Spring WebFlux File download example

In this tutorial, I will show you File download using Spring WebFlux example.

This Spring Boot App works with:
– Angular 8 / Angular 10 / Angular 11 / Angular 12 / Angular 13 / Angular 14 / Angular 15
– Angular Material 12
– Vue Client / Vuetify Client
– React Client / React Hooks Client
– React Image Upload with Preview
– Material UI Client
– Axios Client

Deployment: Deploy Spring Boot App on AWS – Elastic Beanstalk

Contents

Spring WebFlux File download example Overview
Technology
Setup Spring Boot project
Create Service for File Download
Create Controller for WebFlux File download
Source Code
Conclusion
Further Reading

Spring WebFlux File download example Overview

Our Spring Boot Reactive Web – WebFlux File Upload Application will provide API for downloading File from server with the url link.

Here is the API to be exported:

Methods	Urls	Actions
GET	/files/[filename]	download a File

This is the static folder that stores all uploaded files:

For deleting file, kindly visit:
Spring Boot Delete File example

Technology

Java 17/11
Spring Boot 3/2 (with Spring WebFlux)
Maven 3.6.1

Setup Spring Boot project

Open pom.xml and add WebFlux dependency:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

Create Service for File Download

service/FileStorageService.java

package com.bezkoder.spring.webflux.file.service;

import java.net.MalformedURLException;
import java.nio.file.Path;
import java.nio.file.Paths;

import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.core.io.buffer.DefaultDataBufferFactory;
import org.springframework.stereotype.Service;

import reactor.core.publisher.Flux;

@Service
public class FileStorageService {

  private final Path root = Paths.get("uploads");

  @Override
  public Flux<DataBuffer> load(String filename) {
    try {
      Path file = root.resolve(filename);
      Resource resource = new UrlResource(file.toUri());

      if (resource.exists() || resource.isReadable()) {
        return DataBufferUtils.read(resource, new DefaultDataBufferFactory(), 4096);
      } else {
        throw new RuntimeException("Could not read the file!");
      }
    } catch (MalformedURLException e) {
      throw new RuntimeException("Error: " + e.getMessage());
    }
  }
}

Firstly, we read the file content as a Resource.

Then if the resource exists, we create a Flux of DataBuffer from the file content using DataBufferUtils class, and set a buffer size of 4096 bytes. You can adjust the buffer size depending on your use case.

Create Controller for WebFlux File download

In controller package, we create FileController.

controller/FileController.java

package com.bezkoder.spring.webflux.file.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

import com.bezkoder.spring.webflux.file.service.FileStorageService;

import reactor.core.publisher.Flux;

@Controller
@CrossOrigin("http://localhost:8081")
public class FileController {
  @Autowired
  FileStorageService storageService;

  @GetMapping("/files/{filename:.+}")
  public ResponseEntity<Flux<DataBuffer>> getFile(@PathVariable String filename) {
    Flux<DataBuffer> file = storageService.load(filename);

    return ResponseEntity.ok().header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + filename + "\"")
        .contentType(MediaType.APPLICATION_OCTET_STREAM).body(file);
  }
}

– @CrossOrigin is for configuring allowed origins.
– @Controller annotation is used to define a controller.
– @GetMapping annotation is for mapping HTTP GET /files/[filename] requests onto getFile() method.

– We use @Autowired to inject implementation of FileStorageService bean to local variable.
– Then use FileStorageService‘s load() method to create a Flux of DataBuffer from the file, and use the body() method of ResponseEntity to write the file content to the response.
– We also use body() and contentType() method to set the file name and content type in the response headers.