Add bolt-jakarta-servlet and bolt-jakarta-jetty modules for Jakarta EE supports

[seratch]

This pull request partially resolves javax.* dependency transition described #919 by providing the way to switch Web app related dependencies from Java EE Servlet (javax.servlet) to Jakarta EE Servlet (jakarta.servlet). Alsom if we go with this plan, we can resolve #724 in a different approach.

As the majority people in the developer communities are using the Java EE (javax.servlet), we will continue supporting javax.servlet for a long enough time (say, years). That's why we added new dependencies even though these new one are mostly the same with the javax.servlet based ones, except the dependencies and the imports in code.

If you're not familiar with the transition to Jakarta EE, refer to https://blogs.oracle.com/javamagazine/post/transition-from-java-ee-to-jakarta-ee to learn the background.

Code snippets

javax.servlet dependencies (currently available)

dependencies {
  implementation("com.slack.api:bolt:1.18.0-SNAPSHOT")
  implementation("com.slack.api:bolt-servlet:1.18.0-SNAPSHOT")
  implementation("com.slack.api:bolt-jetty:1.18.0-SNAPSHOT")
}

package hello;
import com.slack.api.bolt.App;
import com.slack.api.bolt.jetty.SlackAppServer;
public class MyApp {
  public static void main(String[] args) throws Exception {
    var app = new App();
    var server = new SlackAppServer(app);
    server.start(); // http://localhost:3000/slack/events
  }
}

jakarta.servlet dependencies (will be available in v1.18)

dependencies {
  implementation("com.slack.api:bolt:1.18.0-SNAPSHOT")
  implementation("com.slack.api:bolt-jakarta-servlet:1.18.0-SNAPSHOT")
  implementation("com.slack.api:bolt-jakarta-jetty:1.18.0-SNAPSHOT")
}

package hello;
import com.slack.api.bolt.App;
// This import is the only difference from a user perspective
import com.slack.api.bolt.jakarta_jetty.SlackAppServer;
public class MyApp {
  public static void main(String[] args) throws Exception {
    var app = new App();
    var server = new SlackAppServer(app);
    server.start(); // http://localhost:3000/slack/events
  }
}

Category (place an x in each of the [ ])

• bolt (Bolt for Java)
• bolt-{sub modules} (Bolt for Java - optional modules)
• slack-api-client (Slack API Clients)
• slack-api-model (Slack API Data Models)
• slack-api-*-kotlin-extension (Kotlin Extensions for Slack API Clients)
• slack-app-backend (The primitive layer of Bolt for Java)

Requirements

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[seratch]

This module is a legacy one, which was added before bolt-java development. I don't think that many people are using this but now it's a good timing to mark this simple module as deprecated and encourage people to use bolt-java for new apps.

I'm not planning to remove this class because we're not in a hurry to remove it as the javax.servlet dependency in this module is optional (=provided scope).

[filmaj]

This might be good to remember / extract into the changelog for the next release as it is kind of buried deep within this PR (which focusses on providing Jakarta EE support).

[seratch]

This is used only by the above SlackEventsApiServlet class in this SDK. As this class is public, external projects may rely on it. Event after this deprecation, we can keep the class as long as possible (for the reason I mentioned above)

[seratch]

This line of code is the only difference from the existing way using jetty 9.x (=javax.servlet compatible version).

[seratch]

Imports are changed but they are fully compatible so far. I didn't change any logics this time.

[codecov]

Codecov Report

Merging #920 (830b9c6) into main (caaa7ca) will increase coverage by 0.05%.
The diff coverage is 87.93%.

@@             Coverage Diff              @@
##               main     #920      +/-   ##
============================================
+ Coverage     77.27%   77.33%   +0.05%     
- Complexity     3574     3606      +32     
============================================
  Files           388      394       +6     
  Lines         10626    10742     +116     
  Branches       1035     1044       +9     
============================================
+ Hits           8211     8307      +96     
- Misses         1818     1830      +12     
- Partials        597      605       +8     

Impacted Files	Coverage Δ
...ent/src/main/java/com/slack/api/rtm/RTMClient.java	39.08% <ø> (ø)
..._backend/events/servlet/SlackEventsApiServlet.java	82.05% <ø> (ø)
...backend/events/servlet/SlackSignatureVerifier.java	66.66% <ø> (ø)
...api/bolt/jakarta_servlet/SlackOAuthAppServlet.java	64.70% <64.70%> (ø)
...k/api/bolt/jakarta_servlet/WebEndpointServlet.java	81.48% <81.48%> (ø)
...olt/jakarta_servlet/WebEndpointServletAdapter.java	88.88% <88.88%> (ø)
...lack/api/bolt/jakarta_servlet/SlackAppServlet.java	94.11% <94.11%> (ø)
...ck/api/bolt/jakarta_servlet/ServletAdapterOps.java	100.00% <100.00%> (ø)
...i/bolt/jakarta_servlet/SlackAppServletAdapter.java	100.00% <100.00%> (ø)
...va/com/slack/api/socket_mode/SocketModeClient.java	70.70% <0.00%> (-3.83%)	⬇️

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[filmaj]

Looks good! Lots of code copied around but it is for a good cause: additive support for new runtime without breaking backwards compatibility. Nicely done. Left a couple of questions / comments.

[filmaj]

This might be good to remember / extract into the changelog for the next release as it is kind of buried deep within this PR (which focusses on providing Jakarta EE support).

[filmaj]

Should we make explicit that this is Java EE compatible Jetty here? Just like in the line below we make explicit it is Jakarta EE compatible Jetty?

[seratch]

Good point. I will update these parts before merging this PR!