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package com.sun.org.apache.bcel.internal.util;

import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Locale;

import com.sun.org.apache.bcel.internal.Const;
import com.sun.org.apache.bcel.internal.Repository;
import com.sun.org.apache.bcel.internal.classfile.ClassParser;
import com.sun.org.apache.bcel.internal.classfile.ConstantValue;
import com.sun.org.apache.bcel.internal.classfile.Field;
import com.sun.org.apache.bcel.internal.classfile.JavaClass;
import com.sun.org.apache.bcel.internal.classfile.Method;
import com.sun.org.apache.bcel.internal.classfile.Utility;
import com.sun.org.apache.bcel.internal.generic.ArrayType;
import com.sun.org.apache.bcel.internal.generic.ConstantPoolGen;
import com.sun.org.apache.bcel.internal.generic.MethodGen;
import com.sun.org.apache.bcel.internal.generic.Type;

This class takes a given JavaClass object and converts it to a Java program that creates that very class using BCEL. This gives new users of BCEL a useful example showing how things are done with BCEL. It does not cover all features of BCEL, but tries to mimic hand-written code as close as possible.
/** * This class takes a given JavaClass object and converts it to a * Java program that creates that very class using BCEL. This * gives new users of BCEL a useful example showing how things * are done with BCEL. It does not cover all features of BCEL, * but tries to mimic hand-written code as close as possible. * */
public class BCELifier extends com.sun.org.apache.bcel.internal.classfile.EmptyVisitor {
Enum corresponding to flag source.
/** * Enum corresponding to flag source. */
public enum FLAGS { UNKNOWN, CLASS, METHOD, } // The base package name for imports; assumes Const is at the top level // N.B we use the class so renames will be detected by the compiler/IDE private static final String BASE_PACKAGE = Const.class.getPackage().getName(); private static final String CONSTANT_PREFIX = Const.class.getSimpleName()+"."; private final JavaClass _clazz; private final PrintWriter _out; private final ConstantPoolGen _cp;
Params:
  • clazz – Java class to "decompile"
  • out – where to output Java program
/** @param clazz Java class to "decompile" * @param out where to output Java program */
public BCELifier(final JavaClass clazz, final OutputStream out) { _clazz = clazz; _out = new PrintWriter(out); _cp = new ConstantPoolGen(_clazz.getConstantPool()); }
Start Java code generation
/** Start Java code generation */
public void start() { visitJavaClass(_clazz); _out.flush(); } @Override public void visitJavaClass( final JavaClass clazz ) { String class_name = clazz.getClassName(); final String super_name = clazz.getSuperclassName(); final String package_name = clazz.getPackageName(); final String inter = Utility.printArray(clazz.getInterfaceNames(), false, true); if (!"".equals(package_name)) { class_name = class_name.substring(package_name.length() + 1); _out.println("package " + package_name + ";"); _out.println(); } _out.println("import " + BASE_PACKAGE + ".generic.*;"); _out.println("import " + BASE_PACKAGE + ".classfile.*;"); _out.println("import " + BASE_PACKAGE + ".*;"); _out.println("import java.io.*;"); _out.println(); _out.println("public class " + class_name + "Creator {"); _out.println(" private InstructionFactory _factory;"); _out.println(" private ConstantPoolGen _cp;"); _out.println(" private ClassGen _cg;"); _out.println(); _out.println(" public " + class_name + "Creator() {"); _out.println(" _cg = new ClassGen(\"" + (("".equals(package_name)) ? class_name : package_name + "." + class_name) + "\", \"" + super_name + "\", " + "\"" + clazz.getSourceFileName() + "\", " + printFlags(clazz.getAccessFlags(), FLAGS.CLASS) + ", " + "new String[] { " + inter + " });"); _out.println(" _cg.setMajor(" + clazz.getMajor() +");"); _out.println(" _cg.setMinor(" + clazz.getMinor() +");"); _out.println(); _out.println(" _cp = _cg.getConstantPool();"); _out.println(" _factory = new InstructionFactory(_cg, _cp);"); _out.println(" }"); _out.println(); printCreate(); final Field[] fields = clazz.getFields(); if (fields.length > 0) { _out.println(" private void createFields() {"); _out.println(" FieldGen field;"); for (final Field field : fields) { field.accept(this); } _out.println(" }"); _out.println(); } final Method[] methods = clazz.getMethods(); for (int i = 0; i < methods.length; i++) { _out.println(" private void createMethod_" + i + "() {"); methods[i].accept(this); _out.println(" }"); _out.println(); } printMain(); _out.println("}"); } private void printCreate() { _out.println(" public void create(OutputStream out) throws IOException {"); final Field[] fields = _clazz.getFields(); if (fields.length > 0) { _out.println(" createFields();"); } final Method[] methods = _clazz.getMethods(); for (int i = 0; i < methods.length; i++) { _out.println(" createMethod_" + i + "();"); } _out.println(" _cg.getJavaClass().dump(out);"); _out.println(" }"); _out.println(); } private void printMain() { final String class_name = _clazz.getClassName(); _out.println(" public static void main(String[] args) throws Exception {"); _out.println(" " + class_name + "Creator creator = new " + class_name + "Creator();"); _out.println(" creator.create(new FileOutputStream(\"" + class_name + ".class\"));"); _out.println(" }"); } @Override public void visitField( final Field field ) { _out.println(); _out.println(" field = new FieldGen(" + printFlags(field.getAccessFlags()) + ", " + printType(field.getSignature()) + ", \"" + field.getName() + "\", _cp);"); final ConstantValue cv = field.getConstantValue(); if (cv != null) { final String value = cv.toString(); _out.println(" field.setInitValue(" + value + ")"); } _out.println(" _cg.addField(field.getField());"); } @Override public void visitMethod( final Method method ) { final MethodGen mg = new MethodGen(method, _clazz.getClassName(), _cp); _out.println(" InstructionList il = new InstructionList();"); _out.println(" MethodGen method = new MethodGen(" + printFlags(method.getAccessFlags(), FLAGS.METHOD) + ", " + printType(mg.getReturnType()) + ", " + printArgumentTypes(mg.getArgumentTypes()) + ", " + "new String[] { " + Utility.printArray(mg.getArgumentNames(), false, true) + " }, \"" + method.getName() + "\", \"" + _clazz.getClassName() + "\", il, _cp);"); _out.println(); final BCELFactory factory = new BCELFactory(mg, _out); factory.start(); _out.println(" method.setMaxStack();"); _out.println(" method.setMaxLocals();"); _out.println(" _cg.addMethod(method.getMethod());"); _out.println(" il.dispose();"); } static String printFlags( final int flags ) { return printFlags(flags, FLAGS.UNKNOWN); }
Return a string with the flag settings
Params:
  • flags – the flags field to interpret
  • location – the item type
Returns:the formatted string
Since:6.0 made public
/** * Return a string with the flag settings * @param flags the flags field to interpret * @param location the item type * @return the formatted string * @since 6.0 made public */
public static String printFlags( final int flags, final FLAGS location ) { if (flags == 0) { return "0"; } final StringBuilder buf = new StringBuilder(); for (int i = 0, pow = 1; pow <= Const.MAX_ACC_FLAG_I; i++) { if ((flags & pow) != 0) { if ((pow == Const.ACC_SYNCHRONIZED) && (location == FLAGS.CLASS)) { buf.append(CONSTANT_PREFIX+"ACC_SUPER | "); } else if ((pow == Const.ACC_VOLATILE) && (location == FLAGS.METHOD)) { buf.append(CONSTANT_PREFIX+"ACC_BRIDGE | "); } else if ((pow == Const.ACC_TRANSIENT) && (location == FLAGS.METHOD)) { buf.append(CONSTANT_PREFIX+"ACC_VARARGS | "); } else { if (i < Const.ACCESS_NAMES_LENGTH) { buf.append(CONSTANT_PREFIX+"ACC_") .append(Const.getAccessName(i).toUpperCase(Locale.ENGLISH)) .append( " | "); } else { buf.append(String.format (CONSTANT_PREFIX+"ACC_BIT %x | ", pow)); } } } pow <<= 1; } final String str = buf.toString(); return str.substring(0, str.length() - 3); } static String printArgumentTypes( final Type[] arg_types ) { if (arg_types.length == 0) { return "Type.NO_ARGS"; } final StringBuilder args = new StringBuilder(); for (int i = 0; i < arg_types.length; i++) { args.append(printType(arg_types[i])); if (i < arg_types.length - 1) { args.append(", "); } } return "new Type[] { " + args.toString() + " }"; } static String printType( final Type type ) { return printType(type.getSignature()); } static String printType( final String signature ) { final Type type = Type.getType(signature); final byte t = type.getType(); if (t <= Const.T_VOID) { return "Type." + Const.getTypeName(t).toUpperCase(Locale.ENGLISH); } else if (type.toString().equals("java.lang.String")) { return "Type.STRING"; } else if (type.toString().equals("java.lang.Object")) { return "Type.OBJECT"; } else if (type.toString().equals("java.lang.StringBuffer")) { return "Type.STRINGBUFFER"; } else if (type instanceof ArrayType) { final ArrayType at = (ArrayType) type; return "new ArrayType(" + printType(at.getBasicType()) + ", " + at.getDimensions() + ")"; } else { return "new ObjectType(\"" + Utility.signatureToString(signature, false) + "\")"; } }
Default main method
/** Default main method */
public static void main( final String[] argv ) throws Exception { if (argv.length != 1) { System.out.println("Usage: BCELifier classname"); System.out.println("\tThe class must exist on the classpath"); return; } final JavaClass java_class = getJavaClass(argv[0]); final BCELifier bcelifier = new BCELifier(java_class, System.out); bcelifier.start(); } // Needs to be accessible from unit test code static JavaClass getJavaClass(final String name) throws ClassNotFoundException, IOException { JavaClass java_class; if ((java_class = Repository.lookupClass(name)) == null) { java_class = new ClassParser(name).parse(); // May throw IOException } return java_class; } }