how to show exception message to the user?

how to show exception message to the user?
when task because of an error stops I want to show an error message

someone could help me, thanks.

for example this is the implementation of my connector:

protected void executeBusinessLogic() throws ConnectorException{ //Get access to the connector input parameters //getPath();
	//TODO execute your business logic here 

	//WARNING : Set the output of the connector execution. If outputs are not set, connector fails
	//setStatus(status);
	//setMensaje(mensaje);		
	try {
		File file = new File(getPath());
		InputStream is = new FileInputStream("D:\\Doc.docx");
		OutputStream out = new FileOutputStream(file);
		IOUtils.copy(is, out);
		setStatus(true);		
		
	} catch (final Exception e) {
		// TODO Auto-generated catch block
		setMensaje(e.getMessage());
		e.printStackTrace();	
	}	
 }