How does Dispatcher Servlet works internally?
I have seen that Controllers and it methods(defined by us) can be annotated with #RequestMapping and many other attributes. These controller has methods that have **varying signatures (Thay can take any parameter we like).
How does the Dispatcher servlet know how to pass these parameters in the methods defined by us? I mean how does Dispatcher Servletprepare these objects which we require in the controller methods?
Also what actually happens in WebApplicationContext behind the scenes?
would suggest to read section 15.2 this describes internal about spring mvc framework.
Related
Will multiple dispatcherservlet will share controller and other components in spring MVC
They are working by servlet specification which means that they won't share. It will just for different URI mappings dispatch by different servlets as it suppose to be for servlet. Those controllers should present in web application context provided for dispatcherServlet instance. You can reuse controllers from different contexts.
Dispatcher servlet should be just one as it implements front controller pattern. I don't understand why you need multiple instances in the first place.
I have fundamental idea about servlet and spring mvc. But I don't know that there is a usage of servlets in spring mvc or not. In spring mvc we have controller classes. My thinking is servlet is used in spring mvc as a controller. If I'm incorrect please correct me.
Yes,you are perfectly right. Servlets are used in Spring-MVC. In Spring-MVC when you write annotation like #Controller, indirectly you are using a Servlet called Dispatcher Servlet. Dispatcher Servlet is defined in web.xml file with properties and class name which is mapped to .jsp pages and Controller part.
Related / Duplicated to When to use Servlet or #Controller. The question is not the same but quite the explanation on that question you will be able to understand:
If you're a student interested in learning the language then I would stick with servlets for now. It's possible to write a web app using just servlets but in practice you'll probably want to look at JSP's too.
A JSP is a convenient way to write a servlet that allows you to mix html with scripting elements (although it's recommended to avoid Java code in your jsp in favour of tags and el expressions). Under the covers it will be compiled as a servlet but it avoids you having to use lots of messy print statements.
It's important to have at least a basic understanding of servlets and JSP's. Spring MVC is one of many frameworks built on top of servlets to try make the task of writing a web application a bit easier. Basically all requests are mapped to the DispatcherServlet which acts as a front controller.
The DispatcherServlet will then call the controller whose annotations match the incoming request. This is neater than having to write these mappings yourself in the web.xml (although with servlet 3.0 you can annotate servlets now). But you also get many other benefits that can be used like mapping form fields to an object, validating that object with jsr303 annotations, map inputs and outputs to xml or json etc etc. Plus it's tightly integrated with core spring so you can easily wire in your services for the controller to call.
It's worth noting that there are a plethora of competing frameworks built on top of servlets. Spring MVC is one of the most popular so it's not a bad choice to look into.
Controllers are not Servlets! Controllers are normal Spring MVC beans that do not extend HttpServlet. Instead what Spring has is a custom extension of HttpServlet called DispacherServlet. Looking at the DispacherServlet's source code you can see that the class hierarchy goes: DispatcherServlet extends FrameworkServlet → FrameworkServlet extends HttpServletBean → HttpServletBean extends HttpServlet.
The DispatcherServlet, like any other Servlet, is declared in the web.xml. It handles all incoming HTTP requests. It is called a front controller which provides a single point of entry in your application. It is responsible for request handling by delegating requests to additional components of Spring MVC controllers which do not extend the HTTP Servlet API.
Look at the following diagram
In this picture DispacherServlet is the only HttpServlet. The Controllers, HandlerMapping and ViewResolver are all Spring MVC beans.
Dispatcher servlet invokes a handler (a controller) based on handler mappings and then the matching controller delegates a service object to perform business logic and then returns back the created model to dispatcher servlet and then dispatcher servlet decides which view to pass model to ... blah blah.
my question is whether there is any web page or book that explain about all these things. for example,
what method does dispatcher servlet invoke on handler adaptor in order to invoke the matching controller?
what method does dispatcher servlet invoke on view interface in order to build a view?
etc.
Any web page would be awesome.
You can refer these links :
Spring MVC Framework
Spring MVC Hello World
In case of REST implementations in Spring, spring Controllers are singleton. I want to know why spring controllers are singleton apart from thread-safety issue. Please help in resolving this issue.
This has nothing to do with REST.
Spring beans are, by default, singleton scoped. Since component scanning a #Controller annotated class simply generates a bean, that bean will be singleton scoped.
For reasons why a #Controller bean should be stateless, read any and all of the following:
Are Spring MVC Controllers Singletons?
Controller's life-cycle in Spring MVC
To follow up on the REST question, REST is meant to be stateless. In other words, each request contains all the information it needs for the server to handle it. Knowing that, it's pointless for the server (or #Controller) to keep any information after it's finished handling the request in instance fields and the like. Therefore a singleton is the way to go.
WI have a question about the "Best Practice" Design for controller beans.
I was reading this very good question and the linking article:
Question "JSF backing bean structure (best practices)"
Scoping Best Practice
Online Article
Distinctions between different kinds of JSF Managed-beans
My question is concerning the controller bean. I'm using JSF / Spring and was wondering why I would want to use request scope for Controller beans?
The controller logic being defined as "...execute some kind of business logic and return navigation outcome.." I would think doesn't require a request scope but either session/application scope. Why keep creating those controller objects on every request?
In my case I would create the controller bean in the faces-config obviously and inject it with my managed properties through spring.
Thoughts please around the scoping? Thanks.
Clarification:
Using JSF 1.2, Spring 3. Using faces-config.xml to declare my beans. Not through annotations.