java.io
Class ObjectInputStream.HandleTable

java.lang.Object
  java.io.ObjectInputStream.HandleTable

Enclosing class:

ObjectInputStream

private static class ObjectInputStream.HandleTable

extends Object

Unsynchronized table which tracks wire handle to object mappings, as well as ClassNotFoundExceptions associated with deserialized objects. This class implements an exception-propagation algorithm for determining which objects should have ClassNotFoundExceptions associated with them, taking into account cycles and discontinuities (e.g., skipped fields) in the object graph.

General use of the table is as follows: during deserialization, a given object is first assigned a handle by calling the assign method. This method leaves the assigned handle in an "open" state, wherein dependencies on the exception status of other handles can be registered by calling the markDependency method, or an exception can be directly associated with the handle by calling markException. When a handle is tagged with an exception, the HandleTable assumes responsibility for propagating the exception to any other objects which depend (transitively) on the exception-tagged object.

Once all exception information/dependencies for the handle have been registered, the handle should be "closed" by calling the finish method on it. The act of finishing a handle allows the exception propagation algorithm to aggressively prune dependency links, lessening the performance/memory impact of exception tracking.

Note that the exception propagation algorithm used depends on handles being assigned/finished in LIFO order; however, for simplicity as well as memory conservation, it does not enforce this constraint.

Nested Class Summary

private static class

ObjectInputStream.HandleTable.HandleList Simple growable list of (integer) handles.

Field Summary

(package private) ObjectInputStream.HandleTable.HandleList[]	deps array mapping handle -> list of dependent handles (if any)
(package private) Object[]	entries array mapping handle -> object/exception (depending on status)
(package private) int	lowDep lowest unresolved dependency
(package private) int	size number of handles in table
(package private) byte[]	status array mapping handle -> object status
private static byte	STATUS_EXCEPTION
private static byte	STATUS_OK
private static byte	STATUS_UNKNOWN

Constructor Summary

(package private)

ObjectInputStream.HandleTable(int initialCapacity) Creates handle table with the given initial capacity.

Method Summary

(package private) int	assign(Object obj) Assigns next available handle to given object, and returns assigned handle.
(package private) void	clear() Resets table to its initial state.
(package private) void	finish(int handle) Marks given handle as finished, meaning that no new dependencies will be marked for handle.
private void	grow() Expands capacity of internal arrays.
(package private) ClassNotFoundException	lookupException(int handle) Looks up and returns ClassNotFoundException associated with the given handle.
(package private) Object	lookupObject(int handle) Looks up and returns object associated with the given handle.
(package private) void	markDependency(int dependent, int target) Registers a dependency (in exception status) of one handle on another.
(package private) void	markException(int handle, ClassNotFoundException ex) Associates a ClassNotFoundException (if one not already associated) with the currently active handle and propagates it to other referencing objects as appropriate.
(package private) void	setObject(int handle, Object obj) Assigns a new object to the given handle.
(package private) int	size() Returns number of handles registered in table.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

STATUS_OK

private static final byte STATUS_OK

See Also:

Constant Field Values

STATUS_UNKNOWN

private static final byte STATUS_UNKNOWN

See Also:

Constant Field Values

STATUS_EXCEPTION

private static final byte STATUS_EXCEPTION

See Also:

Constant Field Values

status

byte[] status

array mapping handle -> object status

entries

Object[] entries

array mapping handle -> object/exception (depending on status)

deps

ObjectInputStream.HandleTable.HandleList[] deps

array mapping handle -> list of dependent handles (if any)

lowDep

int lowDep

lowest unresolved dependency

size

int size

number of handles in table

Constructor Detail

ObjectInputStream.HandleTable

ObjectInputStream.HandleTable(int initialCapacity)

Creates handle table with the given initial capacity.

Method Detail

assign

int assign(Object obj)

Assigns next available handle to given object, and returns assigned handle. Once object has been completely deserialized (and all dependencies on other objects identified), the handle should be "closed" by passing it to finish().

markDependency

void markDependency(int dependent,
                    int target)

Registers a dependency (in exception status) of one handle on another. The dependent handle must be "open" (i.e., assigned, but not finished yet). No action is taken if either dependent or target handle is NULL_HANDLE.

markException

void markException(int handle,
                   ClassNotFoundException ex)

Associates a ClassNotFoundException (if one not already associated) with the currently active handle and propagates it to other referencing objects as appropriate. The specified handle must be "open" (i.e., assigned, but not finished yet).

finish

void finish(int handle)

Marks given handle as finished, meaning that no new dependencies will be marked for handle. Calls to the assign and finish methods must occur in LIFO order.

setObject

void setObject(int handle,
               Object obj)

Assigns a new object to the given handle. The object previously associated with the handle is forgotten. This method has no effect if the given handle already has an exception associated with it. This method may be called at any time after the handle is assigned.

lookupObject

Object lookupObject(int handle)

Looks up and returns object associated with the given handle. Returns null if the given handle is NULL_HANDLE, or if it has an associated ClassNotFoundException.

lookupException

ClassNotFoundException lookupException(int handle)

Looks up and returns ClassNotFoundException associated with the given handle. Returns null if the given handle is NULL_HANDLE, or if there is no ClassNotFoundException associated with the handle.

clear

void clear()

Resets table to its initial state.

size

int size()

Returns number of handles registered in table.

grow

private void grow()

Expands capacity of internal arrays.