Sorry friends if this question is very easy but i am confuse i unable to find out solution.
As we all know in spring MVC framework we create controller which will handle multiple request from same page using #requestmapping annotation.
but same thing i want to do in servlet how can i do ?
Suppose i have a jsp which which will contain a jqgrid,and two forms i want to use only one servlet to load the data into jqgrid and that servlet only will handle request from both the form . Since we have only doGet and doPost in servlet how one servlet fulfill all three request. Hope you understand my question if you have and link where i get sample or and tutorial link plz reply me
Well, the only easy way to do this would be to use a request parameter to control how the processing happens.
In a very basic example, you may have something like a requestType value that gets passed as either part of the query string or the request body. You would assign values of 1-3 (or 0-2) with each value indicating a different type of request. Your servlet would then parse the request accordingly.
This actually is how the DispatcherServlet in SpringMVC works. There's only one servlet class instance and when a request comes in, it examines the query string along with other parts of the request to determine which controller should handle the request.
Related
Can I create a response object in java without creating a Servlet? I have a regular java class right now called Menu. It contains not only my menus for my application but it also contains my CRUD functionality that is tied to the database. Which works fine on the console. What I want to do now is to display the result set on a webpage. I want to use AJAX (no frameworks like jQuery etc.) to capture the information from the result set. In the Menu class I am going to convert the extracted information into a Json string with Jackson databinding (object mapper). I want to use a PrintWriter to send this information back to AJAX. I am assuming I need a response object. Do I have to re-write my Menu class as a Servlet or is there another way to accomplish this?
For querying data from server you need to have a resource which has
http url
can accept a form of request as input
can give response based on business logic in menu crud class.
For this querying as you said you can do with ajax call to this servlet with specified url pattern from your frontend webpage.
In short servlet will be essential. It can handle all http method types like get post and so on.
So you can map your crud methods to your servlet methods
eg :
doGet - querying items.
doPost- creation of item.
doDelete- delete an item.
and so on.
further you will call your crud methods from these servlet do* methods.
for example refer: https://www.geeksforgeeks.org/servlet-crud-operation-with-example/
Hope this helps.
I've seen plenty of servlet filters in my time for doing all kinds of things but always on REQUEST never anything else. Does anyone have any use cases or examples of why it might be useful to write a servlet filter for another dispatcherType, other than REQUEST?
The DispatcherTypes as in javax.servlet package.
public enum DispatcherType {
FORWARD, INCLUDE, REQUEST, ASYNC, ERROR
}
Well the names are rather self-explaining. The REQUEST is indeed the most often used one and it's applied on the incoming request chain. Here is when you may need to use the others (because the REQUEST only dispatched filters will not be applied):
FORWARD - if you want to filter request/response when one servlet forwards the request to another servlet. Often this is used when a servlet forwards to a JSP page.
INCLUDE - if you want to filter request/response when one servlet calls another servlet in order to include it's response in the own response. Often this is used when a JSP page includes JSP page.
ASYNC - This is something I personally never used but AFAIK it's needed to be able to filter the asynchronous requests introduced in Servlet 3 spec
ERROR - if you want to filter request/response when the servlet call results in error.
See https://sling.apache.org/documentation/the-sling-engine/filters.html#filter-chains for some more details.
is their a neat way to pass a model to jsp, render the jsp and return the html as string using Spring. The html is then used in an e-mail that is fired off programmitcally, I do not want to use freemarker, but maybe I should ?
The url being requested is part of the same app.
I want one of my service layer classes to be able to call a view and use the html as a String.
You can call requestDispatcher.include(request, response) method.
You will need to implement the request and response objects. The request object will provide all information to the dispatcher which page should be rendered, the response object you will pass to the call will then capture the result to a string (using e.g. a StringBuilder).
See e.g. this tutorial for more info.
I'm guessing a servlet filter will do the trick? Not really a Spring solution, but easy enough to do.
Also this answer seems relevant, although it is DWR that you may not necessarily want to use in this instance.
You can use Velocity to create an email template:
String text = VelocityEngineUtils.mergeTemplateIntoString(
velocityEngine, "emailTemplate.vm", model);
There is a complete chapter in the Spring reference docs of how Spring can be used to send emails of various types.
I'was debugging a client-side AJAX problem that is making request to servlet. But the bug turned out to be at server side. You can refer to my original question here. From the discussion with more experienced people, I found out that servlet is using request.getAttribute() method to retrieve parameters from the request instead of getParameter(). So I thought to open a new question to clear my doubt.
Now my question is: If I use GET method to pass parameters from client to server, getAttribute() in Servlet works fine and I can get param values. But when I use POST method, getAttribute() returns null. Why does it work for GET and not for POST?
You should always use getParameter, when attribute come from GET or POST method. And use getAttribute when request is forwarded from another servlet/jsp. Such as :
ServletA:
request.setAttribute("test","value")
request.getRequestDispatcher("/ServletB").forward(request, response)
ServletB:
request.getAttribute("test") <-- you can get test attribute by using getAttribute
Now my question is: If I use GET method to pass parameters from client to server, getAttribute() in Servlet works fine and I can get param values. But when I use POST method, getAttribute() returns null. Why does it work for GET and not for POST?
Complete nonsense. You're apparently working on an existing project which has a lot of other existing servlets and filters. My cents that there's another filter in the request-response chain which maps request parameters to request attribtues for some unobvious reason.
Please create a blank playground project and create a playground servlet to familarize yourself better with servlets without all that noise in existing projects.
See also:
Our Servlets wiki page
I've one spring controller which is setting some values to request and shows a jsp page. For the view part we use tiles. The result page has 3 parts, header , content and footer jsp's.
This header jsp use a java file and i want to access the attributes created by the first spring controller from this file. Is there any way to do that without using session?
When I tried request.getAttribute, it gives null. I think it's because it's not an immediate file after the request values setting.
As long as everything runs in the same request and the controller code is executed before the view part, setAttribute() should work. To debug issues like that, use a Filter which dumps the request URL and attributes to the console or the log.
If those calls are in different requests, you have two options: The session and a Spring bean (use a session bean or your own implementation). I prefer beans since they are type safe and they allow me to separate my code from the Servlet API which is complex to test.
You'll really need to put some code to get a code answer but unless you're using JSP scriptlets I'm guessing this is a Java bean that you're using in the header. This of course cannot access the request (hence the session) nor should it really. What you probably want to do is convert it to a tag library if you want it to have access to the request/session.