com.google.appinventor.client.utils.Uploader.java Source code

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Here is the source code for com.google.appinventor.client.utils.Uploader.java

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// -*- mode: java; c-basic-offset: 2; -*-
// Copyright 2009-2011 Google, All Rights reserved
// Copyright 2011-2012 MIT, All rights reserved
// Released under the Apache License, Version 2.0
// http://www.apache.org/licenses/LICENSE-2.0

package com.google.appinventor.client.utils;

import com.google.appinventor.shared.rpc.UploadResponse;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.FileUpload;
import com.google.gwt.user.client.ui.FormHandler;
import com.google.gwt.user.client.ui.FormPanel;
import com.google.gwt.user.client.ui.FormSubmitCompleteEvent;
import com.google.gwt.user.client.ui.FormSubmitEvent;
import com.google.gwt.user.client.ui.RootPanel;

/**
 * Utility class to upload files to the server.
 *
 */
public final class Uploader {

    // Singleton Uploader instance
    public static final Uploader INSTANCE = new Uploader();

    // Uploader form
    private final FormPanel form;

    // Callback upon completion of upload
    private AsyncCallback<UploadResponse> callback;

    /**
     * Returns the uploader instance.
     *
     * @return  uploader instance
     */
    public static Uploader getInstance() {
        return INSTANCE;
    }

    /**
     * Creates a new uploader.
     */
    private Uploader() {
        // Because we're going to add a FileUpload widget, we'll need to set the
        // form to use the POST method, and multipart MIME encoding.
        form = new FormPanel();
        form.setEncoding(FormPanel.ENCODING_MULTIPART);
        form.setMethod(FormPanel.METHOD_POST);
        form.setSize("0px", "0px");
        form.setVisible(false);

        // Add an event handler to the form.
        form.addFormHandler(new FormHandler() {
            @Override
            public void onSubmit(FormSubmitEvent event) {
                // nothing
            }

            @Override
            public void onSubmitComplete(FormSubmitCompleteEvent event) {
                // When the form submission is successfully completed, this event is
                // fired. Assuming the service returned a response of type text/html,
                // we can get the result text here (see the FormPanel documentation for
                // further explanation).
                String results = event.getResults();
                // If the submit completely failed, results will be null.
                if (results == null) {
                    callback.onFailure(new RuntimeException("Upload error"));
                } else {
                    // results contains the UploadResponse value as a String. It was written on the server
                    // side in the doPost method in ode/server/UploadServlet.java.
                    UploadResponse uploadResponse = UploadResponse.extractUploadResponse(results);
                    if (uploadResponse != null) {
                        callback.onSuccess(uploadResponse);
                    } else {
                        callback.onFailure(new RuntimeException("Upload error"));
                    }
                }
            }
        });

        RootPanel.get().add(form);
    }

    /**
     * Uploads the given file.
     *
     * @param upload  file upload widget containing file information
     * @param uploadUrl  URL to upload the file to
     */
    public final void upload(FileUpload upload, String uploadUrl, AsyncCallback<UploadResponse> callback) {
        this.callback = callback;

        form.setWidget(upload);
        form.setAction(uploadUrl);
        form.submit();
    }
}