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| − | =VTD-XML Investigation=
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| − | VTD-XML ([http://vtd-xml.sourceforge.net/ http://vtd-xml.sourceforge.net/]) is a high-performance XML processing model that deals with XML in a binary form, instead of the traditional text form. VTD stands for '''V'''irtual '''T'''oken '''D'''escriptor.
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| − | VTD-XML parses an XML document and builds an internal data structure representing the entire XML document in <tt>byte[]</tt> form. Each "token" of the XML document is represented as the following 64-bit integer:
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| − | [[Image:Vtd_layout.jpg]]
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| − | * Big endian
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| − | * Starting offset: 30 bits (b29 ~ b0) maximum value is 2^30 -1 = 1G -1
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| − | * Length: 20 bits (b51 ~ b32) maximum value is 2^20-1 = 1M -1
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| − | ** For some token type
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| − | *** Prefix length: 9 bits (b51~ b43) max value 511
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| − | *** Q-name length: 11 bits (b42 ~ b 32) max value 1023
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| − | * Depth: 8 bits (b59~b52) max value is 2^8-1 = 255
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| − | * Token type: 4 bits (b63~b60)
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| − | * Reserved bit: 2 bits (b31: b30)
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| − | ==VTD-XML Core Concepts==
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| − | ===Generating a VTD-XML Representation of the XML Document (Unmarshal)===
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| − | Instantiate a new <tt>VTDGen</tt> object, and parse a <tt>byte[]</tt>:
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| − | <div style="width:900px">
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| − | <source lang="java">
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| − | VTDGen vg = new VTDGen();
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| − | // from existing byte[]
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| − | // could be either VTD-XML bytes, or bytes from a regular File, etc. (?)
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| − | // true indicates namespace aware
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| − | byte[] bytes = ...
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| − | vg.setDoc(bytes);
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| − | vg.parse(true);
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| − | // - or -
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| − | // from file
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| − | vg.parseFile("old.xml", false);
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| − | </source>
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| − | </div>
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| − | ===Navigating a VTD-XML Document===
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| − | * <tt>VTDNav</tt>
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| − | ** Obtained from <tt>VTDGen</tt> instance
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| − | ** Allows for basic "walking" through elements
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| − | ** Maintains a single cursor into the <tt>byte[]</tt> representation of XML
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| − | <div style="width:900px">
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| − | <source lang="java">
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| − | VTDGen vg = new VTDGen();
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| − | vg.parseFile("old.xml", false);
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| − | VTDNav vn = vg.getNav();
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| − | </source>
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| − | </div>
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| − | * <tt>AutoPilot</tt>
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| − | ** Created from <tt>VTDNav</tt> instance
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| − | ** Allows for XPath execution
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| − | ** Allows for iterating over
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| − | <div style="width:900px">
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| − | <source lang="java">
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| − | VTDGen vg = new VTDGen();
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| − | vg.parseFile("old.xml", false);
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| − | VTDNav vn = vg.getNav();
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| − | </source>
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| − | </div>
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| − | ===Writing a VTD-XML Document (Marshal)===
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| − | <div style="width:900px">
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| − | <source lang="java">
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| − | VTDGen vg = new VTDGen();
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| − | vg.parseFile("old.xml", false);
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| − | VTDNav vn = vg.getNav();
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| − | XMLModifier xm = new XMLModifier();
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| − | xm.bind(vn);
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| − | // ...
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| − | // Write to OutputStream
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| − | xm.output(new FileOutputStream("new.xml"));
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| − | </source>
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| − | </div>
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| − | ===Generating a VTD-XML Index File for Faster Parsing===
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