Hi Ruban - use the below java code
return var1.substring(var1.indexOf("7"),var1.indexOf("7")+9);
where var1 is your input string.
if you don't have 9 char after the index of 7 then you might have to use below UDF
if (var1.length()>(var1.indexOf("7")+9))
return var1.substring(var1.indexOf("7"),var1.indexOf("7")+9);
else
return var1.substring(var1.indexOf("7")); // change it as per your needs..