How Dispatcherservlet Procedure A Asking Inwards Boundary Mvc Application?

One of the mutual enquiry inwards Spring MVC is, how does DispatcherServlet procedure a asking inwards Spring MVC? or What is the portion of DispatcherServlet inwards Spring MVC framework? This is an first-class enquiry to whatever Java or Spring spider web developer, the respond to this enquiry shows how much you lot know virtually Spring MVC framework together with its working. Actually, DispatcherServlet plays a meaning portion inwards Spring MVC. It acts equally a front end controller, together with all incoming asking passes through it, of course, you lot tin configure this inwards URL designing of DispatcherServlet proclamation inwards web.xml, but this is the instance for many Spring based spider web application.

The project of DispatcherServlet is to honour the correct controller for processing the asking together with thus when the handler method returns the logical sentiment name, it likewise consults sentiment resolvers to meet the actual view. Once the existent sentiment is found, together with output is rendered, it sends the reply dorsum to the client.

The DispatchServlet is an implementation of the front end controller designing (see Patterns of Enterprise Application Architecture), but it does to a greater extent than than that. It non solely handles all asking but it is likewise responsible for sentiment resolution, locale resolution together with subject resolution inwards Spring MVC framework, but the most of import project of the DispatcherServlet is to finding the mapping handlers together with routing the asking to them. I'll explicate that inwards the side yesteryear side paragraph.

Btw, if you lot convey worked inwards Spring MVC thus you lot should already convey around basic ideas virtually things works, but if you lot don't convey whatever prior sense together with but started amongst Spring framework together with Spring MVC thus I advise you lot to commencement become through a comprehensive course of educational activity similar Spring Framework 5: Beginner to Guru course of educational activity on Udemy.  One of the most useful courses on Spring framework




How does DispatcherServlet procedure a asking inwards Spring MVC?

As I said before, Dispatcher Servlet is used to grip all incoming requests together with road them through dissimilar Spring Controllers for farther processing, but how does it honour which application needs to survive routed to which controller or handlers?

To arrive at this, DispatcherServlet uses HandlerMapping implementations. It tin grip whatever implementation of HandlerMapping interface, similar pre-built or customized implementations provided yesteryear the application to road incoming requests to handler objects.

By default, it uses BeanNameUrlHandlerMapping together with DefaultAnnotationHandlerMapping, which is driven using @RequestMapping annotation.

In gild to honour the correct methods for treatment the request, it scans through all the classes declared using @Controller annotation together with it likewise uses @RequestMapping annotation to honour the types together with methods responsible for treatment requests.

1. The @RequestMapping annotation tin map the asking yesteryear path, for representative @RequestMapping("/home"),

2. By HTTP method like
@RequestMapping("/home", method=RequestMethod.GET)

3. By asking parameters like
@RequestMapping("/home", method=RequestMethod.POST, params="param1")

4. And, yesteryear presence of http asking header like
@RequestMapping("/home", header="content-type=text/*"). 


You tin likewise apply @RequestMapping annotation at the course of educational activity marking to filter incoming requests.

Though, you lot should recollect that the @RequestMapping annotations volition solely survive processed if a corresponding HandlerMapping (for type-level annotations) and/or HandlerAdapter (for method-level annotations) is introduce inwards the dispatcher servlet configuration file.

This is the instance yesteryear default. However, if you lot are defining custom HandlerMappings or HandlerAdapters, thus you lot demand to brand certain that a corresponding custom DefaultAnnotationHandlerMapping and/or AnnotationMethodHandlerAdapter is defined equally good - provided that you lot think to work @RequestMapping.

After processing the request, the Controller returns the logical sentiment get upwards together with model to DispatcherServlet. It thus consults to sentiment resolvers to honour the actual View to homecoming the output. The sentiment resolution strategy tin survive specified using a ViewResolver implementation, yesteryear default, DispatcherServlet uses InternalResourceViewResolver to convert logical sentiment get upwards to the actual View object similar a JSP.

After this DispatcherServlet contacts the chosen view, similar a JSP file amongst model information together with it renders the output depending on the model data. This rendered output is returned to the customer equally a response.

Sometimes you lot don't fifty-fifty demand a sentiment similar inwards the instance of RESTful Web services. Their handler method straight writes into reply using @ResponseBody annotation together with DispatcherServlet homecoming the respond to the client. See REST amongst Spring Certification class to acquire to a greater extent than virtually developing together with testing RESTful Web service using Spring MVC.

Also, inwards the Spring MVC framework, a spider web application tin define whatever publish of DispatcherServlet. Each servlet volition operate inwards its ain namespace, loading its ain application context amongst mappings, handlers, etc. Only the root application context equally loaded yesteryear ContextLoaderListener, if any, volition survive shared.

DispathcherServlet inwards Spring MVC

Influenza A virus subtype H5N1 painting present is worth a thousand words, fifty-fifty a clumsy i similar this which nicely summarise what happens when a asking striking to boundary container together with how DispatcherServlet procedure a asking inwards Spring MVC application:

 One of the mutual enquiry inwards Spring MVC is How DispatcherServlet procedure a asking inwards Spring MVC Application?


That's all virtually how DispatcherServlet procedure a spider web asking inwards Spring MVC. As I said, it scans through all @Controler classes together with @RequestMapping to honour out all the handler methods together with exercise a mapping of it. It thus routes an incoming asking to appropriate handlers, together with when they homecoming a logical sentiment name, it uses ViewResolver implementations to resolve the get upwards into a View object, which could survive backed amongst whatever JSP or FreeMarker page.

The sentiment thus renders the reply which is sent to the customer yesteryear DispatcherServlet. In the instance of RESTful Web Services together with @RestController classes or handler methods annotated amongst @ResponseBody, the reply is straight sent to the customer equally no sentiment resolution happens.

Further Reading
How Spring MVC works?
Spring MVC Interview Questions

Thanks for reading this article thus far. If you lot similar this Spring MVC tutorial, thus delight portion amongst your friends together with colleagues. If you lot convey whatever questions or feedback, thus delight drib a note.

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