Spring Boot File Download - Hello World Example

In this example we will learn how to to download a file using Spring Boot Application. To do so we will define a Controller having the following -

• The Controller return type is of type void and add HttpServletResponse as an argument to the method.
• In a regular HTTP response, the Content-Disposition response header is a header indicating if the content is expected to be displayed inline in the browser, that is, as a Web page or as part of a Web page, or as an attachment, that is downloaded and saved locally. Set the Content-Disposition accordingly.
• Find the MIME Type of the file to be downloaded. This can be application/pdf, text/html,application/xml etc.
  If the mimetype is of unknown type, then it is set to application/octet-stream. In this case the browser displays the Save As
• Copy bytes to the response OutputStream from the InputStream.

Lets Begin-

Create the Maven Project as follows -

The pom.xml will be as follows -

<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.javainuse</groupId>
	<artifactId>boot-filedownload</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>1.4.1.RELEASE</version>
		<relativePath />
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>1.8</java.version>
	</properties>

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

	</dependencies>
</project>

Create the Bootstrap class as follows -

package com.javainuse;

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

@SpringBootApplication
public class SpringBootFileDownoad {

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

}

Next define the controller for downloading the file -

package com.javainuse.controller;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLConnection;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.util.FileCopyUtils;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/download")
public class FileDownloadController {

	private static final String EXTERNAL_FILE_PATH = "C:/fileDownloadExample/";

	@RequestMapping("/file/{fileName:.+}")
	public void downloadPDFResource(HttpServletRequest request, HttpServletResponse response,
			@PathVariable("fileName") String fileName) throws IOException {

		File file = new File(EXTERNAL_FILE_PATH + fileName);
		if (file.exists()) {

			//get the mimetype
			String mimeType = URLConnection.guessContentTypeFromName(file.getName());
			if (mimeType == null) {
				//unknown mimetype so set the mimetype to application/octet-stream
				mimeType = "application/octet-stream";
			}

			response.setContentType(mimeType);

			/**
			 * In a regular HTTP response, the Content-Disposition response header is a
			 * header indicating if the content is expected to be displayed inline in the
			 * browser, that is, as a Web page or as part of a Web page, or as an
			 * attachment, that is downloaded and saved locally.
			 * 
			 */

			/**
			 * Here we have mentioned it to show inline
			 */
			response.setHeader("Content-Disposition", String.format("inline; filename=\"" + file.getName() + "\""));

			 //Here we have mentioned it to show as attachment
			 //response.setHeader("Content-Disposition", String.format("attachment; filename=\"" + file.getName() + "\""));

			response.setContentLength((int) file.length());

			InputStream inputStream = new BufferedInputStream(new FileInputStream(file));

			FileCopyUtils.copy(inputStream, response.getOutputStream());

		}
	}
}

Start the application -

• Go to http://localhost:8080/download/file/soa.pdf
  
  
• Go to http://localhost:8080/download/file/soa.abc
  
  Since the from file name we get some unknown mime type, so we get the Save As window and content is not shown inline by the browser.
• In the above FileDownloadController set the Content-Disposition as attachment and again go to the url http://localhost:8080/download/file/soa.pdf