SpringMVC | Techartifact

In web application ApplicationContext is created using Context Loaders. there are two implementations of context loader.

ContextLoaderListener : It is listener implementation that is added to web.xml file.
ContextLoaderServlet : It is servlet implementation that is configured with load-on-startup tag in web.xml.

ContextLoaderListener is simple way to use the spring in web application. this listener accept contextConfigLocation parameter from context-parama.
You have to enter following code in web.xml file

define contextConfigLocation parameter in context-param tag.

<context-param>
  <param-name>contextConfigLocation</param-name>
  <param-value>/WEB-INF/services.xml</param-value>
</context-param>

services.xml is the Spring configuration file in which you define beans.

Add the ContextLoaderListener listener.

<listener>
  <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

Here is the complete source code for the example demonstrating this.

InputService.java

package com.techartifact.example.spring.service;
import java.util.Random;
import java.util.Scanner;
public class InputService {
    public int getIntValue() {
        Random r=new Random();
        int val=r.nextInt();
        System.out.println("Returning value = "+val);
        return val;
    }
}

OutputService.java

package com.techartifact.example.spring.service;
public class OutputService{
    public int write(int x) {
        System.out.println("Output is "+x);
        return x;
    }
}

CalServlet .java

package com.techartifact.example.spring.servlets;

import com.techartifact.example.spring.service.CalcMachine;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class CalServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        ApplicationContext ac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
        CalcMachine cal = (CalcMachine) ac.getBean("cal");
        response.getWriter().print("Adding of numbers is = " + cal.doAdd());
        response.getWriter().close();
    }
}

services.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

    <bean id="in" class="com.techartifact.example.spring.service.InputService"/>
    <bean id="out" class="com.techartifact.example.spring.service.OutputService"/>

    <bean id="cal" class="com.techartifact.example.spring.service.CalcMachine">
        <property name="inputService">
            <ref bean="in" />
        </property>
        <property name="outputService">
            <ref bean="out" />
        </property>
    </bean>
</beans>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="WebApp_ID" version="2.5">
    <display-name>DI2_web</display-name>

    <servlet>
        <description></description>
        <display-name>CalServlet</display-name>
        <servlet-name>CalServlet</servlet-name>
        <servlet-class>com.techartifact.example.spring.servlets.CalServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>CalServlet</servlet-name>
        <url-pattern>/CalServlet</url-pattern>
    </servlet-mapping>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/services.xml</param-value>
    </context-param>

     <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener> 
   
</web-app>

Run example

Download full example code from here spring-webapplication

Go to project directory [spring-webapplication] in command shell and run following command using maven

mvn clean package
mvn -Pcargo-run

You should see following output in your browser

http://localhost:8080/springapp/CalServlet

Dependencies

<dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> <version>2.5</version> <scope>provided</scope> </dependency>  <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>3.0.0.RELEASE</version> </dependency>  <dependency> <groupId>taglibs</groupId> <artifactId>standard</artifactId> <version>1.1.2</version> </dependency>

Request Controller

You can use or extend any of controller that comes from Spring or create you own by extendng AbstractController and implement handleRequestInternal method.

package com.techartifact.example.springmvc.controller; import org.springframework.web.servlet.ModelAndView; import org.springframework.web.servlet.mvc.AbstractController; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class HelloController extends AbstractController { private String message; public void setMessage(String message) { this.message = message; } @Override protected ModelAndView handleRequestInternal(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) throws Exception { ModelAndView modelAndView = new ModelAndView("hello"); modelAndView.addObject("message", message); return modelAndView; } }

Flow in a Spring MVC application is as follows:

The request is received by our DispatcherServlet

DispatcherServlet has responsibility to find the controller for request. This process would be done in HandlerMapping phase.

After controller has been found, DispatcherServlet will forward the request to Controller.

Controller has the business logic to compute what model it will return to Dispatcher. It means Controller will return Model and view where it needs to displayed

Once the ModelAndView has been dispatched to the DispatcherServlet from controller, DispatcherServlet will asociate the view name sent by the Controller with the specified view.

After the view had been resolved, our DispatcherServlet will pass our Model object to the concrete View.

Spring Configuration

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <bean name="/hello.htm" class="com.techartifact.example.springmvc.controller.HelloController"> <property name="message" value="This is sample message"/> </bean> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix"> <value>/WEB-INF/jsp/</value> </property> <property name="suffix"> <value>.jsp</value> </property> </bean> </beans>

Web descriptor

<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5"> <display-name>Spring MVC example</display-name> <servlet> <servlet-name>springapp</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>WEB-INF/spring-mvc.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>springapp</servlet-name> <url-pattern>*.htm</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app>