How to add Error messages on Vf Page using Apex in Salesforce?

Hi sushant,

You can do something like this

public with sharing class ErrorMessageInVfController {
public Account acc{get;set;}
public ErrorMessageInVfController(ApexPages.StandardController controller) {
acc = new Account();
}

public void save(){
if(acc.name == '' || acc.name == null)
ApexPages.addmessage(new ApexPages.message(ApexPages.severity.FATAL,'Please enter Account name'));

if(acc.AccountNumber == '' || acc.AccountNumber == null)
ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,'Please enter Account number'));

if(acc.phone == '' || acc.phone == null)
ApexPages.addmessage(new ApexPages.message(ApexPages.severity.WARNING,'Please enter Account phone'));

if(acc.site == '' || acc.site == null)
ApexPages.addmessage(new ApexPages.message(ApexPages.severity.INFO,'Please enter Account site'));

if(acc.industry == '' || acc.industry == null)
ApexPages.addmessage(new ApexPages.message(ApexPages.severity.CONFIRM,'Please enter Account industry'));

}
}

for details go through http://www.sfdcpoint.com/salesforce/show-error-message-visualforce-page/