public interface BinaryFields
UI components
such as ListGrid and FileItem will offer UIs to download, view and upload
files stored in a binary field. DataSource.downloadFile() and DataSource.viewFile() can be used to programmatically trigger download/viewing as well. Note
that these automatic features, and components like TileGrid that make use of them, only work correctly for
DataSources that declare a valid primaryKey field.
If you would like to obtain a URL to the binary data (for example to use
as src), you can use the DataSource.getFileURL() API.
As covered
under the "binary" field type description, binary
fields imply 3 other related metadata fields named after the binary field, which store the file
size, file name and date of creation.
When using one of the built-in server DataSource
types (SQL, JPA, Hibernate), these metadata fields, UI controls and APIs will work with no
special effort - just declare a binary field. For JPA or Hibernate the Java getter/setter for
the binary field must be of type byte[] or Byte[] (this is imposed by the ORM system); if you
are using the SQL DataSource, no additional declarations are required unless you are using
DataSource.beanClassName, in
which case you must add getters/setters of type InputStream, or one of the types listed for
JPA/Hibernate.
For metadata fields like the file size, providing storage for the metadata
fields (SQL columns or JPA/Hibernate getter/setters) is optional but highly recommended. If
you don't want a particular metadata field, you can declare a <field> for it explicitly
and set ignore="true". Note: If you decide not to store the "_filename" metadata
element, the built-in binary UI controls in components like ListGrid, mentioned above, do not
work properly. In the absence of a filename metadata field, it is necessary to set mime-type on the binary field -
otherwise, we can't make a reasonable guess at a MIME type, so the browser tends not to know
what to do with the downloaded content. Omiting the file size metadata will simply cause the
browser not to show a progress dialog during download, or not to show an accurate one.
Downloading from binary fields
If writing a custom DataSource or writing a DMI, implement the "downloadFile" and "viewFile" operationTypes, and return data for a single Record which has binary data as the field value for the binary field - accepted types are InputStream, byte[], java.sql.Blob or String.
For example, you could return a Java bean
with a getter method which returns a byte[], and which is named after the binaryField using
Java Beans conventions: getFieldName(). Or, return a Java Map where a
byte[] is stored under a key named the same as the binary field's name.
As discussed under
FieldType, additional metadata fields are implied when you
declare a binary field. Returning a value for the "_filesize" field will allow the browser to
show progress of the download. Returning a value for the "_filename" field will cause the
downloaded file to be named after the "_filename" value.
Refer to this example to see how this case works.
Uploading to binary fields
Again with the built-in server DataSource types, no special effort is required.
For a custom
DataSource, an upload from a FileItem control
(the default upload control) is treated just like an ordinary "add" or "update" DataSource
operation. The uploaded file(s), if any, are available from the server-side API
dsRequest.getUploadedFile(). Metadata fields such as "_filename" can be populated
from the data in the returned ISCFileItem.
Refer to this example to see how this case works.
Binary fields and normal "fetch"
For an ordinary "fetch" operation, it's generally useless to return data for a binary field, because in most cases code running in the browser would not be able to do anything with a binary value (such as invoke a PDF viewing plugin). For this reason the Smart GWT Server will automatically omit values of type InputStream, byte[] or Blob during a normal "fetch".
However you can deliver the binary data to the browser by transforming it to a Base64-encoded
String by setting DataSourceField.encodeInResponse on your <field> declaration. This can be used with
certain browser features such as image data URIs, but note that some older browsers (notably IE7 and
earlier) do not support data URIs.
Refer to this example to see how this case works.
Downloads unrelated to binary fields
If
you want to download or view a file that is not stored in a DataSource record, for example, you
want to dynamically generate a report of some kind on the fly, any DMI can return a binary
response by calling the server-side API RPCManager.doCustomResponse() and writing
binary data directly to the ServletResponse outputStream.
It's typical to represent an operation that returns a binary stream as a DataSource request with operationType "fetch", especially if it takes Criteria that identify DataSource Records that will be used to create the binary stream.
When initiating such a download, set downloadResult via the
requestProperties argument of DataSource.fetchData() so that the client-side framework knows that a download will occur
instead of a normal response. In this case, callbacks will not be fired because code in the
browser does not receive notification that the download has initiated or has completed.
Refer to this example to see how this case works.
Binary handling without the Smart GWT Server
To download or view files with the Smart GWT Server, you can write a servlet that streams back binary data. For a download, you can then redirect the main page to the servlet by setting window.location - be sure the download can never fail if you this, because any error message returned by the server in lieu of a file will replace the application instead of triggering a "Save As.." dialog.
To view a file, you can open a new browser window to the URL of the servlet.
Refer to this example to see how this case works.