Hello Gary,
I have no strict definition of what I call an interpolation engine, but
I view it as somewhat that is customizable by clients. What is already
implemented in [digester] would to a major part satisfy the needs of
[configuration]. In addition to the basic interpolation functionality we
would like to have
- the VariableResolver concept allowing a user to define a custom set of
sources for variable values,
- support for multiple VariableResolvers at the same time (e.g. by using
certain prefixes for the variables to associate them with a resolver),
- a default VariableResolver, which will be called for all variables
that are not associated with a specific resolver; the configuration
object itself will act as this default resolver maintaining backwards
compatibility with the current interpolation implementation (ATM the
values of configuration properties can be variables, which will be
replaced by the values of the properties in the same configuration
object they refer to).
The code in the bugzilla ticket is different from [digester] in the
following points:
- The VariableResolver interface returns an Object as a variable's
value. [digester]'s pendant has a String. Because [configuration]
supports different data types by default I thought plain Objects would
be more appropriate and would avoid unnecessary type conversions.
- For the same reason the main interpolation method returns an Object
rather than a String, too.
- The prefixes that associate a variable with a VariableResolver are a
bit different (but this is a matter of taste).
- The main interpolation method is extracted from AbstractConfiguration.
It is able to detect cyclic variable replacements and throws an
exception with a nice stack trace in these cases. I don't know how this
is implemented in [digester].
Oliver
Gary Gregory wrote:
Hello:
I think that a good motivation for interpolation in [lang] would be to
have [configuration] as a call site ([configuration] already depends on
[lang]). With that in mind, I would like to see interpolation classes
suitable for [configuration] but not any more complicated for a first
cut.
"I am reluctant to implementing a complete interpolation engine in this
project and expose it in the public API."
I would like us to take an XP approach first by implementing just what
[configuration] needs for example, not a complete engine.
You mention [digester]; does it have what you would call a "complete
interpolation engine"? Do you have a definition of what such a best
features? What are the differences b/w the code in the ticket and a
complete engine or the one in [digester]?
Thanks,
Gary
-----Original Message-----
From: Oliver Heger [mailto:[EMAIL PROTECTED]
Sent: Monday, June 27, 2005 1:08 AM
To: Jakarta Commons Developers List
Subject: Re: [lang] text.Interpolation, on to 2.2
Gary,
that's right, the basic idea is to configure several VariableResolvers
for different purposes. This is pretty much the same as the
interpolation engine of [digester] works. Resolvers for system
properties and map based resolvers are very obvious and simple
implementations. But a VariableResolver could be arbitrary complex, e.g.
a JEXLResolver for expressions (maybe not directly suited for [lang]).
Interolation is an important feature of [configuration], but I am
reluctant to implementing a complete interpolation engine in this
project and expose it in the public API. So I would love to see
something like that in [lang].
Oliver
Gary Gregory wrote:
Hello Oliver:
I took a quick look at the ticket you linked to below. For this to work
for System properties, a simple VariableResolver would do the trick I
think. Maybe a generic MapVariableResolver could also be provided and
maybe a factory methods in order to say simple things like:
Interpolator.newInterpolator(System.getProperties()).resolve("The file
is here ${java.io.tmpdir}");
Would [configuration] be interested in have this in the next version of
[lang]? Assuming that whatever loose requirements created by the
current
lang tests are satisfied.
Gary
-----Original Message-----
From: Oliver Heger [mailto:[EMAIL PROTECTED]
Sent: Saturday, June 25, 2005 7:46 AM
To: Jakarta Commons Developers List
Subject: Re: [lang] text.Interpolation, on to 2.2
I am interested in this topic, too, because I want to implement
enhanced
interpolation suport for [configuration].
I already had a look at the available Interpolation class, but it lacks
some features I need. So I wrote something myself which is similar to
the interpolation engine of digester, but is based on the interpolation
method that existed in configuration. The code and a unit test can be
found at the following bugzilla ticket:
http://issues.apache.org/bugzilla/show_bug.cgi?id=35116
Oliver
<snip>
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