docs/design.html - platform/external/apache-velocity-engine - Git at Google

 <HTML><HEAD><TITLE>Velocity Design</TITLE></HEAD><BODY alink="#023264" bgcolor="#ffffff" leftmargin="4" link="#023264" marginheight="4" marginwidth="4" text="#000000" topmargin="4" vlink="#023264"><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD align="left" valign="top"><A href="http://jakarta.apache.org/index.html"><IMG border="0" hspace="0" src="resources/jakarta-logo.gif" vspace="0"></A></TD><TD align="left" bgcolor="#ffffff" valign="top" width="100%"><IMG align="right" alt="" border="0" hspace="0" src="resources/header.gif" vspace="0"></TD></TR><TR><TD><IMG border="0" height="5" hspace="0" src="resources/void.gif" vspace="0" width="5"></TD></TR><TR><TD background="resources/line.gif" colspan="2" height="2" width="100%"><IMG alt="" border="0" height="2" hspace="0" src="resources/line.gif" vspace="0" width="1"></TD></TR></TABLE><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD valign="top" width="1%"></TD><TD nowrap="1" valign="top" width="14%"><BR>

 <P></P>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="index.html">Overview</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="getting-started.html">Getting Started</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="install.html">Install</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="design.html">Design</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="contributors.html">Contributors</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="code-standards.html">Coding Standards</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="license.html">License</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="todo.html">TODO</A></LI></FONT>
     <P></P>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="user-guide.html">User's Guide</A></LI></FONT>
     <FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="developer-guide.html">Developer's Guide</A></LI></FONT>
 </TD><TD align="left" valign="top" width="*"><TABLE border="0" cellpadding="3" cellspacing="0"><TR><TD><BR>


  <DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="0" width="98%"><TR><TD bgcolor="#023264" width="100%"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="+1"><IMG border="0" height="5" hspace="0" src="resources/void.gif" vspace="0" width="5"><B>Design</B></FONT></TD></TR><TR><TD><IMG border="0" height="5" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE><TABLE border="0" cellpadding="0" cellspacing="0" width="98%"><TR><TD><FONT color="#000000" face="arial,helvetica,sanserif">

  <P align="justify">
     Velocity is a Java-based template engine. It can be used as a
     standalone utility for generating source code, HTML, reports,
     or it can be combined with other systems to provide template
     services. Velocity will be tightly integrated with the
     <A href="http://java.apache.org/turbine">Turbine</A>
     web application framework. Velocity-Turbine
     provide a template service by which web applications may be
     developed according to a true MVC model.
  </P>

  <P align="justify">
     Velocity has a myriad of potential uses -- generating SQL, PostScript,
     or Java source code from templates -- but it is expected to be most
     widely used by web developers looking for a viable alternative to
     <A href="http://www.php.net/">PHP</A> and
     <A href="http://java.sun.com/products/jsp/">Java
     Server Pages</A> (JSPs).
  </P>

  <P align="justify">
     Velocity allows web page designers to embed simple yet powerful script
     elements in their web pages. These script elements work
     in conjunction with a Context object, which is defined in Java code.
     A context object--essentially a Hashtable that provides get and set
     methods for retrieving and setting objects by name within the Context
     --provides a &quot;hook&quot; from the Java code to the Velocity script
     elements. These script elements allow a web designer to retrieve
     objects from the Context and insert these into a web page as text
     values. The web designer has some control over looping (for each)
     and conditional statements (if/else).
  </P>

  <P align="justify">
     Velocity enforces a Model-View-Controller (MVC) style of development
     by separating Java code from HTML template code. Unlike JSPs,
     Velocity does not allow Java code to be embedded in pages. Unlike PHP,
     Velocity does not implement features with other functions. The MVC
     approach is one of Velocity's great strengths, and allows for more
     maintainable and better designed web pages.
  </P>

  <P align="justify">
     Although MVC-style development can sometimes lead to longer incubation
     periods for web sites, particularly if the developers involved are new
     to MVC, this approach saves time over the long term (believe us, we have
     been doing this for a long time now). The MVC abstraction prevents web page
     designers from messing with a software engineer's Java code, and
     programmers from unduly influencing the look of web sites. Velocity enforces
     a contract that defines what roles people play in the web site development
     process.
  </P>

  <P align="justify">
     Velocity uses a grammar-based parser generated by
     <A href="http://www.metamata.com/javacc/">JavaCC</A> (Java Compiler
     Compiler) using the JJTree extension to create an Abstract Syntax Tree.
     Its concept was borrowed from
     <A href="http://www.webmacro.org/">WebMacro</A>. Those involved in
     the Velocity project acknowledge and appreciate the development and design
     work that went into the WebMacro project.
  </P>

 </FONT></TD></TR></TABLE></DIV><BR>


 </TD></TR></TABLE></TD></TR></TABLE><BR><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD bgcolor="#023264"><IMG height="1" src="resources/resources.gif" width="1"></TD></TR><TR><TD align="center"><FONT color="#023264" face="arial,helvetica,sanserif" size="-1"><I>
               Copyright &copy; 2000 The Apache Software Foundation.
               All Rights Reserved.
             </I></FONT></TD></TR></TABLE></BODY></HTML>
	<HTML><HEAD><TITLE>Velocity Design</TITLE></HEAD><BODY alink="#023264" bgcolor="#ffffff" leftmargin="4" link="#023264" marginheight="4" marginwidth="4" text="#000000" topmargin="4" vlink="#023264"><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD align="left" valign="top"><A href="http://jakarta.apache.org/index.html"><IMG border="0" hspace="0" src="resources/jakarta-logo.gif" vspace="0"></A></TD><TD align="left" bgcolor="#ffffff" valign="top" width="100%"><IMG align="right" alt="" border="0" hspace="0" src="resources/header.gif" vspace="0"></TD></TR><TR><TD><IMG border="0" height="5" hspace="0" src="resources/void.gif" vspace="0" width="5"></TD></TR><TR><TD background="resources/line.gif" colspan="2" height="2" width="100%"><IMG alt="" border="0" height="2" hspace="0" src="resources/line.gif" vspace="0" width="1"></TD></TR></TABLE><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD valign="top" width="1%"></TD><TD nowrap="1" valign="top" width="14%"><BR>

	<P></P>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="index.html">Overview</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="getting-started.html">Getting Started</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="install.html">Install</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="design.html">Design</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="contributors.html">Contributors</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="code-standards.html">Coding Standards</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="license.html">License</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="todo.html">TODO</A></LI></FONT>
	<P></P>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="user-guide.html">User's Guide</A></LI></FONT>
	<FONT face="arial,helvetica,sanserif" size="-1"><LI><A href="developer-guide.html">Developer's Guide</A></LI></FONT>
	</TD><TD align="left" valign="top" width="*"><TABLE border="0" cellpadding="3" cellspacing="0"><TR><TD><BR>





	<DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="0" width="98%"><TR><TD bgcolor="#023264" width="100%"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="+1"><IMG border="0" height="5" hspace="0" src="resources/void.gif" vspace="0" width="5"><B>Design</B></FONT></TD></TR><TR><TD><IMG border="0" height="5" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE><TABLE border="0" cellpadding="0" cellspacing="0" width="98%"><TR><TD><FONT color="#000000" face="arial,helvetica,sanserif">

	<P align="justify">
	Velocity is a Java-based template engine. It can be used as a
	standalone utility for generating source code, HTML, reports,
	or it can be combined with other systems to provide template
	services. Velocity will be tightly integrated with the
	<A href="http://java.apache.org/turbine">Turbine</A>
	web application framework. Velocity-Turbine
	provide a template service by which web applications may be
	developed according to a true MVC model.
	</P>

	<P align="justify">
	Velocity has a myriad of potential uses -- generating SQL, PostScript,
	or Java source code from templates -- but it is expected to be most
	widely used by web developers looking for a viable alternative to
	<A href="http://www.php.net/">PHP</A> and
	<A href="http://java.sun.com/products/jsp/">Java
	Server Pages</A> (JSPs).
	</P>

	<P align="justify">
	Velocity allows web page designers to embed simple yet powerful script
	elements in their web pages. These script elements work
	in conjunction with a Context object, which is defined in Java code.
	A context object--essentially a Hashtable that provides get and set
	methods for retrieving and setting objects by name within the Context
	--provides a "hook" from the Java code to the Velocity script
	elements. These script elements allow a web designer to retrieve
	objects from the Context and insert these into a web page as text
	values. The web designer has some control over looping (for each)
	and conditional statements (if/else).
	</P>

	<P align="justify">
	Velocity enforces a Model-View-Controller (MVC) style of development
	by separating Java code from HTML template code. Unlike JSPs,
	Velocity does not allow Java code to be embedded in pages. Unlike PHP,
	Velocity does not implement features with other functions. The MVC
	approach is one of Velocity's great strengths, and allows for more
	maintainable and better designed web pages.
	</P>

	<P align="justify">
	Although MVC-style development can sometimes lead to longer incubation
	periods for web sites, particularly if the developers involved are new
	to MVC, this approach saves time over the long term (believe us, we have
	been doing this for a long time now). The MVC abstraction prevents web page
	designers from messing with a software engineer's Java code, and
	programmers from unduly influencing the look of web sites. Velocity enforces
	a contract that defines what roles people play in the web site development
	process.
	</P>

	<P align="justify">
	Velocity uses a grammar-based parser generated by
	<A href="http://www.metamata.com/javacc/">JavaCC</A> (Java Compiler
	Compiler) using the JJTree extension to create an Abstract Syntax Tree.
	Its concept was borrowed from
	<A href="http://www.webmacro.org/">WebMacro</A>. Those involved in
	the Velocity project acknowledge and appreciate the development and design
	work that went into the WebMacro project.
	</P>

	</FONT></TD></TR></TABLE></DIV><BR>


	</TD></TR></TABLE></TD></TR></TABLE><BR><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD bgcolor="#023264"><IMG height="1" src="resources/resources.gif" width="1"></TD></TR><TR><TD align="center"><FONT color="#023264" face="arial,helvetica,sanserif" size="-1"><I>
	Copyright © 2000 The Apache Software Foundation.
	All Rights Reserved.
	</I></FONT></TD></TR></TABLE></BODY></HTML>