I think that for every request , container will create 1 servlet instance and will spawn multiple threads for every request. But is it possible to create particular servlet instance for every request instead of creating threads.
This is not possible if the servlet container's implementation conforms to the Java servlet specification. (All major application servers do.) You can use class (static) variables and methods to maintain state between invocations but I don't see any compulsion to do this (aside from academic purposes).
I have a JSF2 controller/bean/view that is invoked the standard JSF way. Now I have a need to access this logic from a legacy part of the app that knows servlets and URL params only.
I thought of creating a "loader.xhtm" view that bridges the gap between non-jsf requester and the jsf part of the app. Loader will take URL params and make the necessary JSF post to backing bean. etc. One downside of this approach is - it's one extra client/server hop, a programmatic redirect. However it is simple to implement.
But is there a more clever way? I found someone who created servlet filter and explicitly created a FacesContext, started the lifecycle and the ViewRoot. Conceptually I see what is being done, but I don't know how to put it into practice. Has anyone interfaced with JSF lifecycle directly from a servlet? Do you have a sample?
Another mention of this concept.
When we create Servlet object on JSP page or in Java class, How it works internally ? How it will effect on performance ?
you should not call the servlet explicitly by the new keyword as we normally do.In the case of servlet, servlet container is responsible for instantiating the servlet.
For each servlet defined in the deployment descriptor of the Web application, the servlet container locates and loads a class of the type of the servlet. This can happen when the servlet engine itself is started, or later when a client request is actually delegated to the servlet.
There is only a single instance which answers all requests concurrently. This saves memory and allows a Servlet to easily manage persistent data.
When one create Servlet object on JSP page or in Java class,
You cannot expect to work it as a Servlet.
For More in details answer, Refer BalusC's answer here.
We can create an object of our servlet class. But because servlet operation depends on the servlet context, request, response, etc provided by the web container, there is nothing to be gained by creating one outside the container environment.
In one sentence - By doing so, we cannot expect to work as a servlet.
This question already has answers here:
How do servlets work? Instantiation, sessions, shared variables and multithreading
(8 answers)
Closed 6 years ago.
I need to know why the servlets are not thread safe ? And whats the reason that in Struts 2.0 framework controller servlet is thread safe ?
I need to know why the servlets are not thread safe ?
Servlet instances are inherently not thread safe because of the multi threaded nature of the Java programming language in general. The Java Virtual Machine supports executing the same code by multiple threads. This is a great performance benefit on machines which have multiple processors. This also allows the same code to be executed by multiple concurrent users without blocking each other.
Imagine a server with 4 processors wherein a normal servlet can handle 1000 requests per second. If that servlet were threadsafe, then the web application would act like as if it runs on a server with 1 processor wherein the servlet can handle only 250 requests per second (okay, it's not exactly like that, but you got the idea).
If you encounter threadsafety issues when using servlets, then it is your fault, not Java's nor Servlet's fault. You'd need to fix the servlet code as such that request or session scoped data is never assigned as an instance variable of the servlet. For an in-depth explanation, see also How do servlets work? Instantiation, sessions, shared variables and multithreading.
And whats the reason that in Struts 2.0 framework controller servlet is thread safe ?
It is not thread safe. You're confusing the Struts dispatcher servlet filter with Struts actions. The struts actions are re-created on every single request. So every single request has its own instance of the request scoped Struts action. The Struts dispatcher servlet filter does not store them as its own instance variable. Instead, it stores it as an attribute of the HttpServletRequest.
Servlets are normal java classes and thus are NOT Thread Safe.
But that said, Java classes are Thread safe if you do not have instance variables. Only instance variables need to synchronize. (Instance variable are variables declared in the class and not in within its methods.
Variables declared in the methods are thread safe as each thread creates it own Program Stack and function variables are allocated in the stack. This means that variable in a methods are created for each thread, hence does not have any thread sync issues associated.
Method variables are thread-safe, class variables are not.
There is a single instance of a servlet per servlet mapping; all instance properties are shared between all requests. Access to those properties must take that in to account.
Struts 2 actions (not "controller servlet", they're neither servlets nor controllers) are instantiated per-request. Action properties will be accessed only by a single request's thread.
Servlets are normally multi-threaded.
Servlet containers usually manage concurrent requests by creating a new Java thread for each request. The new thread is given an object reference to the requested servlet, which issues the response through the same thread. This is why it is important to design for concurrency when you write a servlet, because multiple requests may be handled by the same servlet instance.
The way that servlet containers handle servlet requests is implementation dependent; they may use a single servlet, they may use servlet pooling, it depends on the vendor's system architecture.
Struts 2 Action objects are instantiated for each request, so there are no thread-safety issues.
Servlet is not thread safe but we can make it as a thread safe by implementing that servlet class to SingleThreadModel
like the given below class definition but again the performance problem will be there so better option would be use synchronized portion
public class SurveyServlet extends HttpServlet
implements SingleThreadModel
{
servlet code here..
...
}
Servlet is not thread-safe by itself. You can make it thread-safe by making the service method synchronized.
you need to implement SingleThreadInterface to make it thread-safe.
I'm looking for an example showing how can I configure my CXF project, so that I can call a service method asynchronously; meaning my invocation in the client side doesn't block for the response and when the response is ready the logic will be done. I'm very thankful if somebody can help me
Best
The simplest way is to use #Oneway annotation on the server side. CXF will handle the request on the server side in a separate thread, so the client won't be blocked and will return immediately after receiving 200 response code and empty response body.
Of course in this case you cannot receive any response (by definition of request-only SOAP operation), which is not an option for you. Unfortunately you're need to implement this by hand using thread pool and future tasks. Fortunately this is very simple since Java 5, start by studying ExecutorService API.