THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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To
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access
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the
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ValueStack
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from
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third-party
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JSP
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taglibs,
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expose
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property
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values
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to
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JSP
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using
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the
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<saf:set
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tag.
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} <saf:set name="'a'" value="{ 1, 2, 3, 4 }" scope="request"/> {code} |
After
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setting
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parameters,
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third-party
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JSP
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taglibs
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can
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access
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variables
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or
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use
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JSP
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2.0
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EL
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(Expression
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Language).
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This
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is
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convenient
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as
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short
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hand
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EL
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expression
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syntax
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$
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{expression}
can be used in a text or inside of tag attributes:
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}} {{}} can be used in a text or inside of tag attributes: {code:xml} a[0] = ${a[0]} <sample:tag value="${a[1]}"/> {code} |
In
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practice,
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several variables must be exposed to make effective use of third party taglibs like DisplayTag. Unfortunately, this approach leads to a lot of <ww:set/>
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tags.
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| what made me investigate how to make access to ValueStack and OGNL more transparent.
{note:title=Why
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Unfortunately, it isn't that simple. I'vewe tinkered with {{
to wrap around {{
and create {{
that would use OGNL. This strategy works in practice, but code generated by Jasper2 doesn't call {{
but goes directly to static method that is hardwired to Jakarta Commons-EL implementation. Even if it would work itif this approach did work, it wouldn't be _clean _as {{
should only be called by JSP implementation. {note} |
There
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is
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a
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simple,
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if
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not
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elegant,
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solution
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available
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in
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JSP
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2.0
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EL,
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for
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exposing
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ValueStack
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to
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OGNL.
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It
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is
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possible
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to
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create
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custom
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functions
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that
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can
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be
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called
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from
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EL
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expressions.
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Functions
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have
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to
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be
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'public
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static'
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and
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specified
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in
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a
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TLD
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file.
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To
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use
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a
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function,
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import
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the
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TLD
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in
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a
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JSP
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file
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where
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you've
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want
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to
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use
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a
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function.
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For
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example,
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you
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could
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access
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Action
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properties
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by
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evaluating
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OGNL
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expression
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by
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a
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function
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'vs'
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(for
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valuestack)
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in
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EL.
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{code:xml} <%@ taglib uri="/WEB-INF/tld/wwel.tld" prefix="x" %> a[0] = ${x:vs('a[0]')} a[0] * 4 = ${x:vs('a[0] * 4')} Current action name: ${x:name()} Top of ValueStack: ${x:top()} {code} |
To
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use
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this
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code
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you've
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got
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to
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add
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wwel.tld
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and
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Functions.java
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to
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your
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webapp
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project.
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If someone were interested, it would be helpful for a developer (like you!) to define a set of functions that we could include in a future release of the framework. |
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I would urge webworkers to define a set of functions that would be usable to wide community and include this in some future Webwork release. {code:xml|title=wwel.tld} <?xml version="1.0"?> <taglib xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd" version="2.0"> <description> This taglib enables access to the ValueStack from JSP 2.0 Expression Language </description> <tlib-version>1.0</tlib-version> <short-name>wwel</short-name> <function> <name>vs</name> <function-class>com.nmote.wwel.Functions</function-class> <function-signature> java.lang.Object findOnValueStack(java.lang.String) </function-signature> </function> <function> <name>name</name> <function-class>com.nmote.wwel.Functions</function-class> <function-signature> java.lang.Object getActionName() </function-signature> </function> <function> <name>top</name> <function-class>com.nmote.wwel.Functions</function-class> <function-signature> java.lang.Object getTopOfValueStack() </function-signature> </function> </taglib> {code} {code:java|title= |
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} package com.nmote.wwel; import com.opensymphony.xwork.ActionContext; /** * Utility functions for accessing value stack and action context * from JSP 2.0 EL taglibs. */ public class Functions { public static Object findOnValueStack(String expr) { ActionContext a = ActionContext.getContext(); Object value = a.getValueStack().findValue(expr); return value; } public static Object getTopOfValueStack() { ActionContext a = ActionContext.getContext(); Object value = a.getValueStack().peek(); return value; } public static Object getActionName() { ActionContext a = ActionContext.getContext(); Object value = a.getName(); return value; } } {code} |