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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   *  Unless required by applicable law or agreed to in writing, software
12   *  distributed under the License is distributed on an "AS IS" BASIS,
13   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   *  See the License for the specific language governing permissions and
15   *  limitations under the License.
16   *
17   */
18  package org.apache.bcel.util;
19  
20  import java.io.IOException;
21  import java.io.OutputStream;
22  import java.io.PrintWriter;
23  import java.util.Locale;
24  
25  import org.apache.bcel.Const;
26  import org.apache.bcel.Repository;
27  import org.apache.bcel.classfile.ClassParser;
28  import org.apache.bcel.classfile.ConstantValue;
29  import org.apache.bcel.classfile.Field;
30  import org.apache.bcel.classfile.JavaClass;
31  import org.apache.bcel.classfile.Method;
32  import org.apache.bcel.classfile.Utility;
33  import org.apache.bcel.generic.ArrayType;
34  import org.apache.bcel.generic.ConstantPoolGen;
35  import org.apache.bcel.generic.MethodGen;
36  import org.apache.bcel.generic.Type;
37  
38  /**
39   * This class takes a given JavaClass object and converts it to a
40   * Java program that creates that very class using BCEL. This
41   * gives new users of BCEL a useful example showing how things
42   * are done with BCEL. It does not cover all features of BCEL,
43   * but tries to mimic hand-written code as close as possible.
44   *
45   * @version $Id: BCELifier.html 1018313 2017-09-18 09:03:04Z britter $
46   */
47  public class BCELifier extends org.apache.bcel.classfile.EmptyVisitor {
48  
49      /**
50       * Enum corresponding to flag source.
51       */
52      public enum FLAGS {
53          UNKNOWN,
54          CLASS,
55          METHOD,
56      }
57  
58      // The base package name for imports; assumes Const is at the top level
59      // N.B we use the class so renames will be detected by the compiler/IDE
60      private static final String BASE_PACKAGE = Const.class.getPackage().getName();
61      private static final String CONSTANT_PREFIX = Const.class.getSimpleName()+".";
62  
63      private final JavaClass _clazz;
64      private final PrintWriter _out;
65      private final ConstantPoolGen _cp;
66  
67      /** @param clazz Java class to "decompile"
68       * @param out where to output Java program
69       */
70      public BCELifier(final JavaClass clazz, final OutputStream out) {
71          _clazz = clazz;
72          _out = new PrintWriter(out);
73          _cp = new ConstantPoolGen(_clazz.getConstantPool());
74      }
75  
76  
77      /** Start Java code generation
78       */
79      public void start() {
80          visitJavaClass(_clazz);
81          _out.flush();
82      }
83  
84  
85      @Override
86      public void visitJavaClass( final JavaClass clazz ) {
87          String class_name = clazz.getClassName();
88          final String super_name = clazz.getSuperclassName();
89          final String package_name = clazz.getPackageName();
90          final String inter = Utility.printArray(clazz.getInterfaceNames(), false, true);
91          if (!"".equals(package_name)) {
92              class_name = class_name.substring(package_name.length() + 1);
93              _out.println("package " + package_name + ";");
94              _out.println();
95          }
96          _out.println("import " + BASE_PACKAGE + ".generic.*;");
97          _out.println("import " + BASE_PACKAGE + ".classfile.*;");
98          _out.println("import " + BASE_PACKAGE + ".*;");
99          _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 }