WHITEBOARD.html - commons-chain - Git at Google

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   <title>Whiteboard notes for Chain of Responsibility
   Package</title>
 </head>

 <body bgcolor="white">
   <div align="center">
     <h1>Whiteboard notes for <em>Chain of Responsibility</em>
     Package</h1>
   </div>

   <h3>Agility</h3>

   <p>Agility is a working project name for a business applications
   framework based on the Commons Chain package.</p>

   <p>The core idea behind Agility that is as much work as possible
   should be pushed up to the business layer. Input and output is
   encapsulated with a Context object that is passed to and from
   Agility using a ProtocolAdaptor. Depending on its implementation,
   a ProtocolAdaptor may collect input and deliver output directly
   from the native platform or from a presentation framework.</p>

   <p>Agility is a Request/Response framework: for each request
   there is a response. The request is encapsulated in a Context
   object, which includes a Command identifier. Each request must
   correspond to a Command, which may also be a Chain of Commands.
   Commands may nest or chain other Commands as needed. The request
   Command is referred to as the "Action".</p>

   <p>When a request comes in from the presentation layer (or a
   presentation framework), it is received by a ProtocolAdaptor. The
   ProtocolAdaptor extracts the Action Command name from the native
   request and consults with a ContextFactory to generate a Context
   for the request. The request Context is then passed to the
   RequestProcessor for the given protocol.</p>

   <p>The RequestProcessor is a Command Chain which includes (at a
   minimum) an Action Command. Each protocol can have its own
   RequestProcessor, which may be a combination of protocol-specific
   and generic commands. The Action Command (or Chain) is the core
   unit of work for the request.</p>

   <p>The Action Command may consult business rules and the
   persistence layer to complete the unit of work. Any output or
   messages generated by the Action may be added to the Context
   under predetermined keys. If the Action completes normally, an
   attribute is added to the Context to signify the outcome of the
   Action. The value of the outcome attribute is arbitrary and
   defined by application implementing the framework ("success",
   "failure", "xylophone").</p>

   <p>When the RequestProcessor Chain completes, the Context is
   returned to the ProtocolAdaptor. Agility defines the
   ProtocolAdaptor interface but does not provide an implementation.
   If the ProtocolAdaptor is a simple Servlet, it may forward to a
   server page by munging the outcome value. If the ProtocolAdaptor
   is a presentation layer framework, it may pass the value to an
   internal mechanism that selects or assembles a server page, or
   generates a dynamic response. A ProtocolAdaptor might even
   utilitize its own "ResponseProcessor" to execute a series of
   Commands to assemble an approriate response.</p>
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	Licensed to the Apache Software Foundation (ASF) under one or more
	contributor license agreements. See the NOTICE file distributed with
	this work for additional information regarding copyright ownership.
	The ASF licenses this file to You under the Apache License, Version 2.0
	(the "License"); you may not use this file except in compliance with
	the License. You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
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	<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
	<meta name="generator" content=
	"HTML Tidy for Windows (vers 1st July 2003), see www.w3.org" />

	<title>Whiteboard notes for Chain of Responsibility
	Package</title>
	</head>

	<body bgcolor="white">
	<div align="center">
	<h1>Whiteboard notes for <em>Chain of Responsibility</em>
	Package</h1>
	</div>

	<h3>Agility</h3>

	<p>Agility is a working project name for a business applications
	framework based on the Commons Chain package.</p>

	<p>The core idea behind Agility that is as much work as possible
	should be pushed up to the business layer. Input and output is
	encapsulated with a Context object that is passed to and from
	Agility using a ProtocolAdaptor. Depending on its implementation,
	a ProtocolAdaptor may collect input and deliver output directly
	from the native platform or from a presentation framework.</p>

	<p>Agility is a Request/Response framework: for each request
	there is a response. The request is encapsulated in a Context
	object, which includes a Command identifier. Each request must
	correspond to a Command, which may also be a Chain of Commands.
	Commands may nest or chain other Commands as needed. The request
	Command is referred to as the "Action".</p>

	<p>When a request comes in from the presentation layer (or a
	presentation framework), it is received by a ProtocolAdaptor. The
	ProtocolAdaptor extracts the Action Command name from the native
	request and consults with a ContextFactory to generate a Context
	for the request. The request Context is then passed to the
	RequestProcessor for the given protocol.</p>

	<p>The RequestProcessor is a Command Chain which includes (at a
	minimum) an Action Command. Each protocol can have its own
	RequestProcessor, which may be a combination of protocol-specific
	and generic commands. The Action Command (or Chain) is the core
	unit of work for the request.</p>

	<p>The Action Command may consult business rules and the
	persistence layer to complete the unit of work. Any output or
	messages generated by the Action may be added to the Context
	under predetermined keys. If the Action completes normally, an
	attribute is added to the Context to signify the outcome of the
	Action. The value of the outcome attribute is arbitrary and
	defined by application implementing the framework ("success",
	"failure", "xylophone").</p>

	<p>When the RequestProcessor Chain completes, the Context is
	returned to the ProtocolAdaptor. Agility defines the
	ProtocolAdaptor interface but does not provide an implementation.
	If the ProtocolAdaptor is a simple Servlet, it may forward to a
	server page by munging the outcome value. If the ProtocolAdaptor
	is a presentation layer framework, it may pass the value to an
	internal mechanism that selects or assembles a server page, or
	generates a dynamic response. A ProtocolAdaptor might even
	utilitize its own "ResponseProcessor" to execute a series of
	Commands to assemble an approriate response.</p>
	</body>
	</html>