Checking textbox through java class which is called in jsp

Question

I have created a text box in html and if the string entered by user is a alphabet it will not show any message ,else it should display a error message..These checking validations of textbox is done in java and called in jsp;
a.html
<font size="4">Enter the search keyword:</font><input type="text" name="key" ><br>
and also submit button is there which goes to main.jsp
main.jsp
<%@page import="gaveshan.checking;"%>
<%
checking ch=new checking();
String trans=request.getParameter("key");
out.println(ch.ParseClean(trans));
session.setAttribute( "trans", trans );
%>
checking.java
package gaveshan;
import java.awt.event.*;
public class checking
{  public String ParseClean(String str)
if(str.length()==100||str.length()==0)
return "Enter String Properly";
for(int i=0;i<str.length();i++)
if(!(str.charAt(i)>65&&str.charAt(i)<122))
return "Enter String Properly";
it is not givng any message when user enters the input in textbox
it is not showing any error

Answer 1

Using javascript.
var lwr = 'abcdefghijklmnopqrstuvwxyz';
var upr = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
function isValid(parm) {
for (i=0; i<parm.length; i++) {
if (val.indexOf(parm.charAt(i),0) == -1) return false;
return true;
}- vignesh