How to format Excel Column in Apex? [closed]

Question

I'm sending an email via scheduler class with an excel file as an attachment, but the data in the file does not appear to be in proper format. Please check the following image:

The code I'm using to generate the file:

enter code here 
private static void sendMailWithAttachment() {

    String subject = 'excel file subject';

    String body = 'excel file body';

    Messaging.SingleEmailMessage emailMessage = new Messaging.SingleEmailMessage();

    emailMessage.subject = subject;

    emailMessage.plaintextbody = body;

    Messaging.EmailFileAttachment excelAttachment = new Messaging.EmailFileAttachment();

    excelAttachment.setFileName('excel_report' + '.xls');

    excelAttachment.setBody(reportPage.getContent());

    excelAttachment.setContentType('application/vnd.ms-excel');

    List<Messaging.EmailFileAttachment> attachments = new List<Messaging.EmailFileAttachment>();

    attachments.add(excelAttachment);

    emailMessage.setFileAttachments(attachments);

    Messaging.sendEmail(emailMessage);

}

1.23457E+14 is not a proper format.

How to fix the format of the number through apex?

Answer 1

The general answer is "you can't". Excel (and other document formats) are complex, and there aren't any (or are only very few, and quite limited) tools on-platform that can manipulate such documents. We only have a basic ability to create such documents through setting the content-type (as you are doing).

The formatting you're seeing is auto-applied by Excel based on its detection of the type of data.