Re: simple jelly explanation
This is true, but only if outputDir is a java.lang.String (or an empty
Map, Collection, or Array). Properties in maven are
org.apache.commons.jelly.expression.ConstantExpression, so they are only
empty() if they are undefined.
A jexl workaround to this would be
${empty(myEmptyProperty.toString())}. A possible long-term solution
would be to return true in jexl's ASTEmptyFunction.java if
Object.toString() is an empty string, rather than using an instanceof
test. Unfortunately, this does break with the spec. Alternatively,
ConstantExpression could extend String, although that might be taking it
a bit far :-)
Matt
James Strachan wrote:
On 6 Nov 2003, at 00:43, matt wrote:
You could also use ${empty(outputDir)}, or ${outputDir == null},
which are both identical in meaning to ${empty outputDir}.
Not quite, empty(outputDir) is also true if outputDir ==
Jelly uses the Jexl Expression Language, which is a superset of JSTL
(Java Standard Tag Library). To quote from JSTL in Action,
The empty operator determines whether a collection or string is
empty or null. For instance, ${empty param.firstname} will be true
only if a request parameter named firstname is not present. JSTL
expressions can also compare items directly against the keyword null,
as in ${param.firstname == null}, but this is an advanced use.
Although Jelly is not always in a web context (ie, doesn't have the
param implicit object), the same rules apply. In addition, to quote
from the jexl home page (http://jakarta.apache.org/commons/jexl.html):
Jexl has extended the JSTL in a few ways :
- Support for invocation of any accessible method (see example
above).
- Added a general size() method, which works on String, returning
length, Map, returning # of keys, and List and arrays, returning the
number of elements.
- Optional syntax for the 'empty' function : empty(obj)
- Misc : '+' has been overloaded to be use as a String
concatenation operator
The invocation of any accessible method means that you can call
${object.getProperty()}, and it will be the same as
${object.property}, or ${object.setProperty(someOtherObject)}. You
can also call methods that do not correspond to properties, such as
${someString.endsWith(otherString)}.
Strongly recommend reading up on Jexl and JSTL.
Good answer Matt :)
James
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simple jelly explanation
Hi Guys,
I have this line in one of the jelly script in a maven plugin. I don't know
jelly but have checked out its major tags. Could you pls help me understand
this:
j:if test=${empty outputDir}
I undertand j:if test
But in ${empty outputDir} does empty refers to some inbuilt function of
checking the outputDir or what ?
Or is it supposed to be some function written somewhere in the jelly script
that I'm using.
Please guide
Thanks
Vikas
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RE: simple jelly explanation
Yes. This will evaluate true is the jelly value outputDir is empty. I
think that means null or , but am not certain.
You might also see it written as ${empty(outputDir)}
- Brett
-Original Message-
From: Vikas Phonsa [mailto:[EMAIL PROTECTED]
Sent: Thursday, 6 November 2003 11:14 AM
To: 'Maven Users List'
Subject: simple jelly explanation
Hi Guys,
I have this line in one of the jelly script in a maven
plugin. I don't know jelly but have checked out its major
tags. Could you pls help me understand
this:
j:if test=${empty outputDir}
I undertand j:if test
But in ${empty outputDir} does empty refers to some inbuilt
function of checking the outputDir or what ?
Or is it supposed to be some function written somewhere in
the jelly script that I'm using.
Please guide
Thanks
Vikas
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
Re: simple jelly explanation
You could also use ${empty(outputDir)}, or ${outputDir == null}, which
are both identical in meaning to ${empty outputDir}.
Jelly uses the Jexl Expression Language, which is a superset of JSTL
(Java Standard Tag Library). To quote from JSTL in Action,
The empty operator determines whether a collection or string is empty
or null. For instance, ${empty param.firstname} will be true only if a
request parameter named firstname is not present. JSTL expressions can
also compare items directly against the keyword null, as in
${param.firstname == null}, but this is an advanced use.
Although Jelly is not always in a web context (ie, doesn't have the
param implicit object), the same rules apply. In addition, to quote
from the jexl home page (http://jakarta.apache.org/commons/jexl.html):
Jexl has extended the JSTL in a few ways :
- Support for invocation of any accessible method (see example above).
- Added a general size() method, which works on String, returning
length, Map, returning # of keys, and List and arrays, returning the
number of elements.
- Optional syntax for the 'empty' function : empty(obj)
- Misc : '+' has been overloaded to be use as a String concatenation
operator
The invocation of any accessible method means that you can call
${object.getProperty()}, and it will be the same as ${object.property},
or ${object.setProperty(someOtherObject)}. You can also call methods
that do not correspond to properties, such as
${someString.endsWith(otherString)}.
Strongly recommend reading up on Jexl and JSTL.
Matt
Vikas Phonsa wrote:
Hi Guys,
I have this line in one of the jelly script in a maven plugin. I don't know
jelly but have checked out its major tags. Could you pls help me understand
this:
j:if test=${empty outputDir}
I undertand j:if test
But in ${empty outputDir} does empty refers to some inbuilt function of
checking the outputDir or what ?
Or is it supposed to be some function written somewhere in the jelly script
that I'm using.
Please guide
Thanks
Vikas
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
-
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
Re: simple jelly explanation
On 6 Nov 2003, at 00:43, matt wrote:
You could also use ${empty(outputDir)}, or ${outputDir == null}, which
are both identical in meaning to ${empty outputDir}.
Not quite, empty(outputDir) is also true if outputDir ==
Jelly uses the Jexl Expression Language, which is a superset of JSTL
(Java Standard Tag Library). To quote from JSTL in Action,
The empty operator determines whether a collection or string is empty
or null. For instance, ${empty param.firstname} will be true only if
a request parameter named firstname is not present. JSTL expressions
can also compare items directly against the keyword null, as in
${param.firstname == null}, but this is an advanced use.
Although Jelly is not always in a web context (ie, doesn't have the
param implicit object), the same rules apply. In addition, to quote
from the jexl home page (http://jakarta.apache.org/commons/jexl.html):
Jexl has extended the JSTL in a few ways :
- Support for invocation of any accessible method (see example
above).
- Added a general size() method, which works on String, returning
length, Map, returning # of keys, and List and arrays, returning the
number of elements.
- Optional syntax for the 'empty' function : empty(obj)
- Misc : '+' has been overloaded to be use as a String
concatenation operator
The invocation of any accessible method means that you can call
${object.getProperty()}, and it will be the same as
${object.property}, or ${object.setProperty(someOtherObject)}. You
can also call methods that do not correspond to properties, such as
${someString.endsWith(otherString)}.
Strongly recommend reading up on Jexl and JSTL.
Good answer Matt :)
James
---
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