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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 a 64-bit integer.
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| − | ==VTD-XML Core Concepts==
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| − |
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| − | ===Generating a VTD-XML Representation of the XML Document (Unmarshal)===
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| − |
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| − | Instantiate a new <tt>VTDGen</tt> object, and parse a <tt>byte[]</tt>:
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| − |
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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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| − |
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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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| − |
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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 (using VTDNav)===
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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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| − | XML:
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| − | <div style="width:900px">
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| − | <source lang="xml">
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| − | <?xml version="1.0" encoding="UTF-8"?>
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| − | <ns0:Test xmlns:ns0="uri" xmlns:ns1="n">
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| − | <ns1:name>OBJ1</ns1:name>
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| − | <sub-bean>
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| − | <ns1:name>OBJ2</ns1:name>
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| − | </sub-bean>
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| − | <sub-bean>
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| − | <ns1:name>OBJ3</ns1:name>
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| − | </sub-bean>
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| − | </ns0:Test>
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| − | </source>
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| − | </div>
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| − |
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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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| − |
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| − | VTDNav vn = vg.getNav();
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| − |
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| − | // Move cursor to ROOT
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| − | if (vn.toElement(VTDNav.ROOT)) {
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| − | System.out.println("Found Root: " + vn.getCurrentIndex());
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| − | // Move cursor to first occurrance of 'name', searching in forward direction (FIRST_CHILD)
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| − | if (vn.toElementNS(VTDNav.FIRST_CHILD, "n", "name")) {
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| − | System.out.println("Found 'name': " + vn.getCurrentIndex());
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| − | // Get the index of the text belonging to the current node
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| − | int textIndex = vn.getText();
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| − | if (textIndex != -1) {
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| − | System.out.println("Getting 'name' text: " + textIndex);
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| − | System.out.println(vn.toNormalizedString(textIndex));
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| − | }
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| − | }
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| − |
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| − | while (vn.toElementNS(VTDNav.NEXT_SIBLING, null, "sub-bean")) {
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| − | int subBeanIndex = vn.getCurrentIndex();
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| − | System.out.println("Found 'sub-bean': " + subBeanIndex);
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| − | if (vn.toElementNS(VTDNav.FIRST_CHILD, "n", "name")) {
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| − | System.out.println("Found 'name': " + vn.getCurrentIndex());
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| − | // Get the index of the text belonging to the current node
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| − | int textIndex = vn.getText();
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| − | if (textIndex != -1) {
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| − | System.out.println("Getting 'name' text: " + textIndex);
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| − | System.out.println(vn.toNormalizedString(textIndex));
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| − | }
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| − | }
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| − | // Rewind to top of "sub-bean", to get the next child;
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| − | vn.toElement(VTDNav.PARENT);
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| − | }
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| − | }
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| − | </source>
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| − | </div>
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| − |
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| − | Output:
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| − | <div style="width:900px">
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| − | <source lang="text">
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| − | Found Root: 5
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| − | Found 'name': 17
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| − | Getting 'name' text: 18
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| − | --> OBJ1
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| − | Found 'sub-bean': 28
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| − | Found 'name': 38
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| − | Getting 'name' text: 39
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| − | --> OBJ2
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| − | Found 'sub-bean': 49
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| − | Found 'name': 59
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| − | Getting 'name' text: 60
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| − | --> OBJ3
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| − | </source>
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| − | </div>
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| − |
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| − | ===Navigating a VTD-XML Document (using AutoPilot)===
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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 elements selected by XPath
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| − |
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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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| − |
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| − | VTDNav vn = vg.getNav();
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| − | </source>
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| − | </div>
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| − |
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| − |
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| − | ===Writing a VTD-XML Document (Marshal)===
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| − |
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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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| − |
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| − | XMLModifier xm = new XMLModifier();
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| − | xm.bind(vn);
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| − |
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| − | // ...
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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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| − |
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| − | ===Generating a VTD-XML Index File for Faster Parsing===
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| − | ==Appendix==
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| − | ===VTD-XML Binary Format===
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| − | With VTD-XML, 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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