Java tutorial
/* * Copyright 2008 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. */ package com.google.gwt.gdata.sample.hellogdata.client; import com.google.gwt.accounts.client.AuthSubStatus; import com.google.gwt.accounts.client.User; import com.google.gwt.gdata.client.FeedLink; import com.google.gwt.gdata.client.GData; import com.google.gwt.gdata.client.GDataSystemPackage; import com.google.gwt.gdata.client.gbase.GoogleBaseService; import com.google.gwt.gdata.client.gbase.ItemsEntry; import com.google.gwt.gdata.client.gbase.ItemsFeed; import com.google.gwt.gdata.client.gbase.ItemsFeedCallback; import com.google.gwt.gdata.client.gbase.MediaEntry; import com.google.gwt.gdata.client.gbase.MediaFeed; import com.google.gwt.gdata.client.gbase.MediaFeedCallback; import com.google.gwt.gdata.client.impl.CallErrorException; import com.google.gwt.gdata.client.mediarss.MediaContent; import com.google.gwt.gdata.client.mediarss.MediaThumbnail; import com.google.gwt.user.client.ui.FlexTable; import com.google.gwt.user.client.ui.HTML; import com.google.gwt.user.client.ui.Label; /** * The following example demonstrates how to retrieve a list of * media attachments. */ public class GoogleBaseRetrieveMediaDemo extends GDataDemo { /** * This method is used by the main sample app to obtain * information on this sample and a sample instance. * * @return An instance of this demo. */ public static GDataDemoInfo init() { return new GDataDemoInfo() { @Override public GDataDemo createInstance() { return new GoogleBaseRetrieveMediaDemo(); } @Override public String getDescription() { return "<p>This sample uses the private, read/write media feed " + "to query an item's attached media. Each item has an associated " + "media feed which can contain up to 10 binary attachments. Use " + "this feed to manage binary attachments for your Google Base " + "items. Google Base creates a set of thumbnails for each " + "attachment, and stores the thumbnails on the Google Base " + "server.</p>"; } @Override public String getName() { return "Base - Retrieving media"; } }; } private GoogleBaseService service; private FlexTable mainPanel; private final String scope = "http://www.google.com/base/feeds/"; /** * Setup the Google Base service and create the main content panel. * If the user is not logged on to Google Base display a message, * otherwise start the demo by retrieving the user's items. */ public GoogleBaseRetrieveMediaDemo() { mainPanel = new FlexTable(); initWidget(mainPanel); if (!GData.isLoaded(GDataSystemPackage.GBASE)) { showStatus("Loading the GData Google-Base package...", false); GData.loadGDataApi(GDATA_API_KEY, new Runnable() { public void run() { startDemo(); } }, GDataSystemPackage.GBASE); } else { startDemo(); } } /** * Retrieve the items feed using the Google Base service and * the items feed uri. In GData all get, insert, update * and delete methods always receive a callback defining success * and failure handlers. * Here, the failure handler displays an error message while the * success handler obtains the first item entry that is associated * with on or more media attachments and calls getMedia to * retrieve its media entries. * * @param itemsFeedUri The uri of the items feed */ private void getItems(String itemsFeedUri) { showStatus("Loading items feed...", false); service.getItemsFeed(itemsFeedUri, new ItemsFeedCallback() { public void onFailure(CallErrorException caught) { showStatus("An error occurred while retrieving the items feed: " + caught.getMessage(), true); } public void onSuccess(ItemsFeed result) { ItemsEntry[] entries = result.getEntries(); ItemsEntry targetItem = null; for (ItemsEntry entry : entries) { FeedLink<MediaFeed> link = entry.getFeedLink().cast(); if (link.getCountHint() > 0) { targetItem = entry; break; } } if (targetItem == null) { showStatus("You have no items containing media.", false); } else { String itemsEntryUri = targetItem.getSelfLink().getHref(); getMedia(itemsEntryUri); } } }); } /** * Retrieve the media feed using the Google Base service and * the media feed uri for a given item. In GData all get, insert, update * and delete methods always receive a callback defining success * and failure handlers. * Here, the failure handler displays an error message while the * success handler calls showData to display the media entries. * * @param itemsEntryUri The uri of the items entry for which to * retrieve the media feed */ private void getMedia(String itemsEntryUri) { showStatus("Loading media feed...", false); String mediaFeedUri = itemsEntryUri + "/media/"; service.getMediaFeed(mediaFeedUri, new MediaFeedCallback() { public void onFailure(CallErrorException caught) { showStatus("An error occurred while retrieving the media feed: " + caught.getMessage(), true); } public void onSuccess(MediaFeed result) { MediaEntry[] entries = result.getEntries(); if (entries.length == 0) { showStatus("No media found.", false); } else { showData(entries); } } }); } /** * Displays a set of Google Base media entries in a tabular * fashion with the help of a GWT FlexTable widget. The data fields * Title and Type, along with a thumbnail preview (if available), * are displayed. * * @param entries The Google Base media entries to display. */ private void showData(MediaEntry[] entries) { mainPanel.clear(); String[] labels = new String[] { "Title", "Type", "Thumbnail" }; mainPanel.insertRow(0); for (int i = 0; i < labels.length; i++) { mainPanel.addCell(0); mainPanel.setWidget(0, i, new Label(labels[i])); mainPanel.getFlexCellFormatter().setStyleName(0, i, "hm-tableheader"); } for (int i = 0; i < entries.length; i++) { MediaEntry entry = entries[i]; MediaContent media = entry.getMediaContent(); String fileType = media.getType(); String fileUrl = media.getUrl(); MediaThumbnail[] thumbs = media.getThumbnails(); int row = mainPanel.insertRow(i + 1); mainPanel.addCell(row); mainPanel.setWidget(row, 0, new HTML( "<a href=\"" + fileUrl + "\" target=\"_blank\">" + entry.getTitle().getText() + "</a>")); mainPanel.addCell(row); mainPanel.setWidget(row, 1, new Label(fileType)); mainPanel.addCell(row); if (thumbs.length > 0) { MediaThumbnail thumb = thumbs[0]; String thumbSource = thumb.getUrl(); double thumbWidth = thumb.getWidth(); double thumbHeight = thumb.getHeight(); mainPanel.setWidget(row, 2, new HTML("<img src=\"" + thumbSource + " width=\"" + thumbWidth + "px\" height=\"" + thumbHeight + "px\" border=\"0px\" />")); } else { mainPanel.setWidget(row, 2, new Label("Not Available")); } } } /** * Displays a status message to the user. * * @param message The message to display. * @param isError Indicates whether the status is an error status. */ private void showStatus(String message, boolean isError) { mainPanel.clear(); mainPanel.insertRow(0); mainPanel.addCell(0); Label msg = new Label(message); if (isError) { msg.setStylePrimaryName("hm-error"); } mainPanel.setWidget(0, 0, msg); } /** * Starts this demo. */ private void startDemo() { service = GoogleBaseService.newInstance("HelloGData_GoogleBase_RetrieveMediaDemo_v2.0"); if (User.getStatus(scope) == AuthSubStatus.LOGGED_IN) { getItems("http://www.google.com/base/feeds/items"); } else { showStatus("You are not logged on to Google Base.", true); } } }