GWT UiBinder で FileUpload を使う

<!DOCTYPE ui:UiBinder SYSTEM "http://dl.google.com/gwt/DTD/xhtml.ent">
<ui:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder"
 xmlns:g="urn:import:com.google.gwt.user.client.ui">
 <ui:style>
  
 </ui:style>
 <g:HTMLPanel>
   <g:VerticalPanel>
     <g:HTML><h2>Select a file:</h2></g:HTML>
     <g:FileUpload ui:field="fileUpload"></g:FileUpload>
     <g:HTML><br/></g:HTML>
     <g:Button ui:field="button">Upload File</g:Button>
   </g:VerticalPanel>
 </g:HTMLPanel>
</ui:UiBinder> 

package yanzm.example.hellowtgt.client;

import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.uibinder.client.UiBinder;
import com.google.gwt.uibinder.client.UiField;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.Composite;
import com.google.gwt.user.client.ui.FileUpload;
import com.google.gwt.user.client.ui.Widget;

public class FileUploadButton extends Composite {

 private static FileUploadUiBinder uiBinder = GWT
   .create(FileUploadUiBinder.class);

 interface FileUploadUiBinder extends UiBinder<Widget, FileUploadButton> {
 }
 
 @UiField
 FileUpload fileUpload;
 
 @UiField
 Button button;

 public FileUploadButton() {
  initWidget(uiBinder.createAndBindUi(this));
  
  button.addClickHandler(new ClickHandler() {
   @Override
   public void onClick(ClickEvent event) {
    String filename = fileUpload.getFilename();
    if(filename.length() == 0) {
     Window.alert("No file selected");
    }
    else {
     Window.alert("Start upload " + filename);
    }
   }
  });
 }
}

■ その他
・Java code による実装例 (Showcase)
・com.google.gwt.user.client.ui.FileUpload