    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 * @version $Id: BCELifier.java 1806200 2017-08-25 16:33:06Z ggregory $
    046 */
    047public class BCELifier extends org.apache.bcel.classfile.EmptyVisitor {
    048
    049    /**
    050     * Enum corresponding to flag source.
    051     */
    052    public enum FLAGS {
    053        UNKNOWN,
    054        CLASS,
    055        METHOD,
    056    }
    057
    058    // The base package name for imports; assumes Const is at the top level
    059    // N.B we use the class so renames will be detected by the compiler/IDE
    060    private static final String BASE_PACKAGE = Const.class.getPackage().getName();
    061    private static final String CONSTANT_PREFIX = Const.class.getSimpleName()+".";
    062
    063    private final JavaClass _clazz;
    064    private final PrintWriter _out;
    065    private final ConstantPoolGen _cp;
    066
    067    /** @param clazz Java class to "decompile"
    068     * @param out where to output Java program
    069     */
    070    public BCELifier(final JavaClass clazz, final OutputStream out) {
    071        _clazz = clazz;
    072        _out = new PrintWriter(out);
    073        _cp = new ConstantPoolGen(_clazz.getConstantPool());
    074    }
    075
    076
    077    /** Start Java code generation
    078     */
    079    public void start() {
    080        visitJavaClass(_clazz);
    081        _out.flush();
    082    }
    083
    084
    085    @Override
    086    public void visitJavaClass( final JavaClass clazz ) {
    087        String class_name = clazz.getClassName();
    088        final String super_name = clazz.getSuperclassName();
    089        final String package_name = clazz.getPackageName();
    090        final String inter = Utility.printArray(clazz.getInterfaceNames(), false, true);
    091        if (!"".equals(package_name)) {
    092            class_name = class_name.substring(package_name.length() + 1);
    093            _out.println("package " + package_name + ";");
    094            _out.println();
    095        }
    096        _out.println("import " + BASE_PACKAGE + ".generic.*;");
    097        _out.println("import " + BASE_PACKAGE + ".classfile.*;");
    098        _out.println("import " + BASE_PACKAGE + ".*;");
    099        _out.println("import java.io.*;");
    100        _out.println();
    101        _out.println("public class " + class_name + "Creator {");
    102        _out.println("  private InstructionFactory _factory;");
    103        _out.println("  private ConstantPoolGen    _cp;");
    104        _out.println("  private ClassGen           _cg;");
    105        _out.println();
    106        _out.println("  public " + class_name + "Creator() {");
    107        _out.println("    _cg = new ClassGen(\""
    108                + (("".equals(package_name)) ? class_name : package_name + "." + class_name)
    109                + "\", \"" + super_name + "\", " + "\"" + clazz.getSourceFileName() + "\", "
    110                + printFlags(clazz.getAccessFlags(), FLAGS.CLASS) + ", "
    111                + "new String[] { " + inter + " });");
    112        _out.println();
    113        _out.println("    _cp = _cg.getConstantPool();");
    114        _out.println("    _factory = new InstructionFactory(_cg, _cp);");
    115        _out.println("  }");
    116        _out.println();
    117        printCreate();
    118        final Field[] fields = clazz.getFields();
    119        if (fields.length > 0) {
    120            _out.println("  private void createFields() {");
    121            _out.println("    FieldGen field;");
    122            for (final Field field : fields) {
    123                field.accept(this);
    124            }
    125            _out.println("  }");
    126            _out.println();
    127        }
    128        final Method[] methods = clazz.getMethods();
    129        for (int i = 0; i < methods.length; i++) {
    130            _out.println("  private void createMethod_" + i + "() {");
    131            methods[i].accept(this);
    132            _out.println("  }");
    133            _out.println();
    134        }
    135        printMain();
    136        _out.println("}");
    137    }
    138
    139
    140    private void printCreate() {
    141        _out.println("  public void create(OutputStream out) throws IOException {");
    142        final Field[] fields = _clazz.getFields();
    143        if (fields.length > 0) {
    144            _out.println("    createFields();");
    145        }
    146        final Method[] methods = _clazz.getMethods();
    147        for (int i = 0; i < methods.length; i++) {
    148            _out.println("    createMethod_" + i + "();");
    149        }
    150        _out.println("    _cg.getJavaClass().dump(out);");
    151        _out.println("  }");
    152        _out.println();
    153    }
    154
    155
    156    private void printMain() {
    157        final String class_name = _clazz.getClassName();
    158        _out.println("  public static void main(String[] args) throws Exception {");
    159        _out.println("    " + class_name + "Creator creator = new " + class_name + "Creator();");
    160        _out.println("    creator.create(new FileOutputStream(\"" + class_name + ".class\"));");
    161        _out.println("  }");
    162    }
    163
    164
    165    @Override
    166    public void visitField( final Field field ) {
    167        _out.println();
    168        _out.println("    field = new FieldGen(" + printFlags(field.getAccessFlags()) + ", "
    169                + printType(field.getSignature()) + ", \"" + field.getName() + "\", _cp);");
    170        final ConstantValue cv = field.getConstantValue();
    171        if (cv != null) {
    172            final String value = cv.toString();
    173            _out.println("    field.setInitValue(" + value + ")");
    174        }
    175        _out.println("    _cg.addField(field.getField());");
    176    }
    177
    178
    179    @Override
    180    public void visitMethod( final Method method ) {
    181        final MethodGen mg = new MethodGen(method, _clazz.getClassName(), _cp);
    182        _out.println("    InstructionList il = new InstructionList();");
    183        _out.println("    MethodGen method = new MethodGen("
    184                + printFlags(method.getAccessFlags(), FLAGS.METHOD) + ", "
    185                + printType(mg.getReturnType()) + ", "
    186                + printArgumentTypes(mg.getArgumentTypes()) + ", "
    187                + "new String[] { " + Utility.printArray(mg.getArgumentNames(), false, true)
    188                + " }, \"" + method.getName() + "\", \"" + _clazz.getClassName() + "\", il, _cp);");
    189        _out.println();
    190        final BCELFactory factory = new BCELFactory(mg, _out);
    191        factory.start();
    192        _out.println("    method.setMaxStack();");
    193        _out.println("    method.setMaxLocals();");
    194        _out.println("    _cg.addMethod(method.getMethod());");
    195        _out.println("    il.dispose();");
    196    }
    197
    198
    199    static String printFlags( final int flags ) {
    200        return printFlags(flags, FLAGS.UNKNOWN);
    201    }
    202
    203    /**
    204     * Return a string with the flag settings
    205     * @param flags the flags field to interpret
    206     * @param location the item type
    207     * @return the formatted string
    208     * @since 6.0 made public
    209     */
    210    public static String printFlags( final int flags, final FLAGS location ) {
    211        if (flags == 0) {
    212            return "0";
    213        }
    214        final StringBuilder buf = new StringBuilder();
    215        for (int i = 0, pow = 1; pow <= Const.MAX_ACC_FLAG; i++) {
    216            if ((flags & pow) != 0) {
    217                if ((pow == Const.ACC_SYNCHRONIZED) && (location == FLAGS.CLASS)) {
    218                    buf.append(CONSTANT_PREFIX+"ACC_SUPER | ");
    219                } else if ((pow == Const.ACC_VOLATILE) && (location == FLAGS.METHOD)) {
    220                    buf.append(CONSTANT_PREFIX+"ACC_BRIDGE | ");
    221                } else if ((pow == Const.ACC_TRANSIENT) && (location == FLAGS.METHOD)) {
    222                    buf.append(CONSTANT_PREFIX+"ACC_VARARGS | ");
    223                } else {
    224                    if (i < Const.ACCESS_NAMES_LENGTH) {
    225                        buf.append(CONSTANT_PREFIX+"ACC_").append(Const.getAccessName(i).toUpperCase(Locale.ENGLISH)).append( " | ");
    226                    } else {
    227                        buf.append(String.format (CONSTANT_PREFIX+"ACC_BIT %x | ", pow));
    228                    }
    229                }
    230            }
    231            pow <<= 1;
    232        }
    233        final String str = buf.toString();
    234        return str.substring(0, str.length() - 3);
    235    }
    236
    237
    238    static String printArgumentTypes( final Type[] arg_types ) {
    239        if (arg_types.length == 0) {
    240            return "Type.NO_ARGS";
    241        }
    242        final StringBuilder args = new StringBuilder();
    243        for (int i = 0; i < arg_types.length; i++) {
    244            args.append(printType(arg_types[i]));
    245            if (i < arg_types.length - 1) {
    246                args.append(", ");
    247            }
    248        }
    249        return "new Type[] { " + args.toString() + " }";
    250    }
    251
    252
    253    static String printType( final Type type ) {
    254        return printType(type.getSignature());
    255    }
    256
    257
    258    static String printType( final String signature ) {
    259        final Type type = Type.getType(signature);
    260        final byte t = type.getType();
    261        if (t <= Const.T_VOID) {
    262            return "Type." + Const.getTypeName(t).toUpperCase(Locale.ENGLISH);
    263        } else if (type.toString().equals("java.lang.String")) {
    264            return "Type.STRING";
    265        } else if (type.toString().equals("java.lang.Object")) {
    266            return "Type.OBJECT";
    267        } else if (type.toString().equals("java.lang.StringBuffer")) {
    268            return "Type.STRINGBUFFER";
    269        } else if (type instanceof ArrayType) {
    270            final ArrayType at = (ArrayType) type;
    271            return "new ArrayType(" + printType(at.getBasicType()) + ", " + at.getDimensions()
    272                    + ")";
    273        } else {
    274            return "new ObjectType(\"" + Utility.signatureToString(signature, false) + "\")";
    275        }
    276    }
    277
    278
    279    /** Default main method
    280     */
    281    public static void main( final String[] argv ) throws Exception {
    282        if (argv.length != 1) {
    283            System.out.println("Usage: BCELifier classname");
    284            System.out.println("\tThe class must exist on the classpath");
    285            return;
    286        }
    287        final JavaClass java_class = getJavaClass(argv[0]);
    288        final BCELifier bcelifier = new BCELifier(java_class, System.out);
    289        bcelifier.start();
    290    }
    291
    292
    293    // Needs to be accessible from unit test code
    294    static JavaClass getJavaClass(final String name) throws ClassNotFoundException, IOException {
    295        JavaClass java_class;
    296        if ((java_class = Repository.lookupClass(name)) == null) {
    297            java_class = new ClassParser(name).parse(); // May throw IOException
    298        }
    299        return java_class;
    300    }
    301}