Tag Archives: spring mvc

Spring Book – Chapter 14 – Spring MVC and Spring Web Flow

Disclaimer: The chapter have been written with figures sourced from various on-line materials. I haven’t been bale to attribute these figures with source. Really apologize for this. In case anyone has any issues in me using the figures and content, please drop an email to me at tomcyjohnatgmail.com. I will make sure that the details are either attributed or the image/content removed from my blog post. Thanks in advance.

Spring Framework’s web application support is through two sub-projects namely Spring MVC and Spring Web Flow.

Spring Framework has its own MVC based web application framework in the form of Spring MVC. They conceived and developed its web framework to address some of the deficiencies and poor design consideration in other popular framework available in the market. One of the main deficiencies identified was the lack of separation of concerns like proper separation between the presentation and request handling layer and between request handling layer and the model layer. Similar to Struts, Spring MVC is a request-based web application framework. Spring MVC makes sure that all the interfaces are tightly coupled with the core Servlet API’s rather than the Spring API’s.

Spring Web Flow is one of the sub-project which aims at providing the infrastructure for developing and running web application. It tries to aid web application developers in defining appropriate navigation rules, manage navigation and conversational state as well as facilitating high level reuse and modularization.

Spring MVC as well as Spring Web Flow is a very huge topic to cover in one Chapter. There are books written only on these topics. I would cover some basic concepts of both Spring MVC and Spring Web Flow in this Chapter. The first part of this Chapter makes you walk through Spring MVC and the second part of this Chapter walks through Spring Web Flow. I will try to cover basic detail of both frameworks so that you will get a heads up on these and can start off developing using these.

Spring MVC

Spring MVC allows you to build extensible, robust and loosely coupled MVC-based web application. With the use of the famous Model-View-Controller pattern, it inherently brings separation of the various layers in a typical web application namely business, presentation and navigation in a clear way.

We have covered MVC pattern in detail in this book, but just to refresh your mind, the responsibility of Model is to encapsulate the application data, the responsibility of View is to render the response to the user with the help from the Model object and the responsibility of Controller is to receive the request from the end user and transfer it to the back-end services which will populate the Model objects and sends the view object to the user.

Spring MVC's fit in an enterprise application containing other layers

Figure 14-1. Spring MVC’s fit in an enterprise application containing other layers

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Post-Redirect-Get Pattern in Spring MVC

Do you have back button issues? Duplicate form submissions when you click back button? I think you have landed in right blog. With respect to Spring MVC, the blog even tries to give the complete solution by which to handle it.

One of the easiest way by which you can handle these issues is by implementing Post-Redirect-Get (PRG) pattern.

What is Post-Redirect-Get Pattern?

Post/Redirect/Get (PRG) is a web development design pattern that prevents duplicate form submission. When a web form is submitted to a server through an HTTP POST request, a web user that attempts to refresh the server response in certain user agents can cause the contents of the original HTTP POST request to be resubmitted, possibly causing undesired results, such as a duplicate web purchase.

To avoid this problem, PRG pattern is used, instead of returning a web page directly, the POST operation returns a redirection command. The HTTP 1.1 specification introduced the HTTP 303 response code to ensure that in this situation, the web user’s browser can safely refresh the server response without causing the initial HTTP POST request to be resubmitted.

I don’t want to re-invent the wheel, so i would just let the reader go through the Wikipedia which has explained it beautifully. Please follow the following URL:

http://en.wikipedia.org/wiki/Post/Redirect/Get

Beautiful well constructed figures in Wikipedia will make you understand this pattern in minutes.

I hope you would now have a clear picture of PRG pattern after going through the above URL and are ready to see this implemented in your Spring MVC application as detailed below in this blog post.

I really don’t know whether this is the best approach by which Post-Redirect-Get pattern can be achieved in Spring MVC. Nevertheless i am sharing an approach below by which PRG pattern can be achieved. If this is not at all right approach, or there is another good way by which to do it, please let me know through your comments to this blog post and i promise to correct it accordingly.

In Spring MVC PRG is implemented by having two request-mappings for each page one for GET and the other for POST. The page should always be rendered using GET method and the form should always use POST method for submitting data to controller. To achieve PRG after submitting the form in the POST method of the request should send the response with redirect to the page, by doing this the page will be rendered using GET request. The following a sample code.

The flow of the above example is {GET(prgTest.html} –> {POST(prgTest.html)} –> {REDIRECT(prgTest.html)} –> {GET(prgTest.html)}

I thank my dear friend Karthikeyan Vaithilingam, for allowing me to print his R&D on this in my blog. Please follow the following link to his other blog entries:

http://seenukarthi.com/blog/index.html

I would also suggest reader to go through another approach as given in the below blog post and implement whichever is the best approach in your web application.

http://www.mkyong.com/spring-mvc/handling-duplicate-form-submission-in-spring-mvc/

If you are using JSF or one its implementations like RichFaces as your choice of web application, to implement PRG, please blog my blog in here.

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