docs/samples-socket.xml

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<!DOCTYPE s1 SYSTEM 'dtd/document.dtd'>
<s1 title='Socket Samples'>
 <s2 title='Overview'>
  <p>
   Very often, applications need to transmit XML documents over
   the network using a socket stream. However, XML is not designed
   to make this possible because XML documents do not contain an
   explicit end-of-document terminal. Therefore, the stream must
   end (i.e. the socket must close) in order for the parser to
   finish parsing the complete XML document.
  </p>
  <p>
   Since creating socket streams is expensive the application needs
   to re-use the same stream but XML doesn't define an end-of-document. 
   Therefore, another solution must be found. The socket samples 
   included with Xerces can be used to learn how to overcome this 
   common problem in a general way.
  </p>
  <p>Socket samples:</p>
  <ul>
   <li><link anchor='DelayedInput'>socket.DelayedInput</link></li>
   <li><link anchor='KeepSocketOpen'>socket.KeepSocketOpen</link></li>
  </ul>
 </s2>
 <anchor name='DelayedInput'/>
 <s2 title='Sample socket.DelayedInput'>
  <p>
   This sample delays the input to the SAX parser to simulate reading data
   from a socket where data is not always immediately available. An XML
   parser should be able to parse the input and perform the necessary
   callbacks as data becomes available. So this is a good way to test
   any parser that implements the SAX2 <code>XMLReader</code> interface
   to see if it can parse data as it arrives.
  </p>
  <p>
   <strong>Note:</strong> This sample uses NSGMLS-like output of elements
   and attributes interspersed with information about how many bytes are
   being read at a time.
  </p>
  <s3 title='usage'>
   <source>java socket.DelayedInput (options) filename ...</source>
  </s3>
  <s3 title='options'>
   <table>
    <tr><th>Option</th><th>Description</th></tr>
    <tr><td>-p name</td><td>Select SAX2 parser by name.</td></tr>
    <tr><td>-n | -N</td><td>Turn on/off namespace processing.</td></tr>
    <tr><td>-v | -V</td><td>Turn on/off validation.</td></tr>
    <tr>
     <td>-s | -S</td>
     <td>
      Turn on/off Schema validation support.<br/>
      <strong>NOTE:</strong> Not supported by all parsers.");
     </td>
    </tr>
    <tr>
     <td>-f  | -F</td>
     <td>
      Turn on/off Schema full checking.<br/>
      <strong>NOTE:</strong> Requires use of -s and not supported by all parsers.
     </td>
    </tr>
    <tr><td>-h</td><td>Display help screen.</td></tr>
   </table>
  </s3>
 </s2>
 <anchor name='KeepSocketOpen'/>
 <s2 title='Sample socket.KeepSocketOpen'>
  <p>
   This sample provides a solution to the problem of 1) sending multiple
   XML documents over a single socket connection or 2) sending other types
   of data after the XML document without closing the socket connection.
  </p>
  <p>
   The first situation is a problem because the XML specification does
   not allow a document to contain multiple root elements. Therefore a
   document stream must end (or at least appear to end) for the XML
   parser to accept it as the end of the document.
  </p>
  <p>
   The second situation is a problem because the XML parser buffers the
   input stream in specified block sizes for performance reasons. This
   could cause the parser to accidentally read additional bytes of data
   beyond the end of the document. This actually relates to the first
   problem if the documents are encoding in two different international
   encodings.
  </p>
  <p>
   The solution that this sample introduces wraps both the input and
   output stream on both ends of the socket. The stream wrappers 
   introduce a protocol that allows arbitrary length data to be sent
   as separate, localized input streams. While the socket stream
   remains open, a separate input stream is created to "wrap" an
   incoming document and make it appear as if it were a standalone
   input stream.
  </p>
  <p>
   To use this sample, enter any number of filenames of XML documents
   as parameters to the program. For example:
  </p>
  <source>java socket.KeepSocketOpen doc1.xml doc2.xml doc3.xml</source>
  <p>
   This program will create a server and client thread that communicate
   on a specified port number on the "localhost" address. When the client
   connects to the server, the server sends each XML document specified
   on the command line to the client in sequence, wrapping each document
   in a <code>WrappedOutputStream</code>. The client uses a 
   <code>WrappedInputStream</code> to read the data and pass it to the
   parser.
  </p>
  <note>
   Do not send any XML documents with associated grammars to the client. 
   In other words, don't send any documents that contain a DOCTYPE line
   that references an external DTD because the client will not be able 
   to resolve the location of the DTD and an error will be issued by 
   the client.
  </note>
 </s2>
</s1>