Spring MVC

Question 1

Explain MVC

Answer 1

MVC is web application architectural pattern that aims to reduce coupling between different aspects of web application.
MVC stands for Model-View-Controller.
Model - Model domain contains the business logic and functions that manipulate the business data. It is also called domain layer. It provides updated information to view layer and replies to the query. And the controller can access the functionality encapsulated in model.
View - View is concerned with the presentation aspect of the application according to the model data and also responsible to forward query response to controller.
Controller - Accepts and intercepts user requests and controls the business objects to fulfil these requests. it works as orchestrator to fulfil the request. A controller can talk with multiple business objects to complete request.

Question 2

Which pattern does Spring MVC implement which listens for all the web requests and then forwards it to respective controllers?

Answer 2

FrontController. All requests first lant on this servlet which then forwards it to proper controller based on url mapping.

Question 3

What does controller return and who processes that information.

Answer 3

Controller returns logical view name and then dispatcher servlet uses ViewResolver to resolve the logical name to actual view and passes the model to JSP.

Question 4

What is the name of FrontController in spring?

Answer 4

DispatcherServlet.

Question 5

Which class creates WebApplication context, etc?

Answer 5

DispatcherServlet creates web related context and view resolvers. It is then nested inside root application context so that web components can easily find their dependencies.

Question 6

How is xml file for web application context located?

Answer 6

The dispatcher servlet will by default take name of its servlet from web.xml and search for name-servlet.xml in /WEB-INF. For example if servlet is named spring, then it will search for spring-servlet.xml

Question 7

Which are mandatory configurations in web.xml for spring?

Answer 7

Servlet name
Servlet class - DispatcherServlet
Load on startup - 1

Servlet mapping
servlet name
url pattern -> /

mapping / to dispatcher servlet means all requests will be routed through dispatcher servlet.

Question 8

Role of controllers in spring?

Answer 8

execute the actual request, prepare the model and select a view to render. Controller is the glue that glues logic and web interface.

Question 9

Which annotation is used to desginate a class as controller

Answer 9

@Controller is used. Don’t forget to enable component scan in xml.

Question 10

Which configuration is required for enabling of creation of controller and other stereotypes using annotation?

Answer 10

context:component-scan - property base package = “co.edureka.package”
So all the classes inside that package are scanned.

Question 11

Which annotation is required to declare that a method will handle requests for a particular endpoint?

Answer 11

@RequestMapping is used. Need to provide endpoint in it.

@RequestMapping(value=”/home”, method=POST)

Question 12

What are the objects that hold form values called?

Answer 12

Command objects. In form tag you need to configure command name which is the name of model.

Question 13

How to do data binding in spring?

Answer 13

Need to include Spring form tag library which is integrated with Spring and provides tags access to command object and reference data your controller deals with.

Question 14

Which jar contains Spring form tag library

Answer 14

spring-webmvc.jar contains it.

Question 15

Sample spring form configuration

Answer 15

form:form action=”register” method=”post” commandName=”userForm”
form:input path=”username”
form:password path=”password”
input type=”submit” value=”Register”

Question 16

Sample controller that handles user form with command name of “userForm”

Answer 16

@RequestMapping(method=RequestMethod.POST)
public String registerUser(@ModelAttribute(“userForm”) User user, Map model) {
….
}

Question 17

Form validation in Spring using javax.validation?

Answer 17

User {
   @NotNull
   @Size(min=4, max=15)
   private String username;
   @Pattern(emailPattern)
   private String email;
}

@RequestMapping(“/signup”, RequestMethod.POST)
public String signup(Model model, @Valid User user, BindingResult result) {
if (result.hasErrors()) {
….
}
}

Question 18

To use Internationalization which extra beans need to be configured?

Answer 18

LocalChangeInterceptor - You can enable changing locale by adding it to one of handler mappings. It will detect parameter in request and change the locale.
SessionLocaleResolver - Allows you to retrieve locale and timezone from session that might be associated with user’s request
ResourceBundleMessageSource - resolves text messages from properties file based on selected locales.

If localeResolver is not added, then deafult of AcceptHeaderLocaleResolver is used. It uses accept-language in HTTP request.

Question 19

Which tag is used for internationalization support of showing locale specific text?

Answer 19

spring:message tag is used
code property is used to denote key in properties file
text property is the default value if key is not found in file

Question 20

Which class is used to upload file in Spring?

Answer 20

Spring provides CommonsMultipartResolver bean to handle file upload and multi part file that represents file uploaded by user.
It is defined in Jakarta commons FileUpload.

Question 21

Which class represents file contents uploaded by user?

Answer 21

MultipartFile repsents the multi part file uploaded by user. The contents can be stored in memory or temporarily on disk. It is the responsibility of user to store the contents in persistent storage.

Question 22

How to upload file from spring jsp?

Answer 22

form:form metho=”POST” commandName=”ResumeUploadForm” encType=”multipart/form-data”
input type=”file” name=”file”
input type=”submit” value=”Upload”

Question 23

Where should one keep static files in Spring MVC application?

Answer 23

Best practice is to keep in one parent directory like static and create seperate directories for images, javascript, css etc.

Question 24

Can one directly access static files from jsp?

Answer 24

No. We have to configure static files path in spring mvc file. We must use mvc:resources tag and provide path to static files and give mapping.
so lets say path is /resources/ and mapping is /staticContent/**. Then you can use /staticContent/css/main.css in your jsp.

Question 25

How to show form errors on spring form?

Answer 25

with each form element you can have form:errors tag.

tr
td
form:input path=”username”
form:errors path=”username”

Question 26

How can one handle exception thrown from controller in spring?

Answer 26

@ExceptionHandler annotation can be used to annotate a method which will handle that exception.

@ExceptionHandler(ClassNotFoundException.class)
public String handleClassNotFound(Exception ex) {
…. do logic
return “logicalViewName”;
}

Question 27

How can one handle exception thrown from any controller globally?

Answer 27

@ControllerAdvice anotation can be used to annotate a class. And then this class becomes global exception handler for all controllers.

Question 28

What is shortcoming of @ExceptionHandler anotation?

Answer 28

It only works for current controller so one will have to repeat exception handling logic in all controllers. To avoid that use @ControllerAdvice to define a class that handles exceptions on global level for resuability.

Question 29

What is apache tiles?

Answer 29

Apache tiles is template framework to simplify development of web applications. We can define page fragments which are then combined at runtime. Like header, footer, maincontent, left panel, right panel etc.
These templates are useful for consistent look and feel across application.

Question 30

How to integrate tiles in spring? Which configurations are required in spring mvc xml

Answer 30

TilesViewResolver bean
TilesConfigurer bean and it has property “definitions” which is list of tiles layout definitions.

/WEB-INF/layouts/default.xml
/WEB-INF/layouts/index.xml

Question 31

What is configured in tiles definition file?

Answer 31

tiles-definition
definition name=”home” template=”/WEB-INF/views/template/SiteTemplate.jsp”
put-attribute name=”title” value=”Home”
put-attribute name=”header” value=”/WEB-INF/views/template/header.jsp”

div …
img …
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