Resending my previous post ... I see that the formatting I wrote
it with
went away and it became impossible to read. Congratulations to
anyone that
got anything out of it at all :-)
Sorry about that,
Frank.
Here is a proposal for moving forward on this issue that I think (am
hoping :-) everyone can live with.
1. Remove the existing logical and physical models (and
corresponding
transformer code) and replace them with a single logical model
created as follows:
a. One-time generate a pure JavaBean model from the XMLSchema
(sca-core.xsd) using a hacked up prototype of the SDO
generator.
This prototype suppresses SDO things (e.g., reflective methods,
for example), so the generated classes are not SDOs - they're
POJOs.
b. Hand modify the generated classes to add additional methods
needed
for the logical model. The end result, will look very
similar, but
not identical, to the current logical model, so a small
amount of
work will be needed to port client code from the current
logical
model to this new combined "logical/physical" model.
2. Modify Jeremy's StAX handlers to work with this new model, and
also
use them as the prototypical example of the output for a new
-generateLoader option for the SDO generator. The plan for the
May
release will be to use the modified hand written StAX
handlers, but
they will be marked as "to be generated", so that it's clear
that in
the future these handlers will be replaced with generated ones.
3. Start immediately on the SDO -generateLoader and -simpleBeans
options.
We will use -generateLoader for the core model, as soon as it's
available (target 2-3 months?), but we will not plan to regen
the core
model using -simpleBeans. The model will remain hand coded
indefinitely, but we can revisit the possibility of generating
parts
of it in the future (but this won't be a priority). The -
simpleBeans
option will be available for use by people adding extensions
to the
model, if they want to start with XSDs.
4. Also start immediately on a -generateSerializer option so that
we will
be able to use simple beans that need to be saved as well as
loaded.
Given that we support generation of POJOs, we need both generated
loaders and serializers to use them. We also need to start
work on
defining the necessary Java annotations to support generating
loaders/serializers from hand-written POJOs (or more generally
to also
generate SDOs from hand written Java interfaces.
I think this approach is a win-win for both the SCA and SDO
projects.
Thoughts?
Thanks,
Frank.
Frank Budinsky/Toronto/[EMAIL PROTECTED] wrote on 03/27/2006 01:26:46 PM:
Jim Marino <[EMAIL PROTECTED]> wrote on 03/24/2006 05:53:46 PM:
Thanks Frank for answering these questions. I have a few more
that
maybe you or others could offer opinions on.
On Mar 24, 2006, at 12:10 PM, Frank Budinsky wrote:
I don't know much about how the sca properties are
configured, but
I'll
try to answer your questions anyway.
- As a user what steps do I need to take to provide custom data
values for config properties? In a previous post, I listed an
example
of a concrete "Foo" class
Option 1)
Provide an XML schema completxType definition for the Type
and let
the
generator gen the impl including the deserialization support. In
the
future, we plan to also let you provide a Java interface (with
annotations, if necessary) to define the type, and then have the
implementation class generated for you.
The SDO generator will essentially generate the same Foo class
that
you
showed in the other thread, just with the addition of a base
class
(DataObjectBase), and some get/set method overrides that
implement
efficient switch-based reflective accessors - used by the
generic
XML
serializer/deserializer. If we also provide an option to
generated
a
loader, in the future, we could also provide an option to
supress
the
generation of the reflective accessors. The resulting class
would
no
longer be an SDO object in this case - but it would be easy
to do
as
a
value-add feature in our generator (i.e., a -generateSimpleBean
option).
Option 2)
Write the Foo implementation class yourself (or maybe
generate it
with
some other technology - like JAXB) and then simply register
it as
a
DataType with SDO. Remember that not all objects in an SDO model
need to
be DataObjects. If you want non-DataObjects, they're modeled as
DataTypes,
and you need to provide create from and convert to String
methods
for
them.
I think option two is the more appealing one for applications
developers. I read option 1 to require a schema, which we may be
able
to do for extensions, but is a bit much to ask application
developers
to produce. So, I'm curious as to how the conversion methods you
mentioned look like. Assume I have the following Java
implementation
and configuration class:
I wouldn't write off option 1 so quickly. For your example, a
schema
(or
equivalent SDO metadata) something like this is all that one
needs:
<element name="myFoo" type="Foo"/>
<complexType name="Foo">
<sequence>
<element name="name" type="xsd:int"/>
<element name="foo" type="Foo"/>
<element name="myJaxBThing" type="jaxb:jaxBThing"/>
</sequence>
</complexType>
This schema could be deduced (under the covers) from the Java
classes
you
show below, so you wouldn't need to actually write it (once we
get the
Java import support working, of course).
public class MyComponent{
@Property
private Foo; myFoo;
}
public class Foo{
public Foo(){}
private String name;
public setName(String val){
name = val;
}
private Foo foo;
public void setFoo(Foo val){
foo = val;
}
private MyJaxBThing jaxBThing;
public void setMyJaxBThing(MyJaxBThing thing){
jaxBthing = thing;
}
}
And I want to use the following configuration:
<component name="myComp>
<implementation.java class="MyComponent/>
<properties>
<v:myFoo>
<v:name>my name</v:name>
<v:foo>
<v:name>my sub name</v:name>
</v:foo>
<jaxb:jaxBThing>
<!-- other configuration according
to
JAX-B--->
<jaxb:jaxBThing>
<v:myFoo>
</properties>
</component>
I'm assuming I would have to register Foo and MyJaxBThing with
SDO?
Could someone walk through the steps I would need to do to
tell the
runtime how to take the particular configuration and
deserialize it?
Assuming, however, that we don't have metadata, but just want to
deserialize by hand. I don't think the SDO approach is any
easier or
more
difficult than the StAX approach. By default the SDO
deserializer will
represent the "untyped" properties section of the model as a
Sequence
(i.e., an unstructured representation of the "xsd:any" contents).
We'll
need some way to plug-in a converter, maybe something like a
FooFactory,
similar to what Jeremy described for the StAX approach. Btw,
SDO has
createFromString methods for all the standard basic types plus a
generic
createFromString method that work like Jeremy described (i.e., try
valueOf, constructors, etc.).
Also, what would the string transformation methods look like
in this
case? I'm also having difficulty pinning down how the JAXB
class is
instantiated (I'm assuming something needs to access a JAXB
factory
at some point).
I don't know enough about JAXB to say. Maybe someone else knows?
Another really common use case (sorry to keep harping on this
one,
but I see it all of the time) is support for List and Map. I
should
be able to specify some type of XML serialized form and have
property
configuration injected on a component as a List or Map. I'm
assuming
based on your comments below this can be done to the SDO
implementation and we could provide this to end-users without
them
having to configure something?
Yes ... the Sequence (DOM-like) view of the properties is there by
default.
One final scenario, related to this, is support for factories for
property instantiation. IoC containers such as Spring have a
way to
pass a factory in to the injection engine to delegate to for
creating
property instances. Could this be done with SDO?
I think we could provide something like this in Tuscany ... a
Tuscany-specific extension SPI.
- What steps do I need to extend the current model? What
dependencies
are there?
I'm not sure about this, it depends on the model. Is there a
base
type in
the XSD for these properties. If so, then I suspect that you
need
to
define the schema for your extension. If you go with option 1,
above, that
comes for free. If you want to do things by hand, then I
think you
could
just treat your extension as unstructured XML (in the open
content
extension points in the model). Maybe someone else
understands the
model
here better than I do?
- Can I use a custom binding technology to produce my model
object?
I think I answered this in the option 2) section, above.
- Is it easy to support isolation between classloaders in
managed
environments? My impression is that this is extremely
problematic
due
to required support of .INSTANCE. If that is the case, what is
the
likelihood that the spec can be changed in a timely manner to
improve
this?
I don't think I understand where this problem will come up.
In the
static
generated class scenarios that we're talking about, there really
shouldn't
be any access to .INSTANCE variables. Maybe someone can give a
concrete
example where this might be a problem, and we can try to figure
out
the
solution from there.
I have two concrete examples here where I have seen problems in
other
projects:
1. Assume there are two nested components whose implementation
types
are loaded by different classloaders. These two nested components
have a property that takes a "Foo". The configuration schema
is the
same but the "Foo" classes are different because they are
loaded by
different classloaders. Do you think we will run into any issues
here?
Not unless the first Foo instance is passed to the second
component
(that's expecting the second Foo). But this doesn't strike me
as an
SDO
issue, it would be a problem even if the Foo class was hand coded,
don't
you think?
2. Another concern is around application reloadability. If I
have a
registered type of "Foo" and the application it was registered by
needs to be reloaded, how is it flushed from SDO? Does the
container
have to call a flush method somewhere?
This depends on how we handle the scoping. If the TypeHelper that
knows
about Foo is in a private application scope then it should go away
with
the application.
I think we need to be clear that any shortcomings in the SDO
spec
should
not be a problem in generated scenarios. Other than saying that
the
generated interfaces for SDO types are bean-like, the SDO spec
dictates
very little about the nature of the generated code. We can fix
whatever we
need to.
I appreciate that and you taking the time to help explain this
stuff
to me. I guess I'm going to be a typical example of someone who
wants
to extend the container and has a bunch of questions :-)
This is a good excersize for me as well. Regardless of the actual
decision
of whether or not to use SDO for this particular purpose in
SCA, it
will
help to clarify the issues and what parts of the SDO impl need
attention.
Thanks, Frank.
We really are just trying to leverage the Tuscany generator
to do
XML binding here ... our config loader does not need to be a
fully
compliant SDO application.
Thanks,
Frank.
Jim Marino <[EMAIL PROTECTED]> wrote on 03/24/2006
01:31:20 PM:
I think there may be some issues uncovered with the
requirements
and
I'm not sure we all understand the advantages/disadvantages of
each
approach. We may be over-analyzing this but the discussion was
getting very heated, there was a lot of disagreement over what
the
actual (dis)advantages were, and I wanted to understand (at
least
for
myself) the broader implications. I thought stepping back a
bit
what
help clarify these things. For example, I am personally unclear
on
how to do the following with SDO:
- As a user what steps do I need to take to provide custom data
values for config properties? In a previous post, I listed an
example
of a concrete "Foo" class
- What steps do I need to extend the current model? What
dependencies
are there?
- Can I use a custom binding technology to produce my model
object?
- Is it easy to support isolation between classloaders in
managed
environments? My impression is that this is extremely
problematic
due
to required support of .INSTANCE. If that is the case, what is
the
likelihood that the spec can be changed in a timely manner to
improve
this?
I thought Jeremy's list was good and would provide a way to
"weight"
answers to these and other questions.
Jim
On Mar 24, 2006, at 6:10 AM, Frank Budinsky wrote:
Jim, looking at your requirements (which I don't disagree
with),
I
think
that both approaches, if not already, can be made to meet
them.
Personally I think that we're over analyzing this. Both
approaches
have
some advantages and disadvantages, but both will work.
Whichever
approach
we take, I suspect that some people will like it and others
won't
.
For
example, people that know how to program with StAX will say
it's
easy to
use ... people who don't will say the opposite. If we can
get to
the point
that we effectively generate the logical model (so the user
has
to
write
no code), I think everyone will agree it's easy to use, since
doing
nothing is easy by definition :-) Of course we need to take a
leap of
faith that the current painful SDO codegen will evolve to that
in
the end.
Having a vested interest to make the SDO binding technology as
good as
possible, I would support, and obviously love to see the
decision
go that
way, That said, I think it's got to be about time to just
make a
decision
and run with it. If this much discussion went into every
design
decision,
we'd still be sharpening our chisels and working on carving
the
wheel :-)
Thanks,
Frank
Jim Marino <[EMAIL PROTECTED]>
03/23/2006 02:53 PM
Please respond to
tuscany-dev
To
[email protected]
cc
Subject
Re: Framework for StAX-based model loading
There has been a lot of discussion on this topic and Jeremy's
point
brings up an issue I think needs to be fleshed out.
Specifically,
what are the requirements and priorities for loading
configuration.
Could we perhaps take the following approach?
1. Agree on the requirements and their priorities without
getting
into a technical discussion. I would suggest we rank
requirements
by
absolute priority, i.e. the most important first, the next
important,
etc. rather than "requirements A and B are p1, requirements X
and
Y p2"
2. Based on the requirements and priorities, compare the StAX
and
SDO
approaches for each
3. Agree on one approach moving forward for configuration
If this acceptable, my opinion on requirements in priority
order
are:
1. The configuration mechanism must be easy for end-users
to use
to
promote widespread adoption of Tuscany
- For example, basic types defined by the spec should
be a
given, but it should also be easy for someone to add a custom
type.
For instance, my Foo component may take a Bar type as
configuration.
Based on past experience with IoC containers, I have found
this
to be
a very common situation.
-I assume this would have to involve describing the type
and
registering some kind of custom handler with the runtime
2. The configuration mechanism must be easy for container
extenders
to promote widespread adoption of Tuscany in the developer
community
- Similar to point 1, although I think the
requirements on
ease-
of-use may be slightly different.
- One additional item here is the configuration mechanism
should
follow Java idioms as closely as possible. Manipulating the
model
should not be foreign to Java developers
- As a side note, I think items 1 and 2 are intimately
related,
but 1 is slightly more important since Tuscany developers will
have a
higher pain threshold than end-users
3. Operation in a variety of deployment environments. For
example,
how does each approach handle different classloader hierarchy
scenarios?
4. Ability to handle serializations other than XML. This
was one
of
the reasons why we went to a separate logical model. It's also
not
just related to testing although that is one use case. For
example,
configuration may be pulled from sources other than XML
such as
a
registry.
5. Maintenance
- There are probably two considerations here. First, what
we
use
should be easily understood and used by Java developers
wanting
to
contribute to Tuscany. A second consideration is as the
spec XML
changes, is it easy for us to evolve the code. Here, I
would say
we
concentrate on the first. The second use case has a lower
priority
I
have put to item 8.
6. Versioning
- We need a mechanism that easily supports versioning. In
the
future, we will need to support multiple configuration format
versions
7. Performance
- We need something that will be performant. On at least
two
separate occasions, I have seen IoC container start-up brought
to
its
knees handling configuration processing. This may not seem
like
a
big deal but when there are 1,000s (or even a couple
hundred) of
components, it rears its head.
8. Ease on "us", the commiters (the second maintenance
consideration)
- This is where I would say how easy is it to accommodate
spec
changes comes in. Either approach can handle changes so the
question
becomes which alternative offers a better solution for
commiters.
Perhaps we could come up with a set of objective criteria to
judge by
and then move to a technical discussion of each approach?
Jim
On Mar 23, 2006, at 11:02 AM, Jeremy Boynes wrote:
I think we need to be careful to distinguish the needs we
have
for
loading our configurations from the needs users have of
SDO in
general. I think the SCA schemas have things in them that are
atypical: lots of extensibility, many namespaces, custom data
types, few attributes/properties and so forth. On the other
hand,
our use case doesn't need things like change tracking or
streaming
that SDO provides.
We need a good SDO implementation, we need a loading
mechanism
that
can handle our configurations; the two don't have to be the
same.
If they are, that is good; if they aren't, that's not bad.
--
Jeremy
Jean-Sebastien Delfino wrote:
Raymond Feng wrote:
Hi, Frank.
I think I fully agree with you. An efficient databinding is
what
we're looking for.
Ideally, if SDO later on supports lazy-loading (create the
DataObject skeleton first and pull in properties as they're
assessed) from XMLStreamReader, I assume we'll take
advantage
of
the benifits advocated by both camps (Databinding vs.
StAX).
Raymond
----- Original Message ----- From: "Frank Budinsky"
<[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Thursday, March 23, 2006 9:37 AM
Subject: Re: Framework for StAX-based model loading
I stand by my statement that the EMF problem is short term
pain
for long
term gain :-) I think that in the long term using the SDO
generator will
be the best and easiest way to do this. Yes I am
biased, but
I've seen it
before - avoiding reuse/dependencies works nicely at
first,
but
as things
grow/change and get more comlicated, the amount of
reworking/
reinventing
becomes quite a nightmare. The opposite problem, which I
think
we're
suffering from here, is that the reusable component
that we
are
trying to
leverage isn't as nice and clean and a perfect fit as we'd
like,
so it
really looks undesirable. Since we have control of all the
pieces, in this
case, I think we have a great opportunity to make it a
clean
fit. And like
I said in my reply to Jeremy, earlier, I really strongly
feel
that the
problems that we're identifying here are not unique to
SCA,
so
fixing them
is really in our best interest.
Frank.
"ant elder" <[EMAIL PROTECTED]> wrote on 03/23/2006
10:13:24 AM:
On 3/23/06, Guillaume Nodet <[EMAIL PROTECTED]> wrote:
<snip/>
As the binding itself uses JAXB2 (though it may
change in
the future), I have to include all eclipse dependencies
and
SDO stuff,
just to load the system configuration files :(
From the discussion I'm starting to be persuaded by
some of
the
arguments
for the SDO approach, but this EMF dependency seems a
draw
back. If
we're
going to support alternate data bindings for the WS
binding
its
not
great to
still be dragging in EMF to run the thing. And I'd
guess it
would be
much
easier to sell SDO to say the Axis2 guys to use
instead of
XmlBeans if
there
was a pure Java SDO impl. Any Axis2 guys listening who'd
comment on
this?
As another comparison look at Axis2, they have their own
very
simple
Axis
Data Binding (ADB) which supports simple XSDs, and
they use
XmlBeans for
all
the complicated stuff. They don't use XmlBeans all the
time
because lots
of
things don't need the complexity a full blown data
binding
brings. And
as
Guillaume points out, the SCA binding schema are usually
pretty
simple.
...ant
Raymond,
That's a very good point, I agree.
I think that this whole discussion thread is very useful
as it
helps us identify requirements and areas of improvement for
our
SDO databinding and codegen story. For example, Guillaume
mentioned that it would be great to have a Maven 1 SDO
codegen
plugin, as ServiceMix is still built with Maven 1 at the
moment
(and I guess a number of other projects out there still use
Maven
1 as well). I can spend some time in the next few days and
work
with anybody who would like to volunteer and try to wrap the
code
generator in a Maven 1 plugin, if it helps. Guillaume,
are you
using Ant at all? or just Maven 1?
