For Explanation watch video

to generate QR we will use ZXing

ZXing (“Zebra Crossing”) barcode scanning library for Java, Android

QR code is used to store large amounts of data in a limited space

Directoy Structure

step 1 : create project with web dependency

Add below dependencies to use ZXing

<!-- https://mvnrepository.com/artifact/com.google.zxing/core -->
  <dependency>
   <groupId>com.google.zxing</groupId>
   <artifactId>core</artifactId>
   <version>3.5.2</version>
  </dependency>

  <dependency>
   <groupId>com.google.zxing</groupId>
   <artifactId>javase</artifactId>
   <version>3.5.2</version>
  </dependency>

pom.xml

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>3.2.1</version>
  <relativePath /> <!-- lookup parent from repository -->
 </parent>
 <groupId>com.example</groupId>
 <artifactId>SpringBootQrCode</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 <name>SpringBootQrCode</name>
 <description>Demo project for Spring Boot</description>
 <properties>
  <java.version>17</java.version>
 </properties>
 <dependencies>
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  <!-- https://mvnrepository.com/artifact/com.google.zxing/core -->
  <dependency>
   <groupId>com.google.zxing</groupId>
   <artifactId>core</artifactId>
   <version>3.5.2</version>
  </dependency>

  <dependency>
   <groupId>com.google.zxing</groupId>
   <artifactId>javase</artifactId>
   <version>3.5.2</version>
  </dependency>

  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-test</artifactId>
   <scope>test</scope>
  </dependency>
  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-devtools</artifactId>
  </dependency>
 </dependencies>

 <build>
  <plugins>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
   </plugin>
  </plugins>
 </build>

</project>

SpringBootQrCodeApplication

we need to manually register a message converter for BufferedImage HTTP Responses

package com.example.demo;

import java.awt.image.BufferedImage;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.http.converter.BufferedImageHttpMessageConverter;
import org.springframework.http.converter.HttpMessageConverter;

@SpringBootApplication
public class SpringBootQrCodeApplication {

 public static void main(String[] args) {
  SpringApplication.run(SpringBootQrCodeApplication.class, args);
 }

 @Bean
 public HttpMessageConverter<BufferedImage> createImageHttpMessageConverter() {
  return new BufferedImageHttpMessageConverter();
 }
}

QrCodeController

package com.example.demo.controller;

import java.awt.image.BufferedImage;

import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.google.zxing.BarcodeFormat;
import com.google.zxing.client.j2se.MatrixToImageWriter;
import com.google.zxing.common.BitMatrix;
import com.google.zxing.qrcode.QRCodeWriter;

@RestController
@RequestMapping("/qr")
public class QrCodeController {

 @GetMapping(value = "/{barcode}", produces = MediaType.IMAGE_PNG_VALUE)
 public ResponseEntity<BufferedImage> barbecueEAN13Barcode(@PathVariable("barcode") String barcode)
   throws Exception {

  QRCodeWriter barcodeWriter = new QRCodeWriter();
     BitMatrix bitMatrix = 
       barcodeWriter.encode(barcode, BarcodeFormat.QR_CODE, 200, 200);

  return new ResponseEntity<>(MatrixToImageWriter.toBufferedImage(bitMatrix),HttpStatus.OK);
 }

}