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Posted to dev@avalon.apache.org by Peter Donald <pe...@apache.org> on 2001/12/01 05:07:28 UTC
[phoenix] ClassLoader section in environment.xml
Hi,
Heres some thoughts about a possible way to define ClassLoader structure in
the environment.xml file. Tell us what you think
<classloaders default="*application*">
<classloader name="foo" parent="*api*">
<entry location="sar:/some/dir/classes"/>
<entry location="sar:/some/dir/mypackage.jar"/>
<entry url="http://www.realityforge.org/some.jar"/>
</classloader>
<classloader name="bar" parent="*system*">
<extension>
<name>javax.servlet</name>
<specification-version>2.3</specification-version>
<vendor-id>org.apache.jakarta</vendor-id>
<vendor-version>1.2.3.4</vendor-version>
</extension>
</classloader>
<join name="baz">
<classloader name="foo">
<classloader name="bar">
</join>
<classloader name="common" parent="bar">
<entry location="sar:/some/more/classes"/>
</classloader>
</classloaders>
So in this case we have explicitly defined 4 classloaders; foo, bar, baz and
common. The names of these classloaders are completely arbitrary. You will
notice that I also refer to other predefined classloaders. These special
classloaders can not be overiden and are defined by system. They are
o *system* (The System classloader)
o *api* (The classloader for phoenix API - will just contain framework.jar
and phoenix-client.jar in future but now contains a wealth of other jars)
o *common* (The classloader that is shared between apps and container - empty
now but will contain things like excalibur classes)
o *application* (Contains contents of SAR-INF/lib/*.jar + SAR-INF/classes. I
am not sure if this is strictly needed though ...)
The <join/> classloader assumes that each classloader that it is made up of
has a disjoint set of classes/resources contained in it. So it was the
"aggregator" ClassLoader I was talking about.
You will also notice the "default" attribute of <classloaders/> section. This
specifies the ClassLoader via which the blocks are loaded. The only
requirement being that one of it's parent classloaders must be "*api*".
So if/when this is implemented what does it mean ? Well we could finally
implement a spec complaint servlet engine without jumping through loops. See
below for a sample of how I would do it. We could also support nested
"applications" like Stephen wanted. Woohoo!
<classloaders default="servlet-container">
<classloader name="jndi-api" parent="*system*">
<entry location="sar:SAR-INF/ext/jndi.jar"/>
</classloader>
<classloader name="servlet-api" parent="*system*">
<extension>
<name>javax.servlet</name>
<specification-version>2.3</specification-version>
<vendor-id>org.apache.jakarta</vendor-id>
<vendor-version>1.2.3.4</vendor-version>
</extension>
</classloader>
<join name="common">
<classloader name="servlet-api"/>
<classloader name="jndi-api"/>
</join>
<classloader name="servlet-container" parent="common">
<entry location="sar:SAR-INF/lib/*.jar"/>
<entry location="sar:SAR-INF/classes/"/>
</classloader>
</classloaders>
Anyways - thoughts?
--
Cheers,
Pete
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Re: [phoenix] ClassLoader section in environment.xml
Posted by Paul Hammant <Pa...@yahoo.com>.
Peter,
Sorry dude, after reading it back it is not the solve-all suggestion I
thought it was (even though you never understood it). It was a good
suggestion for namespace but it needless used classes to communicate
that uniqueness.
- Paul
>On Sat, 1 Dec 2001 21:27, Paul Hammant wrote:
>
>>Peter,
>>
>>This and the other email. I like a lot. I think you'll have trouble
>>with <join>, but you knew I'd say that ;-)
>>
>
>;)
>
>>The multiple "foo" scenario, which is a real namespace issue, could it
>>not be address java-package style? :
>>
>> org.apache.avalon.fooservice.FooClassLoaderNode
>>
>
>Not sure what you mean? Do you mean ask users to use classloader names with a
>specific format in their blocks. So if we had a block
>
>org.apache.avalon.fooservice.FooBlock
>
>It should use classloader
>
>org.apache.avalon.fooservice.FooClassLoader
>
>???
>
>What happens when multiple Blocks all require the same resources? Or worse
>require same resources but different versions ? Do we support this or not??
>
>>We could actually have an interface called ClassLoaderNode that a real
>>class could impl. It has in it some getters that pheonix could use for
>>semi-hard coded checking against the assembly manifest? ... similar to
>><required> functionality of manifest. It is class loaded by full class
>>name via the getClassLoader() as you described.
>>
>
>Parsing sentence ... syntax valid.
>Semantic error: Compiler unable to determine what the hell you are on about
>
>;)
>
>Pretend I am stupid and explain it to me in those terms.
>
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Re: [phoenix] ClassLoader section in environment.xml
Posted by Peter Donald <pe...@apache.org>.
On Sat, 1 Dec 2001 21:27, Paul Hammant wrote:
> Peter,
>
> This and the other email. I like a lot. I think you'll have trouble
> with <join>, but you knew I'd say that ;-)
;)
> The multiple "foo" scenario, which is a real namespace issue, could it
> not be address java-package style? :
>
> org.apache.avalon.fooservice.FooClassLoaderNode
Not sure what you mean? Do you mean ask users to use classloader names with a
specific format in their blocks. So if we had a block
org.apache.avalon.fooservice.FooBlock
It should use classloader
org.apache.avalon.fooservice.FooClassLoader
???
What happens when multiple Blocks all require the same resources? Or worse
require same resources but different versions ? Do we support this or not??
> We could actually have an interface called ClassLoaderNode that a real
> class could impl. It has in it some getters that pheonix could use for
> semi-hard coded checking against the assembly manifest? ... similar to
> <required> functionality of manifest. It is class loaded by full class
> name via the getClassLoader() as you described.
Parsing sentence ... syntax valid.
Semantic error: Compiler unable to determine what the hell you are on about
;)
Pretend I am stupid and explain it to me in those terms.
--
Cheers,
Pete
----------------------------------------------------
"The only way to discover the limits of the possible
is to go beyond them into the impossible."
-Arthur C. Clarke
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Re: [phoenix] ClassLoader section in environment.xml
Posted by Paul Hammant <Pa...@yahoo.com>.
Peter,
This and the other email. I like a lot. I think you'll have trouble
with <join>, but you knew I'd say that ;-)
The multiple "foo" scenario, which is a real namespace issue, could it
not be address java-package style? :
org.apache.avalon.fooservice.FooClassLoaderNode
We could actually have an interface called ClassLoaderNode that a real
class could impl. It has in it some getters that pheonix could use for
semi-hard coded checking against the assembly manifest? ... similar to
<required> functionality of manifest. It is class loaded by full class
name via the getClassLoader() as you described.
Regards,
- Paul H
>Hi,
>
>One thing I forgot to mention was how Blocks aquire the ClassLoaders. I
>propose that we add another method to BlockContext interface, namely
>
>ClassLoader getClassLoader(String name)
>
>This raises an interesting question though. How should a Block declare that
>it needs a ClassLoader named "foo" and "foo" must contain classes X, Y and Z?
>Should it declare that?
>
>My initial though was that you could add another section to the BlockInfo
>file like
>
><classloaders>
> <classloader name="foo">
> <description>
> This ClassLoader must contain classes X, Y and Z. It is
> part of the foo API and we use it to do "Something".
> </description>
> <required classname="com.biz.ClassToCheckFor"/>
> </classloader>
></classloaders>
>
>Then I realized - what would happen if 2 Blocks declared that they depended
>on ClassLoaders named "foo" but which had different contents. So in this case
>it would be required that you map the application-wide name into a
>block-local name ... which seems like overkill/flexability syndrome.
>
>So options that I could think of are;
>1. ignore the issue and make it a requirement that Block writers document it
>so that assemblers can build it
>2. have basic structures in blockinfo but keep names global
>3. Same as 3 but we map classloader names from global namespace to
>application local namespace.
>
>Thoughts?
>
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Re: [phoenix] ClassLoader section in environment.xml
Posted by Peter Donald <pe...@apache.org>.
Hi,
One thing I forgot to mention was how Blocks aquire the ClassLoaders. I
propose that we add another method to BlockContext interface, namely
ClassLoader getClassLoader(String name)
This raises an interesting question though. How should a Block declare that
it needs a ClassLoader named "foo" and "foo" must contain classes X, Y and Z?
Should it declare that?
My initial though was that you could add another section to the BlockInfo
file like
<classloaders>
<classloader name="foo">
<description>
This ClassLoader must contain classes X, Y and Z. It is
part of the foo API and we use it to do "Something".
</description>
<required classname="com.biz.ClassToCheckFor"/>
</classloader>
</classloaders>
Then I realized - what would happen if 2 Blocks declared that they depended
on ClassLoaders named "foo" but which had different contents. So in this case
it would be required that you map the application-wide name into a
block-local name ... which seems like overkill/flexability syndrome.
So options that I could think of are;
1. ignore the issue and make it a requirement that Block writers document it
so that assemblers can build it
2. have basic structures in blockinfo but keep names global
3. Same as 3 but we map classloader names from global namespace to
application local namespace.
Thoughts?
--
Cheers,
Pete
---------------------------------------------
We shall not cease from exploration, and the
end of all our exploring will be to arrive
where we started and know the place for the
first time -- T.S. Eliot
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