Seq Diagram Drawing try catch block in UML

Question

I have a question, how can I draw try catch block in sequence diagram in UML? Can I draw the try as the normal case and the catch as the alternative case or no?

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Answer 1

There is no standard way to model exception handling in a sequence diagram. Here is how I handle it:

The above diagram is generated with Web Sequence a free (open source) chrome extension. You can get it from here: https://chrome.google.com/webstore/detail/web-sequence/kcpganeflmhffnlofpdmcjklmdpbbmef or from the official site: https://www.zenuml.com . To test it out, you can simply paste the following code into the code editor of the above plugin or on the site.

JobTask.Run() {
  try() {
    Action.Execute() {
      InternalException.throw()
    }
  }
  InternalException.Catch() {
    Logger.Error()
    HighLevelException.throw()
  }
}

It demonstrates that we have a try block. Within this block, we execute Action.Execute() in which InternalException could be thrown. Then we catch it, log an error and rethrow a HighLevelException, which is a quite typical exception handling strategy.

Answer 2

UML sequence diagram lacks of being able to visualize exceptions. There are "workarounds" however, please refer to:

• Break
• Sequence Diagrams: Questions & Answers
• Stackoverflow answer