Check if an input is numeric or not
In our email to case functionality, we plan to introduce a feature via which the users will be able to input the Legacy Account Id which is numeric along with the Salesforce Account Id which is alphanumeric.
Is there any method available in Saleforce library that can indicate whether the data is a string or number ?
Yes. The Salesforce dev guide has a bunch of String methods for this kind of stuff.
Methods of interest are: