Spring Boot Model

last modified July 24, 2023

In this article we show how to work with a model in a Spring Boot application.The model is represented byModel,ModelMap, andModelAndView in Spring.

Spring is a popular Java application framework andSpring Bootis an evolution of Spring that helps create stand-alone, production-grade Springbased applications easily.

MVC

MVC (Model-View-Controller) is a software architecture pattern, whichseparates application into three parts: model, view, and controller. The modelrepresents a Java object carrying data. The view visualizes the data that themodel contains. The controller manages the data flow into model object andupdates the view whenever data changes; it keeps view and model separate.

Spring MVC

Spring MVC is the original web framework built on the Servlet API. Itis build on the MVC design pattern. Spring Framework 5.0 introduced a parallelreactive stack web framework calledSpring WebFlux.

Model, ModelMap, ModelAndView

Model,ModelMap, andModelAndView are used todefine a model in a Spring MVC application.Model defines a holder for model attributes and is primarily designed for addingattributes to the model.ModelMap is an extension ofModel withthe ability to store attributes in a map and chain method calls.ModelAndViewis a holder for a model and a view; it allows to return both model and view in onereturn value.

Spring Boot Model example

The following simple web application usesModel,ModelMap,andModelAndView in the controller methods. The model holdsapplication data, which is displayed in the view. We use the Freemaker libraryfor the view layer.

build.gradle...src├── main│   ├── java│   │   └── com│   │       └── zetcode│   │           ├── Application.java│   │           └── controller│   │               └── MyController.java│   └── resources│       ├── application.properties│       ├── static│       │   └── index.html│       └── templates│           └── show.ftlh└── test    ├── java    └── resources

This is the project structure of the Spring application.

plugins {    id 'org.springframework.boot' version '3.1.1'    id 'io.spring.dependency-management' version '1.1.0'    id 'java'}group = 'com.example'version = '0.0.1-SNAPSHOT'sourceCompatibility = '17'repositories {    mavenCentral()}dependencies {    implementation 'org.springframework.boot:spring-boot-starter-web'    implementation 'org.springframework.boot:spring-boot-starter-freemarker'}

This is the Gradle build file.

spring.main.banner-mode=offspring.main.log-startup-info=falsemymessage=Hello there

Theapplication.properties is the main configuration file in SpringBoot. We turn off the Spring banner and startup logging of the Spring framework.Themymessage property contains the message.

package com.zetcode.controller;import org.springframework.beans.factory.annotation.Value;import org.springframework.stereotype.Controller;import org.springframework.ui.Model;import org.springframework.ui.ModelMap;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.servlet.ModelAndView;import java.time.LocalDateTime;import java.time.ZoneId;import java.time.format.DateTimeFormatter;import java.time.format.FormatStyle;import java.util.Locale;@Controllerpublic class MyController {    @Value("${mymessage}")    private String message;    @GetMapping("/getMessage")    public String getMessage(Model model) {        model.addAttribute("message", message);        return "show";    }    @GetMapping("/getMessage2")    public ModelAndView getMessage() {        var mav = new ModelAndView();        mav.addObject("message", message);        mav.setViewName("show");        return mav;    }    @GetMapping("/getMessageAndTime")    public String getMessageAndTime(ModelMap map) {        var ldt = LocalDateTime.now();        var fmt = DateTimeFormatter.ofLocalizedDateTime(                FormatStyle.MEDIUM);        fmt.withLocale(new Locale("sk", "SK"));        fmt.withZone(ZoneId.of("CET"));        String time = fmt.format(ldt);        map.addAttribute("message", message).addAttribute("time", time);        return "show";    }}

This isMyController. It has three methods that respond toclient requests.

@Controllerpublic class MyController {

MyController is annotated with the@Controller annotation.

@Value("${mymessage}")private String message;

With the@Value annotation, we insert themymessageproperty from theapplication.properties file into themessage attribute.

@GetMapping("/getMessage")public String getMessage(Model model) {    model.addAttribute("message", message);    return "show";}

The@GetMapping maps the/getMessage URL pattern to thegetMessage method. In thegetMessage method, weuse theModel. It receives amessage attribute withtheaddAttribute method. The return keyword returns the name ofthe view, which will be resolved toshow.ftlh, because we use theFreemarker template system.

@GetMapping("/getMessage2")public ModelAndView getMessage() {    var mav = new ModelAndView();    mav.addObject("message", message);    mav.setViewName("show");    return mav;}

In the second case, we use theModelAndView. We useaddObject andsetViewName to add the model dataand the view name. The method returnsModelAndView object.

@GetMapping("/getMessageAndTime")public String getMessageAndTime(ModelMap map) {    var ldt = LocalDateTime.now();    var fmt = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM);    fmt.withLocale(new Locale("sk", "SK"));    fmt.withZone(ZoneId.of("CET"));    var time = fmt.format(ldt);    map.addAttribute("message", message).addAttribute("time", time);    return "show";}

In thegetMessageAndTime method, we useModelMap.The model map receives two attributes: message and time.

<!DOCTYPE html><html>    <head>        <title>Home page</title>        <meta charset="UTF-8"/>        <meta name="viewport" content="width=device-width, initial-scale=1.0">    </head>    <body>        <ul>            <li><a href="getMessage">Get message</a></li>            <li><a href="getMessage2">Get message 2</a></li>            <li><a href="getMessageAndTime">Get message and time</a></li>        </ul>    </body></html>

This is the home page. It contains three links that call the Spring controllermethods. It is a static resource and is located in the predefinedsrc/main/resources/static directory.

<!DOCTYPE html><html>    <head>        <title>Message</title>        <meta charset="UTF-8">        <meta name="viewport" content="width=device-width, initial-scale=1.0">    </head>    <body>        <p>            Message: ${message}        </p>        <#if time??>            <p>Date and time: ${time}</p>        </#if>    </body></html>

Theshow.ftlh is a Freemarker template file. It is located in thepredefinedsrc/main/resources/templates directory. It outputs themessage and optionally the time with the${} syntax.

package com.zetcode;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublic class Application  {    public static void main(String[] args) {        SpringApplication.run(Application.class, args);    }}

Application is the entry point which sets up Spring Bootapplication.

$ ./gradlew bootRun

After we start the application, we navigate tolocalhost:8080.

In this article we have have worked with a model in a Spring application.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensiveprogramming experience. I have been writing programming articles since 2007.To date, I have authored over 1,400 articles and 8 e-books. I possess morethan ten years of experience in teaching programming.

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