| 摘要 |
A set of stream writer and reader class and methods enable object frameworks to communicate with each other despite problems with missing classes due to mismatched versions. The stream writers are modified to deal with a new version of a class that extends from a class in an existing version by writing alternate object information compatible with the existing version when the future object class information is streamed. In this manner, alternate object information is written for each older version. The information for each of the alternate objects corresponding to each oder version is added after the existing object information as an extension with the length of the extension written at the beginning. The stream readers are modified so that when an older version stream reader reads the object information and does not understand the first alternate object (which might correspond to a later version), it skips the length specified for that extension and reads the second alternate object. If the second alternate object information is not understood, the reader skips the non-understood object information and continues with each alternate object. If none of the alternates is understood, then an exception is thrown. In one embodiment, the information for alternate objects which are not used is not discarded, butis instead saved in a temporary storage. Then, if the object is streamed out again, the stored information is added back into the stream.
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