proxy.java

gcc的组建

          // handler.Code.exception_table.start_pc
          putU2(0);
          // handler.Code.exception_table.end_pc
          putU2(end_pc);
          // handler.Code.exception_table.handler_pc
          putU2(handler_pc);
          // handler.Code.exception_table.catch_type
          putU2(classInfo("java/lang/Error"));
          // handler.Code.exception_table.start_pc
          putU2(0);
          // handler.Code.exception_table.end_pc
          putU2(end_pc);
          // handler.Code.exception_table.handler_pc
          putU2(handler_pc);
          // handler.Code.exception_table.catch_type
          putU2(classInfo("java/lang/RuntimeException"));
          for (int j = 0; j < e.length; j++)
            {
              // handler.Code.exception_table.start_pc
              putU2(0);
              // handler.Code.exception_table.end_pc
              putU2(end_pc);
              // handler.Code.exception_table.handler_pc
              putU2(handler_pc);
              // handler.Code.exception_table.catch_type
              putU2(classInfo(e[j]));
            }
          // handler.Code.exception_table.start_pc
          putU2(0);
          // handler.Code.exception_table.end_pc
          putU2(end_pc);
          // handler.Code.exception_table.handler_pc -
          //   -8 for undeclared handler, which falls thru to normal one
          putU2(handler_pc - 8);
          // handler.Code.exception_table.catch_type
          putU2(0);
        }
      // handler.Code.attributes_count
      putU2(0);
      // handler.Code.attributes[]

      if (e.length > 0)
        {
          // handler.Exceptions.attribute_name_index
          putU2(utf8Info("Exceptions"));
          // handler.Exceptions.attribute_length
          putU4(2 * e.length + 2);
          // handler.Exceptions.number_of_exceptions
          putU2(e.length);
          // handler.Exceptions.exception_index_table[]
          for (int j = 0; j < e.length; j++)
            putU2(classInfo(e[j]));
        }
    }

    /**
     * Creates the Class object that corresponds to the bytecode buffers
     * built when this object was constructed.
     *
     * @param loader the class loader to define the proxy class in; null
     *        implies the bootstrap class loader
     * @return the proxy class Class object
     */
    Class generate(ClassLoader loader)
    {
      byte[] bytecode = new byte[pool.length() + stream.length()];
      // More efficient to bypass calling charAt() repetitively.
      char[] c = pool.toString().toCharArray();
      int i = c.length;
      while (--i >= 0)
        bytecode[i] = (byte) c[i];
      c = stream.toString().toCharArray();
      i = c.length;
      int j = bytecode.length;
      while (i > 0)
        bytecode[--j] = (byte) c[--i];

      // Patch the constant pool size, which we left at 0 earlier.
      int count = poolEntries.size() + 1;
      bytecode[8] = (byte) (count >> 8);
      bytecode[9] = (byte) count;

      try
        {
          Class vmClassLoader = Class.forName("java.lang.VMClassLoader");
          Class[] types = {ClassLoader.class, String.class,
                           byte[].class, int.class, int.class,
                           ProtectionDomain.class };
          Method m = vmClassLoader.getDeclaredMethod("defineClass", types);
          // We can bypass the security check of setAccessible(true), since
	  // we're in the same package.
          m.flag = true;

          Object[] args = {loader, qualName, bytecode, new Integer(0),
                           new Integer(bytecode.length),
                           Object.class.getProtectionDomain() };
          Class clazz = (Class) m.invoke(null, args);

          // Finally, initialize the m field of the proxy class, before
          // returning it.
          Field f = clazz.getDeclaredField("m");
          f.flag = true;
          // we can share the array, because it is not publicized
          f.set(null, methods);

          return clazz;
        }
      catch (Exception e)
        {
          // assert false;
          throw (Error) new InternalError("Unexpected: " + e).initCause(e);
        }
    }

    /**
     * Put a single byte on the stream.
     *
     * @param i the information to add (only lowest 8 bits are used)
     */
    private void putU1(int i)
    {
      stream.append((char) i);
    }

    /**
     * Put two bytes on the stream.
     *
     * @param i the information to add (only lowest 16 bits are used)
     */
    private void putU2(int i)
    {
      stream.append((char) (i >> 8)).append((char) i);
    }

    /**
     * Put four bytes on the stream.
     *
     * @param i the information to add (treated as unsigned)
     */
    private void putU4(int i)
    {
      stream.append((char) (i >> 24)).append((char) (i >> 16));
      stream.append((char) (i >> 8)).append((char) i);
    }

    /**
     * Put bytecode to load a constant integer on the stream. This only
     * needs to work for values less than Short.MAX_VALUE.
     *
     * @param i the int to add
     */
    private void putConst(int i)
    {
      if (i >= -1 && i <= 5)
        putU1(ICONST_0 + i);
      else if (i >= Byte.MIN_VALUE && i <= Byte.MAX_VALUE)
        {
          putU1(BIPUSH);
          putU1(i);
        }
      else
        {
          putU1(SIPUSH);
          putU2(i);
        }
    }

    /**
     * Put bytecode to load a given local variable on the stream.
     *
     * @param i the slot to load
     * @param type the base type of the load
     */
    private void putLoad(int i, Class type)
    {
      int offset = 0;
      if (type == long.class)
        offset = 1;
      else if (type == float.class)
        offset = 2;
      else if (type == double.class)
        offset = 3;
      else if (! type.isPrimitive())
        offset = 4;
      if (i < 4)
        putU1(ILOAD_0 + 4 * offset + i);
      else
        {
          putU1(ILOAD + offset);
          putU1(i);
        }
    }

    /**
     * Given a primitive type, return its wrapper class name.
     *
     * @param clazz the primitive type (but not void.class)
     * @return the internal form of the wrapper class name
     */
    private String wrapper(Class clazz)
    {
      if (clazz == boolean.class)
        return "java/lang/Boolean";
      if (clazz == byte.class)
        return "java/lang/Byte";
      if (clazz == short.class)
        return "java/lang/Short";
      if (clazz == char.class)
        return "java/lang/Character";
      if (clazz == int.class)
        return "java/lang/Integer";
      if (clazz == long.class)
        return "java/lang/Long";
      if (clazz == float.class)
        return "java/lang/Float";
      if (clazz == double.class)
        return "java/lang/Double";
      // assert false;
      return null;
    }

    /**
     * Returns the entry of this String in the Constant pool, adding it
     * if necessary.
     *
     * @param str the String to resolve
     * @return the index of the String in the constant pool
     */
    private char utf8Info(String str)
    {
      String utf8 = toUtf8(str);
      int len = utf8.length();
      return poolIndex("\1" + (char) (len >> 8) + (char) (len & 0xff) + utf8);
    }

    /**
     * Returns the entry of the appropriate class info structure in the
     * Constant pool, adding it if necessary.
     *
     * @param name the class name, in internal form
     * @return the index of the ClassInfo in the constant pool
     */
    private char classInfo(String name)
    {
      char index = utf8Info(name);
      char[] c = {7, (char) (index >> 8), (char) (index & 0xff)};
      return poolIndex(new String(c));
    }

    /**
     * Returns the entry of the appropriate class info structure in the
     * Constant pool, adding it if necessary.
     *
     * @param clazz the class type
     * @return the index of the ClassInfo in the constant pool
     */
    private char classInfo(Class clazz)
    {
      return classInfo(TypeSignature.getEncodingOfClass(clazz.getName(),
                                                        false));
    }

    /**
     * Returns the entry of the appropriate fieldref, methodref, or
     * interfacemethodref info structure in the Constant pool, adding it
     * if necessary.
     *
     * @param structure FIELD, METHOD, or INTERFACE
     * @param clazz the class name, in internal form
     * @param name the simple reference name
     * @param type the type of the reference
     * @return the index of the appropriate Info structure in the constant pool
     */
    private char refInfo(byte structure, String clazz, String name,
                         String type)
    {
      char cindex = classInfo(clazz);
      char ntindex = nameAndTypeInfo(name, type);
      // relies on FIELD == 1, METHOD == 2, INTERFACE == 3
      char[] c = {(char) (structure + 8),
                  (char) (cindex >> 8), (char) (cindex & 0xff),
                  (char) (ntindex >> 8), (char) (ntindex & 0xff)};
      return poolIndex(new String(c));
    }

    /**
     * Returns the entry of the appropriate nameAndTyperef info structure
     * in the Constant pool, adding it if necessary.
     *
     * @param name the simple name
     * @param type the reference type
     * @return the index of the NameAndTypeInfo structure in the constant pool
     */
    private char nameAndTypeInfo(String name, String type)
    {
      char nindex = utf8Info(name);
      char tindex = utf8Info(type);
      char[] c = {12, (char) (nindex >> 8), (char) (nindex & 0xff),
                  (char) (tindex >> 8), (char) (tindex & 0xff)};
      return poolIndex(new String(c));
    }

    /**
     * Converts a regular string to a UTF8 string, where the upper byte
     * of every char is 0, and '\\u0000' is not in the string.  This is
     * basically to use a String as a fancy byte[], and while it is less
     * efficient in memory use, it is easier for hashing.
     *
     * @param str the original, in straight unicode
     * @return a modified string, in UTF8 format in the low bytes
     */
    private String toUtf8(String str)
    {
      final char[] ca = str.toCharArray();
      final int len = ca.length;

      // Avoid object creation, if str is already fits UTF8.
      int i;
      for (i = 0; i < len; i++)
        if (ca[i] == 0 || ca[i] > '\u007f')
          break;
      if (i == len)
        return str;

      final StringBuffer sb = new StringBuffer(str);
      sb.setLength(i);
      for ( ; i < len; i++)
        {
          final char c = ca[i];
          if (c > 0 && c <= '\u007f')
            sb.append(c);
          else if (c <= '\u07ff') // includes '\0'
            {
              sb.append((char) (0xc0 | (c >> 6)));
              sb.append((char) (0x80 | (c & 0x6f)));
            }
          else
            {
              sb.append((char) (0xe0 | (c >> 12)));
              sb.append((char) (0x80 | ((c >> 6) & 0x6f)));
              sb.append((char) (0x80 | (c & 0x6f)));
            }
        }
      return sb.toString();
    }

    /**
     * Returns the location of a byte sequence (conveniently wrapped in
     * a String with all characters between \u0001 and \u00ff inclusive)
     * in the constant pool, adding it if necessary.
     *
     * @param sequence the byte sequence to look for
     * @return the index of the sequence
     * @throws IllegalArgumentException if this would make the constant
     *         pool overflow
     */
    private char poolIndex(String sequence)
    {
      Integer i = (Integer) poolEntries.get(sequence);
      if (i == null)
        {
          // pool starts at index 1
          int size = poolEntries.size() + 1;
          if (size >= 65535)
            throw new IllegalArgumentException("exceeds VM limitations");
          i = new Integer(size);
          poolEntries.put(sequence, i);
          pool.append(sequence);
        }
      return (char) i.intValue();
    }
  } // class ClassFactory
}