Spring Boot @RequestParam tutorial
last modified July 6, 2020
In this tutorial, we are going to use the @RequestParam annotation
in a controller to read request parameters.
Spring is a popular Java application framework and Spring Boot is an evolution of Spring which helps create stand-alone, production-grade Spring based applications easily.
Spring @RequestParam
@RequestParam is a Spring annotation used to bind a web request parameter to a method parameter.
It has the following optional elements:
- defaultValue - used as a fallback when the request parameter is not provided or has an empty value
- name - name of the request parameter to bind to
- required - tells whether the parameter is required
- value - alias for name
Spring @RequestParam example
The following example creates a Spring Boot web application which uses @RequestParam.
We have an HTML form with two tags: text input and check box. These two tags create request
parameters that are read in the controller with @RequestParam.
pom.xml
src
├── main
│ ├── java
│ │ └── com
│ │ └── zetcode
│ │ ├── Application.java
│ │ └── controller
│ │ └── MyController.java
│ └── resources
│ └── static
│ └── index.html
└── test
└── java
This is the project structure of the Spring Boot application.
<?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>requestparamex</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>2.2.2.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
In the the Maven build file we have the spring-boot-starter-web, which is a starter
for building web applications using Spring MVC. It uses Tomcat as the default
embedded container. The spring-boot-devtools is an artifact useful
when developing Spring Boot applications; it allows automatic restart or live reload
of applications. The application is packaged into a JAR file.
package com.zetcode.controller;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
public class MyController {
@RequestMapping(path="/message", produces=MediaType.TEXT_PLAIN_VALUE)
@ResponseBody
public String processForm(@RequestParam(defaultValue="Guest") String name,
@RequestParam(required = false) String adult) {
var greet = "on".equals(adult) ? "Good morning" : "Hi";
return String.format("%s %s!", greet, name);
}
}
The controller processes the HTML form. It reads two parameters from the request.
@Controller
public class MyController {
A controller class is annotated with the @Controller annotation in Spring.
@RequestMapping(path="/message", produces=MediaType.TEXT_PLAIN_VALUE) @ResponseBody
The processForm() method is mapped to the /message path
and returns plain text. The @ResponseBody annotation indicates that
the method return value is bound to the web response body.
public String processForm(@RequestParam(defaultValue="Guest") String name,
@RequestParam(required = false) String adult) {
With the @RequestParam annotation, we bind the request parameter
to the method variable. The defaultValue option gives a default
value if the parameter is not available (the text input was left empty).
The required option tells that the parameter is required.
The method retuns a string.
var greet = "on".equals(adult) ? "Good morning" : "Hi";
return String.format("%s %s!", greet, name);
We build the message and return it.
<!DOCTYPE html>
<html lang="en">
<head>
<title>Home page</title>
<meta charset="UTF-8"/>
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
</head>
<body>
<form action="message">
<div>
<label>Name:</label>
<input type="text" name="name">
</div>
<div>
<label><input type="checkbox" name="adult">Adult</label>
</div>
<button type="submit">Submit</button>
</form>
</body>
</html>
The index.html file is the home page. The file is located in the src/main/resources/static
directory, where Spring Boot expects static resources such as HTML or CSS files.
We have a simple HTML form with input text and check box tags.
<form action="message">
The action option contains a string that is used in controller method mapping.
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.
$ mvn spring-boot:run
After the application is run, we can navigate to localhost:8080.
In this tutorial, we have created web application with Spring Boot framework.
We have demonstrated the usage of @RequestParam.