sign-up form validations in java

Question

i have a signup page connected to sql database.now i want to have validations in signup page like firstname,lastname,username etc can not be empty using java how can i do that My code is

String fname=Fname.getText();
    String lname=Lname.getText();
    String uname=Uname.getText();
    String emailid=Emailid.getText();
    String contact=Contact.getText();
    String pass=String.valueOf(Pass.getPassword());
    Connection conn=null;
    PreparedStatement pstmt=null;
    try
    {
        Class.forName("com.mysql.jdbc.Driver");
        conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/zeeshan","root","sHaNi97426");
        pstmt=conn.prepareStatement("Insert into signup1 values(?,?,?,?,?,?)");
        pstmt.setString(1,fname);
        pstmt.setString(2,lname);
        pstmt.setString(3,uname);
        pstmt.setString(4,emailid);
        pstmt.setString(5,contact);
        pstmt.setString(6,pass);
        int i=pstmt.executeUpdate();
        if(i>0)
        {
            JOptionPane.showMessageDialog(null,"Successfully Registered");
        }
        else
        {
            JOptionPane.showMessageDialog(null,"Error");
        }
    }
    catch(Exception e)
    {
        JOptionPane.showMessageDialog(null,e);
    } 

Answer 1

First your question is not direct. Validation occurs before database query. You should not proceed to database Connetction or making any query.

What should you do:

public static boolean nullOrEmpty(String value) {
        return value == null || value.trim().equals("") ? true : false;
    }
public void yourMethod(){
    try{
        //YourCode Here
        String fname=Fname.getText();

        if(nullOrEmpty(fname)){
            new throw ValidationException("First name should not be null.");
        }
        //YourCode Here
   }catch(ValidationException e){
     System.err.println("Exception:"+e.getMessage());
   }
}

Check for every string to validate.

Answer 2

that should not be hard, you can do it with simple if and else like below

   if(fname != null && fname.isEmpty()){
                throw new Exception(fname+" cannot be empty");
            }else if(lname != null && lname.isEmpty()){
                throw new Exception(fname+" cannot be empty");
            }
   .....

as a recommendation you should abstract validation and database access objects . see example of MVC here

Answer 3

You may do it just by downloading a jar named org.apache.commons.lang Stringutils Class Reference

Sample Code

    StringUtils.isBlank(null)      = true
    StringUtils.isBlank("")        = true  
    StringUtils.isBlank(" ")       = true  
    StringUtils.isBlank("bob")     = false  
    StringUtils.isBlank("  bob  ") = false

or

  StringUtils.isEmpty(obj_String); // Another method to check either null or "";

Answer 4

To check if a String is empty you can use the method .isEmpty() . You'll probably want to use .trim() first, as this removes all the whitespaces at the beginning and ending of the String. For more options check out the full documentationhere .