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}