Spring
Spring MVC

Spring MVC

Spring MVC is a framework for building web applications in Java based on the Model-View-Controller design patter.

MVC Pattern

  • The Front Controller is known as DispatcherServlet:
    • It is part of the Spring Framework
    • Pre-processes and delegates requests from the web browser to your controllers
  • The MVC pattern is made up of:
    • Model objects: contains the data
    • View templates: UI of the app that displays data (most common templates: JSP + JSLT)
    • Controller classes: business logic (handle request, access db, etc.)

It includes the features of the Core Spring Framework (Inversion of Control and Dependency Injection)

Configuration

Configuration on web.xml

We have to add an entry for our Front Controller: DispatcherServlet

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

	<display-name>spring-mvc-demo</display-name>

	<absolute-ordering />

	<!-- Step 1: Configure Spring MVC Dispatcher Servlet -->
	<servlet>
		<!-- Name to reference this servlet -->
		<servlet-name>dispatcher</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<!-- File of configuration of spring application -->
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>/WEB-INF/spring-mvc-demo-servlet.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>

	<!-- Step 2: Set up URL mapping for Spring MVC Dispatcher Servlet -->
	<servlet-mapping>
		<servlet-name>dispatcher</servlet-name>
		<!-- For any url that comes in pass it to the "dispatcher" servlet -->
		<url-pattern>/</url-pattern>
	</servlet-mapping>
</web-app>

Configuration on spring-mvc-demo-servlet.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"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:mvc="http://www.springframework.org/schema/mvc"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans
    	http://www.springframework.org/schema/beans/spring-beans.xsd
    	http://www.springframework.org/schema/context
    	http://www.springframework.org/schema/context/spring-context.xsd
    	http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">

	<!-- Step 3: Add support for component scanning -->
	<context:component-scan base-package="com.springdemo" />

	<!-- Step 4: Add support for conversion, formatting and validation support -->
	<mvc:annotation-driven/>

	<!-- Step 5: Define Spring MVC view resolver -->
	<bean
		class="org.springframework.web.servlet.view.InternalResourceViewResolver">
		<!-- Specify where to look for view files -->
		<property name="prefix" value="/WEB-INF/view/" />
		<property name="suffix" value=".jsp" />
	</bean>

</beans>

Controller

Create Controller Class 

package com.springdemo.mvc;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

// Add controller annotation
@Controller
public class HomeController {

    // Add request mapping: this method controls the request coming to this url
    @RequestMapping("/")
    public String showPage() {
      // Name of the view that is returned: note they are stored in WEB-INF/view/
        return "main-menu";
    }
}

Now, we can create the view. Inside WEB-INF/view we create a file main-menu.jsp:

<!DOCTYPE>
<html>
  <body>
    <h2>Spring MVC Demo - Home Page</h2>
  </body>
</html>

Read HTML Form Data

Controller 

package com.springdemo.mvc;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class HelloWorldController {

	// need a controller method to show the initial HTML form
	@RequestMapping("/showForm")
  // The method name can be anything
	public String showForm() {
		return "helloworld-form";
	}

	// need a controller method to process the HTML form
	@RequestMapping("/processForm")
	public String processForm() {
		return "helloworld";
	}

}

View

We create WEB-INF/view/helloworld-form.jsp

<!DOCTYPE html>
<html>
<head>
	<title>Hello World - Input Form</title>
</head>

<body>
  <!-- The action is the request url -->
	<form action="processForm" method="GET">
		<input type="text" name="studentName"
			placeholder="What's your name?" />
		<input type="submit" />
	</form>
</body>
</html>

And we create WEB-INF/view/helloworld-form.jsp

<!DOCTYPE html>
<html>
<body>
  Hello World of Spring!
  <br><br>
  <!-- name of HTML form field from previous jsp view -->
  Student name: ${param.studentName}
</body>
</html>

Model

Example

Controller 

package com.springdemo.mvc;

import javax.servlet.http.HttpServletRequest;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class HelloWorldController {

  // new a controller method to read form data and
  // add data to the model

  @RequestMapping("/processFormVersionTwo")
  // the HttpServletRequest allows you to retrieve information from the request (like the parameters of a form)
  // the model is our Model where we will store data
  public String parseString(HttpServletRequest request, Model model) {

    // read the request parameter from the HTML form
    String theName = request.getParameter("studentName");

    // convert the data to all caps
    theName = theName.toUpperCase();

    // create the message
    String result = "Yo! " + theName;

    // add message attribute to the model
    model.addAttribute("message", result);

    return "helloworld";
  }

}

View

Now, on the view, we can access the Model data:

<!DOCTYPE html>
<html>
<body>
  Hello World of Spring!
  <br><br>
  Student name: ${param.studentName}
  <br><br>
  <!-- Access model data by the attribute's name-->
  The message: ${message}
</body>
</html>

Add CSS and JS

Here are the steps on how to access static resources in a Spring MVC. For example, you can use this to access images, css, JavaScript files etc.

You can configure references to static resources in the spring-mvc-demo-servlet.xml.

  • Add the following entry to your Spring MVC configuration file: spring-mvc-demo-servlet.xml
<mvc:resources mapping="/resources/**" location="/resources/"></mvc:resources>
  • Now in your view pages, you can access the static files using this syntax:
<img src="${pageContext.request.contextPath}/resources/images/spring-logo.png">

Request Params and Request Mappings

Request Params

Spring provides for a specific annotation that allows you to retrieve request parameters directly without using the HttpServletRequest object. Given the form:

package com.springdemo.mvc;

import javax.servlet.http.HttpServletRequest;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
public class HelloWorldController {

    @RequestMapping("/processFormVersionThree")
    public String processFormVersionThree(
      // We use the annotation to obtain the parameter
            @RequestParam("studentName") String theName,
            Model model) {

        // convert the data to all caps
        theName = theName.toUpperCase();

        // create the message
        String result = "Hey My Friend from v3! " + theName;

        // add message to the model
        model.addAttribute("message", result);

        return "helloworld";
    }
}

Controller Request Mappings

  • They serve as a parent mapping for the controller
  • All request mappings on methods in the controller are relative

For example:

package com.springdemo.mvc;

import javax.servlet.http.HttpServletRequest;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
// This is the request mapping for the controller
@RequestMapping("/hello")
public class HelloWorldController {

    // Both of these request mappings are relative to the parent mapping
    // that is the mapping translates to domain/hello/showForm
    // need a controller method to show the initial HTML form
    @RequestMapping("/showForm")
    public String showForm() {
        return "helloworld-form";
    }

    // need a controller method to process the HTML form
    @RequestMapping("/processForm")
    public String processForm() {
        return "helloworld";
    }
}

Forms

Form Tags Form Validation