Spring MVC Interview Questions

Spring MVC Interview Questions

1. Explain Spring MVC Execution Flow

The DispatcherServlet is an actual Servlet and inherits from the HttpServlet base class. When a request is sent to the web application, the workflow of handling a request is as below:
• When DispatcherServlet receives the request, it dispatches the task of selecting an appropriate controller to HandlerMapping. Then, HandlerMapping selects the controller which is mapped to the incoming request URL and returns the (selected Handler) and Controller to DispatcherServlet.
• DispatcherServlet dispatches the task of executing the business logic by Controller to HandlerAdapter. HandlerAdapter calls the business logic process of Controller. When the HandlerAdapter calls the controller, Interceptor is invoked to intercept the request.
• Then, Controller executes the business logic and sets the processing result in Model. Then, if there is any Interceptor to intercept the response, is invoked as a post process. Then Controller returns the logical name of view to HandlerAdapter.
• DispatcherServlet dispatches the task of resolving the View corresponding to the View name to ViewResolver. ViewResolver returns the View mapped to View name.
• DispatcherServlet dispatches the rendering process to returned View.
• View renders Model data and returns the response

2. How to Take attributes from Spring MVC form

Please make sure you have same name in form and in bean while taking the input from form.
1. @RequestParam

public ModelAndView addForm(@RequestParam("firstName") String fName, @RequestParam("lastName") String lName)

2. @ModelAttribute – Used to take the object from form

public ModelAndView addForm(@ModelAttribute("student1") StudentBean student1)

ModelAttribute can also e used for Common codewe can write in a single method which will be called before calling any other method like ininBinder () or the request mapping handler method.

3. How to do the form validation in Spring MVC?

1. Binding Result
Many time while submitting the form we face 404 error because of incorrect data binding or some exception occurred while converting the datatypes. To debug this issue we should have below changes.

1.1. Java– add org.springframework.validation.BindingResult object to the form submission method and add below line to it.

public ModelAndView addForm(@ModelAttribute("student1") StudentBean student1, BindingResult result){
/*BindingResult object will contain the error if the values are not converted from form to the object.*/
      if(result.hasErrors()){

        ModelAndView view = new ModelAndView("addForm"); 

        return view

      }

}

1.2  JSP – add below lines on jsp to display the errors

<%@taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<form:errors path=”student1.*”>

2. Inbuilt custom property editor
Define a method with @InitBinder with param WebDataBinder binder, in this method you can specify the custom / in built property editors for validation. We can have any name to the method, this method will be called before the submit method of the form.

@InitBinder
public void bindData(WebDataBinder binder){
 System.out.println("Entered in bindData");
 binder.setDisallowedFields(new String [] {"telephone"} ); // this will skip the internal validation part for tel
 SimpleDateFormat dateFormat = new SimpleDateFormat("yyy.dd.mm");
 binder.registerCustomEditor(Date.class,"dob", new CustomDateEditor(dateFormat, true)); // spring provide lots of custom editors
 // to customize the inbuilt datatypes, the 2nd param true defines - allow empty value
 System.out.println("Exited from bindData");
}

3. Adding validation annotation and message file on variables
Spring allows any validation vendor which implements the JSR-303 or JSR 314X specifications.
A. Add validation annotation in POJO

@Data
public class PersonForm {

    @NotNull
    @Size(min=2, max=30)
    private String name;

    @NotNull
    @Min(18)
    private Integer age;
}

B. To work it add @Valid annotation as a parameter to the handler method.

public ModelAndView addForm(@Valid @ModelAttribute("student1") StudentBean student1, BindingResult result){

C. Add below entry in the Spring-dispatcher.xml to read the message.properties file.

<bean id="messageSource" class="org.springframework.context.support.ReloadableResourceBundleMessageSource">
    <property name="basename" value="/WEB-INF/messages">
    </property>
</bean>

D. Create messages.properties file in web-inf folder.
E. Spring will read the validation error messages like below hierarchy.

F. In order to make the error messages dynamic we can place {0} in the messages to take the dynamic values.
Size.student1.firstName={0} should have minimum {2} and maximum {1} characters.

<web-app>
  <display-name>Archetype Created Web Application</display-name>
 
  <servlet>
        <servlet-name>spring</servlet-name>
            <servlet-class>
                org.springframework.web.servlet.DispatcherServlet
            </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>spring</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
     
</web-app>

<servlet>
    <servlet-name>spring</servlet-name>
    <servlet-class>
        org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
     
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/applicationContext.xml</param-value>
    </init-param>
     
    <load-on-startup>1</load-on-startup>
</servlet>

5. Can we have multiple Spring configuration files?

YES. You can have multiple spring context files. There are two ways to make spring read and configure them.
a) Specify all files in web.xml file using contextConfigLocation init parameter.

<servlet>
        <servlet-name>spring</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>
                WEB-INF/spring-dao-hibernate.xml,
                WEB-INF/spring-services.xml,
                WEB-INF/spring-security.xml
            </param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>spring</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

b) You can import them into existing configuration file you have already configured.

<beans>
    <import resource="spring-dao-hibernate.xml"/>
    <import resource="spring-services.xml"/>
    <import resource="spring-security.xml"/>
   
    ... //Other configuration stuff

</beans>

6. Difference between <context:annotation-config> vs <context:component-scan>?

1. First big difference between both tags is that <context:annotation-config> is used to activate applied annotations in already registered beans in application context. Note that it simply does not matter whether bean was registered by which mechanism e.g. using <context:component-scan> or it was defined in application-context.xml file itself.
2. Second difference is driven from first difference itself. It registers the beans defined in config file into context + it also scans the annotations inside beans and activate them. So <context:component-scan> does what <context:annotation-config> does, but additionally it scan the packages and register the beans in application context.

7. What are different View Resolvers available in Spring?

1. UrlBasedViewResolver
The UrlBasedViewResolver   provides the mapping logical view names and URLs directly that hands over to the view class specified. Javadoc for UrlBasedViewResolver mentions: “Note: When chaining ViewResolvers, a UrlBasedViewResolver always needs to be last, as it will attempt to resolve any view name, no matter whether the underlying resource actually exists.” It will resolve the controller based on the URL. For e.g. if below URL comes then :
http://localhost:8080/Rent/UrlBasedViewResolver
then it will search for the controller names UrlBasedViewResolver and execute the code written in protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)throws Exception {
method.

2. InternalResourceViewResolver
This ViewResolver allows us to set properties such as prefix or suffix to the view name to generate the final view page URL:

@Bean
public ViewResolver internalResourceViewResolver() {
    InternalResourceViewResolver bean = new InternalResourceViewResolver();
    bean.setViewClass(JstlView.class);
    bean.setPrefix("/WEB-INF/view/");
    bean.setSuffix(".jsp");
    return bean;
}

11. Explain Model, ModelMap and ModelAndView?