Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 org.apache.wicket.core.util.resource; import java.io.IOException; import java.io.InputStream; import java.net.URL; import java.net.URLConnection; import java.util.ArrayList; import java.util.List; import org.apache.wicket.Application; import org.apache.wicket.util.io.Connections; import org.apache.wicket.util.io.IOUtils; import org.apache.wicket.util.lang.Args; import org.apache.wicket.util.lang.Bytes; import org.apache.wicket.util.lang.Objects; import org.apache.wicket.util.resource.AbstractResourceStream; import org.apache.wicket.util.resource.IFixedLocationResourceStream; import org.apache.wicket.util.resource.ResourceStreamNotFoundException; import org.apache.wicket.util.time.Time; import org.slf4j.Logger; import org.slf4j.LoggerFactory; /** * UrlResourceStream implements IResource for URLs. * * @see org.apache.wicket.util.resource.IResourceStream * @see org.apache.wicket.util.watch.IModifiable * @author Jonathan Locke * @author Igor Vaynberg */ public class UrlResourceStream extends AbstractResourceStream implements IFixedLocationResourceStream { private static final long serialVersionUID = 1L; /** Logging. */ private static final Logger log = LoggerFactory.getLogger(UrlResourceStream.class); /** * The meta data for this stream. Lazy loaded on demand. */ private transient StreamData streamData; /** The URL to this resource. */ private final URL url; /** Last known time the stream was last modified. */ private Time lastModified; /** * Meta data class for the stream attributes */ private static class StreamData { private URLConnection connection; /** * The streams read from this connection. * Some URLConnection implementations return the same instance of InputStream * every time URLConnection#getInputStream() is called. Other return a new instance * of InputStream. * Here we keep a list of all returned ones and close them in UrlResourceStream#close(). * Even it is the same instance several times we will try to close it quietly several times. */ private List<InputStream> inputStreams; /** Length of stream. */ private long contentLength; /** Content type for stream. */ private String contentType; } /** * Construct. * * @param url * URL of resource */ public UrlResourceStream(final URL url) { this.url = Args.notNull(url, "url"); } /** * Lazy loads the stream settings on demand * * @param initialize * a flag indicating whether to load the settings * @return the meta data with the stream settings */ private StreamData getData(boolean initialize) { if (streamData == null && initialize) { streamData = new StreamData(); try { streamData.connection = url.openConnection(); streamData.contentLength = streamData.connection.getContentLength(); if (Application.exists()) { streamData.contentType = Application.get().getMimeType(url.getFile()); } else { streamData.contentType = streamData.connection.getContentType(); } if (streamData.contentType == null || streamData.contentType.contains("unknown")) { streamData.contentType = URLConnection.getFileNameMap().getContentTypeFor(url.getFile()); } } catch (IOException ex) { throw new IllegalArgumentException("Invalid URL parameter " + url, ex); } } return streamData; } /** * Closes this resource. * * @throws IOException */ @Override public void close() throws IOException { StreamData data = getData(false); if (data != null) { Connections.closeQuietly(data.connection); if (data.inputStreams != null) { for (InputStream is : data.inputStreams) { IOUtils.closeQuietly(is); } } streamData = null; } } /** * @return A readable input stream for this resource. * @throws ResourceStreamNotFoundException */ @Override public InputStream getInputStream() throws ResourceStreamNotFoundException { try { StreamData data = getData(true); InputStream is = data.connection.getInputStream(); if (data.inputStreams == null) { data.inputStreams = new ArrayList<>(); } data.inputStreams.add(is); return is; } catch (IOException e) { throw new ResourceStreamNotFoundException("Resource " + url + " could not be opened", e); } } /** * @return The URL to this resource (if any) */ public URL getURL() { return url; } /** * @see org.apache.wicket.util.watch.IModifiable#lastModifiedTime() * @return The last time this resource was modified */ @Override public Time lastModifiedTime() { try { // get url modification timestamp final Time time = Connections.getLastModified(url); // if timestamp changed: update content length and last modified date if (Objects.equal(time, lastModified) == false) { lastModified = time; updateContentLength(); } return lastModified; } catch (IOException e) { log.warn("getLastModified() for '{}' failed: {}", url, e.getMessage()); // allow modification watcher to detect the problem return null; } } private void updateContentLength() throws IOException { StreamData data = getData(false); if (data != null) { URLConnection connection = url.openConnection(); try { data.contentLength = connection.getContentLength(); } finally { Connections.close(connection); } } } @Override public String toString() { return url.toString(); } /** * @return The content type of this resource, such as "image/jpeg" or "text/html" */ @Override public String getContentType() { return getData(true).contentType; } @Override public Bytes length() { long length = getData(true).contentLength; if (length == -1) { return null; } return Bytes.bytes(length); } @Override public String locationAsString() { return url.toExternalForm(); } }