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Posted to dev@cocoon.apache.org by vo...@basf-it-services.com on 2002/04/26 18:38:06 UTC
Creating dynamic content using JSP like Tag implementation
Hi all,
let me start with a short introduction of my company and what we have done so
far.
Before being founded on April 1, 2001 as BASF IT Services we were an integrated
part of BASF Aktiengesellschaft in Ludwigshafen, Germany and BASF Computer
Services in Europe. We focus on high-quality IT-Development and Services
throughout Europe. E-Commerce is one of our businesses we have been working with
since several years and where we are very experienced in developing successful
solutions for BASF.
End of 2000, BASF started their global E-Commerce initiative named
"WorldAccount", focusing on a worldwide and integrated extranet platform for
their customers (have a look at it: http://worldaccount.basf.com).
To realize such a complex solution we had the idea to develop a publishing
framework which should also cover issues like session management, multi-language
support, layout and security. After evaluating Cocoon2 we decided to base on the
concepts of Avalon and the basic interfaces of Cocoon2, but due to its pre-alpha
version we needed to do some additional development (interpreted Sitemap,
LayoutTransformer, RequestProcessor, ValidationEngine, ErrorHandler, simple
module concept (like Blocks but really simple)......)
One other example: instead of using XSP-Logicsheets we developed a
tag-implementation similar to JSP-tags, but which uses a SAX-pipeline instead of
an output stream. The tags are interpreted during run-time by the appropriate
tag-transformer.
We needed approx. half a year to develop this framework where then the
WorldAccount functionalities could be placed on top and finally could go-live in
the 3rd quarter of 2001. In the last few months we transferred our framework to
Cocoon2 and would now like to present some of our solutions to the Open Source
community, hoping we can help to become Cocoon2 even more powerful and
successful than it already is.
Ok, lets start with the Java-Code ;-) also part of the attachment.
The Tag Interface:
public interface Tag extends XMLPipe, Component
{
String ROLE = Tag.class.getName();
/**
* Evaluate body content
* Valid return value for doStartTag.
*/
int EVAL_BODY = 0;
/**
* Skip body evaluation.
* Valid return value for doStartTag.
*/
int SKIP_BODY = 1;
/**
* Continue evaluating the page.
* Valid return value for doEndTag().
*/
int EVAL_PAGE = 2;
/**
* Process the end tag for this instance.
*
* @returns EVAL_PAGE.
* @throws SAXException.
*/
int doEndTag(String namespaceURI, String localName, String qName) throws
SAXException;
/**
* Process the start tag for this instance.
* <p>
* The doStartTag method assumes that parent have been set.
* It also assumes that any properties exposed as
* attributes have been set too. When this method is invoked, the body
* has not yet been evaluated.
*
* @returns EVAL_BODY or SKIP_BODY.
*/
int doStartTag(String namespaceURI, String localName, String qName,
Attributes atts) throws SAXException;
/**
* Get the parent (closest enclosing tag handler) for this tag handler.
*
* @returns the current parent or null if none.
*/
Tag getParent();
/**
* Set the <code>SourceResolver</code>, objectModel <code>Map</code>
* and sitemap <code>Parameters</code> used to process the request.
*/
void setup(SourceResolver resolver, Map objectModel, Parameters parameters)
throws SAXException, IOException;
/**
* Set the parent (closest enclosing tag handler) of this tag handler.
* Invoked by the implementation object prior to doStartTag().
*
* @param parent The parent tag or null.
*/
void setParent(Tag parent);
}
The Tag Implementation works like a JSP Tag but generate SAX output.
Simple Tag Implementation:
public class XMLDateTag extends AbstractTag
{
public int doStartTag(String namespaceURI, String localName,
String qName, Attributes atts)
throws SAXException
{
String date = new Date(System.currentTimeMillis()).toString();
characters(date.toCharArray(), 0, date.length());
return EVAL_BODY;
}
}
In the current implementation the Tag's are configured in cocoon.xconf. All Tags
are managed by a ComponentSelector and grouped by a namespace (name of the
taglib Element). We are using URN's as namespace. The name of a tag is then
mapped to it's implementation.
Example configuration:
<component role="org.apache.cocoon.xml.taglib.TagSelector"
class="org.apache.cocoon.components.ExtendedComponentSelector">
<taglib name="urn:apache:taglib:general"
class="org.apache.cocoon.components.ExtendedComponentSelector"
logger="sitemap.tag">
<tag name="date" class="org.apache.cocoon.xml.taglib.general.XMLDateTag"
logger="sitemap.tag.xmldate" />
<tag name="..." class="..." />
</taglib>
<taglib name="urn:apache:taglib:... />
<tag ..... />
</taglib>
</component>
Simple example page:
<page>
<title xmlns:tag="urn:apache:taglib:general">Hello</title>
<content>
<para>This is my first Cocoon page!</para>
<para>Today, <tag:date /></para>
</content>
</page>
How does it work?
In the pipeline you need to configure the TagTransformer and add it to your
pipeline. Set the pool-min to "0" because of a bug in excalibur, instead you run
in a endless loop.
<map:transformer name="tag"
src="org.apache.cocoon.transformation.TagTransformer"
pool-max="64" pool-min="0" pool-grow="2"
logger="sitemap.transformer.tag">
<transformer-hint>tag</transformer-hint>
</map:transformer>
The TagTransformer looks if the namespace of an element belongs to a configured
taglib namespace and tag name (see startElement). If it founds a Tag, this Tag
is dynamically inserted to the current SAX-Pipeline and the doStartTag method is
called. If the Tag implements some "SAX Event handling" methods, the Tag is able
to work like a Transformer. The default behavior is a XMLPipe. The doEndTag
method is called if the endElement SAX Event is called (see endElement of
TagTransformer) and the Tag is removed from the pipeline. In the doStartTag
and/or in the doEndTag you can emit additional SAX events to the Pipeline (see
XMLDateTag which only sends the current date). Tags can be nested and a inner
Tag can get a reference to the parent Tag (getParent method).
The TagTransformer can be configured with a "transformer-hint". If the
TagTransformer add a Tag to the Pipeline the Transformer which belongs to this
hint is also add to the pipeline (after the Tag). If this hint is the
TagTransformer itself, a Tag can send out other Tags which are automatic
interpreted again.
Any comments ?
If you find this usefull, is it possible that a committer put this to scratchpad
?
Thanks Volker
(See attached file: source.zip)
Re: Creating dynamic content using JSP like Tag implementation
Posted by Matt Sergeant <ma...@sergeant.org>.
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On Friday 26 April 2002 5:38 pm, volker.schmitt@basf-it-services.com wrote:
> Example configuration:
>
> <component role="org.apache.cocoon.xml.taglib.TagSelector"
> class="org.apache.cocoon.components.ExtendedComponentSelector">
> <taglib name="urn:apache:taglib:general"
> class="org.apache.cocoon.components.ExtendedComponentSelector"
> logger="sitemap.tag">
> <tag name="date"
> class="org.apache.cocoon.xml.taglib.general.XMLDateTag"
> logger="sitemap.tag.xmldate" />
> <tag name="..." class="..." />
> </taglib>
> <taglib name="urn:apache:taglib:... />
> <tag ..... />
> </taglib>
> </component>
This is a bit of a maintainence problem - different people can use the same
tag using different names. Can't you push this into the class somehow?
- --
<:->get a SMart net</:->
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Re: Creating dynamic content using JSP like Tag implementation
Posted by Konstantin Piroumian <kp...@apache.org>.
Hi!
This looks very similar to what is a transformer doing, except for the using
separate classes to handle every tag. And it's also looks like the SAXLet
idea, that has been proposed and maybe even implemented a while ago.
I've been thinking about reimplementing I18nTransformer using something like
this to be able to easily add new elements. Could you please elaborate more
on the advantages of your solution against the transformer approach, except
the flexible configuration?
Regards,
Konstantin
From: <vo...@basf-it-services.com>
>
>
> Hi all,
>
> let me start with a short introduction of my company and what we have done
so
> far.
> Before being founded on April 1, 2001 as BASF IT Services we were an
integrated
> part of BASF Aktiengesellschaft in Ludwigshafen, Germany and BASF Computer
> Services in Europe. We focus on high-quality IT-Development and Services
> throughout Europe. E-Commerce is one of our businesses we have been
working with
> since several years and where we are very experienced in developing
successful
> solutions for BASF.
> End of 2000, BASF started their global E-Commerce initiative named
> "WorldAccount", focusing on a worldwide and integrated extranet platform
for
> their customers (have a look at it: http://worldaccount.basf.com).
> To realize such a complex solution we had the idea to develop a publishing
> framework which should also cover issues like session management,
multi-language
> support, layout and security. After evaluating Cocoon2 we decided to base
on the
> concepts of Avalon and the basic interfaces of Cocoon2, but due to its
pre-alpha
> version we needed to do some additional development (interpreted Sitemap,
> LayoutTransformer, RequestProcessor, ValidationEngine, ErrorHandler,
simple
> module concept (like Blocks but really simple)......)
> One other example: instead of using XSP-Logicsheets we developed a
> tag-implementation similar to JSP-tags, but which uses a SAX-pipeline
instead of
> an output stream. The tags are interpreted during run-time by the
appropriate
> tag-transformer.
> We needed approx. half a year to develop this framework where then the
> WorldAccount functionalities could be placed on top and finally could
go-live in
> the 3rd quarter of 2001. In the last few months we transferred our
framework to
> Cocoon2 and would now like to present some of our solutions to the Open
Source
> community, hoping we can help to become Cocoon2 even more powerful and
> successful than it already is.
>
> Ok, lets start with the Java-Code ;-) also part of the attachment.
> The Tag Interface:
>
> public interface Tag extends XMLPipe, Component
> {
> String ROLE = Tag.class.getName();
>
> /**
> * Evaluate body content
> * Valid return value for doStartTag.
> */
> int EVAL_BODY = 0;
>
> /**
> * Skip body evaluation.
> * Valid return value for doStartTag.
> */
> int SKIP_BODY = 1;
>
> /**
> * Continue evaluating the page.
> * Valid return value for doEndTag().
> */
> int EVAL_PAGE = 2;
>
> /**
> * Process the end tag for this instance.
> *
> * @returns EVAL_PAGE.
> * @throws SAXException.
> */
> int doEndTag(String namespaceURI, String localName, String qName)
throws
> SAXException;
>
> /**
> * Process the start tag for this instance.
> * <p>
> * The doStartTag method assumes that parent have been set.
> * It also assumes that any properties exposed as
> * attributes have been set too. When this method is invoked, the body
> * has not yet been evaluated.
> *
> * @returns EVAL_BODY or SKIP_BODY.
> */
> int doStartTag(String namespaceURI, String localName, String qName,
> Attributes atts) throws SAXException;
>
> /**
> * Get the parent (closest enclosing tag handler) for this tag
handler.
> *
> * @returns the current parent or null if none.
> */
> Tag getParent();
>
> /**
> * Set the <code>SourceResolver</code>, objectModel <code>Map</code>
> * and sitemap <code>Parameters</code> used to process the request.
> */
> void setup(SourceResolver resolver, Map objectModel, Parameters
parameters)
> throws SAXException, IOException;
>
> /**
> * Set the parent (closest enclosing tag handler) of this tag handler.
> * Invoked by the implementation object prior to doStartTag().
> *
> * @param parent The parent tag or null.
> */
> void setParent(Tag parent);
> }
>
>
>
> The Tag Implementation works like a JSP Tag but generate SAX output.
>
> Simple Tag Implementation:
>
> public class XMLDateTag extends AbstractTag
> {
> public int doStartTag(String namespaceURI, String localName,
> String qName, Attributes atts)
> throws SAXException
> {
> String date = new Date(System.currentTimeMillis()).toString();
> characters(date.toCharArray(), 0, date.length());
> return EVAL_BODY;
> }
> }
>
> In the current implementation the Tag's are configured in cocoon.xconf.
All Tags
> are managed by a ComponentSelector and grouped by a namespace (name of the
> taglib Element). We are using URN's as namespace. The name of a tag is
then
> mapped to it's implementation.
>
> Example configuration:
>
> <component role="org.apache.cocoon.xml.taglib.TagSelector"
> class="org.apache.cocoon.components.ExtendedComponentSelector">
> <taglib name="urn:apache:taglib:general"
> class="org.apache.cocoon.components.ExtendedComponentSelector"
> logger="sitemap.tag">
> <tag name="date"
class="org.apache.cocoon.xml.taglib.general.XMLDateTag"
> logger="sitemap.tag.xmldate" />
> <tag name="..." class="..." />
> </taglib>
> <taglib name="urn:apache:taglib:... />
> <tag ..... />
> </taglib>
> </component>
>
> Simple example page:
>
> <page>
> <title xmlns:tag="urn:apache:taglib:general">Hello</title>
> <content>
> <para>This is my first Cocoon page!</para>
> <para>Today, <tag:date /></para>
> </content>
> </page>
>
> How does it work?
>
> In the pipeline you need to configure the TagTransformer and add it to
your
> pipeline. Set the pool-min to "0" because of a bug in excalibur, instead
you run
> in a endless loop.
>
> <map:transformer name="tag"
> src="org.apache.cocoon.transformation.TagTransformer"
> pool-max="64" pool-min="0" pool-grow="2"
> logger="sitemap.transformer.tag">
> <transformer-hint>tag</transformer-hint>
> </map:transformer>
>
> The TagTransformer looks if the namespace of an element belongs to a
configured
> taglib namespace and tag name (see startElement). If it founds a Tag, this
Tag
> is dynamically inserted to the current SAX-Pipeline and the doStartTag
method is
> called. If the Tag implements some "SAX Event handling" methods, the Tag
is able
> to work like a Transformer. The default behavior is a XMLPipe. The
doEndTag
> method is called if the endElement SAX Event is called (see endElement of
> TagTransformer) and the Tag is removed from the pipeline. In the
doStartTag
> and/or in the doEndTag you can emit additional SAX events to the Pipeline
(see
> XMLDateTag which only sends the current date). Tags can be nested and a
inner
> Tag can get a reference to the parent Tag (getParent method).
> The TagTransformer can be configured with a "transformer-hint". If the
> TagTransformer add a Tag to the Pipeline the Transformer which belongs to
this
> hint is also add to the pipeline (after the Tag). If this hint is the
> TagTransformer itself, a Tag can send out other Tags which are automatic
> interpreted again.
>
> Any comments ?
> If you find this usefull, is it possible that a committer put this to
scratchpad
> ?
>
> Thanks Volker
>
> (See attached file: source.zip)
>
>
----------------------------------------------------------------------------
----
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> For additional commands, email: cocoon-dev-help@xml.apache.org
---------------------------------------------------------------------
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Re: Creating dynamic content using JSP like Tag implementation
Posted by Ivelin Ivanov <iv...@apache.org>.
Impressive !
Isn't this a generalized implementation of Berin's call back proposal.
I like it. It steals away the most powerful concept from JSPs and gives it
to Cocoon.
How did you guys do input/form handling?
Ivelin
----- Original Message -----
From: <vo...@basf-it-services.com>
To: <co...@xml.apache.org>
Sent: Friday, April 26, 2002 11:38 AM
Subject: Creating dynamic content using JSP like Tag implementation
>
>
> Hi all,
>
> let me start with a short introduction of my company and what we have done
so
> far.
> Before being founded on April 1, 2001 as BASF IT Services we were an
integrated
> part of BASF Aktiengesellschaft in Ludwigshafen, Germany and BASF Computer
> Services in Europe. We focus on high-quality IT-Development and Services
> throughout Europe. E-Commerce is one of our businesses we have been
working with
> since several years and where we are very experienced in developing
successful
> solutions for BASF.
> End of 2000, BASF started their global E-Commerce initiative named
> "WorldAccount", focusing on a worldwide and integrated extranet platform
for
> their customers (have a look at it: http://worldaccount.basf.com).
> To realize such a complex solution we had the idea to develop a publishing
> framework which should also cover issues like session management,
multi-language
> support, layout and security. After evaluating Cocoon2 we decided to base
on the
> concepts of Avalon and the basic interfaces of Cocoon2, but due to its
pre-alpha
> version we needed to do some additional development (interpreted Sitemap,
> LayoutTransformer, RequestProcessor, ValidationEngine, ErrorHandler,
simple
> module concept (like Blocks but really simple)......)
> One other example: instead of using XSP-Logicsheets we developed a
> tag-implementation similar to JSP-tags, but which uses a SAX-pipeline
instead of
> an output stream. The tags are interpreted during run-time by the
appropriate
> tag-transformer.
> We needed approx. half a year to develop this framework where then the
> WorldAccount functionalities could be placed on top and finally could
go-live in
> the 3rd quarter of 2001. In the last few months we transferred our
framework to
> Cocoon2 and would now like to present some of our solutions to the Open
Source
> community, hoping we can help to become Cocoon2 even more powerful and
> successful than it already is.
>
> Ok, lets start with the Java-Code ;-) also part of the attachment.
> The Tag Interface:
>
> public interface Tag extends XMLPipe, Component
> {
> String ROLE = Tag.class.getName();
>
> /**
> * Evaluate body content
> * Valid return value for doStartTag.
> */
> int EVAL_BODY = 0;
>
> /**
> * Skip body evaluation.
> * Valid return value for doStartTag.
> */
> int SKIP_BODY = 1;
>
> /**
> * Continue evaluating the page.
> * Valid return value for doEndTag().
> */
> int EVAL_PAGE = 2;
>
> /**
> * Process the end tag for this instance.
> *
> * @returns EVAL_PAGE.
> * @throws SAXException.
> */
> int doEndTag(String namespaceURI, String localName, String qName)
throws
> SAXException;
>
> /**
> * Process the start tag for this instance.
> * <p>
> * The doStartTag method assumes that parent have been set.
> * It also assumes that any properties exposed as
> * attributes have been set too. When this method is invoked, the body
> * has not yet been evaluated.
> *
> * @returns EVAL_BODY or SKIP_BODY.
> */
> int doStartTag(String namespaceURI, String localName, String qName,
> Attributes atts) throws SAXException;
>
> /**
> * Get the parent (closest enclosing tag handler) for this tag
handler.
> *
> * @returns the current parent or null if none.
> */
> Tag getParent();
>
> /**
> * Set the <code>SourceResolver</code>, objectModel <code>Map</code>
> * and sitemap <code>Parameters</code> used to process the request.
> */
> void setup(SourceResolver resolver, Map objectModel, Parameters
parameters)
> throws SAXException, IOException;
>
> /**
> * Set the parent (closest enclosing tag handler) of this tag handler.
> * Invoked by the implementation object prior to doStartTag().
> *
> * @param parent The parent tag or null.
> */
> void setParent(Tag parent);
> }
>
>
>
> The Tag Implementation works like a JSP Tag but generate SAX output.
>
> Simple Tag Implementation:
>
> public class XMLDateTag extends AbstractTag
> {
> public int doStartTag(String namespaceURI, String localName,
> String qName, Attributes atts)
> throws SAXException
> {
> String date = new Date(System.currentTimeMillis()).toString();
> characters(date.toCharArray(), 0, date.length());
> return EVAL_BODY;
> }
> }
>
> In the current implementation the Tag's are configured in cocoon.xconf.
All Tags
> are managed by a ComponentSelector and grouped by a namespace (name of the
> taglib Element). We are using URN's as namespace. The name of a tag is
then
> mapped to it's implementation.
>
> Example configuration:
>
> <component role="org.apache.cocoon.xml.taglib.TagSelector"
> class="org.apache.cocoon.components.ExtendedComponentSelector">
> <taglib name="urn:apache:taglib:general"
> class="org.apache.cocoon.components.ExtendedComponentSelector"
> logger="sitemap.tag">
> <tag name="date"
class="org.apache.cocoon.xml.taglib.general.XMLDateTag"
> logger="sitemap.tag.xmldate" />
> <tag name="..." class="..." />
> </taglib>
> <taglib name="urn:apache:taglib:... />
> <tag ..... />
> </taglib>
> </component>
>
> Simple example page:
>
> <page>
> <title xmlns:tag="urn:apache:taglib:general">Hello</title>
> <content>
> <para>This is my first Cocoon page!</para>
> <para>Today, <tag:date /></para>
> </content>
> </page>
>
> How does it work?
>
> In the pipeline you need to configure the TagTransformer and add it to
your
> pipeline. Set the pool-min to "0" because of a bug in excalibur, instead
you run
> in a endless loop.
>
> <map:transformer name="tag"
> src="org.apache.cocoon.transformation.TagTransformer"
> pool-max="64" pool-min="0" pool-grow="2"
> logger="sitemap.transformer.tag">
> <transformer-hint>tag</transformer-hint>
> </map:transformer>
>
> The TagTransformer looks if the namespace of an element belongs to a
configured
> taglib namespace and tag name (see startElement). If it founds a Tag, this
Tag
> is dynamically inserted to the current SAX-Pipeline and the doStartTag
method is
> called. If the Tag implements some "SAX Event handling" methods, the Tag
is able
> to work like a Transformer. The default behavior is a XMLPipe. The
doEndTag
> method is called if the endElement SAX Event is called (see endElement of
> TagTransformer) and the Tag is removed from the pipeline. In the
doStartTag
> and/or in the doEndTag you can emit additional SAX events to the Pipeline
(see
> XMLDateTag which only sends the current date). Tags can be nested and a
inner
> Tag can get a reference to the parent Tag (getParent method).
> The TagTransformer can be configured with a "transformer-hint". If the
> TagTransformer add a Tag to the Pipeline the Transformer which belongs to
this
> hint is also add to the pipeline (after the Tag). If this hint is the
> TagTransformer itself, a Tag can send out other Tags which are automatic
> interpreted again.
>
> Any comments ?
> If you find this usefull, is it possible that a committer put this to
scratchpad
> ?
>
> Thanks Volker
>
> (See attached file: source.zip)
>
----------------------------------------------------------------------------
----
> ---------------------------------------------------------------------
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> For additional commands, email: cocoon-dev-help@xml.apache.org
---------------------------------------------------------------------
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Re: Creating dynamic content using JSP like Tag implementation
Posted by Ivelin Ivanov <iv...@apache.org>.
Volker,
After I looked at the implementation of the TagTransformer code, I realized
that it's very similar to the AbstractSaxTransformer class currently in
Cocoon2.
Can you elaborate a bit on the differences and provide a non trivial example
of a tag.
For example how would an iterator tag look like.
If you see the XMLForm namespace tags, the repeat tag works like this:
<xf:repeat nodeset="user/favorite">
<xf:output ref="url">
<xf:caption>URL :</xf:caption>
</xf:output>
</xf:repeat>
If you have time, please look at the XMLFormTransformer in Scratchpad which
extends AbstractSaxTransformer and advise if it could be written more
optimally as a set of tags.
Thanks,
Ivelin
----- Original Message -----
From: <vo...@basf-it-services.com>
To: <co...@xml.apache.org>
Sent: Friday, April 26, 2002 11:38 AM
Subject: Creating dynamic content using JSP like Tag implementation
>
>
> Hi all,
>
> let me start with a short introduction of my company and what we have done
so
> far.
> Before being founded on April 1, 2001 as BASF IT Services we were an
integrated
> part of BASF Aktiengesellschaft in Ludwigshafen, Germany and BASF Computer
> Services in Europe. We focus on high-quality IT-Development and Services
> throughout Europe. E-Commerce is one of our businesses we have been
working with
> since several years and where we are very experienced in developing
successful
> solutions for BASF.
> End of 2000, BASF started their global E-Commerce initiative named
> "WorldAccount", focusing on a worldwide and integrated extranet platform
for
> their customers (have a look at it: http://worldaccount.basf.com).
> To realize such a complex solution we had the idea to develop a publishing
> framework which should also cover issues like session management,
multi-language
> support, layout and security. After evaluating Cocoon2 we decided to base
on the
> concepts of Avalon and the basic interfaces of Cocoon2, but due to its
pre-alpha
> version we needed to do some additional development (interpreted Sitemap,
> LayoutTransformer, RequestProcessor, ValidationEngine, ErrorHandler,
simple
> module concept (like Blocks but really simple)......)
> One other example: instead of using XSP-Logicsheets we developed a
> tag-implementation similar to JSP-tags, but which uses a SAX-pipeline
instead of
> an output stream. The tags are interpreted during run-time by the
appropriate
> tag-transformer.
> We needed approx. half a year to develop this framework where then the
> WorldAccount functionalities could be placed on top and finally could
go-live in
> the 3rd quarter of 2001. In the last few months we transferred our
framework to
> Cocoon2 and would now like to present some of our solutions to the Open
Source
> community, hoping we can help to become Cocoon2 even more powerful and
> successful than it already is.
>
> Ok, lets start with the Java-Code ;-) also part of the attachment.
> The Tag Interface:
>
> public interface Tag extends XMLPipe, Component
> {
> String ROLE = Tag.class.getName();
>
> /**
> * Evaluate body content
> * Valid return value for doStartTag.
> */
> int EVAL_BODY = 0;
>
> /**
> * Skip body evaluation.
> * Valid return value for doStartTag.
> */
> int SKIP_BODY = 1;
>
> /**
> * Continue evaluating the page.
> * Valid return value for doEndTag().
> */
> int EVAL_PAGE = 2;
>
> /**
> * Process the end tag for this instance.
> *
> * @returns EVAL_PAGE.
> * @throws SAXException.
> */
> int doEndTag(String namespaceURI, String localName, String qName)
throws
> SAXException;
>
> /**
> * Process the start tag for this instance.
> * <p>
> * The doStartTag method assumes that parent have been set.
> * It also assumes that any properties exposed as
> * attributes have been set too. When this method is invoked, the body
> * has not yet been evaluated.
> *
> * @returns EVAL_BODY or SKIP_BODY.
> */
> int doStartTag(String namespaceURI, String localName, String qName,
> Attributes atts) throws SAXException;
>
> /**
> * Get the parent (closest enclosing tag handler) for this tag
handler.
> *
> * @returns the current parent or null if none.
> */
> Tag getParent();
>
> /**
> * Set the <code>SourceResolver</code>, objectModel <code>Map</code>
> * and sitemap <code>Parameters</code> used to process the request.
> */
> void setup(SourceResolver resolver, Map objectModel, Parameters
parameters)
> throws SAXException, IOException;
>
> /**
> * Set the parent (closest enclosing tag handler) of this tag handler.
> * Invoked by the implementation object prior to doStartTag().
> *
> * @param parent The parent tag or null.
> */
> void setParent(Tag parent);
> }
>
>
>
> The Tag Implementation works like a JSP Tag but generate SAX output.
>
> Simple Tag Implementation:
>
> public class XMLDateTag extends AbstractTag
> {
> public int doStartTag(String namespaceURI, String localName,
> String qName, Attributes atts)
> throws SAXException
> {
> String date = new Date(System.currentTimeMillis()).toString();
> characters(date.toCharArray(), 0, date.length());
> return EVAL_BODY;
> }
> }
>
> In the current implementation the Tag's are configured in cocoon.xconf.
All Tags
> are managed by a ComponentSelector and grouped by a namespace (name of the
> taglib Element). We are using URN's as namespace. The name of a tag is
then
> mapped to it's implementation.
>
> Example configuration:
>
> <component role="org.apache.cocoon.xml.taglib.TagSelector"
> class="org.apache.cocoon.components.ExtendedComponentSelector">
> <taglib name="urn:apache:taglib:general"
> class="org.apache.cocoon.components.ExtendedComponentSelector"
> logger="sitemap.tag">
> <tag name="date"
class="org.apache.cocoon.xml.taglib.general.XMLDateTag"
> logger="sitemap.tag.xmldate" />
> <tag name="..." class="..." />
> </taglib>
> <taglib name="urn:apache:taglib:... />
> <tag ..... />
> </taglib>
> </component>
>
> Simple example page:
>
> <page>
> <title xmlns:tag="urn:apache:taglib:general">Hello</title>
> <content>
> <para>This is my first Cocoon page!</para>
> <para>Today, <tag:date /></para>
> </content>
> </page>
>
> How does it work?
>
> In the pipeline you need to configure the TagTransformer and add it to
your
> pipeline. Set the pool-min to "0" because of a bug in excalibur, instead
you run
> in a endless loop.
>
> <map:transformer name="tag"
> src="org.apache.cocoon.transformation.TagTransformer"
> pool-max="64" pool-min="0" pool-grow="2"
> logger="sitemap.transformer.tag">
> <transformer-hint>tag</transformer-hint>
> </map:transformer>
>
> The TagTransformer looks if the namespace of an element belongs to a
configured
> taglib namespace and tag name (see startElement). If it founds a Tag, this
Tag
> is dynamically inserted to the current SAX-Pipeline and the doStartTag
method is
> called. If the Tag implements some "SAX Event handling" methods, the Tag
is able
> to work like a Transformer. The default behavior is a XMLPipe. The
doEndTag
> method is called if the endElement SAX Event is called (see endElement of
> TagTransformer) and the Tag is removed from the pipeline. In the
doStartTag
> and/or in the doEndTag you can emit additional SAX events to the Pipeline
(see
> XMLDateTag which only sends the current date). Tags can be nested and a
inner
> Tag can get a reference to the parent Tag (getParent method).
> The TagTransformer can be configured with a "transformer-hint". If the
> TagTransformer add a Tag to the Pipeline the Transformer which belongs to
this
> hint is also add to the pipeline (after the Tag). If this hint is the
> TagTransformer itself, a Tag can send out other Tags which are automatic
> interpreted again.
>
> Any comments ?
> If you find this usefull, is it possible that a committer put this to
scratchpad
> ?
>
> Thanks Volker
>
> (See attached file: source.zip)
>
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