Validating xml with sax parser

Note the "throws Exception" wimp-out; real applications would need real error handling: We can use this object to parse XML documents, but first, we have to register event handlers that the parser can use for reporting information, using the set Content Handler and set Error Handler methods from the XMLReader interface. Things get interesting when you start implementing methods to respond to XML parsing events (remember that we registered our class to receive XML parsing events in the previous section).In a real-world application, the handlers will usually be separate objects, but for this simple demo, we've bundled the handlers into the top-level class, so we just have to instantiate the class and register it with the XML reader: This code creates an instance of My SAXApp to receive XML parsing events, and registers it with the XML reader for regular content events and error events (there are other kinds, but they're rarely used). The most important events are the start and end of the document, the start and end of elements, and character data.Progress Software Corporation makes all reasonable efforts to verify this information.However, the information provided is for your information only.Called by the parser to give the application a locator for locating the origin of document events.SAX parsers are strongly encouraged (though not absolutely required) to supply a locator: if it does so, it must supply the locator to the application by invoking this method before invoking any of the other methods in the Document Handler interface.Now, let's assume that all of the command-line args are file names, and we'll try to parse them one-by-one using the parse method from the XMLReader interface: import To find out about the start and end of the document, the client application implements the start Document and end Document methods: method once (even if there have been errors). Default Handler; public class My SAXApp extends Default Handler Start document Start element: poem Characters: "\n" Start element: title Characters: "Roses are Red" End element: title Characters: "\n" Start element: l Characters: "Roses are red," End element: l Characters: "\n" Start element: l Characters: "Violets are blue;" End element: l Characters: "\n" Start element: l Characters: "Sugar is sweet," End element: l Characters: "\n" Start element: l Characters: "And I love you." End element: l Characters: "\n" End element: poem End document Note that even this short document generates (at least) 25 events: one for the start and end of each of the six elements used (or, if you prefer, one for each start tag and one for each end tag), one of each of the eleven chunks of character data (including whitespace between elements), one for the start of the document, and one for the end.

Typically, the application will use this information for reporting its own errors (such as character content that does not match an application’s business rules).SAX requires much less memory than DOM since SAX does not create an internal tree structure of the XML data, as a DOM does. In the following we are going to see a demo application which output all SAX events. In particular, environments with JAXP 1.1 support include SAX2.Start by creating a class that extends Default Handler: method that uses the the create XMLReader method from the XMLReader Factory class to choose a SAX driver dynamically. Default Handler; public class My SAXApp extends Default Handler You can compile this code and run it (make sure you specify the SAX driver class in the sax.driver property), but nothing much will happen unless the document contains malformed XML, because you have not yet set up your application to handle SAX events.

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Both the sample procedures and the sample XML and XSD documents were copied from the ' CREATE SAX-READER h Parser.

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