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From "Bill Halchin" <bhalc...@hotmail.com>
Subject Re: [Sample] Parsing XML Documents on Socket
Date Thu, 01 Jan 1970 00:00:00 GMT

Thanks Andy.

I will look at your code.

Regards,

Bill Halchin

>From: Andy Clark <andyc@apache.org>
>Reply-To: general@xml.apache.org
>To: xerces-j-dev@xml.apache.org
>CC: general@xml.apache.org
>Subject: [Sample] Parsing XML Documents on Socket
>Date: Sun, 03 Dec 2000 20:37:51 -0800
>
>We have another posting about how to read XML documents on a
>socket connection. Instead of answering the question, I've
>done one better by writing a new sample that shows you how
>to read XML documents from a socket connection!
>
>The solution to reading an XML document on a socket is to wrap
>the input and output with a protocol. This enables the parser
>to parse a document on the socket stream and detect the end of
>the document and (even more important) not close the socket
>connection by closing the input stream.
>
>My sample code works regardless of the encoding of the XML
>document and is general enough that it can be used to handle
>any variable length data being transferred on a socket. This
>is basically how it works: the server "wraps" the output
>stream when sending the XML document and the client "unwraps"
>the input stream when receiving the XML document. I'll detail
>exactly how this works below but what's important is that it
>works transparently to the server and client as long as they
>use the appropriate "wrapper" classes for the input/output
>streams.
>
>The wrapper input/output streams introduce a "packet" kind
>of protocol onto the stream. Therefore, when the server
>writes data to the output stream, the wrapper class breaks
>the input into a series of packets. These packets contain
>a simple header that just states how many bytes are in the
>packet (not including the header), followed by the packet
>data. The receiving input stream knows how to read the
>header and return only the bytes in the packet data to the
>calling client code.
>
>These input/output classes provide a general mechanism for
>sending variable length data on a socket connection. It
>acts as if there is a localized input/output stream within
>the socket stream. And the wrapper classes can be used
>independently from the socket sample. There are a few
>caveats, though: 1) the server code MUST close the wrapper
>output stream; 2) the client code MUST close the wrapper
>input stream. The second requirement is only needed if you
>detect a parse error and need to skip to the end of the
>wrapper input stream to continue processing the next
>piece of information.
>
>I added the sample to the Xerces2 codebase with the
>assumption that we'll be moving that code over soon and it
>can find a permanent home. If you would like to check it
>out now, here's how you do it (this will only checkout the
>socket samples dir from CVS):
>
>   set CVSROOT=:pserver:anoncvs@xml.apache.org:/home/cvspublic
>   cvs login        (password: anoncvs)
>   cvs checkout -d socket -r xerces_j_2 xml-xerces/java/samples/socket
>
>This will create a directory called "socket" which contains
>the sample "socket.KeepSocketOpen". You can read the javadoc
>for information about how to use this sample. Or, you can
>just use the wrapper streams independently. They're in the
>"socket.io" package and are called "WrappedOutputStream"
>and "WrappedInputStream", respectively.
>
>We'll have to put some explanation in the actual Xerces
>documentation so that people know about this sample and
>how to solve the XML-on-a-socket problem, though. Any
>volunteers?
>
>Let me know if this sample helps.
>
>--
>Andy Clark * IBM, TRL - Japan * andyc@apache.org
>
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