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tgbotapi/readmes/exceptions_handling.md

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Exceptions handling

Unfortunatelly, exceptions handling in this library is a bit difficult in some places, but that have at least two reasons: flexibility and usability.

"In place" handling

In case you know, where exceptions are happening, you may use several tools for exceptions catching:

  • Catching with result
  • Catching with callback

Catching with result

If you prefer to receive Result objects instead of some weird callbacks, you may use the next syntax:

safelyWithResult {
    // do something
}.onSuccess { // will be called if everything is right
    // handle success
}.onFailure { // will be called if something went wrong
    // handle error
    it.printStackTrace()
}.getOrThrow() // will return value or throw exception

Catching with callback

Also there is more simple (in some cases) way to handle exceptions with callbacks:

safely(
  {
      // handle error
      it.printStackTrace()
      null // return value
  }
) {
    // do something
}

Bonus: different types of handling

There are two types of handling:

  • Just safely - when you are using something to obviously retrieve value or throw exception. When handling callback has been skipped, it will throw exception by default. For example:
safely(
    {
        it.printStackTrace()
        "error"
    }
) {
    error("Hi :)") // emulate exception throwing
    "ok"
} // result will be with type String
  • Safely without exceptions - almost the same as safely, but this type by default allow to return nullable value (when exception was thrown) instead of just throwing (as with safely):
safelyWithouExceptions {
    // do something
} // will returns nullable result type

Global exceptions handling

The most simple way to configure exceptions handling is to change CoroutineContext when you are creating your CoroutineScope for bot processing:

val bot = telegramBot("TOKEN")

bot.buildBehaviour (
    scope = scope,
    defaultExceptionsHandler = {
        it.printStackTrace()
    }
) {
    // ...
}

OR

val bot = telegramBotWithBehaviour (
    "TOKEN",
    scope = scope,
    defaultExceptionsHandler = {
        it.printStackTrace()
    }
) {
    // ...
}

Here we have used ContextSafelyExceptionHandler class. It will pass default handling of exceptions and will call the block in most cases when something inside of your bot logic has thrown exception.