Java. Getting IOException after trying to print on JSP page using simple scheduler(Timer, TimerTask). Need help

Question

i'm trying to make simple scheduler using Timer and TimerTask classses see the code below, inside of the task i just want to print "Hello, World!" on the page, but it throws IOException: Stream closed. Please help!

JSP page code:

<% Test t = new Test(out);%>

Test class code:

public class Test {
    public Test(JspWriter out){
        Timer timer = new Timer();
        LpdbTask lTask = new LpdbTask();
        lTask.out = out;
        timer.scheduleAtFixedRate(lTask, 1000*5, 1000*60);
    }
}

LpdbTask code:

public class LpdbTask extends TimerTask{
    public JspWriter out;
    public void run(){
        try {
            out.println("Hello, World!");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Error:

java.io.IOException: Stream closed
    at org.apache.jasper.runtime.JspWriterImpl.ensureOpen(JspWriterImpl.java:204)
    at org.apache.jasper.runtime.JspWriterImpl.write(JspWriterImpl.java:312)
    at org.apache.jasper.runtime.JspWriterImpl.write(JspWriterImpl.java:342)
    at org.apache.jasper.runtime.JspWriterImpl.print(JspWriterImpl.java:468)
    at org.apache.jasper.runtime.JspWriterImpl.println(JspWriterImpl.java:576)
    at scheduler.LpdbTask.run(LpdbTask.java:14)
    at java.util.TimerThread.mainLoop(Unknown Source)
    at java.util.TimerThread.run(Unknown Source)

Answer 1

The Java code for a JSP all runs before the user sees your page at all. By the time the Timer fires, the JSP has already been sent to the browser and rendered; the stream is indeed closed because it's no longer needed. This just isn't something that's possible to do.

If you want time-dependent things to happen on your page in the user's browser, then you have to do it in Javascript, Flash, or a Java Applet; all of these run on the desktop, as opposed to your JSP, which runs on the server.