Spring MVC

Spring MVC has below major components :

DispacherServlet : it is a common entry point of all http request . It forwards the request to the controller .Spring MVC follows front controller design pattern in which there is one controller which responds to all the requests.

HandlerMapping : it determines the controller to be called from request url .

Controller : it services the request and sets up data to the model and pass it to View.

ViewResolver : it determines the view to which request is to be transferred.

Lets see how can make use for the above Spring components in a web application.

In web.xml file  make an entry for dispatcher servlet.

<servlet-name>spring-web</servlet-name>
<servlet-class>
                    org.springframework.web.servlet.DispatcherServlet
                </servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>

Then map your application URL to the disptcher servlet.

<servlet-mapping>
<servlet-name>spring-web</servlet-name>
<url-pattern>/urlOfApp</url-pattern>
</servlet-mapping>

Create a file spring-web-servlet.xml and place it in WEB-INF with the following content.

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="
        http://www.springframework.org/schema/beans  
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.2.xsd">



<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix">
<value>/WEB-INF/views/jsp/</value>
</property>
<property name="suffix">
<value>.jsp</value>
</property>
</bean>
<mvc:resources mapping="/resources/**" location="/resources/" />

<mvc:annotation-driven />

</beans>

The naming convention of this file is [servlet name]-servlet.xml  , if we need to put a custom name or place it in custom path you need to configure the  listener class .We can also specify multiple application context xml  using the attribute. This is usually done to separate the web application context with the spring root application context. The web application context can be placed in WEB-INF folder which will be created when dispatcher servlet is loaded . The root application context can be created when the Context Loader Listener is loaded .

<listener>
<listener-class>org.spring.framework.web.context.ContextLoaderListener</listener-class>

</listener>
context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:spring/common-config.xml</param-value>
</context-param>

If we need to have multiple web application configuration in different XML files we can also configure that.

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

<servlet>
    <servlet-name>spring-web2</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/sub.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

To use annotations to configure beans instead of xml configuration we need to add the following line of code in Spring configuration xml.

<context:component-scan base-package="org.myProject.question" />

To create a controller class use annotation @Controller:
Controller :

@Controller
public class SampleController
{
@RequestMapping(value = "/controllerUrl")
public String performAction(ModelMap requestResponse)
{
String viewName =" home";
requestResponse.put("message","Welcome to Home page");
return viewName;
}
}

Controller returns the view name , View page is a jsp. Which has to be placed in the path specified for the ViewResolver bean , if you look into the spring-web-servlet.xml we have specified the path as WEB-INF/views/jsp using prefix and suffix attributes .

<%@ page contentType = "text/html; charset = UTF-8" %>
<html>
   <head>
      <title>Home Page</title>
   </head>

   <body>
      <h2>${message}</h2>
   </body>
</html>

So let's try to build a web application with a home page .

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

    <display-name>My App </display-name>
<servlet>
<servlet-name>spring-web</servlet-name>
<servlet-class>
                    org.springframework.web.servlet.DispatcherServlet
                </servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>spring-web</servlet-name>
<url-pattern>/home</url-pattern>
</servlet-mapping>
</web-app>

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xsi:schemaLocation="
        http://www.springframework.org/schema/beans  
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.2.xsd">



<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix">
<value>/WEB-INF/views/jsp/</value>
</property>
<property name="suffix">
<value>.jsp</value>
</property>
</bean>
<mvc:resources mapping="/resources/**" location="/resources/" />

<mvc:annotation-driven />

</beans>

@Controller
public class SampleController
{
@RequestMapping(value = "/home")
public String performAction(ModelMap requestResponse)
{
String viewName =" home";
requestResponse.put("message","Welcome to Home page");
return viewName;
}
}

<%@ page contentType = "text/html; charset = UTF-8" %>
<html>
   <head>
      <title>Hello World</title>
   </head>
 
   <body>
      <h2>${message}</h2>
   </body>
</html>

Let's try to build a restful web service using Spring MVC framework .
The following example will create a web service and list all the products .

Rest Controller :

@Controller
public class ProductController
{
@RequestMapping(value = "/products")
public @ResponseBody ProductListVO getAllProducts()
{
ProductListVO products = new ProductListVO();
//service call to get the products
return products;
}
} 

End

Explain Normalization of database

The database normalization is a measure of stability .
There are 4 forms of Normalization

First Normal Form or 1NF

To be first normalized a database table should not have a duplicate data . Reference for a data should be unique . Lets assume there is a table Customer and another table Customer_Details . Both having columns customer_name and customer_id . In this situation,if we want to change customer_name , it is required to be changed in both the columns of the table , therefore is not first normalized.

Second Normal Form or 2NF

If the table is in 1NF then we can check for 2NF.

Java pass by value vs pass by reference

Hi guys,

This blog is about pass by value and pass by reference concept and understanding. Primitives are always pass by value, objects are always pass by reference.

If only the fields of the parameter are modified in the called method , the changes will be reflected in the calling method . If the reference of the parameter is assigned to a new object , the change will not be reflected in calling method .

Declarative Exception handling in struts

Declarative programming is a way to separate Control from computation logic . Exception handling in java is usually done using try catch and throws . In jsp we can handle exceptions using errorPage attribute of page declarative . Any exception occurred will be routed to the value of errorPage attribute . In addition to this struts offer similar way of handling exception . Use exception tags in StrutsConfig.xml to declare excpetion handling . All exception tags should be enclosed under global-Exception tag. Type of exception is mentioned in type attribute , exception message is mentioned in key attribute and the page which is called in case of exception is mentioned in path attribute of exception tag . The action exception message is picked from MessageResource.properties file for the key in key attribute .