In this post, we'll take a look at how to implement a file upload in a Spring Boot application.
We'll start by looking at the @ConfigurationProperties annotation and how it can be used to configure file uploads in Spring Boot. We'll then create a simple HTML form that allows users to select a file to upload. Finally, we'll implement a controller that handles the file upload and saves the file to a directory on the server.
Spring Boot provides a number of properties that can be used to configure file uploads in a Spring Boot application. These properties are prefixed with spring.servlet.multipart.
.
The most important property is spring.servlet.multipart.enabled
. This property must be set to true
to enable file uploads in Spring Boot.
The next property is spring.servlet.multipart.file-size-threshold
. This property specifies the size threshold for files that will be stored in memory. Files that are larger than this threshold will be written to a temporary file on disk.
The last property we'll look at is spring.servlet.multipart.location
. This property specifies the location on the server where uploaded files will be stored. This location must be a directory that is writable by the user that the application is running as.
Now that we've configured Spring Boot for file uploads, we need to create an HTML form that allows users to select a file to upload.
The form should have a file
input field and a submit
button. The file
input field should have the multiple
attribute set to true
. This will allow users to select multiple files to upload.
The action
attribute of the form
element should be set to the URL of the controller that will handle the file upload. The method
attribute should be set to POST
.
Now that we have a form for uploading files, we need to implement a controller that handles the file upload.
The controller should have a @PostMapping
annotation with the value /upload
. This will map the URL /upload
to the controller method.
The controller method should have a @RequestParam
annotation with the value file
. This will bind the file
input field to a MultipartFile
object.
The controller method should also have a @ResponseBody
annotation. This will cause the controller method to return the contents of the uploaded file as the response to the request.
Finally, the controller method should have a @RequestMapping
annotation with the value /upload
. This will map the URL /upload
to the controller method.
Once the file has been uploaded, we need to save it to the directory that we configured earlier. We can do this by calling the transferTo()
method on the MultipartFile
object.
The transferTo()
method takes a File
object as an argument. We can create a File
object by concatenating the configured location with the original filename of the uploaded file.
Once the file has been transferred, we can return a ResponseEntity
object with a 201
status code to indicate that the file was successfully uploaded.
In this post, we've looked at how to implement a file upload in a Spring Boot application. We've started by looking at the @ConfigurationProperties annotation and how it can be used to configure file uploads in Spring Boot. We've then created a simple HTML form that allows users to select a file to upload. Finally, we've implemented a controller that handles the file upload and saves the file to a directory on the server.