RE: [Springframework-developer] XML bean references

[Trevor C. <pr...@se...>]

+1

Trevor

-----Original Message-----
From: spr...@li...
[mailto:spr...@li...]On Behalf
Of j=C3=BCrgen h=C3=B6ller [werk3AT]
Sent: October 18, 2003 5:42 PM
To: spr...@li...
Subject: [Springframework-developer] XML bean references


Everybody,
=20
On the occasion of allowing a single application context to be loaded =
from multiple XML files, I've reconsidered a detail of our XML syntax: =
The "ref" tag currently has two different attributes:
- "bean" to reference a bean in the same application context via its id =
attribute (the XML id);
- "external" to reference a bean in a parent context.
The latter can basically address any bean, be it in the same context or =
a parent, an id or an alias name.
=20
The main rationale behind the "bean"/"external" separation was simply =
separating between XML validation of id refs (by the XML parser) and =
referencing any kind of name (validated by the bean factory). The latter =
was mainly necessary for referencing beans outside of the current XML =
file, at that time a parent context. In the mean time, a single context =
can be defined by multiple XML files; thus I don't consider the =
"bean"/"external" naming appropriate anymore.
=20
Instead, let me suggest different attribute names:
- keep a "bean" attribute to reference *any* kind of name, be it id or =
alias, just like the current "external" attribute;
- introduce a new "bean-id" attribute to reference a bean in the same =
XML file via its XML id, like the current "bean" attribute.
=20
If we keep the "external" attribute for the moment as an equivalent of =
the proposed "bean" attribute, this would be fully compatible with =
existing bean definition files. Of course, "bean" attributes would not =
get validated by the XML parser anymore, but that would not break the =
files in any way. "external" attributes would still work too, the same =
as before.
=20
We should recommend migrating to the new pattern though, i.e.:
- rename "bean" to "bean-id";
- rename "external" to "bean".
That should be easy to do; and as the old pattern still works, there is =
no need to migrate existing bean definition files immediately.
=20
I've thought about this for a while, and I consider it very important to =
clarify the attributes in a way like the above. Else, it will be pretty =
hard to explain the rationale behind "bean" and "external", especially =
when using multiple XML files for a single context. "bean" and "bean-id" =
are far easier to explain: "bean" always works, "bean-id" adds =
validation by the XML parser if specifying a bean id in the same =
context.
=20
Any thoughts on this, any strong objections? I would actually like to =
get this into M2, although it's pretty close already. As the change is =
trivial to implement and fully backward compatible, that shouldn't =
matter too much.
=20
Juergen
=20
P.S.:
The same issue exists with the rarely used "parent" attribute of the =
"bean" tag. Currently, "parent" can reference any kind of name; we could =
introduce the above pattern a la "parent" and "parent-id" for the sake =
of consistency.
=20
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