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Posted to users@tomcat.apache.org by Thorsten Schöning <ts...@am-soft.de> on 2018/07/31 16:06:27 UTC
What is the correct place to specifiy SPI service files for Java?
Hi all,
I would like to get some attention on some older SO-question[1] about
where to place SPI-service files of Java.
Following the docs, those should be placed in META-INF at the top
level of some JAR and webapps designed to be used with Tomcat provide
such a folder. But it seems to be ignored during search for
SPI-service files, instead those seem to be assumed in
WEB-INF/classes/META-INF/services. The can easily be seen e.g. using
Process Monitor in Windows.
As the SO-question lacks some official Tomcat-documentation or such, I
am asking here: What is the correct place for such service files? Can
this be configured somehow? Why is META-INF at the top level ignored?
Is it used at all for anything or only WEB-INF/classes/META-INF for
anything which is normally assumed to be in META-INF itself?
Thanks!
[1]: https://stackoverflow.com/questions/7692497/tomcat-wont-load-my-meta-inf-services-javax-servlet-servletcontainerinitializ
Mit freundlichen Grüßen,
Thorsten Schöning
--
Thorsten Schöning E-Mail: Thorsten.Schoening@AM-SoFT.de
AM-SoFT IT-Systeme http://www.AM-SoFT.de/
Telefon...........05151- 9468- 55
Fax...............05151- 9468- 88
Mobil..............0178-8 9468- 04
AM-SoFT GmbH IT-Systeme, Brandenburger Str. 7c, 31789 Hameln
AG Hannover HRB 207 694 - Geschäftsführer: Andreas Muchow
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Re: What is the correct place to specifiy SPI service files for Java?
Posted by Thorsten Schöning <ts...@am-soft.de>.
Guten Tag Mark Thomas,
am Mittwoch, 1. August 2018 um 21:12 schrieben Sie:
> The servlet expert group recently discussed WAR vs JAR[...]
Thanks for the explanation, make things more clear tor me. I've added
your answer to the SO-question, because it provides the missing
background I wanted to read about, but if you want the credits, feel
free to add it yourself and I will delete mine.
Mit freundlichen Grüßen,
Thorsten Schöning
--
Thorsten Schöning E-Mail: Thorsten.Schoening@AM-SoFT.de
AM-SoFT IT-Systeme http://www.AM-SoFT.de/
Telefon...........05151- 9468- 55
Fax...............05151- 9468- 88
Mobil..............0178-8 9468- 04
AM-SoFT GmbH IT-Systeme, Brandenburger Str. 7c, 31789 Hameln
AG Hannover HRB 207 694 - Geschäftsführer: Andreas Muchow
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Re: What is the correct place to specifiy SPI service files for Java?
Posted by Thorsten Schöning <ts...@am-soft.de>.
Guten Tag Mark Thomas,
am Mittwoch, 1. August 2018 um 21:12 schrieben Sie:
> Service files are loaded by class loaders from the META-INF/services
> directory.
> *.jar!/META-INF/services
> and
> *.war/WEB-INF/classes/META-INF/services
> are visible to class loaders
> *.war!/META-INF/services
> is not.
I just came across another issue with using service files in my
environment: "Something" works in Ubuntu 16.04 with Tomcat 7 and Java
8, while it doesn't in Windows 10 with the same version of Tomcat and
Java.
The important thing to note is that I'm using Axis 2 in this scenario
and the service file is part of a service I'm hosting within Axis 2.
This results in the following directory in both environments:
> [...]\webapps\axis2\WEB-INF\services\de.am_soft.sm_mtg.backend\META-INF\services\SOME_FILE
Using Process Monitor I can see that only the following directories
are queried on Windows:
> [...]\webapps\axis2\WEB-INF\classes\META-INF\services\SOME_FILE
> [...]\lib\META-INF\services\SOME_FILE
Querying the above two dirs looks like what you have written before
and that explains why it fails on Windows. But it doesn't on Ubuntu,
while it does fail if I remove the "services"-dir where it is
currently. So querying this dir seems non-standard.
But who is querying it most likely, Tomcat or Axis 2? I came across
different classloaders in Axis 2 for different OS in the past already,
so I guess it has to do with Axis 2. What do you think?
I'm using ServiceLoader the following way:
> ClassLoader cl = MdRecOmsEnc.class.getClassLoader();
> ServiceLoader<MdRecOmsEnc> sl = ServiceLoader.load(MdRecOmsEnc.class, cl);
> Iterator<MdRecOmsEnc> it = sl.iterator();
Providing the classloader is needed for other issues in very specific
environments, but in my opinion shouldn't be the root cause, as that
is provided with Ubuntu as well.
Mit freundlichen Grüßen,
Thorsten Schöning
--
Thorsten Schöning E-Mail: Thorsten.Schoening@AM-SoFT.de
AM-SoFT IT-Systeme http://www.AM-SoFT.de/
Telefon...........05151- 9468- 55
Fax...............05151- 9468- 88
Mobil..............0178-8 9468- 04
AM-SoFT GmbH IT-Systeme, Brandenburger Str. 7c, 31789 Hameln
AG Hannover HRB 207 694 - Geschäftsführer: Andreas Muchow
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Re: What is the correct place to specifiy SPI service files for Java?
Posted by Mark Thomas <ma...@apache.org>.
On 01/08/18 17:29, Thorsten Schöning wrote:
> Guten Tag Mark Thomas,
> am Mittwoch, 1. August 2018 um 17:34 schrieben Sie:
>
>> Nor should it. foo.war!/META-INF/services is not a valid location for an
>> SPI file.
> [...]
>> The correct locations are:
>> foo.war!/WEB-INF/lib/*.jar!/META-INF/services
>
> So your argument is that a WAR is not a JAR and only JARs can contain
> META-INF/services? Is there a reason for such decision, is it
> something Java demands?
Service files are loaded by class loaders from the META-INF/services
directory.
*.jar!/META-INF/services
and
*.war/WEB-INF/classes/META-INF/services
are visible to class loaders
*.war!/META-INF/services
is not.
The servlet expert group recently discussed WAR vs JAR in the context of
Java 9 and mutli-version JARs. The conclusion was (I'm paraphrasing)
that WARs are not a specialised form of JAR and while they share a
common format a feature that is available to a JAR is NOT automatically
available to a WAR unless the Servlet spec (of Java EE spec) explicitly
states otherwise.
Containers are free to add container specific extensions if they wish
but they come with the usual (lack of) interoperability warnings.
Mark
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Re: What is the correct place to specifiy SPI service files for Java?
Posted by Thorsten Schöning <ts...@am-soft.de>.
Guten Tag Mark Thomas,
am Mittwoch, 1. August 2018 um 17:34 schrieben Sie:
> Nor should it. foo.war!/META-INF/services is not a valid location for an
> SPI file.
[...]
> The correct locations are:
> foo.war!/WEB-INF/lib/*.jar!/META-INF/services
So your argument is that a WAR is not a JAR and only JARs can contain
META-INF/services? Is there a reason for such decision, is it
something Java demands? Regarding the SO-question, JBoss seems to work
differently:
> What I do find odd however is that JBoss does seem to work with my
> setup and can discover services inside the Services folder even if
> you don't have them wrapped in a Jar file...
https://stackoverflow.com/questions/7692497/tomcat-wont-load-my-meta-inf-services-javax-servlet-servletcontainerinitializ#comment9883761_8057393
Which makes sense to me, reusing META-INF of the WAR is the first
thing one most likely considers. The docs for ServiceLoader seem to at
least not forbid this as well:
> Service providers can be installed in an implementation of the Java
> platform in the form of extensions, that is, jar files placed into
> any of the usual extension directories. Providers can also be made
> available by adding them to the application's class path or by some
> other platform-specific means.
https://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html
So, Tomcat prefers Jars because only those are explicitly mentioned or
what is the reason?
Mit freundlichen Grüßen,
Thorsten Schöning
--
Thorsten Schöning E-Mail: Thorsten.Schoening@AM-SoFT.de
AM-SoFT IT-Systeme http://www.AM-SoFT.de/
Telefon...........05151- 9468- 55
Fax...............05151- 9468- 88
Mobil..............0178-8 9468- 04
AM-SoFT GmbH IT-Systeme, Brandenburger Str. 7c, 31789 Hameln
AG Hannover HRB 207 694 - Geschäftsführer: Andreas Muchow
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Re: What is the correct place to specifiy SPI service files for Java?
Posted by Mark Thomas <ma...@apache.org>.
On 01/08/18 08:20, Thorsten Schöning wrote:
> Guten Tag Mark Thomas,
> am Dienstag, 31. Juli 2018 um 19:30 schrieben Sie:
>
>> Correct.[...]
>
> But as could have been read in the following paragraph of my mail and
> the SO-link, it doesn't work that way at least in Tomcat 7.0.90 even
> without absolute ordering in web.xml.
>
>> Enumeration<URL> resources;
>> if (loader == null) {
>> resources = ClassLoader.getSystemResources(configFile);
>> } else {
>> resources = loader.getResources(configFile);
>> }
>
> https://github.com/apache/tomcat/blob/trunk/java/org/apache/catalina/startup/WebappServiceLoader.java#L132
>
> That code is NOT using "META-INF/services" at the top level of the web> project,
Nor should it. foo.war!/META-INF/services is not a valid location for an
SPI file.
> but "WEB-INF/classes/META-INF/services" instead. That can be
> clearly seen e.g. using Process Monitor.
The correct locations are:
foo.war!/WEB-INF/lib/*.jar!/META-INF/services
which is where Tomcat looks.
Tomcat uses ClassLoader.getResources() which will also pick up
foo.war!/WEB-INF/classes/META-INF/services since the class loader
doesn't differentiate between a resource located at the root of a JAR or
a resource located in at the root of /WEB-INF/classes
There are benefits to this as IDE / Tomcat integrations have a habit of
placing classes in /WEB-INF/classes rather than in JAR file in /WEB-INF/lib
> So is this a bug or needs some configuration or has changed in newer
> versions of Tomcat or whatever?
No bug. No configuration required. No change in newer Tomcat versions.
Mark
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Re: What is the correct place to specifiy SPI service files for Java?
Posted by Thorsten Schöning <ts...@am-soft.de>.
Guten Tag Mark Thomas,
am Dienstag, 31. Juli 2018 um 19:30 schrieben Sie:
> Correct.[...]
But as could have been read in the following paragraph of my mail and
the SO-link, it doesn't work that way at least in Tomcat 7.0.90 even
without absolute ordering in web.xml.
> Enumeration<URL> resources;
> if (loader == null) {
> resources = ClassLoader.getSystemResources(configFile);
> } else {
> resources = loader.getResources(configFile);
> }
https://github.com/apache/tomcat/blob/trunk/java/org/apache/catalina/startup/WebappServiceLoader.java#L132
That code is NOT using "META-INF/services" at the top level of the web
project, but "WEB-INF/classes/META-INF/services" instead. That can be
clearly seen e.g. using Process Monitor.
So is this a bug or needs some configuration or has changed in newer
versions of Tomcat or whatever?
Mit freundlichen Grüßen,
Thorsten Schöning
--
Thorsten Schöning E-Mail: Thorsten.Schoening@AM-SoFT.de
AM-SoFT IT-Systeme http://www.AM-SoFT.de/
Telefon...........05151- 9468- 55
Fax...............05151- 9468- 88
Mobil..............0178-8 9468- 04
AM-SoFT GmbH IT-Systeme, Brandenburger Str. 7c, 31789 Hameln
AG Hannover HRB 207 694 - Geschäftsführer: Andreas Muchow
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Re: What is the correct place to specifiy SPI service files for Java?
Posted by Mark Thomas <ma...@apache.org>.
On 31/07/18 17:06, Thorsten Schöning wrote:
> Hi all,
>
> I would like to get some attention on some older SO-question[1] about
> where to place SPI-service files of Java.
>
> Following the docs, those should be placed in META-INF at the top
> level of some JAR and webapps designed to be used with Tomcat provide
> such a folder.
Correct. With the caveat that if the web application defines an
<absolute-ordering> in web.xml, only those JARs are searched.
See
https://github.com/apache/tomcat/blob/trunk/java/org/apache/catalina/startup/WebappServiceLoader.java
for details.
Mark
> But it seems to be ignored during search for
> SPI-service files, instead those seem to be assumed in
> WEB-INF/classes/META-INF/services. The can easily be seen e.g. using
> Process Monitor in Windows.
>
> As the SO-question lacks some official Tomcat-documentation or such, I
> am asking here: What is the correct place for such service files? Can
> this be configured somehow? Why is META-INF at the top level ignored?
> Is it used at all for anything or only WEB-INF/classes/META-INF for
> anything which is normally assumed to be in META-INF itself?
>
> Thanks!
>
> [1]: https://stackoverflow.com/questions/7692497/tomcat-wont-load-my-meta-inf-services-javax-servlet-servletcontainerinitializ
>
> Mit freundlichen Grüßen,
>
> Thorsten Schöning
>
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