Constructor Problem

[Farakh khan]

	String referer=req.getHeader("Referer");
	
	HttpSession session=req.getSession();
	String userID=(String)session.getAttribute("userID");	


	if(userID==null || userID.equals("") || userID.equalsIgnoreCase("null")){

	Login refer=new Login(referer);

	out.println(wp.pagePrint1()+
	"<br><br><center><span class=gull><b>Please Login</b></font></center>"+
	wp.pagePrint2());
	}
	else
	{
	
	}

My Login.java
=============

import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;


public class Login extends HttpServlet{

	Connection 	cnn=null;
	ResultSet 	 rs=null;

String referer="";

public Login(String refLink){
referer=refLink;
}

public void doPost(HttpServletRequest req, HttpServletResponse res)throws IOException, ServletException{

	res.setContentType("text/html");
	PrintWriter out=res.getWriter();

try{
	
	if ((cnn==null)||cnn.isClosed()){
	cnn=DB.getOracleConnection();
	}
		
String login=req.getParameter("login");
String pass=req.getParameter("password");

login=login.toLowerCase();	


	out.println("<link rel=stylesheet href=/css/khan.css type=text/css media=screen>");

	int type=0;
	String userID="",name="",dblogin="",dbPass="";
	String sql="select r_id,login,password from users_login where login=?";

	PreparedStatement ps=cnn.prepareStatement(sql);
	ps.setString(1, login);
	rs=ps.executeQuery();
	if(rs.next()){
		userID=rs.getString(1);
		dblogin=rs.getString(2);
		dbPass=rs.getString(3);
		}
	ps.close();

	WebPage wp=new WebPage();
	
		if(dblogin.equals(login) && !dbPass.equals(pass)){
		out.println("<br><br><center><font color=red size=3><b>Password is incorrect</b></font>"+
		"<br><br><input type=button value=Back class=khan onClick=\"javascript:history.back(-1)\">");
		}
			
		else if(dblogin.equals(login) && dbPass.equals(pass)){
			
		HttpSession session=req.getSession();
		session.setAttribute("userID",userID);		
		
		res.sendRedirect(referer);
			
		}
		else{
		out.println("<br><br><br><center><font color=red size=3><b>Login not Found</b></font>"+
		"<br><br><input type=button value=Back class=khan onClick=\"javascript:history.back(-1)\">");
		}
			
}catch(Exception ee){
	out.println("Login.java "+ee.toString()); 
	System.out.println("Login.java "+ee.toString());  
}

finally  {      
	try {        
		if ( rs  != null ) 	 rs.close();                
		if ( cnn != null )  	cnn.close();      

	} catch(SQLException ex) {          
	out.println("Login.java "+ex.toString()); 
	System.out.println("Login..java "+ex.toString());  
	}
}
}

}

I am trying to pass referer to my Login.java. The browser is displaying following error:

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Error instantiating servlet class Login
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
	org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
	org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
	org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	java.lang.Thread.run(Thread.java:619)

root cause

java.lang.InstantiationException: Login
	java.lang.Class.newInstance0(Class.java:340)
	java.lang.Class.newInstance(Class.java:308)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
	org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
	org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
	org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	java.lang.Thread.run(Thread.java:619)

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.18 logs.
Apache Tomcat/6.0.18

Thanks in anticipation

[avi sinha]

A servlet must have a no-arg constructor.

avi sinha

[Farakh khan]

avi sinha wrote:A servlet must have a no-arg constructor.

avi sinha

What you suggest in case of my problem. I mean I want to pass referer to Login.java

Thanks for your prompt reply

[avi sinha]

the way you are moving on here is not correct. you are treating your servlet class like a plain java class . a servlet will work only if it is being called by the container.

keep this in mind:

a servlet class becomes a servlet when the container calls the init(ServletConfig) method of the servlet by passing ServletConfig object .

avi sinha

[avi sinha]

also give some information about the servlet or jsp from where you are trying to call this servlet.

avi sinha

[Farakh khan]

avi sinha wrote:also give some information about the servlet or jsp from where you are trying to call this servlet.

avi sinha

I provided this in first part of my question

Thanks again

[Bear Bibeault]

Do not declare constructors for Servlets. Use the init() method to initialize a servlet.

Also, please indent your code properly.

Also, servlets should not have instance variables.

What are you actually trying to accomplish?

[avi sinha]

ok i got it .

create mapping in the DD for the second servlet .
for ex : /serv2

now your first servlet should be

  	String referer=req.getHeader("Referer");
	
	HttpSession session=req.getSession();
	String userID=(String)session.getAttribute("userID");	


	if(userID==null || userID.equals("") || userID.equalsIgnoreCase("null")){

        // set attribute for referer value
        request.setAttribute("referer",referer);

        // forward the request to the second servlet
	RequestDispatcher  view =request.getRequestDispatcher("/serv2");

	}
	else
	{
	
	}

Second Servlet :

// getting referer value 
String referer = request.getAttribute("referer");

  

but i think you will have to change a lot of code. its better to start from scratch for these two servlets and you should keep your business logic outside the servlet.
create a java file for database related works and call it from the servlet

avi sinha

[Farakh khan]

Appreciated!!

Thanks from the bottom of my heart

[avi sinha]

Farakh khan wrote:Appreciated!!

Thanks from the bottom of my heart

you're welcome

avi sinha

[Farakh khan]

String referer=req.getHeader("Referer");

Error:
incompatible type
found	:	java.lang.Object
Required:	java.lang.String

what I did is:

String referer=req.getHeader("Referer");   
       
    	HttpSession session=req.getSession();   
    	String userID=(String)session.getAttribute("userID");        
  
    	if(userID==null || userID.equals("") || userID.equalsIgnoreCase("null")){   
  
        // attribute set for referer value   
        req.setAttribute("referer",referer);   
        
	out.println(wp.pagePrint1()+
	"<br><br><center><span class=gull><b>Please Login</b></font></center>"+	
	wp.pagePrint2());
	}
	else
	{
	
	}

//Servlet-2
String referer = req.getAttribute("referer");
//DB check true then

res.sendRedirect(referer);

but this will display the referer in iFrame and will not break the frame. The problem will still exist

Best Regards

[avi sinha]

sorry a cast is needed here my mistake.

write

String referer=(String) request.getAttribute("referer");
or you can directly use 
String referer=request.getHeader("referer");    

avi sinha

[Farakh khan]

avi sinha wrote:sorry a cast is needed here my mistake.

write

String referer=(String) request.getAttribute("referer");
or you can directly use 
String referer=request.getHeader("referer");    

avi sinha

I am thankful for your favorable replies

	String referer=req.getHeader("Referer");   
       
    	HttpSession session=req.getSession();   
    	String userID=(String)session.getAttribute("userID");      
  
  
    	if(userID==null || userID.equals("") || userID.equalsIgnoreCase("null")){   
         	
        req.setAttribute("referer",referer);   
          
	out.println(referer);

OUTPUT:
=======
null


My Servlet-2
==============

String referer= (String) req.getAttribute("referer");

out.println("referer="+referer);

OUTPUT:
=======
referer=null


Best Regards

[avi sinha]

please post the complete code of your servlets then may be we can identify what the problem is ??

avi sinha

[Charles 'King]

The referer isnt a mandatory field and usually only available if the client sends it - if the request originates from a link or resource. Direct requests do not contain a referrer. The referer field can be stripped from the HTTP header by a proxy or firewall. Session and request scoped attributes are a better solution.

[Bear Bibeault]

Even after all these posts, I still have no good idea what is trying to be accomplished. And yes, relying upon the unreliable "referer" probably dooms it to failure.

Perhaps the actual goal might be posted at some point?

[Farakh khan]

Thankful to all professionals who helped me and beared me

Actually the origional problem is this that I have an iFrame in all pages of the website that have source (/servlet/User). This servlet checks that if the user logged in successfully then displaying control panel else displaying html static contents to log in with action /servlet/Login

Login.java matches the login/pass from db and if ok then redirect to /servlet/User

Now the problem is this that when am redirecting any file then it displayed in iFrame instead of main page and I am unable to redirect my user from where they are comming

Thanks again

[Bear Bibeault]

So what does all that have to do with the referer? It's like saying "My car won't start, so I decide to trim this tree over here."

If you want to make something happen in the parent, you'll need to include script in your iframe response to trigger behavior in the parent.

[Farakh khan]

Bear Bibeault wrote:So what does all that have to do with the referer? It's like saying "My car won't start, so I decide to trim this tree over here."

If you want to make something happen in the parent, you'll need to include script in your iframe response to trigger behavior in the parent.

Thanks for your reply

You mean javascript? or something in java servlet?

Best Regards

[Bear Bibeault]

JavaScript. There is nothing you can do on the server to affect the behavior of anything outside of the window/iframe that the response is being sent to.

[Farakh khan]

Bear Bibeault wrote:JavaScript. There is nothing you can do on the server to affect the behavior of anything outside of the window/iframe that the response is being sent to.

Thanks for your favorable reply

I tried a lot java scripts but as I am not good in Javascripts, unable to write. Can you help me to guide little bit

Thanks again & best regards

[Farakh khan]

Bear Bibeault wrote:JavaScript. There is nothing you can do on the server to affect the behavior of anything outside of the window/iframe that the response is being sent to.

I posted this problem https://coderanch.com/t/474517/Servlets/java/Java-with-Java-Script for getting any help regarding javascript that is in my mind but yet not get any response

Thanks again & best regards