Threads in JSP

Hello Friends

I am developing one project which use only jsp and no beans.

I have to check the database for change in value. If there is a change in the values the page will have to be reloaded.

I prefer to use threds for this background process. But I dont know how to implement threads in jsp. If anybody know please help me via some sample codings.

Thanks for your interest.

By

Sadiq

That shouldn't be too much of an issue. Perhaps if you write your thread class somewhere (extend thread) then just create an instance of that thread in the JSP.

I tried creating threaded class seperately as a java program. But it creates one error.

My code is as follows
--------------------------------------------------------------------------------------------------------------------
package dbs;

import java.io.*;
import java.lang.*;
import java.sql.*;

public class Change implements Runnable
{
public void run()
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con;
Statement st=con.createStatement();
String sql="select * from temp";
ResultSet rs;
try
{
con=DriverManager.getConnection("jdbc:odbc:vr");
rs=st.executeQuery(sql);
if(rs.next())
{
if(rs.getString(1)=="ok")
{
st.executeUpdate("Update temp set id='cancel'");
response.sendRedirect("test1.jsp");
}
}
}
catch(SQLException e1)
{
// System.out.println(e1);
}
catch(InterruptedException e2)
{
}
}
}

--------------------------------------------------------------------------------------------------------------------

When compiling it produces the following error
--------------------------------------------------------------------------------------------------------------------
D:\SADIQ\JSP\DBS>javac Change.java
Change.java:25: cannot resolve symbol
symbol : variable response
location: class dbs.Change
response.sendRedirect("test1.jsp");
^
1 error

--------------------------------------------------------------------------------------------------------------------

Bur I have to redirect the page if the value of the field changes...

Do you know why this error occurs and the way to avoid this..


Thanks for your interest

By

Sadiq

I tried creating threaded class seperately as a java program. But it creates one error.

My code is as follows
--------------------------------------------------------------------------------------------------------------------
package dbs;

import java.io.*;
import java.lang.*;
import java.sql.*;

public class Change implements Runnable
{
public void run()
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con;
Statement st=con.createStatement();
String sql="select * from temp";
ResultSet rs;
try
{
con=DriverManager.getConnection("jdbc:odbc:vr");
rs=st.executeQuery(sql);
if(rs.next())
{
if(rs.getString(1)=="ok")
{
st.executeUpdate("Update temp set id='cancel'");
response.sendRedirect("test1.jsp");
}
}
}
catch(SQLException e1)
{
// System.out.println(e1);
}
catch(InterruptedException e2)
{
}
}
}

--------------------------------------------------------------------------------------------------------------------

When compiling it produces the following error
--------------------------------------------------------------------------------------------------------------------
D:\SADIQ\JSP\DBS>javac Change.java
Change.java:25: cannot resolve symbol
symbol : variable response
location: class dbs.Change
response.sendRedirect("test1.jsp");
^
1 error

--------------------------------------------------------------------------------------------------------------------

Bur I have to redirect the page if the value of the field changes...

Do you know why this error occurs and the way to avoid this..


Thanks for your interest

By

Sadiq

That will not work! The response object is available in the JSP not in the thread.

wont work too. When making comparisons use the .equals method. == compares equality of memory locations which is not what you want to compare here.

The thread class and the JSP must be separate files. Is this the thread that is supposed to be checking for changes in the database?

Ok thanks for your answer

If there is any other alternative way to do this page redirection when the value of the field changes.. I need to check the database continuously while the page is running..

I am in urgent need to complete the project within a week..

Tahanks in advance..

By

Sadiq

Ok thanks for your answer

If there is any other alternative way to do this page redirection when the value of the field changes.. I need to check the database continuously while the page is running..

I am in urgent need to complete the project within a week..

Tahanks in advance..

By

Sadiq

How is the data loaded into the database? The best approach would be to refresh that JSP soon after the data is inserted into the database.

Actually my project is virtual class room

In which staff could be logged in one system and student could be logged in another system.

When student post query, the query and its response from the staff are displayed in seperate window. Whenever the response is recieved a flag field is changed in the databaase.

Whenever the flag changes the window have to be reloaded to display the current data.

So I need the codings...

Thanks for your response

By

Sadiq

hi friend..

if you know about " TimerTask " in java using this method you can check the
DB for a time of period

Hello Friends

I am developing one project which use only jsp and no beans.

I have to check the database for change in value. If there is a change in the values the page will have to be reloaded.

I prefer to use threds for this background process. But I dont know how to implement threads in jsp. If anybody know please help me via some sample codings.

Thanks for your interest.

By

Sadiq

u better to use AJAX ....