Class GraphBuildingHandler

Object

DefaultHandler

GraphBuildingHandler

public class GraphBuildingHandler
extends DefaultHandler

Parses OSM XML files using an XML SAX parser. Used to construct the graph of roads for pathfinding, under some constraints. See OSM documentation on the highway tag, the way XML element, the node XML element, and the java SAX parser tutorial. You may find the CSCourseGraphDB and CSCourseGraphDBHandler examples useful. The idea here is that some external library is going to walk through the XML file, and your override method tells Java what to do every time it gets to the next element in the file. This is a very common but strange-when-you-first-see it pattern. It is similar to the Visitor pattern we discussed for graphs.

Constructor Summary

Constructors

Constructor	Description
GraphBuildingHandler(GraphDB g)	Create a new GraphBuildingHandler.

Method Summary

Modifier and Type	Method	Description
void	endElement(String uri, String localName, String qName)	Receive notification of the end of an element.
void	startElement(String uri, String localName, String qName, Attributes attributes)	Called at the beginning of an element.

Methods inherited from class DefaultHandler

characters, endDocument, endPrefixMapping, error, fatalError, ignorableWhitespace, notationDecl, processingInstruction, resolveEntity, setDocumentLocator, skippedEntity, startDocument, startPrefixMapping, unparsedEntityDecl, warning

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GraphBuildingHandler

public GraphBuildingHandler(GraphDB g)

Create a new GraphBuildingHandler.

Parameters:

g - The graph to populate with the XML data.

Method Detail

startElement

public void startElement(String uri,
                         String localName,
                         String qName,
                         Attributes attributes)
                  throws SAXException

Called at the beginning of an element. Typically, you will want to handle each element in here, and you may want to track the parent element.

Overrides:

startElement in class DefaultHandler

Parameters:

uri - The Namespace URI, or the empty string if the element has no Namespace URI or if Namespace processing is not being performed.

localName - The local name (without prefix), or the empty string if Namespace processing is not being performed.

qName - The qualified name (with prefix), or the empty string if qualified names are not available. This tells us which element we're looking at.

attributes - The attributes attached to the element. If there are no attributes, it shall be an empty Attributes object.

Throws:

SAXException - Any SAX exception, possibly wrapping another exception.

See Also:

Attributes

endElement

public void endElement(String uri,
                       String localName,
                       String qName)
                throws SAXException

Receive notification of the end of an element. You may want to take specific terminating actions here, like finalizing vertices or edges found.

Overrides:

endElement in class DefaultHandler

Parameters:

uri - The Namespace URI, or the empty string if the element has no Namespace URI or if Namespace processing is not being performed.

localName - The local name (without prefix), or the empty string if Namespace processing is not being performed.

qName - The qualified name (with prefix), or the empty string if qualified names are not available.

Throws:

SAXException - Any SAX exception, possibly wrapping another exception.