Spring rest: @RequestParam: Bind query parameter to a list

In this post, I am going to explain how to bind query parameter to a list.

 

For example,

to-upper?str=myValue1&str=myValue2&str=myValue3

In the above example, query parameter str is repeated thrice, I want to bind all the values associated with query parameter str to a list of strings. I can do this by mapping RequestParam to list of strings like below.

@RequestMapping("/to-upper")
public List<String> home(@RequestParam(name = "str") List<String> strs) {
	.......
	.......
}

Find the below working application.

 

Step 1: Create new maven project ‘map-query-param-to-list’.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

 

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.sample.app</groupId>
	<artifactId>map-query-param-to-list</artifactId>
	<version>1</version>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.1.6.RELEASE</version>
	</parent>

	<name>springbootApp</name>
	<url>http://maven.apache.org</url>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>

	<dependencies>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>
</project>

 

Step 3: Create a package ‘com.sample.app.controller’ and define the class StringController.

 

StringController.java

 

package com.sample.app.controller;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class StringController {
	@RequestMapping("/to-upper")
	public List<String> home(@RequestParam(name = "str") List<String> strs) {
		if (strs == null || strs.isEmpty()) {
			return Collections.EMPTY_LIST;
		}

		List<String> upperCaseStrings = new ArrayList<>();

		for (String str : strs) {
			upperCaseStrings.add(str.toUpperCase());
		}

		return upperCaseStrings;
	}
}

 

Step 4: Define main application class.

 

App.java

 

package com.sample.app;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App {
    public static void main(String[] args) {

        SpringApplication.run(App.class, args);

    }
}

 

Total project structure looks like below.

 

 

Run App.java.

 

Open the url 'http://localhost:8080/to-upper?str=ram&str=ptr&str=krishna' in browser, you will see the strings converted to uppercase in browser output.

 

["RAM","PTR","KRISHNA"]

 

You can download complete working application from below link.

https://github.com/harikrishna553/springboot/tree/master/rest/map-query-param-to-list

 

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