Nested Custom Tags
Hello,
I have a custom tag that I've written that has some
attributes. I want to nest that tag inside of itself, and access
the attibutes of the parent tag. However, when I try to access the
parent tag's data from the child all I get is the child tag's data!
If there are two of the same custom tags in the context stack, is
it possible to access one from the other? Thanks for your help.
Tim
> I can't use the
> CALLER scope, as that references the page that called
the first custom tag, no
> matter how deeply nested I am.
I think you should test the advice, before you make
assertions like this.
The CALLER scope refers to the variables scope of the
template that called
the currently executing custom tag. If your calling stack is
like this:
index.cfm
customTagA.cfm
customTagB.cfm
Then the situation is this:
1) In index.cfm: no caller scope.
2) In customTagA.cfm: caller scope references index.cfm's
variables scope.
3) custoTagB.cfm: caller scope references customTagA.cfm's
variables scope
(NOT index.cfm's one).
Similarly, if your calling stack is like this:
index.cfm
customTag.cfm (*)
customTag.cfm
customTag.cfm
customTag.cfm
Then the caller scope in each customTag.cfm instance refers
to the
variables scope of the file above it. The only caller scope
that
references index.cfm's variables scope is the customTag
instance marked
with (*).
If I understand your requirement, this is what you want. This
is why I
suggested it.
Adam
Similar Messages
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Hi,
How can I use nested custom tags in jsp?Note that not all custom tags will work like this. The tag must be designed to work this way. Some tags will not accept a body, others will accept a body, but will not process it through the JSP compiler, rather handling it as text/html.
Have you tried nesting them and you're not getting the expected results? Have you written these tags yourself and they're not working? -
Rendering Querydata in nested Custom-Tags
Hi all
I have built two custom-tags to render the results of a query
in a table (a bit like the display-tag-library or the datatable-tag
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some other things like records per page.
the child-tag defines a single column. the developer can
define a query-column-name in an attribute as well as the label and
so on.
the typical code looks like this and this works fine:
<tags:dataTable collection="#AddressQuery#"
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<tags:dataTableColumn column="id" label=""
selection="true" />
<tags:dataTableColumn column="name" label="Name"
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Can I prevent CF to execute the tag-content, but instead save
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If not can I solve this problem otherwise?
thanks
stefanHi Jesse.
I'm also working on something very similar to the tab pane you are talking about. Mine was inspired by the CoreJSF book (I used some of the downloadable pre-release chapters). Great book. It's at www.corejsf.com
The basic idea behind theirs (and mine) is that the tab pane widget maintains a collection of tabs as a property. In the tag handler class you can specify the tabs themselves as either child components or facets (they used f:selectItem and f:selectItems, along with facets). I liked the f:selectItems the best.
All of the rendering is done in the renderer class. The book has examples of how to include additional jsp content specified as a fragment.
I would really suggest having a look at the book.
Regards,
Dave Haas -
Is possible to write a custom tag inside another custom tag ??
Hi
I�m trying to reduce the time needed to code mi app presentation layer, it uses some custom tags with certain configuration, i would like to know if its possible to do something like this inside my custom tag doAfterBody().
public int doAfterBody() throws JspException {
JspWriter writer=bodyContent.getEnclosingWriter();
try {
writer.print("<customTag:myAnotherTag someEspecificConfigurationParams="someEspecificValues"/>");
} catch (IOException e) {
pageContext.getServletContext().log("Error: "+e.getMessage());
}return SKIP_BODY;
}The goal is to simplify the jsp code because the configuration params for the custom tags (css styles and similar) are allways the same.
That don�t work, it simply prints <customTag:myAnotherTag/> in screen but the tag is not evaluated, i�ve tried too something like
public int doAfterBody() throws JspException {
if (repeat) {
JspWriter writer = bodyContent.getEnclosingWriter();
try {
writer.print("<customTag:myAnotherTag/>");
} catch (IOException e) {
pageContext.getServletContext().log("Error: " + e.getMessage());
repeat = false;
return EVAL_BODY_AGAIN;
return SKIP_BODY;
}And it doesn�t worked worked. Maybe using the taghandler classes and calls to the doAfterBody could make it work, but when you need to nest tags it could be a little hell of coupling calls, so before doing it i would like to know if what i want is possible. After reading some books i tought it could work because the stack of out objects, but i can�t make it work.
Another idea is to inherit from tagHandler and override some properties in the tags, but i don�t like the idea to much.
So, can anyone help me??
Thanks.You cannot do that and I have listed out the reason and a possible solution in this post http://forum.java.sun.com/thread.jspa?threadID=697243 from yesterday.
cheers,
ram. -
How to use a variable of jsp custom tag in my java code?
hi folks,
i got a folderList tag like this:
ArrayList list = new ArrayList(20);
%>
<foo:folderList path="${attributes.newsPath}" var="year" contentType="folder">
<%
list.add(${year.contentEntryName}); // of course, this doesn't work
%>
</foo:folderList>I think, its clear what I want to do. I am just wondering how I can use my Variable "year" in the Java code between <% %>...<% list.add(year.getContentEntryName()); %>
You have to have defined in the custom tag that "var" relates to a scripting variable that you want defined.
<tag>
<variable>
<name-given>var</name-given>
<variable-class>myPackage.myClass</variable-class>
<declare>true</declare>
<scope>NESTED</scope>
</variable>
</tag> Cheers,
evnafets -
Custom Tag with open body loop
Hi
I'm fairly new to custom tags. I want to do something like the following
index.jsp
<mytag:allItems>
${item.name} ${item.url}
</mytag:allItems>
At the moment I have the following which works fine
menu.tag
<jsp:useBean id="items" class="com.content.urls"/>
<c:forEach var="menuItem" items="${items.attachedItems}">
${menuItem.name}
</c:forEach>
index.jsp
<mytags:menu />
The bean returns a list and the tag file produces the urls which is great. However what I would like to do is using the example above not have the content of the loop fixed. For exmaple I could do
<mytag:allItems>
${item.name}
</mytag:allItems>
or
<mytags:menu>
<li>${item.name}</li>
</mytags:menu>
I would also like to leave it so that closing the tag would still produce the list of urls as a default.
any help much appreciated.Rob - replace your forEach with:
<c:forEach var="menuItem" items="${items.attachedItems}">
<%@ variable name-given="menuItem" scope="NESTED" %>
<jsp:doBody />
</c:forEach>The key here is that the menuItem variable is then exposed to the tag body before it is output.
then your jsp will be:
<mytag:allItems>
<a href="${menuItem.url}">${menuItem.name}</a>
</mytag:allItems>To do the last bit - you just need to define a variable for the body and then test whether it is set:
<jsp:doBody var="body" />
<c:forEach var="menuItem" items="${items}">
<c:if test="${not empty body}">
<%@ variable name-given="menuItem" scope="NESTED" %>
<jsp:doBody />
</c:if>
<c:if test="${empty body}">
<a href="${menuItem.path}">${menuItem.name}</a>
</c:if>
</c:forEach>Peter. -
Controlling the output of custom tags
Hi everybody
I'm developing some special custom tags and I have a main tag and several nested ones. I want the nested ones to put their output String into JspWriter buffer when the main tag doEndTag() happens or use the JspWriter and print a sign when each nested tag are processed and then on doEndTag() of the main tag modify the buffer and replace the signs with their actual values. But so far I havn't got anywhere.
Because JspWriter doesn't allow manual modification of buffer and doesn't even let you to access the content of the biffer either all one can do is to print more String into the buffer!
Any suggestion would be a great help to me.
Thanks a lotHere's an example that saves up the bodies of the nested tags and prints them out when the main tag is finished.
index.jsp
<%@ taglib prefix="mytags" uri="/WEB-INF/mytags.tld" %>
<html>
<body>
<h1>index.jsp</h1>
<mytags:main>
<mytags:nested>value 1</mytags:nested>
<mytags:nested>second value</mytags:nested>
<mytags:nested>3RD VALUE</mytags:nested>
</mytags:main>
</body>
</html>mytags.tld
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
"http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>mytags</short-name>
<tag>
<name>main</name>
<tag-class>mytags.MainTag</tag-class>
<body-content>JSP</body-content>
</tag>
<tag>
<name>nested</name>
<tag-class>mytags.NestedTag</tag-class>
<body-content>JSP</body-content>
</tag>
</taglib>/mytags/MainTag.java
package mytags;
import java.io.IOException;
import java.util.Iterator;
import java.util.LinkedList;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
public class MainTag extends TagSupport
public int doStartTag() throws JspException
LinkedList nesteds = new LinkedList();
pageContext.setAttribute("MainTagNesteds", nesteds);
return EVAL_BODY_INCLUDE;
public int doEndTag() throws JspException
JspWriter out = pageContext.getOut();
try {
LinkedList nesteds = (LinkedList)pageContext.getAttribute("MainTagNesteds");
Iterator iterator = nesteds.iterator();
while( iterator.hasNext() ) {
out.println( iterator.next() + "<br>" );
catch(IOException exc) {
exc.printStackTrace();
return EVAL_PAGE;
}/mytags/NestedTag.java
package mytags;
import java.util.LinkedList;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
public class NestedTag extends BodyTagSupport
public int doAfterBody() throws JspException
BodyContent bc = getBodyContent();
String bodyAsString = bc.getString();
LinkedList nesteds = (LinkedList)pageContext.getAttribute("MainTagNesteds");
nesteds.add( bodyAsString );
return SKIP_BODY;
-
Question: TLD and custom Tag Usage.
Hi, I am new to the custom tags and I am confused with one of the examples.
The TLD has
<tag>
<name>item</name>
<tagclass>com.taglib.wdjsp.mut.OutlineItemTag</tagclass>
<bodycontent>JSP</bodycontent>
<info>
Delineates an item, possibly including subitems,
within a nested outline.
</info>
<attribute>
<name>text</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
This TLD specifies that the tag has body content that is JSP and not empty.
The author uses the tag in the JSP page in the following way..
<mut:item text="What is JSP"/>
<mut:item text="Evolution of dynamic content technologies">
<mut:item text="Common Gateway Interface"/>
</mut:item>
I wonder why the usage "<mut:item text="What is JSP"/>" - where the
bodycontent is empty - does not violate the TLD.
Is the bodycontent optional even if it is specified in TLD. What if it is
tagdependent?
thanks - Sri
then in your code
public void setEnabled(String enabled) {
this.enabled = true;
in your endtag reset the boolean to false;
IMO, a cleaner approach would be
private boolean enabled = false;
public void setEnabled(boolean enabled) {
this.enabled = enabled;
}The advanatge is that
<foo other_attributes enabled= "false"/> and
<foo other_attributes/> will both evaluate to false;
<foo other_attributes enabled= "true"/> will evaluate to true
<foo other_attributes enabled= "will_this_work"/> will give an exception
as the container cannot resolve it to a boolean value so that users will
be forced to use true or false (or skip the attribute) which is how it
should be.
Also note the container cannot convert runtime expressions to boolean
values. So if there's a String variable,say prompt in scope that has the
value true, then<%
String prompt = "true";
pageContext.setAttribute("prompt", prompt);
%>
<foo other_attributes enabled= "<%=prompt>"/>
will throw an error. (to do this you would have to specify rtexpr value of
this attribute to true)
For the above to work, your tag should be coded as shown below
private boolean enabled = false;
//note rtexpr value will always be Strings
//container does not provide auto conversions
public void setEnabled(String enabled) {
this.enabled = new Boolean(enabled).booleanValue();
}cheers,
ram. -
Recursive custom tag: different behaviour in WinXP and Linux
Hi all,
I've a strange behaviour on a web application for which I developed a custom tag to render a tree structure.
This tag take in input an object representing the tree with all its nodes, and render every node, calling hitself recursively for every child of every node.
This tag is used inside a jsp.
I deployed my webapp on JBoss in a WinXP Pro environment, and everything is ok. Then I deployed the same webapp on JBoss in a Linux Env, and the call to the custom tag... doesn't write anything (with the same input).
Used jdk are 1.6.0_10 on WinXP and 1.6.0_7 on Linux (an OpenSuse professional distribution). JBoss is 4.2 (I did tests with JBoss 4.2.2 and 4.2.3).
Here is a sample code of my tag (file outree.tag):
<%@ tag language="java" pageEncoding="UTF-8" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib uri="http://jakarta.apache.org/taglibs/log-1.0" prefix="log" %>
*<%@ taglib prefix="ousel" tagdir="/WEB-INF/tags/ouselector" %>*
<%@ attribute name="subtree"
required="true"
type="my.webapp.TreeObject" %>
<%@ attribute name="subroot_index" required="true" type="java.lang.Integer"%>
<log:debug category="my.webapp.ousearch.taglib" message="Tag library called, starting operations..." />
<c:if test="${not empty subtree.children}">
<c:set var="next_subtree_index" value="${subroot_index + 1}"/>
<ul class="subtree" id="subtree-${subroot_index}">
<log:debug category="${logcategory}" message="We have children, calling recursively tag library on them (next subtree index: ${next_subtree_index})..." />
<c:forEach var="currentOUChild" items="${subtree.children}">
*<ousel:outree subtree="${currentOUChild}" subroot_index="${next_subtree_index}"/>*
<c:set var="next_subtree_index" value="${next_subtree_index + 1}"/>
</c:forEach>
</ul>
</c:if>
</li>The TreeObject contains a list of children that can contain other children and so on. On every child, I call recursively my custom tag to render with a set of nested <ul> elements the entire tree structure.
Here the call from the jsp:
<%@ taglib uri="http://jakarta.apache.org/taglibs/log-1.0" prefix="log" %>
*<%@ taglib prefix="ousel" tagdir="/WEB-INF/tags/ouselector" %>*
<log:debug category="${logcategory}" message="Building subtree ${ouSubtree} HTML structure..." />
*<ousel:outree subtree="${ouSubtree}" subroot_index="1"/>*
<log:debug category="${logcategory}" message="Subtree ${ouSubtree} HTML structure built" />
...Jakarta log taglibs is used to log the value of the parameter passed to the custom tag. In the Linux env I see that the passed object is not empty (it couldn't be null because the tag enforce it as a mandatory value).
Any idea?I have found a workaround.
Simply substitute the recursive invocation, with an import of a jsp that will call the custom tag.
Note: You have to set your needed variable in request to make it visible to the jsp
<%@ tag language="java" pageEncoding="UTF-8" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib uri="http://jakarta.apache.org/taglibs/log-1.0" prefix="log" %>
<%@ attribute name="subtree"
required="true"
type="my.webapp.TreeObject" %>
<%@ attribute name="subroot_index" required="true" type="java.lang.Integer"%>
<log:debug category="my.webapp.ousearch.taglib" message="Tag library called, starting operations..." />
<c:if test="${not empty subtree.children}">
<c:set var="next_subtree_index" value="${subroot_index + 1}"/>
<ul class="subtree" id="subtree-${subroot_index}">
<log:debug category="${logcategory}" message="We have children, calling recursively tag library on them (next subtree index: ${next_subtree_index})..." />
<c:forEach var="currentOUChild" items="${subtree.children}">
*<c:set var="_currentOUChild" value="${currentOUChild}" scope="request"/>*
*<c:set var="_next_subtree_index" value="${next_subtree_index}" scope="request"/>*
*<c:import url="/WEB-INF/tags/outtree.jsp"/>*
<c:set var="next_subtree_index" value="${next_subtree_index + 1}"/>
</c:forEach>
</ul>
</c:if>
</li>Here is the imported jsp (outtree.jsp):
<%@ taglib prefix="ousel" tagdir="/WEB-INF/tags/ouselector" %>
<ousel:outree subtree="${_currentOUChild}" subroot_index="${_next_subtree_index}"/> -
Custom tag library called multiple times
Hi ppl ,
I have a custom tag library which i use to populate some menu components. When i do call my custom tag library though , it is called multiple times, use case is as follows.
I have menu tabs and menu bars which thanks to Mr.Brenden is working splendidly as so:-
<af:menuTabs>
<af:forEach var="menuTab" items="#{bindings.menu.vwUserMenuTabRenderer.rangeSet}">
<af:commandMenuItem text="#{menuTab.MenuLabel}"
shortDesc="#{menuTab.MenuHint}"
rendered="true"
immediate="true"
selected="#{sessionScope.selectedMenuId == menuTab.MenuId }"
onclick="fnSetSelectedValue('#{menuTab.MenuId}')" >
</af:commandMenuItem>
</af:forEach>
</af:menuTabs>
<af:menuBar>
<af:forEach var="menuBar" items="#{bindings.menu.vwUserMenuBarRenderer.rangeSet}">
<af:commandMenuItem onclick="return clickreturnvalue()"
onmouseover="dropdownmenu(this, event,#{menuBar.MenuId}, '150px')"
onmouseout="delayhidemenu()"
text="#{menuBar.MenuLabel}"
action="#{menuBar.MenuUri}"
rendered="#{menuBar.ParentId == sessionScope.selectedMenuId}"
immediate="true" />
</af:forEach>
</af:menuBar>
</afc:cache>
now all of this code is within a subview , and just directly below the subview tag , i have the call to my custom tag library:-
<myCustomTagLib:menuCascade />
only issue now is that assuming i have in all 7 menu bar components, the doStartTag is called 7 times. the relevant code within my custom tag class is as follows :-
public int doStartTag() throws JspException {
return (EVAL_BODY_INCLUDE);
public int doEndTag() throws JspException {
try {
declareVariables();
return EVAL_PAGE;
}catch (Exception ioe) {
throw new JspException(ioe.getMessage());
and within my declareVariables method i do an out of the jscript ( out.print(jscript.toString()); ) which is a simple string generated based on certain conditions...
now it seems to be working fine on the front end , but when i view the source of the page, i notice that the declaration is called multiple times, and this happens because the doStartTag method is called multiple times, i haven't even nested the call to the custom tag within the menu components , any clue as to whats going wrong ?
Cheers
KHi,
if you add the following print statement
System.out.println("rendering "+FacesContext.getCurrentInstance().getViewRoot().getViewId());
Then the output in my case is
07/04/24 08:14:04 rendering /BrowsePage.jsp
07/04/24 08:14:05 rendering /otn_logo_small.gif
The image comes from the file system, which means it is rendered by the JSF lifecycle. If you reference the image with a URL then the lifecycle doesn't render the image but only refrences it.
To avoid your prepare render code to be executed multiple times, just check for jsp and jspx file extensions, which will guarantee that your code only executes for JSF pages, not for loaded files.
The reason why this happens is because the JSF filter is set to /faces , which means all files that are loaded through that path
Frank -
I have implemented what I thought was a simple custom tag to handle if
conditions. In the page that I am using to test this new tag, I have
two instances of this tag - one right after another - the second of
which is giving me an error in parsing the page saying that there is a
close tag for which there is no start. The page looks like this:
<prefix:if expr="<%=expr here%>" >
<p>some text</p>
</prefix:if>
<prefix:if expr="<%=expr here%>" >
<p>some more text</p>
</prefix:if>
Where prefix is really the prefix I identified in my taglib directive
and "expr here" are two different boolean expressions.
I have search the page for an errant closing tag - but they are all
matched up just fine. At first I had these tags nested - and thinking
that was the problem - I unrolled the nesting so that the start and
end pairs were always matched up - i.e. an end for this tag always
came after the start without an intervening start for the same tag.
But doing that unrolling had no effect - and I always seem to get the
error on the second close tag being encountered by the parser.
My tld file specifies the body content for this tab as JSP and the
expr attribute as a run-time evaluated attribute which is required. My
tag class file extends TagSupport and implements the doStartTag and
setExpr() methods.
This problem occurrs for me running both WLS 5.1 SP5 and SP6.
Is there something simple that I am missing here? Note also that I
have two other custom tags which work just fine in the same page -
however both of those tags specify an empty bodycontent.
I found my problem - as I had thought I had a typo - I was missing the
'=' between expr and the quoted expression in the second tag. I sure
wish my eyes would quit filling in those missing pieces! :)
On Wed, 08 Nov 2000 13:21:47 GMT, [email protected] (Scott Jacobs)
wrote:
>I have implemented what I thought was a simple custom tag to handle if
>conditions. In the page that I am using to test this new tag, I have
>two instances of this tag - one right after another - the second of
>which is giving me an error in parsing the page saying that there is a
>close tag for which there is no start. The page looks like this:
>
><prefix:if expr="<%=expr here%>" >
> <p>some text</p>
></prefix:if>
><prefix:if expr="<%=expr here%>" >
> <p>some more text</p>
></prefix:if>
>
>Where prefix is really the prefix I identified in my taglib directive
>and "expr here" are two different boolean expressions.
>
>I have search the page for an errant closing tag - but they are all
>matched up just fine. At first I had these tags nested - and thinking
>that was the problem - I unrolled the nesting so that the start and
>end pairs were always matched up - i.e. an end for this tag always
>came after the start without an intervening start for the same tag.
>But doing that unrolling had no effect - and I always seem to get the
>error on the second close tag being encountered by the parser.
>
>My tld file specifies the body content for this tab as JSP and the
>expr attribute as a run-time evaluated attribute which is required. My
>tag class file extends TagSupport and implements the doStartTag and
>setExpr() methods.
>
>This problem occurrs for me running both WLS 5.1 SP5 and SP6.
>
>Is there something simple that I am missing here? Note also that I
>have two other custom tags which work just fine in the same page -
>however both of those tags specify an empty bodycontent.
-
Custom Tag Implementation seems inefficient
I've been playing around a bit (alright, so maybe not all that much)
with custom tags, and it seems like the actual implementation of custom
tags (tag handler object(s) per tag) is much more resource-intensive
than would be justified. With Weblogic 5.1 SP6, has anyone had the
opportunity to compare performance of a typical JSP page w/ and w/out
custom tags?
My first impression of custom tags was that you could define tags
and behaviors that the JSP compiler would then compile into your JSP
class; there would be no performance hit during page execution. The Java
code used to write these tags would either be included inline in the JSP
page code, or else act essentially as static (threadsafe) classes into
which threads executing JSP pages would call into. This approach means
less resources consumed and less setup/teardown time in exchange for
fatter JSPC'd code.
Instead (and correct me if I am wrong), it appears that each
distinct custom tag has a pool of instantiated handler objects lying
around in memory, and each time a custom tag is used, there is a
little performance hit in the setup & teardown of each handler object's
pageContext, etc...
Now admittedly, as another poster (I believe Mr. Purdy) pointed out,
a "little" ain't all that much... unless there are thousands of those
"little" hits.
Moreover, I don't see much benefit in having instantiated objects do
the heavy lifting. I'd rather have my auto-compiled JSP classes be a
little more bloated than suffer any performance hit. (I do, however,
like the fact that custom tags allows for cleaner JSP code, not to
mention makes for a cleaner break between the creative and coding work.)
For those of you who've had more extensive experience with custom
tags, am I missing the target? Is the performance hit negligible for
heavily-used or complex pages? And/or is the performance hit outweighed
by code and development cleanliness?
Thanks for any input.
Jack
Hi Sri
Looks like you've found an inefficiency in WebLogic's JSP compiler - it
should be reusing tag instances within the same page. BEA should fix this
hopefully.
> So even if a page has 4 tags and 100 users, we have 400 objects just
> because we use tags.
Sure, assuming you have 100 concurrent users (and 100 threads in the servlet
engine). Though creating 400 objects is not a big deal in Java; most non
trivial Java applications / services create millions of objects.
Its also worth noting that having a seperate object instance per tag per
calling thread means that you don't have to do any synchronisation in the
custom tag (since you're guarenteed to be called by one thread only) so you
get maximum thread throughput at the expense of some object allocation.
If you really don't like the idea of creating a few java objects per request
you could use XSLT to post process JSP files to replace tag occurencies with
Java scriptlets - though I'm not sure the extra complexity and restrictions
that this mechanism imposes is worth it at all. Custom tags rock! ;-)
J.
James Strachan
=============
email: [email protected]
web: http://www.metastuff.com
"Sri" <[email protected]> wrote in message
news:[email protected]...
> This post had some interesting aspects about custom tags that contradict
> what I see in the generated java code by the JSP container. I am using
> weblogic 5.1 sp6 and I have a jsp file that uses a custom tag "xyz:for" a
> couple of times. the tags are not nested.
> The java code indicates that two separate instances for the "xyz:for" tag
> were created.
>
> try
>
> calicothunder_presentation_tags_ForTag_0 = new
> calico.thunder.presentation.tags.ForTag();
>
> ..............
>
> } finally
>
> if (_calico_thunder_presentation_tags_ForTag_0 != null)
> calicothunder_presentation_tags_ForTag_0.release();
> }
>
> Further down
>
> try {
> calicothunder_presentation_tags_ForTag_1 = new
> calico.thunder.presentation.tags.ForTag();
> ...............
>
> } finally
>
> if (_calico_thunder_presentation_tags_ForTag_1 != null)
> calicothunder_presentation_tags_ForTag_1.release();
> }
>
> The code is creating two different objects for every request. It is not
> reusing the same object.
> The release is just cleaning up the current instance, which may be garbage
> collected at some later stage.
> So even if a page has 4 tags and 100 users, we have 400 objects just
> because we use tags.
>
> Just trying to understand this better..
> thanks - Sri
>
>
>
> "James Strachan" <[email protected]> wrote in message
> news:[email protected]...
> > Hi Jack
> >
> > I think you're right to be concerned and it is a valid concern.
> >
> > In the scheme of things in my experience the cost of using custom tags
is
> > quite minimal. Tag instances are reused on the same page so if I have
> > several non-nested <foo:bar> tags on a page the single FooBarTag
instance
> > will be reused for each tag occurance.
> >
> > Consider other Java code, say, string concatenation. Consider the
> following
> > expression.
> >
> > String c = a + b;
> >
> > Fairly minimal code you might think. However this line actually involves
> the
> > creation of a StringBuffer instance, the call of 2 methods and the
> creation
> > of a second String object instance (never mind the internal char[]
object
> > instance that is created inside the new Strings constructor).
> >
> > A typical use of a custom tag involves one object construction, N
> > setProperty() method calls (one for each attribute of the tag) and the
> > startTag / endTag method calls.
> >
> > So on balance I'd say the custom tags mechanism is quite small and
> > efficient.
> >
> > Though note that if you use large numbers (say hundreds) of different
> kinds
> > of tags then you'll have a much greater object allocation overhead.
> >
> > --
> > J.
> >
> > James Strachan
> > =============
> > email: [email protected]
> > web: http://www.metastuff.com
> > "Jack Lin" <[email protected]> wrote in message
> > news:[email protected]...
> > > I've been playing around a bit (alright, so maybe not all that much)
> > > with custom tags, and it seems like the actual implementation of
custom
> > > tags (tag handler object(s) per tag) is much more resource-intensive
> > > than would be justified. With Weblogic 5.1 SP6, has anyone had the
> > > opportunity to compare performance of a typical JSP page w/ and w/out
> > > custom tags?
> > >
> > > My first impression of custom tags was that you could define tags
> > > and behaviors that the JSP compiler would then compile into your JSP
> > > class; there would be no performance hit during page execution. The
Java
> > > code used to write these tags would either be included inline in the
JSP
> > > page code, or else act essentially as static (threadsafe) classes into
> > > which threads executing JSP pages would call into. This approach means
> > > less resources consumed and less setup/teardown time in exchange for
> > > fatter JSPC'd code.
> > > Instead (and correct me if I am wrong), it appears that each
> > > distinct custom tag has a pool of instantiated handler objects lying
> > > around in memory, and each time a custom tag is used, there is a
> > > little performance hit in the setup & teardown of each handler
object's
> > > pageContext, etc...
> > > Now admittedly, as another poster (I believe Mr. Purdy) pointed
out,
> > > a "little" ain't all that much... unless there are thousands of those
> > > "little" hits.
> > > Moreover, I don't see much benefit in having instantiated objects
do
> > > the heavy lifting. I'd rather have my auto-compiled JSP classes be a
> > > little more bloated than suffer any performance hit. (I do, however,
> > > like the fact that custom tags allows for cleaner JSP code, not to
> > > mention makes for a cleaner break between the creative and coding
work.)
> > >
> > > For those of you who've had more extensive experience with custom
> > > tags, am I missing the target? Is the performance hit negligible for
> > > heavily-used or complex pages? And/or is the performance hit
outweighed
> > > by code and development cleanliness?
> > >
> > > Thanks for any input.
> > > Jack
> > >
> > >
> >
> >
>
>
-
I have written a custom tag that I am having problems with. It works on some machines, but not on others. I have a page that uses many 'standard' tags. I have correctly set the URI etc, because all of my other tags work. However, on some machines, my custom tag gives me an error:
attribute does not support request time values
I'm assuming that I have the correct versions of standard.jar etc because all of the regular jstl 1.1 tags work. It is just my custom tag that throws an error.
here is the .tld for my tag:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN" "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.1.2</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>My custom tag</short-name>
<uri>http://my.custom/tags</uri>
<tag>
<name>breadcrumb</name>
<tag-class>tag.BreadcrumbTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>breadcrumbs</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
<description>Pass in the list of Breadcrumbs containing the actual information
about what tags need to be rendered on the page.</description>
</attribute>
</tag>
</taglib>
Any thoughts/help greatly appreciated...I encountered the same problem in our environment. I did the same thing as
James. Simply re-initialize all variables in the do end tag.
Also, with the nested tags you use you may also need to implement cloneable
in the inner tag if the outer tag keeps references to all the inner tag
instances.
For instance if the outer tag kept a vector of references to the inner tag,
then you would need to use clone() on the inner tag before adding it to the
vector.
"James Lynn" <[email protected]> wrote in message
news:3af05d29$[email protected]..
> > But
> > with WL 6.0, the cell tag handler reuse the same instance each time the
> cell tag
> > is called and the member field is not reset
>
> I had the same problem. As a work around, I reinitialize everything in my
> doEndTag() method and it works.
>
>
> --
> James Lynn - Lead Software Architect
> Oakscape - Java Powered eBusiness Solutions <http://www.oakscape.com/>
>
>
-
I m looking for some sort of code for designing Custom Tag (Forloop and nested tags). I could not find code that uses new specifications like EVAL_BODY_AGAIN, EVAL_BODY_BUFFERED.
Hi,
How about looking at some of Jakarta's source code? I think their JSTL implementation might be a good place to start. You can browse their CVS at http://cvs.apache.org/viewcvs.cgi/jakarta-taglibs/standard/src/. Hope that helps,
Chris -
Scripting variables and custom tags
Hello,
I wonder how I could use a scripting variable in a custom tag? I have written a tag that formats number and dates, and would like to be able to do somethin like
<% double x = 12,345; %>
<x:write name="x" format="xyz" />
Also I wonder how best to implement tags with parameters? I don't suppose it's possible to nest tags or scriplets in a way like <x:bla name="test" value="<%= 12345 %>" />? It seems tedious having to create an Object just to pass a Parameter.
Many thanks in advance for any help!
BjoernI think I found the solution,
pageContext.setAttribute(...,...)
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