Hi,
The system directives are treated a little differently. The parser
recognizes them and does some syntax checking at compile time. (See "
parser.jjt").
As far as user directives, you can check the argument nodes for specific
types (strings, references, etc) and throw an exception if they are
invalid. For example, require the first and third arguments to be
references. Matching "in" is a bit of a problem since it's not generic
syntax. (e.g. it's not a literal or a reference).
WILL
On 7/26/07, 于世英 <[EMAIL PROTECTED]> wrote:
>
> Hi all,
> I'm going to writing some directives to extend Velocity. now I'm in
> lacking
> of documents.
> I've read the PPT 《Hacking Velocity》by Will Glass-Husain, and some souce
> code of system directive such as "literal", "execute", but I don't
> understand "foreach" till now.
> I've written the following code(Mydd.java) and it can work as coded now:
> -------------------file begin ------------------------------
> import java.io.IOException;
> import java.io.Writer;
> import java.util.Iterator;
>
> import org.apache.velocity.context.InternalContextAdapter;
> import org.apache.velocity.exception.MethodInvocationException;
> import org.apache.velocity.exception.ParseErrorException;
> import org.apache.velocity.exception.ResourceNotFoundException;
> import org.apache.velocity.runtime.directive.Directive;
> import org.apache.velocity.runtime.RuntimeServices;
> import org.apache.velocity.runtime.parser.node.Node;
> import org.apache.velocity.exception.TemplateInitException;
> import org.apache.log4j.Logger;
>
> public class Mydd extends Directive {
>
> private static Logger logger = Logger.getLogger(Mydd.class);
>
> public void init(RuntimeServices rs, InternalContextAdapter context,
> Node node)
> throws TemplateInitException
> {
> super.init(rs, context, node);
>
> }
> @Override
> public String getName() {
> return "mydd";
> }
>
> @Override
> public int getType() {
>
> return LINE;
> }
>
> public boolean render(InternalContextAdapter context,
> Writer writer, Node node) throws IOException
> {
> for (int i = 0; i < node.jjtGetNumChildren(); i ++) {
> logger.debug("debug mydd parameter: " + node.jjtGetChild
> (i).
> toString() + " (" + node.jjtGetChild(i).literal() + ")");
> }
> writer.write("Hello, world!");
> return true;
> }
> }
> -------------------file end ----------------------------------
>
> What I want to know is:
> 1, the above directive's syntax in template is
> #mydd(arg1 arg2 arg3 ...)
> but system directives like "foreach" and "set" have COOL syntax like
> "#foreach ($a in $set)", how to let my directive support syntax like this?
> 2, does the directive mechanism provided Velocity has other convenience or
> power that I don't know ? what I know about is all in the above code :-)
>
> Thanks in advance, any hint will be appreciated!
>
>
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--
Forio Business Simulations
Will Glass-Husain
[EMAIL PROTECTED]
www.forio.com
