Java Code Guru Ji (8920128728): Spring MVC Model Interface

In Spring MVC, the model works a container that contains the data of the application. Here, a data can be in any form such as objects, strings, information from the database, etc.

It is required to place the Model interface in the controller part of the application. The object of HttpServletRequest reads the information provided by the user and pass it to the Model interface. Now, a view page easily accesses the data from the model part.

Methods of Model Interface

Method	Description
Model addAllAttributes(Collection<?> arg)	It adds all the attributes in the provided Collection into this Map.
Model addAllAttributes(Map<String,?> arg)	It adds all the attributes in the provided Map into this Map.
Model addAllAttribute(Object arg)	It adds the provided attribute to this Map using a generated name.
Model addAllAttribute(String arg0, Object arg1)	It binds the attribute with the provided name.
Map<String, Object> asMap()	It return the current set of model attributes as a Map.
Model mergeAttributes(Map< String,?> arg)	It adds all attributes in the provided Map into this Map, with existing objects of the same name taking precedence.
boolean containsAttribute(String arg)	It indicates whether this model contains an attribute of the given name

Spring MVC Model Example

Let's create a login page that contains a username and password. Here, we validate the password with a specific value.

1. Add dependencies to pom.xml

    <!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc -->  
<dependency>  
    <groupId>org.springframework</groupId>  
    <artifactId>spring-webmvc</artifactId>  
    <version>5.1.1.RELEASE</version>  
</dependency>  
  
<!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->  
<dependency>    
    <groupId>javax.servlet</groupId>    
    <artifactId>servlet-api</artifactId>    
    <version>3.0-alpha-1</version>    
</dependency>  

2. Create the request page

Here, we create the login page to receive name and password from the user.

index.jsp

<html>  
<body>  
<form action="hello">  
UserName : <input type="text" name="name"/> <br><br>  
Password : <input type="text" name="pass"/> <br><br>   
<input type="submit" name="submit">  
</form>  
</body>  
</html>  

3. Create the controller class

In controller class:

The HttpServletRequest is used to read the HTML form data provided by the user.
The Model contains the request data and provides it to view page.

HelloController.java

package com.javatpoint;
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 HelloController {
@RequestMapping("/hello")
public String display(HttpServletRequest req,Model m)
{
//read the provided form data
String name=req.getParameter("name");
String pass=req.getParameter("pass");
if(pass.equals("admin"))
{
String msg="Hello "+ name;
//add a message to the model
m.addAttribute("message", msg);
return "viewpage";
}
else
{
String msg="Sorry "+ name+". You entered an incorrect password";
m.addAttribute("message", msg);
return "errorpage";
}
}
}

4. Provide the entry of controller in the web.xml file

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" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">  
  <display-name>SpringMVC</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>  

5. Define the bean in the xml file

spring-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">  
  
    <!-- Provide support for component scanning -->  
    <context:component-scan base-package="com.javatpoint" />  
  
    <!--Provide support for conversion, formatting and validation -->  
    <mvc:annotation-driven/>  
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">  
        <property name="prefix" value="/WEB-INF/jsp/"></property>  
        <property name="suffix" value=".jsp"></property>          
     </bean>  
</beans>  

6. Create the other view components

To run this example, the following view components must be located inside the WEB-INF/jsp directory.

viewpage.jsp

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

errorpage.jsp

<html>  
<body>  
${message}  
<br><br>  
<jsp:include page="/index.jsp"></jsp:include>  
</body>  
</html>  

Output:

Java Code Guru Ji (8920128728)

Sunday, September 15, 2019

Spring MVC Model Interface