From Documentation
File Upload with Servlet Thread
When the event thread is disable (default), it is recommended to use Button or Toolbarbutton with upload="true" instead. For example,
<zk>
<zscript>
void upload(UploadEvent event) {
org.zkoss.util.media.Media media = event.getMedia();
if (media instanceof org.zkoss.image.Image) {
org.zkoss.zul.Image image = new org.zkoss.zul.Image();
image.setContent(media);
image.setParent(pics);
} else {
Messagebox.show("Not an image: "+media, "Error", Messagebox.OK, Messagebox.ERROR);
break; //not to show too many errors
}
}
</zscript>
<button label="Upload" upload="true" onUpload="upload(event)"/>
<toolbarbutton label="Upload" upload="true" onUpload="upload(event)"/>
<vbox id="pics" />
</zk>
If you prefer to use a dialog (Fileupload.get()), please take a look at ZK Component Reference: Fileupload for more inormation.
File Upload with Event Thread
If the event thread is disabled, the developer can use Button or Toolbarbutton with upload="true" instead. They behaves the same no matter the event thread is disabled or not.
However, if the event thread is disabled, it is convenient to use Fileupload.get() and other static methods.
<zk>
<button label="Upload">
<attribute name="onClick">{
org.zkoss.util.media.Media[] media = Fileupload.get(-1);
if (media != null) {
for (int i = 0; i < media.length; i++) {
if (media[i] instanceof org.zkoss.image.Image) {
org.zkoss.zul.Image image = new org.zkoss.zul.Image();
image.setContent(media[i]);
image.setParent(pics);
} else {
Messagebox.show("Not an image: "+media[i], "Error", Messagebox.OK, Messagebox.ERROR);
break; //not to show too many errors
}
}
}
}</attribute>
</button>
<vbox id="pics" />
</zk>
As shown, Fileupload.get(int) won't return until the end user uploads the files (and/or closes the dialog).