How to redirect non-WWW URL to WWW URL

Add the following code on .htaccess file

RewriteEngine On
RewriteCond %{HTTP_HOST}  ^debendramagentoblogspot.com/ [nocase]
RewriteRule ^(.*)         http://www.debendramagentoblogspot.com/$1 [last,redirect=301]

It above one code not worked then add the following code on .htaccess fole

RewriteCond %{HTTP_HOST} ^(?!www\.)(.+) [NC]
RewriteRule ^(.*) http://www.%1/$1 [R=301,NE,L]