How to implement a "task monitor" with JSF - jsf

Question

I need to execute some tasks in the server and show status with JSF (primefaces).
Below I'm describing my last try:
default.xhtml
<p:commandButton
value="execute"
action="#{controller.init()}" /> <!-- initialize and validate data and call task1() -->
<p:fieldset id="messages" legend="Status:">
<ul>
<li>
<h:panelGrid columns="2" id="msg1" styleClass="#{controller.status1}">
<p:outputLabel value="#{controller.msg1}" />
<span class="#{controller.classToIconClass(controller.status1)}"></span>
</h:panelGrid>
</li>
<li>
<h:panelGrid columns="2" id="msg2" styleClass="#{controller.status2}">
<p:outputLabel value="#{controller.msg2}" />
<span class="#{controller.classToIconClass(controller.status2)}"></span>
</h:panelGrid>
</li>
...
<p:remoteCommand name="task1" action="#{controller.task1()}" update="messages" />
<p:remoteCommand name="task2" action="#{controller.task2()}" update="messages" />
Each step is like this: (Controller.java)
#SessionScoped
...
public void task1() {
if(stopExecution) return;
long returnCode = -1;
String errorMessage = "An error occurred in the task1 execution.";
try {
returnCode = execute(comandString);
} catch (Exception e) {
Logger.getLogger(getClass()).error(errorMessage, e);
returnCode = -1;
stopExecution = true;
}
if(returnCode != 0 && returnCode != 4) {
msg1 = errorMessage;
status1 = "error";
stopExecution = true;
return;
} else {
msg1 = "Task1 is finished.";
status1 = "successful";
}
msg2 = "Running task2...";
status2 = "running";
RequestContext requestContext = RequestContext.getCurrentInstance();
requestContext.execute("task2();"); // Calls next step
}
// Everything is like task1() and always call next task at the end:
public void task2() {...}
public void task3() {...}
public void task4() {...}
public void finish() {...}
This way everything runs fine, but the users sometimes refresh the page and the execution chain brokes.
Is there a way to do what a I want to do and surviving a page refresh?
PS:
I also tried to execute task by task with RequestContext.getCurrentInstance().update("form:messages"); between them, but the page only updates at the end of the last task.
EDIT:
As Michele and Xtreme Biker said, I do it in a separate thread:
Controller.java
#SessionScoped
...
RequestContext requestContext;
Callable<Long> task1 = new Callable<Long>() {
#Override
public Long call() throws Exception {
long returnCode = -1;
String errorMessage = "An error occurred in the task1 execution.";
returnCode = execute(comandString);
if(returnCode != 0 && returnCode != 4) {
msg1 = errorMessage;
status1 = "error";
return returnCode;
} else {
msg1 = "Task1 is finished.";
status1 = "successful";
msg2 = "Running task2...";
status2 = "running";
}
requestContext.update("form:messages");
return returnCode;
}
};
public void init() {
requestContext = RequestContext.getCurrentInstance();
List<Future<Long>> tasks = new ArrayList<Future<Long>>();
ExecutorService executor = Executors.newSingleThreadExecutor();
tasks.add(executor.submit(this.task1));
tasks.add(executor.submit(this.task2));
tasks.add(executor.submit(this.task3));
tasks.add(executor.submit(this.task4));
tasks.add(executor.submit(this.finish));
executor.shutdown();
}
All tasks run even if I do a page refresh, good.
But the view doesn't update.
I think that requestContext.update("form:messages"); is in the wrong place.
But if a get RequestContext.getCurrentInstance() from inside the Callable.call, I get a NullPointerException, because I'm not in the JSF life cycle.
What's wrong?
Thanks in advice.