e550. determining the parsing location of an xml sax parser.txt

这里面包含了一百多个JAVA源文件

To get the current URI and location of a SAX parser during parsing, you need to obtain a Locator object. This object can be obtained by installing a ContentHandler and overriding the setDocumentLocator() method. The SAX parser will call this method and deliver the Locator object that you can use anytime it delivers an event (i.e., invokes a callback method in a handler). This method will be called before any other ContentHandler method. 
Note: Not all SAX parser support a Locator. If it doesn't, the setDocumentLocator() method will not be called. 

This example captures the Locator object and uses it whenever it gets a startElement event. 

    // Create a handler for SAX events
    DefaultHandler handler = new MyHandler();
    
    // Parse an XML file using SAX;
    // e517 The Quintessential Program to Parse an XML File Using SAX
    parseXmlFile("infilename.xml", handler, false);
    
    // This class listens for startElement SAX events
    static class MyHandler extends DefaultHandler {
        Locator locator;
        public void setDocumentLocator(Locator locator) {
            this.locator = locator;
        }
        // This method is called when an element is encountered
        public void startElement(String namespaceURI, String localName,
                                 String qName, Attributes atts)  {
            if (locator != null) {
                int col = locator.getColumnNumber();
                int line = locator.getLineNumber();
                String publicId = locator.getPublicId();
                String systemId = locator.getSystemId();
            }
        }
    }