my script file is:
<script> 
    function closeIt() { 
        return "Any string value here forces a dialog box to \n" + 
         "appear before closing the window. Do what you have to do in this method."; 
    } 
    window.onbeforeunload = closeIt; 
</script>
<s:remote include="browserclass"/>
<script type="text/javascript">
window.onbeforeunload = function sayHello() {     
var wtname=Seam.Component.getInstance("browserclass").browser_close_method();    
}
</script>

---------------------------------------
And my java file is:
package org.domain.ezXXX.session;

import java.math.BigDecimal;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.jboss.seam.ScopeType;
import org.jboss.seam.annotations.In;
import org.jboss.seam.annotations.Name;
import org.jboss.seam.annotations.Scope;
import org.jboss.seam.annotations.remoting.WebRemote;

@Name("browserclass")
@Scope(ScopeType.SESSION)
public class BroserClass  {

@In(required=false)
AuthenticatorIF authenticator;
@WebRemote
public void browser_close_method(){
java.sql.Timestamp browserclosesqlDate = new java.sql.Timestamp(new java.util.Date().getTime());
System.out.println("---------------------this is getting login userid123---------------"+authenticator.getLoginuser_id());
System.out.println("----------------------this browser closing time-----------------------------"+browserclosesqlDate);
System.out.println("----------------------ok this is getting-----------------------"+authenticator.getPersist_login_history_id());
Connection connection = null;              
try {                   
java.sql.Timestamp browserclosetime = new java.sql.Timestamp(new java.util.Date().getTime());                        
// Load the JDBC driver         
String driverName = "oracle.jdbc.driver.OracleDriver";
Class.forName(driverName);        
// Create a connection to the database
String serverName = "localhost";
String portNumber = "1521";
String sid = "xxxxxx";
String url = "jdbcracle:thin" + serverName + ":" + portNumber + ":" + sid;
String username = "xxxxxx";
String password = "xxxxx";
connection = DriverManager.getConnection(url, username, password);
System.out.println("-----------------------this is connection established-------------"+connection);           
String updateendtime="UPDATE LOGIN_HISTORY SET END_TIME = ? where LOGIN_ID="+authenticator.getPersist_login_history_id();        
System.out.println("--------------this is query----------------"+updateendtime);
PreparedStatement prest = connection.prepareStatement(updateendtime);            
prest.setTimestamp(1, browserclosetime);       
prest.executeUpdate();
SimpleDateFormat format1 = new SimpleDateFormat("yyyy-MM-dd HH:mms");                    
String time1 = format1.format(authenticator.getTimestamp());              
String time2 = format1.format(browserclosetime);              
Date date1 = format1.parse(time1);
Date date2 = format1.parse(time2);
long difference = date2.getTime() - date1.getTime();
long diffMinutes2 = difference / (60 * 1000);
BigDecimal duration = BigDecimal.valueOf(diffMinutes2);
System.out.println("------------------this is the duration time----------"+duration);         
String updatespenttimerecord1="UPDATE LOGIN_HISTORY SET TIME_SPENT = ? where LOGIN_ID="+authenticator.getPersist_login_history_id();
System.out.println("--------------this is query1------"+updatespenttimerecord1);
prest = connection.prepareStatement(updatespenttimerecord1);         
prest.setBigDecimal(1, duration);
prest.executeUpdate();
prest.close();                                
} catch (Exception e) {
// Could not connect to the database
}finally{
try{              
connection.close();
}catch (Exception e) {
e.printStackTrace();
}
}

}

}