Exception handling example

gistfile1.java

// MyActionHandler throws an exception. Note that we're throwing a custom exception

public class MyActionHandler extends AbstractAction<MyAction, MyActionResult> {
  @Override
  public MyActionResult execute(MyAction action, ExecutionContext context) throws ActionException {
    if (somethingGoesWrong()) {
      throw new MyCustomException("This is my custom message");
    } 
    
    // everything ok
  }
}

// MyCustomException has to be serializable, have a no-arg public constructor, and reside in shared (client + server) path

package com.mycompany.shared;

public class MyCustomException extends ActionException implements Serializable {
  public MyCustomException() {
  }

  public MyCustomException(String msg) {
    super(msg);
  }
}

// on the client side, switch between error classes and handle them accordingly

dispatchAsync.execute(new MyAction(), new AsyncCallbackImpl<MyActionResult>() {
  @Override
  public void onReturn(MyActionResult result) {
    // everything ok
  }

  @Override
  public void onFailure(Throwable caught) {
    try {
      thrown caught;
    } catch (MyCustomException e) {
      handleMyCustomException(e); // possibly display the error message
    } catch (AnotherExceptionType e) {
      // do something else for this particular exception type
    } catch (Throwable e) {
      // last resort, something unexpected happened
    }
  }
});