I should add that there were two main drivers for the way Plugin support was
changed in 3.0.
1. Stop using a custom Log4jPlugins.dat file. Using a data file created all the
problems with shading. Placing all the entries into a Java class solved this
easily.
2. Use ServiceLoader to locate plugins instead of traversing ClassLoaders. We
still end up traversing ClassLoaders but in a way that is very well supported
by the JDK.
So in reality Log4jPlugins.dat was what was converted to be a Java service, not
the plugins themselves.
Ralph
> On Dec 4, 2024, at 10:08 PM, Ralph Goers <ralph.go...@dslextreme.com> wrote:
>
> Some huge points are being overlooked in this discussion.
>
> 1. A Plugin is NOT a Java service. You cannot manually create the
> META-INF/services entry for your plugin as the plugin system won’t recognize
> it.
> 2. A Plugin service is a collection of plugins. This is intentional as
> loading all the plugins one by one via ServiceLoader would be very slow. I
> recall that some testing was done around that when this was first
> implemented. If you look at the Log4jPlugins.java class generated by the
> annotation processor you will see that all the plugins for the module are
> there. It is much easier to do this with a tool than construct it manually.
> 3. While we could have used a JSON or properties file we would have ended up
> right where we are with 2.x with creating shaded jars being a problem and
> needing a custom transformer. Using a Java class file with ServiceLoader
> avoids this.
> 4. Again, module-info.java does NOT reference individual plugins. Instead, it
> references the generated Log4jPlugins.java class.
> 5. Log4jPlugins.java contains almost no code - it has a single method that
> simply returns the list of plugin entries that are provided in the module.
>
> Ralph
>
>> On Dec 4, 2024, at 6:15 AM, Volkan Yazıcı <vol...@yazi.ci> wrote:
>>
>> I agree with Pavel that users should only be required to
>>
>> 1. Provide the interface implementation
>> 2. Create the associated `META-INF/services` file entry
>> 3. [For Java 9 and above] Update their `module-info.java` accordingly
>>
>> Anything more than this is non-idiomatic. Telling users "but processors are
>> helpful", "you can manually create the Java file registering your plugin",
>> etc. is beating around the bush.
>>
>> On Fri, Nov 29, 2024 at 10:26 AM PavelTurk <pavelturk2...@gmail.com> wrote:
>>
>>> Hi Piotr,
>>>
>>> On 11/29/24 10:07, Piotr P. Karwasz wrote:
>>>> Hi Pavel,
>>>>
>>>> On 28.11.2024 19:26, PavelTurk wrote:
>>>>> Thank you very much for your detailed and quick help.
>>>>>
>>>>> However, to tell the truth, I’m a bit confused. I’ve been waiting for a
>>> long time for Log4j to finally work according to the JPMS rules. But in
>>> your message, you talk about compile-time and, as I understood, the use of
>>> some plugin-processor (from your project pom):
>>>>>
>>>>> <annotationProcessorPaths>
>>>>> <path>
>>>>> <groupId>org.apache.logging.log4j</groupId>
>>>>> <artifactId>log4j-plugin-processor</artifactId>
>>>>> <version>3.0.0-beta3</version>
>>>>> </path>
>>>>> </annotationProcessorPaths>
>>>>>
>>>>> Doesn’t all this completely contradict JPMS?
>>>>> (...)
>>>>> By the way, I noticed something seemed off when I saw code duplication
>>> in your project:
>>>>>
>>>>> @Configurable(elementType = Appender.ELEMENT_TYPE, printObject = true)
>>>>> @Plugin(ConsoleAppender.PLUGIN_NAME)
>>>>> public final class ConsoleAppender...
>>>>>
>>>>> and
>>>>>
>>>>> PluginEntry.builder()
>>>>> .setKey("console")
>>>>> .setClassName("org.apache.logging.log4j.core.appender.ConsoleAppender")
>>>>> .setName("Console")
>>>>> .setNamespace("Core")
>>>>> .setElementType("appender")
>>>>> .setPrintable(true)
>>>>> .get(),
>>>>>
>>>>> Or am I mistaken (which is always possible) and misunderstood
>>> everything?
>>>>
>>>> We have an annotation processor that automatically generates the
>>> required `PluginService` implementation, I don't see how that contradicts
>>> the principles behind JPMS.
>>> ...
>>>
>>> Let me explain my point of view. But first of all, I want to emphasize
>>> that I’m not claiming to be right—I could very well be wrong. I’m simply
>>> saying that using a processor seems incorrect to me.
>>>
>>> In the world of JPMS, there’s a service, we implement it, and we add it. I
>>> haven’t heard of a service + PROCESSOR that needs to be used. Can you point
>>> out any other projects that involve a service + processor? The reasoning is
>>> that we should only need to know the INTERFACE, and we’ll handle the
>>> IMPLEMENTATION ourselves. After all, it’s possible to do without it—for
>>> example, by writing a PluginService manually, which would scan the module
>>> itself and return the necessary classes or just data(entries) about them.
>>> That’s why I said that using a processor here seems odd to me. In general,
>>> I think code generation should only be used as a last resort—for example,
>>> for JPA metamodels—but that’s just my opinion.
>>>
>>> I assume module-info was also generated automatically. The problem is that
>>> it’s not present in log4j-core-3.0.0-beta3-sources.jar see [1], but it does
>>> exist in log4j-core-3.0.0-beta3.jar see [2]. Additionally, it’s not in the
>>> repository see [3]. So, it is not possible to see what is in this file. Or
>>> was I looking in the wrong place?
>>>
>>> [1]
>>> https://repo1.maven.org/maven2/org/apache/logging/log4j/log4j-core/3.0.0-beta3/log4j-core-3.0.0-beta3-sources.jar
>>> [2]
>>> https://repo1.maven.org/maven2/org/apache/logging/log4j/log4j-core/3.0.0-beta3/log4j-core-3.0.0-beta3.jar
>>> [3]
>>> https://github.com/apache/logging-log4j2/tree/rel/3.0.0-beta3/log4j-core/src/main/java
>>>
>>> Best regards, Pavel
>>>
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>
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