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 */ 017package org.apache.bcel.util; 018 019import java.io.IOException; 020import java.io.OutputStream; 021import java.io.OutputStreamWriter; 022import java.io.PrintWriter; 023import java.nio.charset.StandardCharsets; 024import java.util.Locale; 025 026import org.apache.bcel.Const; 027import org.apache.bcel.Repository; 028import org.apache.bcel.classfile.ClassParser; 029import org.apache.bcel.classfile.ConstantValue; 030import org.apache.bcel.classfile.ExceptionTable; 031import org.apache.bcel.classfile.Field; 032import org.apache.bcel.classfile.JavaClass; 033import org.apache.bcel.classfile.Method; 034import org.apache.bcel.classfile.Utility; 035import org.apache.bcel.generic.ArrayType; 036import org.apache.bcel.generic.ConstantPoolGen; 037import org.apache.bcel.generic.MethodGen; 038import org.apache.bcel.generic.Type; 039import org.apache.commons.lang3.StringUtils; 040 041/** 042 * This class takes a given JavaClass object and converts it to a Java program that creates that very class using BCEL. 043 * This gives new users of BCEL a useful example showing how things are done with BCEL. It does not cover all features 044 * of BCEL, but tries to mimic hand-written code as close as possible. 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, CLASS, METHOD, 053 } 054 055 // The base package name for imports; assumes Const is at the top level 056 // N.B we use the class so renames will be detected by the compiler/IDE 057 private static final String BASE_PACKAGE = Const.class.getPackage().getName(); 058 private static final String CONSTANT_PREFIX = Const.class.getSimpleName() + "."; 059 060 // Needs to be accessible from unit test code 061 static JavaClass getJavaClass(final String name) throws ClassNotFoundException, IOException { 062 JavaClass javaClass; 063 if ((javaClass = Repository.lookupClass(name)) == null) { 064 javaClass = new ClassParser(name).parse(); // May throw IOException 065 } 066 return javaClass; 067 } 068 069 /** 070 * Default main method 071 */ 072 public static void main(final String[] argv) throws Exception { 073 if (argv.length != 1) { 074 System.out.println("Usage: BCELifier className"); 075 System.out.println("\tThe class must exist on the classpath"); 076 return; 077 } 078 final BCELifier bcelifier = new BCELifier(getJavaClass(argv[0]), System.out); 079 bcelifier.start(); 080 } 081 082 static String printArgumentTypes(final Type[] argTypes) { 083 if (argTypes.length == 0) { 084 return "Type.NO_ARGS"; 085 } 086 final StringBuilder args = new StringBuilder(); 087 for (int i = 0; i < argTypes.length; i++) { 088 args.append(printType(argTypes[i])); 089 if (i < argTypes.length - 1) { 090 args.append(", "); 091 } 092 } 093 return "new Type[] { " + args.toString() + " }"; 094 } 095 096 static String printFlags(final int flags) { 097 return printFlags(flags, FLAGS.UNKNOWN); 098 } 099 100 /** 101 * Return a string with the flag settings 102 * 103 * @param flags the flags field to interpret 104 * @param location the item type 105 * @return the formatted string 106 * @since 6.0 made public 107 */ 108 public static String printFlags(final int flags, final FLAGS location) { 109 if (flags == 0) { 110 return "0"; 111 } 112 final StringBuilder buf = new StringBuilder(); 113 for (int i = 0, pow = 1; pow <= Const.MAX_ACC_FLAG_I; i++) { 114 if ((flags & pow) != 0) { 115 if (pow == Const.ACC_SYNCHRONIZED && location == FLAGS.CLASS) { 116 buf.append(CONSTANT_PREFIX).append("ACC_SUPER | "); 117 } else if (pow == Const.ACC_VOLATILE && location == FLAGS.METHOD) { 118 buf.append(CONSTANT_PREFIX).append("ACC_BRIDGE | "); 119 } else if (pow == Const.ACC_TRANSIENT && location == FLAGS.METHOD) { 120 buf.append(CONSTANT_PREFIX).append("ACC_VARARGS | "); 121 } else if (i < Const.ACCESS_NAMES_LENGTH) { 122 buf.append(CONSTANT_PREFIX).append("ACC_").append(Const.getAccessName(i).toUpperCase(Locale.ENGLISH)).append(" | "); 123 } else { 124 buf.append(String.format(CONSTANT_PREFIX + "ACC_BIT %x | ", pow)); 125 } 126 } 127 pow <<= 1; 128 } 129 final String str = buf.toString(); 130 return str.substring(0, str.length() - 3); 131 } 132 133 static String printType(final String signature) { 134 final Type type = Type.getType(signature); 135 final byte t = type.getType(); 136 if (t <= Const.T_VOID) { 137 return "Type." + Const.getTypeName(t).toUpperCase(Locale.ENGLISH); 138 } 139 if (type.toString().equals("java.lang.String")) { 140 return "Type.STRING"; 141 } 142 if (type.toString().equals("java.lang.Object")) { 143 return "Type.OBJECT"; 144 } 145 if (type.toString().equals("java.lang.StringBuffer")) { 146 return "Type.STRINGBUFFER"; 147 } 148 if (type instanceof ArrayType) { 149 final ArrayType at = (ArrayType) type; 150 return "new ArrayType(" + printType(at.getBasicType()) + ", " + at.getDimensions() + ")"; 151 } 152 return "new ObjectType(\"" + Utility.signatureToString(signature, false) + "\")"; 153 } 154 155 static String printType(final Type type) { 156 return printType(type.getSignature()); 157 } 158 159 private final JavaClass clazz; 160 161 private final PrintWriter printWriter; 162 163 private final ConstantPoolGen constantPoolGen; 164 165 /** 166 * Constructs a new instance. 167 * 168 * @param clazz Java class to "decompile". 169 * @param out where to print the Java program in UTF-8. 170 */ 171 public BCELifier(final JavaClass clazz, final OutputStream out) { 172 this.clazz = clazz; 173 this.printWriter = new PrintWriter(new OutputStreamWriter(out, StandardCharsets.UTF_8), false); 174 this.constantPoolGen = new ConstantPoolGen(this.clazz.getConstantPool()); 175 } 176 177 private void printCreate() { 178 printWriter.println(" public void create(OutputStream out) throws IOException {"); 179 final Field[] fields = clazz.getFields(); 180 if (fields.length > 0) { 181 printWriter.println(" createFields();"); 182 } 183 final Method[] methods = clazz.getMethods(); 184 for (int i = 0; i < methods.length; i++) { 185 printWriter.println(" createMethod_" + i + "();"); 186 } 187 printWriter.println(" _cg.getJavaClass().dump(out);"); 188 printWriter.println(" }"); 189 printWriter.println(); 190 } 191 192 private void printMain() { 193 final String className = clazz.getClassName(); 194 printWriter.println(" public static void main(String[] args) throws Exception {"); 195 printWriter.println(" " + className + "Creator creator = new " + className + "Creator();"); 196 printWriter.println(" creator.create(new FileOutputStream(\"" + className + ".class\"));"); 197 printWriter.println(" }"); 198 } 199 200 /** 201 * Start Java code generation 202 */ 203 public void start() { 204 visitJavaClass(clazz); 205 printWriter.flush(); 206 } 207 208 @Override 209 public void visitField(final Field field) { 210 printWriter.println(); 211 printWriter.println( 212 " field = new FieldGen(" + printFlags(field.getAccessFlags()) + ", " + printType(field.getSignature()) + ", \"" + field.getName() + "\", _cp);"); 213 final ConstantValue cv = field.getConstantValue(); 214 if (cv != null) { 215 printWriter.print(" field.setInitValue("); 216 if (field.getType() == Type.CHAR) { 217 printWriter.print("(char)"); 218 } 219 if (field.getType() == Type.SHORT) { 220 printWriter.print("(short)"); 221 } 222 if (field.getType() == Type.BYTE) { 223 printWriter.print("(byte)"); 224 } 225 printWriter.print(cv); 226 if (field.getType() == Type.LONG) { 227 printWriter.print("L"); 228 } 229 if (field.getType() == Type.FLOAT) { 230 printWriter.print("F"); 231 } 232 if (field.getType() == Type.DOUBLE) { 233 printWriter.print("D"); 234 } 235 printWriter.println(");"); 236 } 237 printWriter.println(" _cg.addField(field.getField());"); 238 } 239 240 @Override 241 public void visitJavaClass(final JavaClass clazz) { 242 String className = clazz.getClassName(); 243 final String superName = clazz.getSuperclassName(); 244 final String packageName = clazz.getPackageName(); 245 final String inter = Utility.printArray(clazz.getInterfaceNames(), false, true); 246 if (StringUtils.isNotEmpty(packageName)) { 247 className = className.substring(packageName.length() + 1); 248 printWriter.println("package " + packageName + ";"); 249 printWriter.println(); 250 } 251 printWriter.println("import " + BASE_PACKAGE + ".generic.*;"); 252 printWriter.println("import " + BASE_PACKAGE + ".classfile.*;"); 253 printWriter.println("import " + BASE_PACKAGE + ".*;"); 254 printWriter.println("import java.io.*;"); 255 printWriter.println(); 256 printWriter.println("public class " + className + "Creator {"); 257 printWriter.println(" private InstructionFactory _factory;"); 258 printWriter.println(" private ConstantPoolGen _cp;"); 259 printWriter.println(" private ClassGen _cg;"); 260 printWriter.println(); 261 printWriter.println(" public " + className + "Creator() {"); 262 printWriter.println(" _cg = new ClassGen(\"" + (packageName.isEmpty() ? className : packageName + "." + className) + "\", \"" + superName 263 + "\", " + "\"" + clazz.getSourceFileName() + "\", " + printFlags(clazz.getAccessFlags(), FLAGS.CLASS) + ", " + "new String[] { " + inter + " });"); 264 printWriter.println(" _cg.setMajor(" + clazz.getMajor() + ");"); 265 printWriter.println(" _cg.setMinor(" + clazz.getMinor() + ");"); 266 printWriter.println(); 267 printWriter.println(" _cp = _cg.getConstantPool();"); 268 printWriter.println(" _factory = new InstructionFactory(_cg, _cp);"); 269 printWriter.println(" }"); 270 printWriter.println(); 271 printCreate(); 272 final Field[] fields = clazz.getFields(); 273 if (fields.length > 0) { 274 printWriter.println(" private void createFields() {"); 275 printWriter.println(" FieldGen field;"); 276 for (final Field field : fields) { 277 field.accept(this); 278 } 279 printWriter.println(" }"); 280 printWriter.println(); 281 } 282 final Method[] methods = clazz.getMethods(); 283 for (int i = 0; i < methods.length; i++) { 284 printWriter.println(" private void createMethod_" + i + "() {"); 285 methods[i].accept(this); 286 printWriter.println(" }"); 287 printWriter.println(); 288 } 289 printMain(); 290 printWriter.println("}"); 291 } 292 293 @Override 294 public void visitMethod(final Method method) { 295 final MethodGen mg = new MethodGen(method, clazz.getClassName(), constantPoolGen); 296 printWriter.println(" InstructionList il = new InstructionList();"); 297 printWriter.println(" MethodGen method = new MethodGen(" + printFlags(method.getAccessFlags(), FLAGS.METHOD) + ", " + printType(mg.getReturnType()) 298 + ", " + printArgumentTypes(mg.getArgumentTypes()) + ", " + "new String[] { " + Utility.printArray(mg.getArgumentNames(), false, true) + " }, \"" 299 + method.getName() + "\", \"" + clazz.getClassName() + "\", il, _cp);"); 300 final ExceptionTable exceptionTable = method.getExceptionTable(); 301 if (exceptionTable != null) { 302 final String[] exceptionNames = exceptionTable.getExceptionNames(); 303 for (final String exceptionName : exceptionNames) { 304 printWriter.print(" method.addException(\""); 305 printWriter.print(exceptionName); 306 printWriter.println("\");"); 307 } 308 } 309 printWriter.println(); 310 final BCELFactory factory = new BCELFactory(mg, printWriter); 311 factory.start(); 312 printWriter.println(" method.setMaxStack();"); 313 printWriter.println(" method.setMaxLocals();"); 314 printWriter.println(" _cg.addMethod(method.getMethod());"); 315 printWriter.println(" il.dispose();"); 316 } 317}