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About Ilias Tsagklis

Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.

File Upload Example

With this example we are going to demonstrate how to make a File Upload using the Google Web Toolkit, that is an open source set of tools that allows web developers to create and maintain complex JavaScript front-end applications in Java. In short, to make a File Upload we have performed the steps below:

  • The FileUploadExample class implements the com.google.gwt.core.client.EntryPoint interface to allow the class to act as a module entry point. It overrides its onModuleLoad() method.
  • Create a new VerticalPanel.
  • Add a Label to the VerticalPanel.
  • Create a new Instance of FileUpload
  • Create a Button for submit. Add a ClickHandler to the button and override its onClick(ClickEvent event) method to handle click events. For example you can check the extension of a file before uploading it.
  • Add the widgets to the VerticalPanel.
  • Add the VerticalPanel to the RootPanel, that is the panel to which all other widgets must ultimately be added.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.enterprise;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.FileUpload;
import com.google.gwt.user.client.ui.HTML;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.VerticalPanel;

public class FileUploadExample implements EntryPoint {
    //Allowed files (.pdf for this example)
	private final String extention = ".pdf";

	public void onModuleLoad() {

  // Create new Instance of vertical panel to align the widgets
		VerticalPanel vp = new VerticalPanel();

  // Add label
		vp.add(new HTML(""));

  // Create new Instance of FileUpload 
		final FileUpload fileUpload = new FileUpload();

  // Create button for submit
		Button uploadButton = new Button("Upload");

  // Add ClickHandler to the button
		uploadButton.addClickHandler(new ClickHandler() {

			public void onClick(ClickEvent event) {

    //Get file name

    String filename = fileUpload.getFilename();

    // Check the length of the filename
				if (filename.length() != 0) {

  // Get the extention 
					String fileExtention = filename.substring(filename.length() - extention.length(), filename.length());

  // Check if the extention is '.pdf'

  if (!fileExtention.equals(extention)) {
						Window.alert("Only .pdf files are allowed");
					Window.alert("File was successfully uploaded");
					Window.alert("No file choosen");

  // Add widgets to Vertical Panel

  //Add Vertical Panel to Root Panel


This was an example of how to make a File Upload using the Google Web Toolkit.

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3 years ago

OK, but how could one get the text inside the file in order to store that?

3 years ago

I have checked the above code it will work for single file,how can we upload multiple files and how can we get names