How do I safely detect if Session Scope exists in a service? - session

Question

I have service that is called both from Quartz (w/o a session scope), and interactively from a Web Flow (w/ a session scope).
When called from the Web Flow, there may be some optional flags set and I would like to safely check for them, IF THEY EXIST.
I'm using session scope because the functions I'm calling are far down a call chain, and passing the options, or scope all the way down will touch a lot of code.
I'm wondering if there is something like:
if(someObject.session?.myFlag)
where "session" refers to the session scope if called from a web flow, or null if called from Quartz.
Thanks in advance!

Answer 1

As you seem to already know, accessing the session scope from a service is not something to be encouraged, because the HTTP session should only be used within the web layer (GSPs, controllers, filters, etc.).
Now you didn't hear this from me, but you can access the current session from anywhere like this:
def session = org.codehaus.groovy.grails.web.util.WebUtils.
retrieveGrailsWebRequest().session
Once you have access to the session you can check if attributes exist or retrieve them using the usual HttpSession API.

Answer 2

I would go with a Filter and ThreadLocal approach.
Create a class with a static ThreadLocal variable which holds a reference to an instance of the class. This instance can then be referenced from anywhere from the executing thread and it will provide access to your variables and flags. This way you are not directly referencing to HTTP session API in your service.
Finally create a Filter in which you set up the ThreadLocal value before executing the rest of the chain. Remember to clear the state of the value after the thread is complete.
class MyExecutionContext {
private static ThreadLocal instance = new ThreadLocal<MyExecutionContext>()
private HttpSession session
private ServletRequest request
// set the state for current thread
// you can add request here too, if you want/need
public static void setContext(ServletRequest req, HttpSession s) {
stateInstance.set(new MyExecutionContext(req, s))
}
// get the state of current thread
public static getContext() {
return instance.get()
}
// clear the current state
public static void clearContext() {
stateInstance.remove()
}
// private constructor
private MyExecutionContext(ServletRequest req, HttpSession s) {
request = req
session = s
}
// now the actual methods to query any kinds of things you need
// from session (or request if you gave it in the constructor)
public String getSomething() {
(String) session?.getAttribute("somethingInSession")
}
public String getSomethingElse() {
(String) request?.getAttribute("somethingInRequest")
}
}
class ContextFilter extends Filter {
public void doFilter(...) {
try {
MyExecutionContext.setContext(request, request.getSession(false))
chain.doFilter(req, res)
} finally {
// make sure you clear the state
MyExecutionContext.clearContext()
}
}
}
// usage in your service
class YourService {
def method() {
if (MyExecutionContext?.context?.something) {
// value exists in session
}
}
}