As per my understanding when a spring application starts, request goes to dispatcher Servlet and from there it gets dispatched to respective controllers. In spring mvc we define Dispatcher Servlet in web.xml file. I want to know is the process is same for Spring boot application also means application request goes to dispatcher Servlet and from there it gets dispatched to respective controllers.
And if it is where are we defining our dispatcher Servlet in Spring boot application?
yes spring boot uses dispatcher servlet and it is located in DispatcherServlet
fully qualified name of class:
org.springframework.web.servlet.DispatcherServlet
in normal java web application web.xml is the source of declaring main components and structure definition of web application like servlets , filters and so on, in other words it's meta data of our web application that the servlet containers like tomcat uses to know how run the application.
in spring boot as mentioned above, dispatcher servelet is declared inside DispatcherServletAutoConfiguration
fully qualified name of class:
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration
Dispatcher Servlet is a part of 'Spring MVC'.
Strictly speaking, Spring boot application doesn't necessarily has to run Spring MVC, although in most of practical cases it does.
So, If spring boot application runs spring mvc there is certainly a DispatcherServlet exists under the hood.
Related
I see here spring boot packages the microservice artifact as jar file . It handles the http web request through module spring-boot-starter-web.
My understanding is spring boot internally does is
Makes the web server up
creates the war file , then host the war file on server.
Then http requests are handled through servlet lying under spring-boot-starter-web
Is my understnading correct ?
Your understanding is almost correct:
Starts a embedded tomcat server
Instructs the tomcat server how to act
HTTP requests are handled by an underlaying DispatcherServlet
spring boot entry point is main method, inside the main method we are calling SpringApplication.run(<#SpringBootApplication annotated class name> ,arguments);
when we invoking main method, SpringApplication class internally start the embedded server, configuratation and deploy the application in server...
here dispatcher servlet registered in servlet context on OnCondtion checking basis, if we are added spring-boot-starter-web then it checking condtion dispatcher-servlet available or not inside the class path if available then it will in registers the dispatcher-servlet in servlet context
I have done my Dynamic web project using Servlet 3.0.
Can I convert this project to Spring project by some kind of web service (REST calls) and Spring Boot.
Or Is there any other possible ways to do that.?
Note: My project includes servlet controller class (GET and POST) , web content like jsp, ajax, javascript, css, html, etc
You can try doing this, if you are using annotations:
Convert your servlet classes to spring controller classes.
Mark class as #Controller and remove extends part of class, in your doGet and doPost add annotation #Requestmapping(value="/someURL" method="RequestMethod.GET" and
#Requestmapping(value="/someURL" method="RequestMethod.Post"
In the above methods return the name of jsp file, where you want to forward your processed data.
You will have access to Model object in the above controller classes and jsp in order to process data.
In your web.xml define DispatcherServlet and a configLocation to scan controllers.
Essentially what you are doing is to introduce Spring just defining DispatcherServlet and then the spring controller classes are loaded.When you hit a URL it will be routed to correct controller.
Good Luck.
I am new to spring mvc and DI. I have came to know about the flow of the spring project and i know how the web projects in spring mvc is developed and worked on few projects too. All the annotation uses and xml configuration files in the spring mvc. But i am confused where the DI is used? and how the DI is implemented in spring with the help of IOC??
Can anyone please explain me the concept of DI and IOC and their implementation in spring mvc.
Thanks in advance!!!
DI and IOC happening through web.xml where you created the dispatcherservlet.
From Spring MVC docs :
The DispatcherServlet, provides a shared algorithm for request processing while actual work is performed by configurable, delegate components
The DispatcherServlet, as any Servlet, needs to be declared and mapped according to the Servlet specification using Java configuration or in web.xml. In turn the DispatcherServlet uses Spring configuration to discover the delegate components it needs for request mapping, view resolution, exception handling, and more.
internally it will register Spring mvc app and it will create an object and inject dependencies .
I am trying to setup a session scoped bean but the spring document said that session scope is only applicable on web-aware application context. No further explanation in the doc. Can someone clarify this?
This means that you can only use the session scoped beans in a an application deployed to a web server. Spring can be used in applications that run in standard JVMs along with applications that run in servlet containers (Tomcat, etc). Session, however, only exists in web servers so it has no meaning if the application is running in a standard desktop environment.
There are basically 5 types of scopes available for spring bean.
1)Singleton
2)Prototype
3)Request
4)Session
5)Global-Session
The first two scopes can be used with any type of spring applications.
But the remaining 3 are related to web applications. They can be used only with the spring applications which are involved in web.
Web aware means when the application provides web endpoints for third party client. I.E When the application contains at least one RestController . You can do this by simply adding #RestController annotation to your class.
ApplicationContext is an interface, spring ships multiple ApplicationContext implementations, according to documentation you need to use one that is web-aware.
The request, session, application, and websocket scopes are available only if you use a web-aware Spring ApplicationContext implementation (such as XmlWebApplicationContext). If you use these scopes with regular Spring IoC containers, such as the ClassPathXmlApplicationContext, an IllegalStateException that complains about an unknown bean scope is thrown.
And as of spring framework core (6.0.4) further configuration might be required:
To support the scoping of beans at the request, session, application, and websocket levels (web-scoped beans), some minor initial configuration is required before you define your beans.
...
If you access scoped beans within Spring Web MVC, in effect, within a request that is processed by the Spring DispatcherServlet, no special setup is necessary. DispatcherServlet already exposes all relevant state.
If you use a Servlet web container, with requests processed outside of Spring’s DispatcherServlet (for example, when using JSF), you need to register the org.springframework.web.context.request.RequestContextListener ServletRequestListener. This can be done programmatically by using the WebApplicationInitializer interface. Alternatively, add the following declaration to your web application’s web.xml file:
<web-app>
...
<listener>
<listener-class>
org.springframework.web.context.request.RequestContextListener
</listener-class>
</listener>
...
</web-app>
Spring boot will automatically configure this for you (couldn't find documentation mentioning this explicitly).
Why do we use dispatcher
servlet.xml?
Is it something like web.xml?
Is application and dispatcher xmls
different from each other, are there
any similar things which both can
do?
I have a value, now i need to send
it to another class? can i do it via
application-context.xml
In addition to Nathans' answer - the dispatcher-servlet.xml defines a child context of the base application context (define in applicationContext.xml)
Child contexts have access to all the beans defined in the parent context, but parents don't have access to beans in the child contexts.
Because people don't want one humongous application-context.xml, they split them up by application layer.
No, it's just a Spring application context file.
They do the same thing.
That's not what it's for, it's for defining what your spring-managed objects get injected with.
Dispatcher servlet.xml is just the convention followed by the Spring front controller for web MVC applications. If you don't use Spring web MVC, you need not have a dispatcher-servlet.xml
web.xml is the configuration file required by a Java web app. You must have a web.xml for a Java web app, but the Spring servlet.xml is only required if you use Spring web MVC.
The Spring servlet XML is just part of a Spring web application configuration. You can put all your Spring configuration in the single XML file if you wish, but usually people have more than one.
Spring's bean factory creates objects and injects their dependencies. Your code does the rest. Define what "send it to another class" means to you.