public interface Upload
MultiFileItem FormItems that enable users to upload
one or more files as a background operation, without leaving the current page
documentation assumes you are using the Smart GWT Java Server. If you are not, skip to the
sections near the end of this document.
Note: This documentation topic is concerned specifically with file upload. Developers looking for a general discussion of how Binary fields are handled with the Smart GWT server may also be interested in the
Binary Fields overview.
Single file upload: "binary" field type
To use Smart GWT's client-server upload system, you use a
DataSource field of
type "binary". By
default, a DynamicForm bound to a DataSource with a field of type "binary" will use the
FileItem, which displays a standard HTML <input
type="upload"> form control.
When you call
DynamicForm.saveData() on a DynamicForm
containing a FileItem, Smart GWT processes the save identically to a saveData() call that did
not include a file upload:
field type "binary".
Client-side callbacks, such as the callback passed to saveData(), fire normally.
Note that FileItems cannot be programmatically
populated - this is a browser security restriction over which we have no control. This
restriction means that we are unable to populate a FileItem with the correct filename when a
form is editing an existing record. Also, when you call saveData() on a form that is editing a
new record, the FileItem will be cleared on successful completion of the saveData() call; this
is a side-effect of the form being placed into "edit" mode. In both of these cases, the fact
that the FileItem has been cleared will not cause the persisted binary data to be removed by
Smart GWT Server on subsequent calls to setData(). If the user selects another file, it will
overwrite the existing one; if the FileItem is left blank, the server simply ignores it. If you
actually wish to wipe out the value of a binary field, call
updateData() on the underlying dataSource,
passing an explicit null value for the binary field.
DataSources can have multiple binary
fields, but developers should be aware that you can not submit more than one FileItem in a
single form. Developers needing to upload multiple files can either use the
MultiFileItem, or use multiple DynamicForms (nested
VStack, or similar), and submit them
separately. For an add operation, the pattern would be to perform the initial submission of
values for the record and then use the
callback to apply the primary key value for the new record to the forms with binary fields and
save them to the server separately. This approach has the advantage that if an error or timeout
occurs, users will not be caught waiting for files to complete uploading before being notified
of the failure and having to repeat the entire transaction.
Note when adding a new record using this pattern, if you have a binary field marked as
required="true" it should
be submitted as part of the initial submission.
Restricting upload sizes
server framework includes mechanisms for setting maximum allowable file sizes. The first,
properties, is meant to prevent an end user from uploading a file large enough to cause
memory issues on the server.
To configure the maximum allowed size of a single uploaded file (disabled by default), set the fileUpload.maxFileSize property's value (in bytes):
To configure the maximum combined size of all files in a single request (disabled by default), set the fileUpload.maxSize property's value (also in bytes):
Another configuration property controls the default value
of a "binary" DataSourceField's
maxFileSize attribute, suitable
for managing storage requirements for a given DataSource over time (e.g., limiting images to
To configure the maximum number of files in a single request (set to 10 by default), set the fileUpload.maxFileCount property's value:
UploadItem is bound to a "binary"
DataSourceField with a
maxFileSize setting, a
automatically added to the item's
validators. In supported
maxFileSize validator is a client-side check that the size of a file
selected for upload does not exceed the field's
maxFileSize. Note, however, that
server-side enforcement of the
maxFileSize is always required because the user's
browser might not support client-side file size checks. Also, any client-side check can be
bypassed by a malicious user.
Processing File Uploads with server-side business logic
Server-side business logic that processes file uploads may retrieve upload files via the server side API dsRequest.getUploadedFile(fieldName). The uploaded file is returned as an instance of ISCFileItem, which provides access to a Java InputStream as well as metadata about the file (size, name). See the server-side JavaDoc (com.isomorphic.*) for details.
Server-side validation errors may be provided, including validation errors for the uploaded file (such as too large or invalid content), and will be displayed in the form that attempted an upload.
Be aware of the following special concerns when processing file uploads:
Multi file upload: MultiFileItem
The MultiFileItem provides an interface for a user to save one or more files that are related to a DataSource record, where each file is represented by a record in a related DataSource.
MultiFileItem docs for details.
Upload without the Smart GWT Server
If it is acceptable that the application will do a full-page reload after the upload completes, you can simply:
DynamicForm.encoding to "multipart"
UploadItem to get a basic HTML
DynamicForm.action to a URL where you have deployed server-side code to handle the upload
to cause the form to be submitted
Note that when you submitForm(), the only values that will be
sent to your actionURL are values for which actual FormItems exist. This differs from
saveData(), in which the entire set of
form values are always sent. To handle
submitting extra values, use
For further details, see the
Background upload without the Smart GWT Server
Achieving background file upload
without using the Smart GWT server is also possible although considerably more advanced. In
addition to the steps above, create a hidden <iframe> element in the page, and use
DynamicForm.target to target the form
submission at this IFRAME. In order receive a callback notification when the upload completes,
after processing the file upload, your server should output HTML content for the IFRAME that
includes a <SCRIPT> block which will navigate out of the IFRAME (generally via the