Java tutorial
/* * Copyright 2000-2018 Vaadin Ltd. * * 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.vaadin.server; import java.io.IOException; import com.vaadin.shared.extension.filedownloader.FileDownloaderState; import com.vaadin.ui.AbstractComponent; /** * Extension that starts a download when the extended component is clicked. This * is used to overcome two challenges: * <ul> * <li>Resource should be bound to a component to allow it to be garbage * collected when there are no longer any ways of reaching the resource.</li> * <li>Download should be started directly when the user clicks e.g. a Button * without going through a server-side click listener to avoid triggering * security warnings in some browsers.</li> * </ul> * <p> * Please note that the download will be started in an iframe, which means that * care should be taken to avoid serving content types that might make the * browser attempt to show the content using a plugin instead of downloading it. * Connector resources (e.g. {@link FileResource} and {@link ClassResource}) * will automatically be served using a * <code>Content-Type: application/octet-stream</code> header unless * {@link #setOverrideContentType(boolean)} has been set to <code>false</code> * while files served in other ways, (e.g. {@link ExternalResource} or * {@link ThemeResource}) will not automatically get this treatment. * </p> * * @author Vaadin Ltd * @since 7.0.0 */ public class FileDownloader extends AbstractExtension { private boolean overrideContentType = true; /** * Creates a new file downloader for the given resource. To use the * downloader, you should also {@link #extend(AbstractClientConnector)} the * component. * * @param resource * the resource to download when the user clicks the extended * component. */ public FileDownloader(Resource resource) { if (resource == null) { throw new IllegalArgumentException("resource may not be null"); } setResource("dl", resource); } /** * Add this extension to the target component. * * @param target * the component to attach this extension to */ public void extend(AbstractComponent target) { super.extend(target); } /** * Add this extension to the {@code EventTrigger}. * * @param eventTrigger * the trigger to attach this extension to * @since 8.4 */ public void extend(EventTrigger eventTrigger) { super.extend(eventTrigger.getConnector()); getState().partInformation = eventTrigger.getPartInformation(); } /** * Gets the resource set for download. * * @return the resource that will be downloaded if clicking the extended * component */ public Resource getFileDownloadResource() { return getResource("dl"); } /** * Sets the resource that is downloaded when the extended component is * clicked. * * @param resource * the resource to download */ public void setFileDownloadResource(Resource resource) { setResource("dl", resource); } /** * Sets whether the content type of served resources should be overridden to * <code>application/octet-stream</code> to reduce the risk of a browser * plugin choosing to display the resource instead of downloading it. This * is by default set to <code>true</code>. * <p> * Please note that this only affects Connector resources (e.g. * {@link FileResource} and {@link ClassResource}) but not other resource * types (e.g. {@link ExternalResource} or {@link ThemeResource}). * </p> * * @param overrideContentType * <code>true</code> to override the content type if possible; * <code>false</code> to use the original content type. */ public void setOverrideContentType(boolean overrideContentType) { this.overrideContentType = overrideContentType; } /** * Checks whether the content type should be overridden. * * @return <code>true</code> if the content type will be overridden when * possible; <code>false</code> if the original content type will be * used. * @see #setOverrideContentType(boolean) */ public boolean isOverrideContentType() { return overrideContentType; } /** * {@inheritDoc} * * @throws IOException * if something goes wrong with the download or the user * cancelled the file download process. */ @Override public boolean handleConnectorRequest(VaadinRequest request, VaadinResponse response, String path) throws IOException { if (!path.matches("dl(/.*)?")) { // Ignore if it isn't for us return false; } VaadinSession session = getSession(); session.lock(); DownloadStream stream; try { Resource resource = getFileDownloadResource(); if (!(resource instanceof ConnectorResource)) { return false; } stream = ((ConnectorResource) resource).getStream(); String contentDisposition = stream.getParameter(DownloadStream.CONTENT_DISPOSITION); if (contentDisposition == null) { contentDisposition = "attachment; " + DownloadStream.getContentDispositionFilename(stream.getFileName()); } stream.setParameter(DownloadStream.CONTENT_DISPOSITION, contentDisposition); // Content-Type to block eager browser plug-ins from hijacking // the file if (isOverrideContentType()) { stream.setContentType("application/octet-stream;charset=UTF-8"); } } finally { session.unlock(); } stream.writeResponse(request, response); return true; } @Override protected FileDownloaderState getState() { return (FileDownloaderState) super.getState(); } @Override protected FileDownloaderState getState(boolean markAsDirty) { return (FileDownloaderState) super.getState(markAsDirty); } }