The given code creates an id based on the previous id of the record.

<%@page import="java.sql.*"%>
<%
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "root");
Statement st = conn.createStatement();
ResultSet rs=st.executeQuery("SELECT id FROM user");
int id=0;
if(rs.last()){
id=rs.getInt("id")+1;
}
st.executeUpdate("insert into user(id,name,address) values("+id+",'rose','delhi')");
out.println("Data is inserted successfully");
}
catch(Exception e){}
%>

You can also generate an id of some format using the following code.

   public class GenerateSerialNumber {

        public static void main (String args[]){

          int serialNo = 000;
          for (int i=0;i<12;i++){
              serialNo++;
          System.out.printf("1/%03d\n",  serialNo);
         }
       }
     }