Re: JSTL and Java Constants
On 8/31/05, Martin Cooper [EMAIL PROTECTED] wrote: On 8/30/05, Rahul Akolkar [EMAIL PROTECTED] wrote: snip/ 2) Another approach that some choose is to provide a Constants bean that supplies getters for the constants, which is what we ended up doing for the RDC taglib. Isn't that effectively the same thing, once all is said and done? Wouldn't accessing a Constants bean be identical to accessing the constants from a map provided by this tag? snip/ Was enumerating all the options, the tag is a convenient option, no doubt. -Rahul -- Martin Cooper - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: JSTL and Java Constants
On 8/31/05, Luca Passani [EMAIL PROTECTED] wrote:
Martin Cooper wrote:
Done. I think. At least, everything seems to have worked out, so it
should
be available in the next nightly build of Unstandard.
will I need to wait tomorrow to download? great. I am eager to try it.
Urk. I just checked, and it looks like Unstandard is not included in the
nighly builds. Glenn, if you're reading this, could you add it please?
In the meantime, I've put my local build up here:
http://people.apache.org/~martinc/taglibs/unstandard/
One little doubt:
|un:useConstants var=const className=java.lang.Integer /
The constants are defined in an interface (not a class).
||
public interface ContentType {
public static final int FOLDER = 1;||
public static final int URL = 2;
:
}
||Will the tag work the same?
Yes, it will work the same.
--
Martin Cooper
Thanks
Luca
||
|
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Re: JSTL and Java Constants
Martin Cooper wrote: Yes, it will work the same. It works like a charm. You rock. Thanks Luca - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: JSTL and Java Constants
I would like to do something like:
a) c:when test=${item.type == ContentType.URL}
This won't work. I could hack it around with a scriptlet and an import
at the top of my JSP, but that seems to me like
violating the separation between View and Control
You may want to see this -
http://forums.java.sun.com/thread.jspa?threadID=508847messageID=2543490
One big tradeoff with that approach is that you have to specify your
constants in one Constant class where they may not naturally belong. Another
one would be that you would have to import all external constants into that
class, thereby creating double maintenance work. And a third would be that
you'd need to import the constant class at the top of each page.
My workaround for the fact that you directly can't reach a static variable
in a java class is to make invoke a static method through the EL which in
turns does some reflective parsing to find the constant. It would look like
this:
c:when test=${item.type == fn:const('URL')}
You could create several different extractor methods to have different level
of generality in the method so that you can reach constants in a predefined
class, in a package, or with the full class name:
c:when test=${item.type == fn:const('ActionHandler.URL')} or
c:when test=${item.type == fn:const('java.lang.Integer.MAX_VALUE')}
With this approach you are guaranteed to not have any hard coded magic
values in your jsp. I do not have the code that does the extraction here at
my work, but if you are interested, I can send it over or post it here.
Regards,
Erik Beijnoff
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Re: JSTL and Java Constants
Erik,
Please posting the code , I am also interested.
Thanks
John
Erik Beijnoff [EMAIL PROTECTED]
Erik Beijnoff [EMAIL PROTECTED]
08/31/2005 02:59 PM
Please respond to Tag Libraries Users List
To: taglibs-user@jakarta.apache.org
cc:
Subject: Re: JSTL and Java Constants
I would like to do something like:
a) c:when test=${item.type == ContentType.URL}
This won't work. I could hack it around with a scriptlet and an import
at the top of my JSP, but that seems to me like
violating the separation between View and Control
You may want to see this -
http://forums.java.sun.com/thread.jspa?threadID=508847messageID=2543490
One big tradeoff with that approach is that you have to specify your
constants in one Constant class where they may not naturally belong. Another
one would be that you would have to import all external constants into that
class, thereby creating double maintenance work. And a third would be that
you'd need to import the constant class at the top of each page.
My workaround for the fact that you directly can't reach a static variable
in a java class is to make invoke a static method through the EL which in
turns does some reflective parsing to find the constant. It would look like
this:
c:when test=${item.type == fn:const('URL')}
You could create several different extractor methods to have different level
of generality in the method so that you can reach constants in a predefined
class, in a package, or with the full class name:
c:when test=${item.type == fn:const('ActionHandler.URL')} or
c:when test=${item.type == fn:const('java.lang.Integer.MAX_VALUE')}
With this approach you are guaranteed to not have any hard coded magic
values in your jsp. I do not have the code that does the extraction here at
my work, but if you are interested, I can send it over or post it here.
Regards,
Erik Beijnoff
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RE: JSTL and Java Constants
Please posting the code , I am also interested.
Thanks
John
The big tradeoff is of course the extra fn:xxx('...') that needs to be
written in the code. But a big plus is that once direct retrieval of
constants from java classes is integrated into the EL, a conversion is
simple a matter of search and replace.
I've extracted the relevant classes into a package attached to this message,
although I'm not sure if this list accepts attachments. The classes have
been extracted from a larger context and converted from Java 5 and may
therefore be erraneous, although they have been tested.
Second, the implementation could have been simpler, but it was built with a
field cache to make sure repeated retrieval of fields is efficient, so I
included that cache too.
If you have any questions about the code, please feel free to ask.
Regards Erik Beijnoff
Anyway, first out is the EL static function mapping file and it's associated
.tld:
---
import java.math.BigInteger;
import fieldreflector.FieldReflector;
import fieldreflector.ReflectionException;
/**
* These classes are static helper functions used by JSP pages. These are
for
* example helper methods to find fields in classes.
*/
public class ELFunctions{
//Cached reference to the math package prefix
private static final String mathPackagePrefix;
private static final String bigIntClassPrefix;
static{
mathPackagePrefix= BigInteger.class.getPackage().getName() +
.;
bigIntClassPrefix= BigInteger.class.getName() + .;
}
/* Private constructor */
private ELFunctions(){
//Do nothing
}
/**
* Retrieves a public static field from a class, and returns the
field value.
*
* @param fullName the full class name followed by the variable name
with
*dot notation: java.lang.Integer.MAX_VALUE
*/
public static Object getConstant(final String fullName) throws
ReflectionException{
return FieldReflector.getFieldValue(fullName);
}
/**
* Retrieves a public field from a class in the java.math package,
* and returns the field value br/br/
*
* @param name the action class name followed by the variable name
with
*dot notation: BigInteger.ONE
* @return the extracted variable value
*/
public static Object getMathConstant(final String name) throws
ReflectionException{
return getConstant(mathPackagePrefix + name);
}
/**
* Retrieves a public field from a class in the java.math.BigInteger
class,
* and returns the field value. br/br/
*
* @param name the action class name followed by the variable name
with
*dot notation: ONE
* @return the extracted variable value
*/
public static Object getBigIntConstant(final String name) throws
ReflectionException{
return getConstant(bigIntClassPrefix + name);
}
}
?xml version=1.0 encoding=ISO-8859-1?
taglib
version=2.0
xmlns=http://java.sun.com/xml/ns/j2ee;
xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance
tlib-version2.0/tlib-version
short-namecommons/short-name
urihttp://com.commons.tag/uri
function
nameconst/name
function-classELFunctions/function-class
function-signature
java.lang.String
getConstant(
java.lang.String)
/function-signature
/function
function
namemathConst/name
function-classELFunctions/function-class
function-signature
java.lang.String
getMathConstant(
java.lang.String)
/function-signature
/function
function
namebigIntConst/name
function-classELFunctions/function-class
function-signature
java.lang.String
getBigIntConstant
java.lang.String)
/function-signature
/function
/taglib
---
A few example ways to extract the constants are included, with the java.math
package as example. Every invokation of a field is stored in a field cache,
since reflection may be a bit slow. This cache is listed in the three
following files. But as mentioned, they are really not needed if you want to
make the implementation simpler. Then the reflection code can be
incorporated
Re: JSTL and Java Constants
You may want to see this -
http://forums.java.sun.com/thread.jspa?threadID=508847messageID=2543490
Cheers,
Sudhaker Raj
http://thej2ee.com
On 8/30/05, Luca Passani [EMAIL PROTECTED] wrote:
Hi there, here is my big problem today. I am using JSTL in some JSPs.
SInce this is a struts project, I would
like to keep my views totally separated from the Java APIs. For this
reason, I need your advice about the
most elegant to compare a given object type (an int constant) with the
possible values using the COSTANT name,
instead of the corresponding int.
The API defines the types of my object as:
public interface ContentType {
public static final int FOLDER = 1;
public static final int URL = 2;
}
in my JSP I have (loop over collection of items with getType() returning
the type int)
c:forEach var=item items=${content_list}
c:choose
c:when test=${item.type == 2}
a href=${item.value}c:out value=${item.name http://item.name
}//a
/c:when
:
I would like to do something like:
a) c:when test=${item.type == ContentType.URL}
This won't work. I could hack it around with a scriptlet and an import
at the top of my JSP, but that seems to me like
violating the separation between View and Control
b) I could do something like this in my action:
String type_url = 5;
request.setAttribute(url, type_url);
and then c:when test=${item.type == url}
but makes me wonder if having this code in the action really makes sense.
Any ideas?
Thanks
Luca
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--
Cheers,
Sudhaker Raj
http://thej2ee.com
Re: JSTL and Java Constants
And If you can't extend from that class then you can write adapter for that
class. Something like this
Using in a JSP page:
[code]
%@ taglib prefix=c uri=http://java.sun.com/jstl/core; %
jsp:useBean id=Constants class=com.utils.JSTLMyConstants/
c:out value=${Constants.name http://Constants.name}/br
c:out value=${Constants.age}/
c:forEach var=day items=${Constants.daysOfTheWeek}
c:out value=${day}/
/c:forEach
[/code]
Where adapter class is
[code]
package com.utils;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.HashMap;
import java.util.Map;
/**
* Class to reveal java constants to JSTL Expression Language
* Uses reflection to scan the declared fields of a Constants class
* Adds these fields to the Map.
* Map is unmodifiable after initialization.
*/
public class JSTLMyConstants extends HashMap {
private boolean initialised = false;
private static final Class adaptee = MyConstant.class;
public JSTLMyConstants() {
Class c = adaptee;
Field[] fields = c.getDeclaredFields();
for (int i = 0; i fields.length; i++) {
Field field = fields[i];
int modifier = field.getModifiers();
if (Modifier.isFinal(modifier) !Modifier.isPrivate(modifier))
try {
this.put(field.getName(), field.get(this));
}
catch (IllegalAccessException e) {}
}
initialised = true;
}
public void clear() {
if (!initialised)
super.clear();
else
throw new UnsupportedOperationException(Cannot modify this map);
}
public Object put(Object key, Object value) {
if (!initialised)
return super.put(key, value);
else
throw new UnsupportedOperationException(Cannot modify this map);
}
public void putAll(Map m) {
if (!initialised)
super.putAll(m);
else
throw new UnsupportedOperationException(Cannot modify this map);
}
public Object remove(Object key) {
if (!initialised)
return super.remove(key);
else
throw new UnsupportedOperationException(Cannot modify this map);
}
}
[/code]
// Main constant class
[code]
package com.utils;
public interface MyConstant {
public static final int age = 30;
public static final String name = Sudhaker Raj;
public static final String programmingSkill = Awesome;
public static final String[] daysOfTheWeek = { Sun, Mon, Tue, Wed,
Thu, Fri, Sat, Sun };
}
[/code]
Hope this helps.
On 8/30/05, Luca Passani [EMAIL PROTECTED] wrote:
Sudhaker Raj wrote:
You may want to see this -
http://forums.java.sun.com/thread.jspa?threadID=508847messageID=2543490
very smart. A bit overkill for my problem, but very smart...
Thanks
Luca
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Cheers,
Sudhaker Raj
http://thej2ee.com
Re: JSTL and Java Constants
Take a look at the 'bind' tag in the Jakarta Taglibs Unstandard tag library.
See:
http://jakarta.apache.org/taglibs/sandbox/doc/unstandard-doc/index.html#bind
I have a useConstants tag that I've been meaning to donate that exposes all
of the constants in a class, but I haven't got around to that yet.
--
Martin Cooper
On 8/30/05, Luca Passani [EMAIL PROTECTED] wrote:
Hi there, here is my big problem today. I am using JSTL in some JSPs.
SInce this is a struts project, I would
like to keep my views totally separated from the Java APIs. For this
reason, I need your advice about the
most elegant to compare a given object type (an int constant) with the
possible values using the COSTANT name,
instead of the corresponding int.
The API defines the types of my object as:
public interface ContentType {
public static final int FOLDER = 1;
public static final int URL = 2;
}
in my JSP I have (loop over collection of items with getType() returning
the type int)
c:forEach var=item items=${content_list}
c:choose
c:when test=${item.type == 2}
a href=${item.value}c:out value=${item.name http://item.name
}//a
/c:when
:
I would like to do something like:
a) c:when test=${item.type == ContentType.URL}
This won't work. I could hack it around with a scriptlet and an import
at the top of my JSP, but that seems to me like
violating the separation between View and Control
b) I could do something like this in my action:
String type_url = 5;
request.setAttribute(url, type_url);
and then c:when test=${item.type == url}
but makes me wonder if having this code in the action really makes sense.
Any ideas?
Thanks
Luca
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
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Re: JSTL and Java Constants
Martin Cooper wrote: Take a look at the 'bind' tag in the Jakarta Taglibs Unstandard tag library. See: http://jakarta.apache.org/taglibs/sandbox/doc/unstandard-doc/index.html#bind interesting. Do you have an example of how that should be used? Thanks Luca - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: JSTL and Java Constants
On 8/30/05, Luca Passani [EMAIL PROTECTED] wrote:
Martin Cooper wrote:
Take a look at the 'bind' tag in the Jakarta Taglibs Unstandard tag
library.
See:
http://jakarta.apache.org/taglibs/sandbox/doc/unstandard-doc/index.html#bind
interesting. Do you have an example of how that should be used?
I believe it's something like:
un:bind var=TheConstant type=com.yourco.ContentType field=URL /
and then you can use 'TheConstant' when you want the value.
My useConstants tag works like this:
un:useConstants var=TheConstants className=com.yourco.ContentType /
and then 'TheConstants' contains a map of all constants in the class, so you
can use, for example:
${TheConstants.URL}
--
Martin Cooper
Thanks
Luca
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Re: JSTL and Java Constants
Martin Cooper wrote:
and then 'TheConstants' contains a map of all constants in the class, so you
can use, for example:
${TheConstants.URL}
bang on. That would be cool. I have worked my problem around in my
application, but your solution would be better, since it would decouple
my action from the underlying API. Should I hold my breath?
Thanks
Luca
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Re: JSTL and Java Constants
On 8/30/05, Luca Passani [EMAIL PROTECTED] wrote:
Martin Cooper wrote:
and then 'TheConstants' contains a map of all constants in the class, so
you
can use, for example:
${TheConstants.URL}
bang on. That would be cool. I have worked my problem around in my
application, but your solution would be better, since it would decouple
my action from the underlying API. Should I hold my breath?
Well, I might have a go at adding it tonight, if I have time. It's been a
*long* time since I've tried to build Taglibs, though, so if I have trouble
with that, it might not happen, since I don't want to break the nightly
builds.
--
Martin Cooper
Thanks
Luca
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Re: JSTL and Java Constants
On 8/30/05, Martin Cooper [EMAIL PROTECTED] wrote:
On 8/30/05, Luca Passani [EMAIL PROTECTED] wrote:
Martin Cooper wrote:
and then 'TheConstants' contains a map of all constants in the class,
so you
can use, for example:
${TheConstants.URL}
bang on. That would be cool. I have worked my problem around in my
application, but your solution would be better, since it would decouple
my action from the underlying API. Should I hold my breath?
Well, I might have a go at adding it tonight, if I have time. It's been a
*long* time since I've tried to build Taglibs, though, so if I have trouble
with that, it might not happen, since I don't want to break the nightly
builds.
Done. I think. At least, everything seems to have worked out, so it should
be available in the next nightly build of Unstandard.
--
Martin Cooper
--
Martin Cooper
Thanks
Luca
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