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Better, Faster XML Processing with VTD-XML : Page 4

VTD-XML is a new open source XML processing API that provides a great alternative to SAX and DOM that doesn't force you to trade processing performance for usability. Find out why this Java-based, non-validating parser is faster than DOM and better than SAX.




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A Sample Project
So far, you have had a high-level overview of VTD-XML. Now it's time to put it into action and demonstrate some of its important concepts and features. The following examples use a ProductDetails.xml file, whose content is shown below.

<?xml version='1.0'?> <Products> <Product ID="1" Name="Chai" Price="13"> <Desc Value="10 boxes x 20 Bags"/> </Product> <Product ID="2" Name="Chang" Price="10"> <Desc Value="24 -12 oz bottles"/> </Product> <Product ID="3" Name="Tofu" Price="23.25"> <Desc Value="40-100 kg pkgs"/> </Product> </Products>

The sample code parses the file using VTDGen, navigates the hierarchy using VTDNav, and then performs a simple element node iteration using AutoPilot. Also you will see how to incrementally update the content of this XML file.

For this project, create a Java class named project1.java, which only has a main() method. To handle all possible exceptions, the code uses a single try/catch block wrapped around the application logic.

try { // application logic goes here } catch (ParseException e){ System.out.println( " XML file parsing error \n"+e); } catch (NavException e){ System.out.println( " Exception during navigation "+e); } catch (java.io.IOException e) { System.out.println(" IO exception condition"+e); }

The following code snippet reads the file content into a buffer, and then generates a parsed representation for ProductDetails.xml.

// parse XML File f = new File("ProductDetails.xml"); FileInputStream fis = new FileInputStream(f); // find out file length and allocate buffer byte[] b = new byte[(int) f.length()]; // read file content into the buffer fis.read(b); //create an instance of VTDGen VTDGen vg = new VTDGen(); // assign the buffer to VTDGen vg.setDoc(b); // parse with namespace awareness turned off vg.parse(false);

Next, it obtains an instance of VTDNav from VTDGen and moves the cursor to a child element named product whose id attribute equals "3."

// manual navigation // get the navigator VTDNav vn = vg.getNav(); // verify the root element name if (vn.matchElement("Products")){ // move the cursor to first child // named "product" if (vn.toElement( VTDNav.FIRST_CHILD,"Product")) { // stepping across every sibling // named "Product" do { int i = vn.getAttrVal("ID"); if (vn.matchRawTokenString(i,"3")) { System.out.println("element name ==>" + vn.toString(vn.getCurrentIndex())); System.out.println( "element fragement is ==>"); // then print out element fragment // using getElementFragment(); long l = vn.getElementFragment(); int len = (int) (l>>32); int offset = (int) l; System.out.println(new String( b,offset, len)); } } while(vn.toElement( VTDNav.NEXT_SIBLING,"Product")); } else System.out.println("no child named Product"); }

The output from executing the code snippet above is shown below.

element name ==> Product element fragment is ==> <Product ID="3" Name="Tofu" Price="23.25"> <Desc Value="40-100 kg pkgs"/> </Product>

Next, the cursor gets reset to the root, then the code creates an instance of AutoPilot to iterate through all elements of the name "Desc."

// iterate over element using AutoPilot vn.toElement(VTDNav.ROOT); AutoPilot ap = new AutoPilot(vn); ap.selectElement("Desc"); //select "Desc" while(ap.iterate()) { long l = vn.getElementFragment(); int len = (int) (l>>32); int offset = (int) l; System.out.println(new String(b,offset,len)); }

And its corresponding output looks like this:

<Desc Value="10 boxes x 20 Bags"/> <Desc Value="24 -12 oz bottles"/> <Desc Value="40-100 kg pkgs"/>

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