objectstreamclass.java

gcc的组建

  {
    String name1 = c1.getName();
    String name2 = c2.getName();

    int id1 = name1.lastIndexOf('.');
    int id2 = name2.lastIndexOf('.');

    // Handle the default package
    if (id1 == -1 || id2 == -1)
      return id1 == id2;

    String package1 = name1.substring(0, id1);
    String package2 = name2.substring(0, id2);

    return package1.equals(package2);
  }

  final static Class[] noArgs = new Class[0];

  private static Method findAccessibleMethod(String name, Class from)
  {
    for (Class c = from; c != null; c = c.getSuperclass())
      {
	try
	  {
	    Method res = c.getDeclaredMethod(name, noArgs);
	    int mods = res.getModifiers();
	    
	    if (c == from  
		|| Modifier.isProtected(mods)
		|| Modifier.isPublic(mods)
		|| (! Modifier.isPrivate(mods) && inSamePackage(c, from)))
	      {
		AccessController.doPrivileged(new SetAccessibleAction(res));
		return res;
	      }
	  }
	catch (NoSuchMethodException e)
	  {
	  }
      }

    return null;
  }

  private void cacheMethods()
  {
    Method[] methods = forClass().getDeclaredMethods();

    readObjectMethod = findMethod(methods, "readObject",
				  new Class[] { ObjectInputStream.class },
				  Void.TYPE, true);
    writeObjectMethod = findMethod(methods, "writeObject",
                                   new Class[] { ObjectOutputStream.class },
                                   Void.TYPE, true);

    // readResolve and writeReplace can be in parent classes, as long as they
    // are accessible from this class.
    readResolveMethod = findAccessibleMethod("readResolve", forClass());
    writeReplaceMethod = findAccessibleMethod("writeReplace", forClass());
  }

  private ObjectStreamClass(Class cl)
  {
    uid = 0;
    flags = 0;
    isProxyClass = Proxy.isProxyClass(cl);

    clazz = cl;
    cacheMethods();
    name = cl.getName();
    setFlags(cl);
    setFields(cl);
    // to those class nonserializable, its uid field is 0
    if ( (Serializable.class).isAssignableFrom(cl) && !isProxyClass)
      uid = getClassUID(cl);
    superClass = lookup(cl.getSuperclass());
  }


  // Sets bits in flags according to features of CL.
  private void setFlags(Class cl)
  {
    if ((java.io.Externalizable.class).isAssignableFrom(cl))
      flags |= ObjectStreamConstants.SC_EXTERNALIZABLE;
    else if ((java.io.Serializable.class).isAssignableFrom(cl))
      // only set this bit if CL is NOT Externalizable
      flags |= ObjectStreamConstants.SC_SERIALIZABLE;

    if (writeObjectMethod != null)
      flags |= ObjectStreamConstants.SC_WRITE_METHOD;
  }


  // Sets fields to be a sorted array of the serializable fields of
  // clazz.
  private void setFields(Class cl)
  {
    SetAccessibleAction setAccessible = new SetAccessibleAction();

    if (!isSerializable() || isExternalizable())
      {
	fields = NO_FIELDS;
	return;
      }

    try
      {
	final Field f =
	  cl.getDeclaredField("serialPersistentFields");
	setAccessible.setMember(f);
	AccessController.doPrivileged(setAccessible);
	int modifiers = f.getModifiers();

	if (Modifier.isStatic(modifiers)
	    && Modifier.isFinal(modifiers)
	    && Modifier.isPrivate(modifiers))
	  {
	    fields = getSerialPersistentFields(cl);
	    if (fields != null)
	      {
		Arrays.sort (fields);
		// Retrieve field reference.
		for (int i=0; i < fields.length; i++)
		  {
		    try
		      {
			fields[i].lookupField(cl);
		      }
		    catch (NoSuchFieldException _)
		      {
			fields[i].setToSet(false);
		      }
		  }
		
		calculateOffsets();
		return;
	      }
	  }
      }
    catch (NoSuchFieldException ignore)
      {
      }
    catch (IllegalAccessException ignore)
      {
      }

    int num_good_fields = 0;
    Field[] all_fields = cl.getDeclaredFields();

    int modifiers;
    // set non-serializable fields to null in all_fields
    for (int i = 0; i < all_fields.length; i++)
      {
	modifiers = all_fields[i].getModifiers();
	if (Modifier.isTransient(modifiers)
	    || Modifier.isStatic(modifiers))
	  all_fields[i] = null;
	else
	  num_good_fields++;
      }

    // make a copy of serializable (non-null) fields
    fields = new ObjectStreamField[ num_good_fields ];
    for (int from = 0, to = 0; from < all_fields.length; from++)
      if (all_fields[from] != null)
	{
	  final Field f = all_fields[from];
	  setAccessible.setMember(f);
	  AccessController.doPrivileged(setAccessible);
	  fields[to] = new ObjectStreamField(all_fields[from]);
	  to++;
	}

    Arrays.sort(fields);
    // Make sure we don't have any duplicate field names
    // (Sun JDK 1.4.1. throws an Internal Error as well)
    for (int i = 1; i < fields.length; i++)
      {
	if(fields[i - 1].getName().equals(fields[i].getName()))
	    throw new InternalError("Duplicate field " + 
			fields[i].getName() + " in class " + cl.getName());
      }
    calculateOffsets();
  }

  // Returns the serial version UID defined by class, or if that
  // isn't present, calculates value of serial version UID.
  private long getClassUID(Class cl)
  {
    try
      {
	// Use getDeclaredField rather than getField, since serialVersionUID
	// may not be public AND we only want the serialVersionUID of this
	// class, not a superclass or interface.
	final Field suid = cl.getDeclaredField("serialVersionUID");
	SetAccessibleAction setAccessible = new SetAccessibleAction(suid);
	AccessController.doPrivileged(setAccessible);
	int modifiers = suid.getModifiers();

	if (Modifier.isStatic(modifiers)
	    && Modifier.isFinal(modifiers)
	    && suid.getType() == Long.TYPE)
	  return suid.getLong(null);
      }
    catch (NoSuchFieldException ignore)
      {
      }
    catch (IllegalAccessException ignore)
      {
      }

    // cl didn't define serialVersionUID, so we have to compute it
    try
      {
	MessageDigest md;
	try 
	  {
	    md = MessageDigest.getInstance("SHA");
	  }
	catch (NoSuchAlgorithmException e)
	  {
	    // If a provider already provides SHA, use it; otherwise, use this.
	    Gnu gnuProvider = new Gnu();
	    Security.addProvider(gnuProvider);
	    md = MessageDigest.getInstance("SHA");
	  }

	DigestOutputStream digest_out =
	  new DigestOutputStream(nullOutputStream, md);
	DataOutputStream data_out = new DataOutputStream(digest_out);

	data_out.writeUTF(cl.getName());

	int modifiers = cl.getModifiers();
	// just look at interesting bits
	modifiers = modifiers & (Modifier.ABSTRACT | Modifier.FINAL
				 | Modifier.INTERFACE | Modifier.PUBLIC);
	data_out.writeInt(modifiers);

	// Pretend that an array has no interfaces, because when array
	// serialization was defined (JDK 1.1), arrays didn't have it.
	if (! cl.isArray())
	  {
	    Class[] interfaces = cl.getInterfaces();
	    Arrays.sort(interfaces, interfaceComparator);
	    for (int i = 0; i < interfaces.length; i++)
	      data_out.writeUTF(interfaces[i].getName());
	  }

	Field field;
	Field[] fields = cl.getDeclaredFields();
	Arrays.sort(fields, memberComparator);
	for (int i = 0; i < fields.length; i++)
	  {
	    field = fields[i];
	    modifiers = field.getModifiers();
	    if (Modifier.isPrivate(modifiers)
		&& (Modifier.isStatic(modifiers)
		    || Modifier.isTransient(modifiers)))
	      continue;

	    data_out.writeUTF(field.getName());
	    data_out.writeInt(modifiers);
	    data_out.writeUTF(TypeSignature.getEncodingOfClass (field.getType()));
	  }

	// write class initializer method if present
	if (VMObjectStreamClass.hasClassInitializer(cl))
	  {
	    data_out.writeUTF("<clinit>");
	    data_out.writeInt(Modifier.STATIC);
	    data_out.writeUTF("()V");
	  }

	Constructor constructor;
	Constructor[] constructors = cl.getDeclaredConstructors();
	Arrays.sort (constructors, memberComparator);
	for (int i = 0; i < constructors.length; i++)
	  {
	    constructor = constructors[i];
	    modifiers = constructor.getModifiers();
	    if (Modifier.isPrivate(modifiers))
	      continue;

	    data_out.writeUTF("<init>");
	    data_out.writeInt(modifiers);

	    // the replacement of '/' with '.' was needed to make computed
	    // SUID's agree with those computed by JDK
	    data_out.writeUTF 
	      (TypeSignature.getEncodingOfConstructor(constructor).replace('/','.'));
	  }

	Method method;
	Method[] methods = cl.getDeclaredMethods();
	Arrays.sort(methods, memberComparator);
	for (int i = 0; i < methods.length; i++)
	  {
	    method = methods[i];
	    modifiers = method.getModifiers();
	    if (Modifier.isPrivate(modifiers))
	      continue;

	    data_out.writeUTF(method.getName());
	    data_out.writeInt(modifiers);

	    // the replacement of '/' with '.' was needed to make computed
	    // SUID's agree with those computed by JDK
	    data_out.writeUTF
	      (TypeSignature.getEncodingOfMethod(method).replace('/', '.'));
	  }

	data_out.close();
	byte[] sha = md.digest();
	long result = 0;
	int len = sha.length < 8 ? sha.length : 8;
	for (int i = 0; i < len; i++)
	  result += (long) (sha[i] & 0xFF) << (8 * i);

	return result;
      }
    catch (NoSuchAlgorithmException e)
      {
	throw new RuntimeException
	  ("The SHA algorithm was not found to use in computing the Serial Version UID for class "
	   + cl.getName(), e);
      }
    catch (IOException ioe)
      {
	throw new RuntimeException(ioe);
      }
  }

  /**
   * Returns the value of CLAZZ's private static final field named
   * `serialPersistentFields'. It performs some sanity checks before
   * returning the real array. Besides, the returned array is a clean
   * copy of the original. So it can be modified.
   *
   * @param clazz Class to retrieve 'serialPersistentFields' from.
   * @return The content of 'serialPersistentFields'.
   */
  private ObjectStreamField[] getSerialPersistentFields(Class clazz) 
    throws NoSuchFieldException, IllegalAccessException
  {
    ObjectStreamField[] fieldsArray = null;
    ObjectStreamField[] o;

    // Use getDeclaredField rather than getField for the same reason
    // as above in getDefinedSUID.
    Field f = clazz.getDeclaredField("serialPersistentFields");
    f.setAccessible(true);

    int modifiers = f.getModifiers();
    if (!(Modifier.isStatic(modifiers) &&
	  Modifier.isFinal(modifiers) &&
	  Modifier.isPrivate(modifiers)))
      return null;
    
    o = (ObjectStreamField[]) f.get(null);
    
    if (o == null)
      return null;

    fieldsArray = new ObjectStreamField[ o.length ];
    System.arraycopy(o, 0, fieldsArray, 0, o.length);

    return fieldsArray;
  }

  /**
   * Returns a new instance of the Class this ObjectStreamClass corresponds
   * to.
   * Note that this should only be used for Externalizable classes.
   *
   * @return A new instance.
   */
  Externalizable newInstance() throws InvalidClassException
  {
    synchronized(this)
    {
	if (constructor == null)
	{
	    try
	    {
		final Constructor c = clazz.getConstructor(new Class[0]);

		AccessController.doPrivileged(new PrivilegedAction()
		{
		    public Object run()
		    {
			c.setAccessible(true);
			return null;
		    }
		});

		constructor = c;
	    }
	    catch(NoSuchMethodException x)
	    {
		throw new InvalidClassException(clazz.getName(),
		    "No public zero-argument constructor");
	    }
	}
    }

    try
    {
	return (Externalizable)constructor.newInstance(null);
    }
    catch(Exception x)
    {
	throw (InvalidClassException)
	    new InvalidClassException(clazz.getName(),
		     "Unable to instantiate").initCause(x);
    }
  }

  public static final ObjectStreamField[] NO_FIELDS = {};

  private static Hashtable classLookupTable = new Hashtable();
  private static final NullOutputStream nullOutputStream = new NullOutputStream();
  private static final Comparator interfaceComparator = new InterfaceComparator();
  private static final Comparator memberComparator = new MemberComparator();
  private static final
    Class[] writeMethodArgTypes = { java.io.ObjectOutputStream.class };

  private ObjectStreamClass superClass;
  private Class clazz;
  private String name;
  private long uid;
  private byte flags;

  // this field is package protected so that ObjectInputStream and
  // ObjectOutputStream can access it directly
  ObjectStreamField[] fields;

  // these are accessed by ObjectIn/OutputStream
  int primFieldSize = -1;  // -1 if not yet calculated
  int objectFieldCount;

  Method readObjectMethod;
  Method readResolveMethod;
  Method writeReplaceMethod;
  Method writeObjectMethod;
  boolean realClassIsSerializable;
  boolean realClassIsExternalizable;
  ObjectStreamField[] fieldMapping;
  Constructor firstNonSerializableParentConstructor;
  private Constructor constructor;  // default constructor for Externalizable

  boolean isProxyClass = false;

  // This is probably not necessary because this class is special cased already
  // but it will avoid showing up as a discrepancy when comparing SUIDs.
  private static final long serialVersionUID = -6120832682080437368L;


  // interfaces are compared only by name
  private static final class InterfaceComparator implements Comparator
  {
    public int compare(Object o1, Object o2)
    {
      return ((Class) o1).getName().compareTo(((Class) o2).getName());
    }
  }


  // Members (Methods and Constructors) are compared first by name,
  // conflicts are resolved by comparing type signatures
  private static final class MemberComparator implements Comparator
  {
    public int compare(Object o1, Object o2)
    {
      Member m1 = (Member) o1;
      Member m2 = (Member) o2;

      int comp = m1.getName().compareTo(m2.getName());

      if (comp == 0)
        return TypeSignature.getEncodingOfMember(m1).
	  compareTo(TypeSignature.getEncodingOfMember(m2));
      else
        return comp;
    }
  }
}