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ZwiftBooks Goes StAX
Now let’s look at how we might implement our XML extraction of ISBNs with StAX. A StAX version might be useful for our ZwiftBooks warehouse manager who has XML documents delivered to his cell phone and needs a lean parser to deliver alerts when ISBNs are encountered. Listing 5 shows the code.
Listing 5 Using StAX to pull ISBN attributes from XML.
1. import java.io.FileReader;
2. import java.util.Iterator;
3. import javax.xml.stream.*;
4. import javax.xml.namespace.QName;
5. import com.bea.xml.stream.util.ElementTypeNames;
6.
7. /**
8. * A simple parsing example that illustrates
9. * the XMLStreamReader class.
10. *
11. */
12.
13. public class ZBStaxParse {
14. private static String filename = "EuroBooks.xml";
15.
16. public static void main(String[] args) throws Exception {
17.
18. // Specify the Parser Factory we want to use
19. System.setProperty("javax.xml.stream.XMLInputFactory",
20. "com.bea.xml.stream.MXParserFactory");
21.
22. // Get an input factory
23. XMLInputFactory xmlif = XMLInputFactory.newInstance();
24.
25. // Instantiate a reader
26. XMLStreamReader xmlr =
27. xmlif.createXMLStreamReader(new FileReader(filename));
28.
29. // Parse the XML
30. while(xmlr.hasNext()){
31. handleEvent(xmlr);
32. xmlr.next();
33. }
34.
35. }
36.
37. private static void handleEvent(XMLStreamReader xmlr) {
38.
39. switch (xmlr.getEventType()) {
40.
41. case XMLStreamConstants.START_DOCUMENT:
42. System.out.print("Beginning StAX Parse");
43. break;
44.
45. case XMLStreamConstants.START_ELEMENT:
46.
47. if(xmlr.hasName()){
48. String localName = xmlr.getLocalName();
49. if (localName.equals("book")) {
50. System.out.print(localName);
51. processAttributes(xmlr);
52. }
53. }
54. break;
55.
56. case XMLStreamConstants.END_ELEMENT:
57. System.out.print("StAX Parsing Complete");
58. break;
59. }
60.
61. }
62.
63. }
64.
65.
66. private static void processAttributes(XMLStreamReader xmlr){
67.
68. for (int i=0; i < xmlr.getAttributeCount(); i++) {
69. processAttribute(xmlr,i);
70. }
71. }
72.
73. private static void processAttribute(XMLStreamReader xmlr, int index) {
74. String localName = xmlr.getAttributeLocalName(index);
75. if (localName.equals("isbn")) {
76. String value = xmlr.getAttributeValue(index);
77. System.out.println("Alert: " + localName + " = " + value);
78. }
79. }
80. }
The critical lines in Listing 5 are lines 30–32, in which the StAX pull loop is defined. Here the application controls when it needs to get information from the parser. This is especially important for a cell phone, since resources are limited and we don’t want a parser thread continuously calling the handler, possibly slowing down more important phone operations.