A follow-on feature could be a Kotlin DSL. Kotlin is fully typed, but with a lot of Groovy-like features that enable elegant DSLs. The Gradle team, for example, has created a Kotlin DSL that can be used instead of their Groovy DSL. I don't know the details of how it works, but IntelliJ is able to provide type-safe validation and code completion for the Gradle Kotlin DSL. I suspect a Kotlin DSL for Log4j could benefit from the same capabilities.
Regards, Raman On Fri, May 3, 2019 at 1:08 PM Matt Sicker <[email protected]> wrote: > > I believe Ralph has brought up a feature request in the past, though I > don't remember where. Anyways, Logback has a Groovy DSL [1] as an > option to configure itself, and we could introduce a similar feature > built on top of the existing ConfigurationBuilder code from the Java > DSL in log4j-core. After seeing how easily Groovy integrates with Java > to form DSLs in Jenkins [2] (more so in the web framework than in > pipelines, but both are valid), I've been considering working on such > a feature. > > Let's take a random configuration sample from the manual [3]: > > <?xml version="1.0" encoding="UTF-8"?> > <Configuration status="WARN"> > <Appenders> > <Console name="Console" target="SYSTEM_OUT"> > <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level > %logger{36} - %msg%n"/> > </Console> > </Appenders> > <Loggers> > <Logger name="com.foo.Bar" level="trace"> > <AppenderRef ref="Console"/> > </Logger> > <Root level="error"> > <AppenderRef ref="Console"/> > </Root> > </Loggers> > </Configuration> > > If I were to translate this to the equivalent Groovy DSL, here is one > example of how that might look: > > configuration(status: 'warn') { > appenders { > console(name: 'Console', target: 'SYSTEM_OUT') { > patternLayout(pattern: '%d{HH:mm:ss.SSS} [%t] %-5level > %logger{36} - %msg%n') > } > } > loggers { > logger(name: 'com.foo.Bar', level: 'trace') { > appenderRef(ref: 'Console') > } > root(level: 'error') { > appenderRef(ref: 'Console') > } > } > } > > An alternative syntax would be to switch from using method parameters > to properties of the closure. For example, that might look like: > > configuration { > status = 'warn' > console { > name = 'Console' > target = 'SYSTEM_OUT' > patternLayout { > pattern = '%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n' > } > } > // ... > } > > Are there any preferences on syntax? I don't think we can get super > fancy with the DSL due to the underlying APIs (i.e., we can't provide > much in the way of code completion AFAIK), but supporting a dynamic > DSL like that is fairly easy with Groovy. This does open a question of > configuration being scripted versus declarative since we'd be offering > a full script engine technically in order to write your configuration. > I do not expect this feature to offer a programmatic way of > manipulating the underlying plugin objects (i.e., this would be for > building a Configuration, not manipulating a running one); that might > make more sense with a more standardized plugin API which is a > wishlist item I have for 3.0. > > [1]: https://logback.qos.ch/manual/groovy.html > [2]: > https://github.com/stapler/stapler/blob/master/groovy/src/main/java/org/kohsuke/stapler/jelly/groovy/JellyBuilder.java > [3]: https://logging.apache.org/log4j/2.x/manual/configuration.html > > -- > Matt Sicker <[email protected]>
