NcML AIS: Build a BES Handler - Revision history

PatrickWest: /* Build a null Handler */

2009-04-27T20:34:06Z

Build a null Handler

← Older revision		Revision as of 20:34, 27 April 2009
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	* NCMLRequestHandler - this class is where the NCML file will be parsed, containers retrieved, etc... Please refer back to the main documentation of AIS for detailed design.		* NCMLRequestHandler - this class is where the NCML file will be parsed, containers retrieved, etc... Please refer back to the main documentation of AIS for detailed design.

			In addition to the classes being build, a configure.ac, Makefile.am, sample COPYING, COPYRIGHT, NEWS and README files are created. A sample .spec file is also created for building the rpm for this module. The script bes-ncml-data.sh is created, which is used to add this module to the BES configuration file.

			Once all of the files are created, configure is run and the code is built. It should all build properly.

PatrickWest: /* Build a null Handler */

2009-04-27T20:30:19Z

Build a null Handler

← Older revision		Revision as of 20:30, 27 April 2009
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	# Answer the questions as follows:		# Answer the questions as follows:
	## ncml		## ncml
	### This will be the name of the module		##* This will be the name of the module
	## NCML		## NCML
			##* This is the prefix to all of the classes that get created. For example, NCMLModule
	## <enter>		## <enter>
			##* You are not handling any other responses, just the dap2 responses
	## <enter>		## <enter>
			##* You are not adding any additional commands to your module

	Running besCreateModule will create all the files that you will need for the NCML module. This includes:		Running besCreateModule will create all the files that you will need for the NCML module. This includes:

PatrickWest: /* Build a null Handler */

2009-04-27T20:29:03Z

Build a null Handler

← Older revision		Revision as of 20:29, 27 April 2009
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	Use the ''besCreatModule'' script to build a simple DAP module with now new commands or responses.		Use the ''besCreatModule'' script to build a simple DAP module with now new commands or responses.

			# Create a directory, something like ncml_module
			# from the command line run besCreateModule
			# Answer the questions as follows:
			## ncml
			### This will be the name of the module
			## NCML
			## <enter>
			## <enter>

			Running besCreateModule will create all the files that you will need for the NCML module. This includes:
			* NCMLModule - this class implements the initialize and terminate methods for you, registers the request handler for this module, and registers a debug context for the module called "ncml". With this debug context you can add debug statements to your code as follows:

			BESDEBUG( "ncml", "some debug info " << somevar << endl )

			The second part of the function would be something that would be sent to a C++ ostream object like cerr or a fstream.

			A terminate method is also created and removes the request handler. Check out the code. This is where specialized extensions would be added to the BES Framework.

			* NCMLRequestHandler - this class is where the NCML file will be parsed, containers retrieved, etc... Please refer back to the main documentation of AIS for detailed design.

Jimg: /* Build a null Handler */

2009-04-20T22:50:13Z

Build a null Handler

← Older revision		Revision as of 22:50, 20 April 2009
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	==Build a null Handler==		==Build a null Handler==

			Use the ''besCreatModule'' script to build a simple DAP module with now new commands or responses.

Jimg at 22:45, 20 April 2009

2009-04-20T22:45:28Z

← Older revision		Revision as of 22:45, 20 April 2009
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	[[Image:BES Handler class diagram.png\|400px\|right\|thumb\|A UML Class diagram for a Simple BES Handler]]		[[Image:BES Handler class diagram.png\|400px\|right\|thumb\|A UML Class diagram for a Simple BES Handler]]
			[[Image:BES Handler class diagram detailed.png\|400px\|right\|thumb\|The UML class diagram with far more detail regarding classes specific to the DAP]]
	There are several ways to build a shell BES handler and then add specific functionality to it. One way is to use the ''besCreadeModule'' script that is included in the BES source code. A second way is to copy and modify the ''csv handler'' software that's also included in the BES source code. In each case it's important to know that the BES is an object-oriented framework and as such, you will be specializing classes that the framework defines and then adding new classes and/or functions that are specific to your handler. With that in mind a static class diagram can help show how the BES's classes are related to each other and to the software you must write. Shown to the left is a UML class diagram that includes the most important of the BES classes when writing a new data handler.		There are several ways to build a shell BES handler and then add specific functionality to it. One way is to use the ''besCreadeModule'' script that is included in the BES source code. A second way is to copy and modify the ''csv handler'' software that's also included in the BES source code. In each case it's important to know that the BES is an object-oriented framework and as such, you will be specializing classes that the framework defines and then adding new classes and/or functions that are specific to your handler. With that in mind a static class diagram can help show how the BES's classes are related to each other and to the software you must write. Shown to the left is a UML class diagram that includes the most important of the BES classes when writing a new data handler.

	A [http://docs.opendap.org/images/9/9e/BES_Handler_class_diagram.png high resolution] version of the class diagram to the right.		* A [http://docs.opendap.org/images/9/9e/BES_Handler_class_diagram.png high resolution] version of the class diagram to the right.
			* Here's a [http://docs.opendap.org/images/a/a0/BES_Handler_class_diagram_detailed.png link to the detailed diagram].

	Also, be sure to look over ~~hte~~ BES documentation files included on this design's main page and on in the Hyrax documentation. Especially useful is the BES Handler tutorial that covers building the Hello, World and CSV handlers. It's so useful I'll repeat it here: [http://www.opendap.org/support/bom_sdw/SDW_2r0_OLFSExtensions.ppt Extending the OLFS: Writing Custom Dispatch Handlers].		Also, be sure to look over THE BES documentation files included on this design's main page and on in the Hyrax documentation. Especially useful is the BES Handler tutorial that covers building the Hello, World and CSV handlers. It's so useful I'll repeat it here: [http://www.opendap.org/support/bom_sdw/SDW_2r0_OLFSExtensions.ppt Extending the OLFS: Writing Custom Dispatch Handlers].

	==Explanation of the Classes in the Diagram==		==Explanation of the Classes in the Diagram==

Jimg: /* BES Framework Singleton Objects */

2009-04-17T23:03:45Z

BES Framework Singleton Objects

← Older revision		Revision as of 23:03, 17 April 2009
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	The specialization of BESAbstractModule populates these lists, first by making a specialized instance of BESRequestHandler and then adding that to the request handler list. once that's done, the container storage and catalog lists are used to store their respective object types. These three activities are carried out by the module's ''initialize()'' method. By adding the request handler object to the global (singleton) request handler list, a handler's code to process certain requests is mad available to the BES's command processing software. Similarly, any containers or catalog objects defined by a handler are added to the corresponding global lists and can thus be accessed by the command processing software.		The specialization of BESAbstractModule populates these lists, first by making a specialized instance of BESRequestHandler and then adding that to the request handler list. once that's done, the container storage and catalog lists are used to store their respective object types. These three activities are carried out by the module's ''initialize()'' method. By adding the request handler object to the global (singleton) request handler list, a handler's code to process certain requests is mad available to the BES's command processing software. Similarly, any containers or catalog objects defined by a handler are added to the corresponding global lists and can thus be accessed by the command processing software.

			==Build a null Handler==

Jimg: /* Putting it all Together */

2009-04-17T23:02:09Z

Putting it all Together

← Older revision		Revision as of 23:02, 17 April 2009
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	The specialization of BESAbstractModule populates these lists, first by making a specialized instance of BESRequestHandler and then adding that to the request handler list. once that's done, the container storage and catalog lists are used to store their respective object types. These three activities are carried out by the module's ''initialize()'' method. By adding the request handler object to the global (singleton) request handler list, a handler's code to process certain requests is mad available to the BES's command processing software. Similarly, any containers or catalog objects defined by a handler are added to the corresponding global lists and can thus be accessed by the command processing software.		The specialization of BESAbstractModule populates these lists, first by making a specialized instance of BESRequestHandler and then adding that to the request handler list. once that's done, the container storage and catalog lists are used to store their respective object types. These three activities are carried out by the module's ''initialize()'' method. By adding the request handler object to the global (singleton) request handler list, a handler's code to process certain requests is mad available to the BES's command processing software. Similarly, any containers or catalog objects defined by a handler are added to the corresponding global lists and can thus be accessed by the command processing software.

	~~===Putting it all Together===~~

Jimg: /* BES Framework Singleton Objects */

2009-04-17T23:01:27Z

BES Framework Singleton Objects

← Older revision		Revision as of 23:01, 17 April 2009
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	===BES Framework Singleton Objects===		===BES Framework Singleton Objects===

			The BES uses singleton objects to store lists of things that will be searched to sort out how a given request should be handled. In some ways these lists are like symbol tables in a compiler or interpreter. Once an object is defined and bound to a name it can be added to the correct list and later found and used as commands are parsed and executed. The singleton classes shown in the UML diagram are:

			;BESRequestHandlerList
			:A list of known request handlers
			;BESCatalogList
			:A list of the known catalog objects
			;BESContainerStorageList
			:A list of the known container objects

			The specialization of BESAbstractModule populates these lists, first by making a specialized instance of BESRequestHandler and then adding that to the request handler list. once that's done, the container storage and catalog lists are used to store their respective object types. These three activities are carried out by the module's ''initialize()'' method. By adding the request handler object to the global (singleton) request handler list, a handler's code to process certain requests is mad available to the BES's command processing software. Similarly, any containers or catalog objects defined by a handler are added to the corresponding global lists and can thus be accessed by the command processing software.

	===Putting it all Together===		===Putting it all Together===

Jimg: /* Classes that must be Specialized */

2009-04-17T22:45:02Z

Classes that must be Specialized

← Older revision		Revision as of 22:45, 17 April 2009
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	===Classes that must be Specialized===		===Classes that must be Specialized===

			There are two classes that must be specialized to build a new DAP data handler:
			;BESAbstratModule
			:This class defined the interface for teh BES handler (aka Module). It contains two key methods: ''initialize()'' and ''terminate()''
			;BESRequestHandler
			;This class is (typically) specialized to include five new methods for a DAP data handler, one for each of the DAP response objects (DAS, DDS, DataDDS, version, and help). The constructor for the specialization (again, typically) uses BESRequestHandler::add_handler(...) to bind each of the five methods to a string so that the BES can figure out which of the methods should be called to handle a request for one of the five DAP responses

	===BES Framework Singleton Objects===		===BES Framework Singleton Objects===

	===Putting it all Together===		===Putting it all Together===

Jimg: /* Classes that are Provided */

2009-04-17T22:38:05Z

Classes that are Provided

← Older revision		Revision as of 22:38, 17 April 2009
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	:These holds specific types of responses for the DAP		:These holds specific types of responses for the DAP
	;BESTransmitter		;BESTransmitter
	:Used by BESResponseHandler to transmit a ResponseObject. For DAP, the ~~BESHTTPTransmitter~~ class is actually used.		:Used by BESResponseHandler to transmit a ResponseObject. For DAP, the BESBasicHttpTransmitter class is actually used.
			;BESCatalog
			:A catalog is a way of getting listings (catalogs) of things
			;BESCatalogDirecotry
			:A catalog for a disk directory. This is used to build the Hyrax server's directory pages.
			;BESCatalogList
			:This class is used to for a list that the BES searches when it needs to find a specific catalog that's mentioned in a command. It's one of the singleton objects discussed later
			;BESContainerStorageCatalog
			:Not really sure...
			;BESContainerStorageList
			:A list of ...

	===Classes that must be Specialized===		===Classes that must be Specialized===