Re: java bean program

From:
Lew <noone@lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Thu, 04 Sep 2008 09:33:28 -0400
Message-ID:
<C56dnSXyX840fiLVnZ2dnUVZ_u6dnZ2d@comcast.com>
mpriya2050@gmail.com wrote:

Error in java bean program...
when i [sic] run the above program i [sic] got a following error..please give the
suggestion to run the program ...... some times i [sic] got an empty page
also...

Java Bean program

package test;
import java.util.*;
import java.io.Serializable;
import java.sql.*;
import java.io.*;
public class FindAuthor implements Serializable {
    public String url,authorName,driverName,authorId;


Members should not be public, but private with setters and getters. I don't
think the jsp:useBean mechanism can use 'public' variables, but I have never
tried so I can't be sure.

    public Vector result;


Don't use Vector. Use List and ArrayList.

    public void setUrl(String url)
    {
        if(url!=null)
            this.url=url;


This 'if' test has no net effect. If you pass 'null' to the method,
'this.url' will be null either way. Notice that your error was a
NullPointerException. Coincidence?

    }
     public void setAuthorId(String authorId)
     {
         if(authorId!=null)
             this.authorId=authorId;
     }
      public void setDriverName(String driverName)

      {
          if(driverName!=null)
          this.driverName = driverName;
      }


This is the value that got a NullPointerException. Coincidence?

BTW, you should enclose 'if' (and other control statement) bodies in braces,
not leave them hanging naked like that.

      public String getAuthorId()
      {
          return(this.authorId);
      }
      public Vector getResult()
      {
          Vector v=new Vector();
          try
          {
           Class.forName(driverName);


You must not have set 'driverName'.

          }
          catch(ClassNotFoundException e)
          {
              System.out.println(e);


Never use 'System.out.println()' for error reporting in web apps.

          }
          try
          {
           Connection

con=DriverManager.getConnection(url,"sa","sa");
           PreparedStatement

st=con.prepareStatement("select * from jeas1 where

auid=?");
           st.setString(1,authorId);
           ResultSet rs=st.executeQuery();
              if(rs.next())
              {
                  v.addElement("auname");
                  v.addElement("address");
                  v.addElement("city");
                  v.addElement("state");
                  v.addElement("zip");
              }
      }
      catch(SQLException ex)
      {
          ex.printStackTrace();
      }
            this.result = v;
            return result;

      }
}

Getauthor name.jsp(jsp program)

<html>
<%@ page import="java.util.*" %>
<%@ page import="test.FindAuthor" %>

<jsp:useBean id="FA" scope="application"

class="test.FindAuthor" />
<jsp:setProperty name="FA" property="*" />

        <body>
        <%


Don't use scriptlet in the JSP directly. Use only tags and HTML content.

        Vector v =(Vector)FA.getResult();
        Enumeration enum1=v.elements();


Both 'Vector' and 'Enumeration' have been obsolete since 1998.

        while(enum1.hasMoreElements())
        {
        out.println("Author Name:"+enum1.nextElement());
        %>
        <br>
        <%
        out.println("Address:" +enum1.nextElement());
        %>
        <br>
        <%
        out.println("City:"+enum1.nextElement());
        %>
        <br>
        <%
        out.println("State:"+enum1.nextElement());
        %>
        <br>
        <%
        out.println("ZIP:"+enum1.nextElement());
        }
        %>
    </body>
</html>

Html program

<html>
    <body>
    <form action="/WebApplication12/Getauthorname.jsp"

method="get">
        AuthorId:<input type="text" name="auid"><br>
        URL :<input type="text" name="url"><br>
        DriverName:<input type="text" name="DN"><br>


Since 'DN' is the name of the variable in the JSP, you don't set the
'driverName' property at all, thus it remains 'null'.

        <input type="submit" value="Submit">
    </form>
</body>
</html>

....

root cause

java.lang.NullPointerException
    java.lang.Class.forName0(Native Method)
    java.lang.Class.forName(Class.java:169)
    test.FindAuthor.getResult(FindAuthor.java:35)

You also should not set the driver on EVERY call to the db. You only need to
set it once in the program run. Of course, in this case you never set the driver.

--
Lew

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