Wednesday, October 13, 2021

How to upload/download file using Spring MVC and Spring Boot ? Example Tutorial

Hello guys, if you are wondering how to enable file upload and download from a Spring MVC application then you have come to the right place. This is an important functionality for any real-world application and knowing how to upload a file in a Spring application is important for professional Java developers. Earlier, I have shared how to upload files using Servlet and JSP using Apache Commons FileUpload library and In this tutorial, we are going to discuss how to upload and download files using Spring MVC. In general, spring makes common development tasks easier by providing out-of-box implementation so I expect this would be easier than before, so let's find out.


In the past, I have also shared the best Spring courses and books for Java developers. If you have just started learning the Spring framework or want to learn Spring in-depth, you can also take a look at those resources. 



How to upload/download Files on Spring Web Applications? 

This file upload is a very common task in any web application and this allows to have a good interaction with users with giving an opportunity to upload/download photos, files, and other materials through the web.


So in this article, we are focusing on what Spring offers for multipart support in web applications. So will discuss the MultipartResolver implementation for use with Apache Commons Fileupload.


1.  Add CommonsMultipartResolver Dependency to your spring project

This MultipartResolver resolver variation delegated to the application's local FileUpload library, allowing for optimal portability between Servlet containers. Will see how to add the dependency to our spring application

We will use the FileNameUtils class in commons-io to normalize the file name of the uploaded file.

<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.8.0</version>
</dependency>
<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
<version>1.4</version>
</dependency>




2. Build the frontend of the system using HTML/Javascript

Then we will focus on the file upload frontend of the application, which is used to upload
files to the backend of the system. The below code snippet shows the HTML and JavaScript which are used to upload the data to the spring backend.

<form class="form" id="file-form"
enctype="multipart/form-data">
<div class="form-group">
<label class="form-label required">
Select File (multiple supported)
</label>
<input type="file" multiple class="form-control required"
id="uploaded-file" name="uploaded-file" />
</div>
<div>&nbsp;</div>
<button class="btn btn-primary" type="submit">Upload</button>
</form>

<script>
$(function (){
$("#file-form").submit(function (){
$(this).ajaxSubmit({
beforeSubmit: function (){
return $('#file-form').valid();
},
success: function(response){
alert("Successfully uploaded the files");
},
error: function(){
alert("Error occurred while uploading the files");
},
url: '/api/upload',
type: 'POST'
});
return false;
});
});
</script>







3.Add the CommonsMultipartResolver bean into our Spring configuration 


Then we have to make use of the Spring boot's max file size
and max request size attributes to configure
he CommonsMultipartResolver.

@Bean(name = "multipartResolver")
public CommonsMultipartResolver multipartResolver() {
CommonsMultipartResolver multipartResolver = new CommonsMultipartResolver();
multipartResolver.setMaxUploadSize(100000);
return multipartResolver;
}

Then we have to create the API's to accept the files which is sent from 
the frontend of the application.
    
    
In there, we can use the new method copyFileUsingCommons.

<form:form method="POST" action="/students/uploadStudentFile" 
enctype="multipart/form-data">
    <table>
        <tr>
            <td>Select a file to upload</td>
            <td><input type="file" name="files" /></td>
        </tr>
        <tr>
            <td>Select a file to upload</td>
            <td><input type="file" name="files" /></td>
        </tr>
        <tr>
            <td>Select a file to upload</td>
            <td><input type="file" name="files" /></td>
        </tr>
        <tr>
            <td><input type="submit" value="Submit" /></td>
        </tr>
    </table>
</form:form>

So we can add multiple files using the above method. 
Let's discuss about the spring boot file upload.




4. Spring Boot File Upload

This is same as the normal file upload. but the spring framework makes it easier for developers to start the process of file uploading with minimum number of code lines. No servlet configuration is required because Boot will register and setup it for us if we include the web module in our dependencies.


<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<version>2.5.4.RELEASE</version>
</dependency>

So from the application.properties file, we can allow maxmimum file upload size to files which is uploading.


spring.servlet.multipart.max-file-size=256KB
spring.servlet.multipart.max-request-size=256KB

Other than that, we can control the location of file upload using the following code segement which is
also in the application.properties file.


spring.servlet.multipart.enabled=true
spring.servlet.multipart.location=${java.io.tempDirectory}

Here the tempDirectory means the temporary location which is file is added 
to the operating system.

How to upload/download file using Spring MVC and Spring Boot ?  Example Tutorial


That's all about how to upload or download files from a Spring-based Java application. We have seen how we can use the MultipartResolver to upload files in the Java web application. Spring Boot makes this task easier and you can enable this functionality by just setting spring.servlet.multipart.enabled configuration on Spring application.properties file. 

So in this tutorial, we discussed the different file upload/download methods using Spring MVC.  see you in the next tutorial.


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Thanks for reading this article so far. If you find this Spring File upload and download  Example then please share it with your friends and colleagues. If you have any questions or feedback then please drop a note.

P. S. - If you are a Java beginner and want to learn the Spring MVC from scratch, and looking for some best online resources then you can also check out these best Spring MVC courses for beginners. This list contains free Udemy and Pluralsight courses to learn Spring MVC from scratch.     

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