Add ContextFactory to extend Context with custom methods

To extend a Context with application-specific methods, we could add the following to the Javalin config:

public interface ContextFactory {

    /** Create a new {@link io.javalin.http.Context} */
    public Context createContext(HttpServletRequest request, HttpServletResponse response, Map<Class<?>, Object> appAttributes);

}

The lambdas could directly receive the desired Context subclass by introducing generics to the Handler class:

public interface Handler<T extends Context> {
  void handle(@NotNull T ctx) throws Exception;
}

With this change, Handler lambdas can use directly a subclass of Context as needed. This is an example of use:

private static class MyContext extends Context {
  public String foo() {
      return "bar";
  }
}

private static class MyContextFactory implements ContextFactory {
  @Override
  public Context createContext(HttpServletRequest request, HttpServletResponse response, Map<Class<?>, Object> appAttributes) {
      return new MyContext(request, response, appAttributes);
  }
}

var app = Javalin.create(config -> config.contextFactory(new MyContextFactory())),
app.get("/test", (MyContext ctx) -> ctx.foo());

[icoloma]

In my case, for a personal project:

• context.getCurrentUser() returns the current user, rehydrated from cookies
• context.getUserLocale() returns the locale of the current user, or the preferred locale of the browser if none
• Other classes that need to receive a Context in the constructor could be created from the Context instead, like a MustacheViewBuilder that automatically includes both current locale and current user.

I have seen other issues on GitHub addressing parameter conversion and validation (get an int parameter, throw 400 if needed) which would fit better as a context extension IMHO (the format of JSON error messages are quite often application-specific). Not my case, though.

[tipsy]

I’m afraid I also fall on the side of not seeing enough value in this to implement it. Thanks for the issue and PR though 😃