Try { ... } catch

Classic Servoy
1

Using the XmlReader plugin, I’d like to read a certain element’s attribute using this code:

_ID = _columnNode.getAttributeValue("id");

if (_ID == null) {
  // error handling
} else {
  // do something
}

Now, when this attribute “id” doesn’t exist, a nullpointer exception gets triggered at the first line.

Because exceptions aren’t always bad things, I tried using a try … catch to prevent the exception:

try {
  _ID = _columnNode.getAttributeValue("id");
} catch(theErr)	{
  // error handling
}

Despite the try … catch, the nullpointer exception still gets triggered!

Using the reference guide, I found out that I should loop trough the attributes using the xmlNode.getAttributeNames() function, but I was wondering why the try … catch block doesn’t catch the nullpointer exception. Any ideas or suggestions?

2

You could first call getAttributeNames(). That should give you all the attributes. Then you can check, whether your attribute is present.

Or an even better option: have a look at the XML-Plugin! :lol:

3

Thanks for the quick response patrick, but I already figured that part out. I wonder why the try … catch block doesn’t seem to work in this case. Maybe I’m using it in a wrong way?

4

Do you observer this behavior in developer with the debugger on? Or also in the client? With debugger and exception break enabled, you will end in the catch block…

Anyway: the plugin shouldn’t throw a NullPointerException at that point.

5

It occurs in Developer with both debugger on or off. Client not yet tested, but in my opinion it should just work :wink:.

6 
try { 
  _ID = _columnNode.getAttributeValue("id"); 
} catch(theErr)   { 
  // error handling 
}

Is the error really thrown in Servoy or do you only find it in your stacktrace.
Don’t know about this plugin but it is possible to design a plugin in a way that it doesn’t throw the error in Servoy.
If that is the case your try/catch block will not work.

BTW I agree that, once you get the hang of it, a try/catch/finally block can make an error work FOR you instead of AGAINST you…