How to verify if user already exists in MySQL database using JSP?

Question

Hi, I am trying to create a website that allows users to register and then login. All regsitration details are stored in a MySQL table and I am attempting to have a java bean check that a new user does not already exist by looking up the username. However, I cannot get this to work, the bean is allowing anyone through. I believe there may be a problem with my while loop as the bean checks through the stored usernames in the database. Any suggestions appreciated thanks. See my code below:[
code]package foo;
import java.sql.*;
import java.util.*;
public class FormBean {
     private String firstName;
     private String lastName;
     private String email;
     private String userName;
     private String password1;
     private String password2;
     private Hashtable errors;
     public boolean validate() {
          boolean allOk=true;
          if (firstName.equals("")) {
               errors.put("firstName","Please enter your first name");
               firstName="";
               allOk=false;
          if (lastName.equals("")) {
               errors.put("lastName","Please enter your last name");
               lastName="";
               allOk=false;
          if (email.equals("") || (email.indexOf('@') == -1)) {
               errors.put("email","Please enter a valid email address");
               email="";
               allOk=false;
          if (userName.equals("")) {
               errors.put("userName","Please enter a username");
               userName="";
               allOk=false;
try {
          String database = "******hidden******";
          Class.forName("com.mysql.jdbc.Driver");
          Connection conn = DriverManager.getConnection(database,"********hidden*******");
          Statement stat = conn.createStatement();
          String query="SELECT u_name FROM users;";
          String DbUserName="";
          ResultSet rst=stat.executeQuery(query);
          while(rst.next()) {
DbUserName=rst.getString("u_name");
if (userName.equals(DbUserName)) {
allOk=false;
errors.put("userName","User name already exists, please choose another");
userName="";
conn.close();
break;
} catch (Exception ex) {
ex.printStackTrace();
          if (password1.equals("") ) {
               errors.put("password1","Please enter a valid password");
               password1="";
               allOk=false;
          if (!password1.equals("") && (password2.equals("") || !password1.equals(password2))) {
               errors.put("password2","Please confirm your password");
               password2="";
               allOk=false;
return allOk;
     public String getErrorMsg(String s) {
          String errorMsg =(String)errors.get(s.trim());
     return (errorMsg == null) ? "":errorMsg;
     public FormBean() {
     firstName="";
     lastName="";
     email="";
userName="";
     password1="";
     password2="";
     errors = new Hashtable();
     public String getFirstName() {
          return firstName;
     public String getLastName() {
          return lastName;
     public String getEmail() {
          return email;
     public String getUserName() {
          return userName;
     public String getPassword1() {
          return password1;
     public String getPassword2() {
          return password2;
     public void setFirstName(String fname) {
          firstName =fname;
     public void setLastName(String lname) {
          lastName =lname;
     public void setEmail(String eml) {
          email=eml;
     public void setUserName(String u) {
          userName=u;
     public void setPassword1(String p1) {
          password1=p1;
     public void setPassword2(String p2) {
          password2=p2;
     public void setErrors(String key, String msg) {     
          errors.put(key,msg);

Answer 1

Hmm, tried that and now have more build errors in the finally section.
init:
deps-jar:
Compiling 1 source file to C:\resin-2.1.11\doc\examples\basic\WEB-INF\classes\JavaLibrary1\build\classes
C:\resin-2.1.11\doc\examples\basic\WEB-INF\classes\JavaLibrary1\test\FormBean.java:57: cannot resolve symbol
symbol  : variable rst
location: class foo.FormBean
            if (rst != null) rst.close();
C:\resin-2.1.11\doc\examples\basic\WEB-INF\classes\JavaLibrary1\test\FormBean.java:57: cannot resolve symbol
symbol  : variable rst
location: class foo.FormBean
            if (rst != null) rst.close();
C:\resin-2.1.11\doc\examples\basic\WEB-INF\classes\JavaLibrary1\test\FormBean.java:58: cannot resolve symbol
symbol  : variable stat
location: class foo.FormBean
            if (stat != null) stat.close();
C:\resin-2.1.11\doc\examples\basic\WEB-INF\classes\JavaLibrary1\test\FormBean.java:58: cannot resolve symbol
symbol  : variable stat
location: class foo.FormBean
            if (stat != null) stat.close();
C:\resin-2.1.11\doc\examples\basic\WEB-INF\classes\JavaLibrary1\test\FormBean.java:59: cannot resolve symbol
symbol  : variable conn
location: class foo.FormBean
            if (conn != null)  conn.close();
C:\resin-2.1.11\doc\examples\basic\WEB-INF\classes\JavaLibrary1\test\FormBean.java:59: cannot resolve symbol
symbol  : variable conn
location: class foo.FormBean
            if (con != null)  conn.close();
6 errors
BUILD FAILED (total time: 1 second)Just for a quick test, I deleted the sql exception and finally code and replaced it with a regular exception just to see what happened and got no build errors, however when I run the form I am getting an sql exception from the prepared statement, parameter out of range (1 > 0). I tried reading into prepared statements, and although I now understand their basics, I still have no idea why I'm getting this error?