("  private void createFields() {");
    122            _out.println("    FieldGen field;");
    123            for (final Field field : fields) {
    124                field.accept(this);
    125            }
    126            _out.println("  }");
    127            _out.println();
    128        }
    129        final Method[] methods = clazz.getMethods();
    130        for (int i = 0; i < methods.length; i++) {
    131            _out.println("  private void createMethod_" + i + "() {");
    132            methods[i].accept(this);
    133            _out.println("  }");
    134            _out.println();
    135        }
    136        printMain();
    137        _out.println("}");
    138    }
    139
    140
    141    private void printCreate() {
    142        _out.println("  public void create(OutputStream out) throws IOException {");
    143        final Field[] fields = _clazz.getFields();
    144        if (fields.length > 0) {
    145            _out.println("    createFields();");
    146        }
    147        final Method[] methods = _clazz.getMethods();
    148        for (int i = 0; i < methods.length; i++) {
    149            _out.println("    createMethod_" + i + "();");
    150        }
    151        _out.println("    _cg.getJavaClass().dump(out);");
    152        _out.println("  }");
    153        _out.println();
    154    }
    155
    156
    157    private void printMain() {
    158        final String class_name = _clazz.getClassName();
    159        _out.println("  public static void main(String[] args) throws Exception {");
    160        _out.println("    " + class_name + "Creator creator = new " + class_name + "Creator();");
    161        _out.println("    creator.create(new FileOutputStream(\"" + class_name + ".class\"));");
    162        _out.println("  }");
    163    }
    164
    165
    166    @Override
    167    public void visitField( final Field field ) {
    168        _out.println();
    169        _out.println("    field = new FieldGen(" + printFlags(field.getAccessFlags()) + ", "
    170                + printType(field.getSignature()) + ", \"" + field.getName() + "\", _cp);");
    171        final ConstantValue cv = field.getConstantValue();
    172        if (cv != null) {
    173            final String value = cv.toString();
    174            _out.println("    field.setInitValue(" + value + ")");
    175        }
    176        _out.println("    _cg.addField(field.getField());");
    177    }
    178
    179
    180    @Override
    181    public void visitMethod( final Method method ) {
    182        final MethodGen mg = new MethodGen(method, _clazz.getClassName(), _cp);
    183        _out.println("    InstructionList il = new InstructionList();");
    184        _out.println("    MethodGen method = new MethodGen("
    185                + printFlags(method.getAccessFlags(), FLAGS.METHOD) + ", "
    186                + printType(mg.getReturnType()) + ", "
    187                + printArgumentTypes(mg.getArgumentTypes()) + ", "
    188                + "new String[] { " + Utility.printArray(mg.getArgumentNames(), false, true)
    189                + " }, \"" + method.getName() + "\", \"" + _clazz.getClassName() + "\", il, _cp);");
    190        _out.println();
    191        final BCELFactory factory = new BCELFactory(mg, _out);
    192        factory.start();
    193        _out.println("    method.setMaxStack();");
    194        _out.println("    method.setMaxLocals();");
    195        _out.println("    _cg.addMethod(method.getMethod());");
    196        _out.println("    il.dispose();");
    197    }
    198
    199
    200    static String printFlags( final int flags ) {
    201        return printFlags(flags, FLAGS.UNKNOWN);
    202    }
    203
    204    /**
    205     * Return a string with the flag settings
    206     * @param flags the flags field to interpret
    207     * @param location the item type
    208     * @return the formatted string
    209     * @since 6.0 made public
    210     */
    211    public static String printFlags( final int flags, final FLAGS location ) {
    212        if (flags == 0) {
    213            return "0";
    214        }
    215        final StringBuilder buf = new StringBuilder();
    216        for (int i = 0, pow = 1; pow <= Const.MAX_ACC_FLAG_I; i++) {
    217            if ((flags & pow) != 0) {
    218                if ((pow == Const.ACC_SYNCHRONIZED) && (location == FLAGS.CLASS)) {
    219                    buf.append(CONSTANT_PREFIX+"ACC_SUPER | ");
    220                } else if ((pow == Const.ACC_VOLATILE) && (location == FLAGS.METHOD)) {
    221                    buf.append(CONSTANT_PREFIX+"ACC_BRIDGE | ");
    222                } else if ((pow == Const.ACC_TRANSIENT) && (location == FLAGS.METHOD)) {
    223                    buf.append(CONSTANT_PREFIX+"ACC_VARARGS | ");
    224                } else {
    225                    if (i < Const.ACCESS_NAMES_LENGTH) {
    226                        buf.append(CONSTANT_PREFIX+"ACC_").append(Const.getAccessName(i).toUpperCase(Locale.ENGLISH)).append( " | ");
    227                    } else {
    228                        buf.append(String.format (CONSTANT_PREFIX+"ACC_BIT %x | ", pow));
    229                    }
    230                }
    231            }
    232            pow <<= 1;
    233        }
    234        final String str = buf.toString();
    235        return str.substring(0, str.length() - 3);
    236    }
    237
    238
    239    static String printArgumentTypes( final Type[] arg_types ) {
    240        if (arg_types.length == 0) {
    241            return "Type.NO_ARGS";
    242        }
    243        final StringBuilder args = new StringBuilder();
    244        for (int i = 0; i < arg_types.length; i++) {
    245            args.append(printType(arg_types[i]));
    246            if (i < arg_types.length - 1) {
    247                args.append(", ");
    248            }
    249        }
    250        return "new Type[] { " + args.toString() + " }";
    251    }
    252
    253
    254    static String printType( final Type type ) {
    255        return printType(type.getSignature());
    256    }
    257
    258
    259    static String printType( final String signature ) {
    260        final Type type = Type.getType(signature);
    261        final byte t = type.getType();
    262        if (t <= Const.T_VOID) {
    263            return "Type." + Const.getTypeName(t).toUpperCase(Locale.ENGLISH);
    264        } else if (type.toString().equals("java.lang.String")) {
    265            return "Type.STRING";
    266        } else if (type.toString().equals("java.lang.Object")) {
    267            return "Type.OBJECT";
    268        } else if (type.toString().equals("java.lang.StringBuffer")) {
    269            return "Type.STRINGBUFFER";
    270        } else if (type instanceof ArrayType) {
    271            final ArrayType at = (ArrayType) type;
    272            return "new ArrayType(" + printType(at.getBasicType()) + ", " + at.getDimensions()
    273                    + ")";
    274        } else {
    275            return "new ObjectType(\"" + Utility.signatureToString(signature, false) + "\")";
    276        }
    277    }
    278
    279
    280    /** Default main method
    281     */
    282    public static void main( final String[] argv ) throws Exception {
    283        if (argv.length != 1) {
    284            System.out.println("Usage: BCELifier classname");
    285            System.out.println("\tThe class must exist on the classpath");
    286            return;
    287        }
    288        final JavaClass java_class = getJavaClass(argv[0]);
    289        final BCELifier bcelifier = new BCELifier(java_class, System.out);
    290        bcelifier.start();
    291    }
    292
    293
    294    // Needs to be accessible from unit test code
    295    static JavaClass getJavaClass(final String name) throws ClassNotFoundException, IOException {
    296        JavaClass java_class;
    297        if ((java_class = Repository.lookupClass(name)) == null) {
    298            java_class = new ClassParser(name).parse(); // May throw IOException
    299        }
    300        return java_class;
    301    }
    302}