Handling file uploads

Uploading files in a form using multipart/form-data

The standard way to upload files in a web application is to use a form with a special multipart/form-data encoding, which allows to mix standard form data with file attachments.

Start by writing an HTML form:

include::{sourcedir}/../resources/templates/upload/File-Upload.html[]

Now let’s define the upload action:

include::{sourcedir}/controllers/upload/FileUploadController.java[tags=upload-from-form]

The uploaded file is accessed using the @Attribute("upload") FileItem uploaded. upload is the name of the field used in the upload form. From the file item, you can:

  1. get the file name

  2. get the file size and mime type

  3. get the content of the file as a byte array (will load the content in memory), or as a stream

Important
 Wisdom may decide to store the uploaded file to a temporary directory, but this depends on the file size and current load of the server. If you want to store the file on disk, you must copy the file by yourself.

Direct file upload

Another way to send files to the server is to use Ajax to upload files asynchronously from a form. In this case, the request body will not be encoded as multipart/form-data, but will just contain the plain file contents.

include::{sourcedir}/controllers/upload/FileUploadController.java[tags=upload-from-ajax]

The context().getReader() method lets you access the raw content of the request. content().body() returns the raw content as a String.