Spring Boot @ModelAttribute
last modified July 6, 2020
Spring Boot @ModelAttribute tutorial shows how to use the @ModelAttribute annotation in a Spring
application.
Spring is a popular Java application framework and Spring Boot is an evolution of Spring that helps create stand-alone, production-grade Spring based applications easily.
@ModelAttribute
@ModelAttribute binds a method parameter or method return value to
a named model attribute, which is exposed to web views. Methods annotated with
@ModelAttribute are invoked before the controller methods with
@RequestMapping.
Spring Boot @ModelAttribute example
The following application demonstrates the usage of @ModelAttribute.
It is used to generate a message of the day in the application. The message is
read from the properties file.
pom.xml
src
├── main
│ ├── java
│ │ └── com
│ │ └── zetcode
│ │ ├── Application.java
│ │ ├── controller
│ │ │ └── MyController.java
│ │ └── service
│ │ ├── IMessageService.java
│ │ └── MessageService.java
│ └── resources
│ ├── application.properties
│ ├── static
│ │ └── index.html
│ └── templates
│ ├── pageOne.html
│ └── pageTwo.html
└── test
└── java
This is the project structure.
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.zetcode</groupId>
<artifactId>springbootmodelattributeex</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>11</maven.compiler.source>
<maven.compiler.target>11</maven.compiler.target>
</properties>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.1.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
This is the Maven pom.xml file. The
spring-boot-starter-parent is a parent POM providing dependency and
plugin management for applications built with Maven. The
spring-boot-starter-thymeleaf is a starter for building MVC web
applications using Thymeleaf views. The spring-boot-maven-plugin
packages Spring applications into executable JAR or WAR archives.
spring.main.banner-mode=off logging.level.org.springframework=ERROR messages.motd=Welcome
The application.properties is the main configuration file in Spring Boot.
We turn off the Spring banner and reduce the amount of
logging of the Spring framework by selecting only error messages.
The messages.motd property contains the message.
package com.zetcode.service;
public interface IMessageService {
String getMessage();
}
The IMessageService contains the getMessage()
contract method.
package com.zetcode.service;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;
@Service
public class MessageService implements IMessageService {
@Value("${messages.motd}")
private String motd="Hello";
@Override
public String getMessage() {
return motd;
}
}
The implementation of the getMessage() method retrieves the
message from the properties file, using the @Value annotation.
package com.zetcode.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import com.zetcode.service.IMessageService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;
@Controller
public class MyController {
@Autowired
private IMessageService messageService;
@GetMapping("/pageOne")
public String getPageOne() {
return "pageOne";
}
@GetMapping("/pageTwo")
public String getPageTwo() {
return "pageTwo";
}
@ModelAttribute("motd")
public String message() {
return messageService.getMessage();
}
}
Since MyController is annotated with a @Controller annotation,
it becomes a Spring MVC controller class. With @GetMapping annotation,
we map two URL patterns to Thymeleaf views. Both of these templates receive a motd
model attribute.
@ModelAttribute("motd")
public String message() {
return messageService.getMessage();
}
A method annotated with @ModelAttribute is executed before
@RequestMapping method and their specializations such as @GetMapping.
The message generated from the messageService is stored in the motd
model attribute and will be available to both Thymeleaf views.
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
<title>Page one</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<h2>Page one</h2>
<p th:text="'Message of the day: ' + ${motd}"></p>
</body>
</html>
This is pageOne.html view. The motd attribute is accessed
with ${} syntax.
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
<title>Page two</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<h2>Page two</h2>
<p th:text="'Message of the day:' + ${motd}"></p>
</body>
</html>
This is pageTwo.html view.
<!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>
<a href="pageOne">Go to page one</a><br>
<a href="pageTwo">Go to page two</a>
</body>
</html>
This is home page. It contains two links.
package com.zetcode;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
Application is the entry point which sets up Spring Boot
application. The @SpringBootApplication annotation enables
auto-configuration and component scanning. It is a convenience annotation
for @Configuration, @EnableAutoConfiguration,
and @ComponentScan annotations.
$ mvn spring-boot:run
After the application is run, we can navigate to localhost:8080.
In this tutorial, we have shown how to use @ModelAttribute annotation in a Spring application.