Java tutorial
/* * net/balusc/webapp/FileServlet.java * * Copyright (C) 2009 BalusC * * This program is free software: you can redistribute it and/or modify it under the terms of the * GNU Lesser General Public License as published by the Free Software Foundation, either version 3 * of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License along with this library. * If not, see <http://www.gnu.org/licenses/>. */ package eionet.eunis.servlets; import java.io.Closeable; import java.io.File; import java.io.IOException; import java.io.OutputStream; import java.io.RandomAccessFile; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.zip.GZIPOutputStream; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.lang.StringUtils; import org.apache.log4j.Logger; import eionet.eunis.util.Constants; /** * * @author jaanus * */ public class DownloadServlet extends HttpServlet { // Constants ---------------------------------------------------------------------------------- private static final int DEFAULT_BUFFER_SIZE = 10240; // ..bytes = 10KB. private static final long DEFAULT_EXPIRE_TIME = 604800000L; // ..ms = 1 week. private static final String MULTIPART_BOUNDARY = "MULTIPART_BYTERANGES"; private static final Logger LOGGER = Logger.getLogger(DownloadServlet.class); // Properties --------------------------------------------------------------------------------- private String appHome; /** * @see javax.servlet.GenericServlet#init(javax.servlet.ServletConfig) */ @Override public void init(ServletConfig config) throws ServletException { super.init(config); appHome = config.getServletContext().getInitParameter(Constants.APP_HOME_INIT_PARAM); } // Actions ------------------------------------------------------------------------------------ /** * Process HEAD request. This returns the same headers as GET request, but without content. * * @see HttpServlet#doHead(HttpServletRequest, HttpServletResponse). */ @Override protected void doHead(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Process request without content. processRequest(request, response, false); } /** * Process GET request. * * @see HttpServlet#doGet(HttpServletRequest, HttpServletResponse). */ @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Process request with content. processRequest(request, response, true); } /** * Process the actual request. * * @param request The request to be processed. * @param response The response to be created. * @param content Whether the request body should be written (GET) or not (HEAD). * @throws IOException If something fails at I/O level. * @throws ServletException */ private void processRequest(HttpServletRequest request, HttpServletResponse response, boolean content) throws IOException, ServletException { String requestURI = request.getRequestURI(); String contextPath = request.getContextPath(); String pathInfo = request.getPathInfo(); String servletPath = request.getServletPath(); // Create the abstract file reference to the requested file. File file = null; String fileRelativePath = StringUtils.substringAfter(request.getRequestURI(), request.getContextPath()); fileRelativePath = StringUtils.replace(fileRelativePath, "%20", " "); if (StringUtils.isNotEmpty(fileRelativePath) && StringUtils.isNotEmpty(appHome)) { file = new File(appHome, fileRelativePath); } // If file was not found, send 404. if (file == null || !file.exists() || file.isDirectory()) { response.sendError(HttpServletResponse.SC_NOT_FOUND); return; } // Prepare some variables. The ETag is an unique identifier of the file. String fileName = file.getName(); long length = file.length(); long lastModified = file.lastModified(); String eTag = fileName + "_" + length + "_" + lastModified; // Validate request headers for caching --------------------------------------------------- // If-None-Match header should contain "*" or ETag. If so, then return 304. String ifNoneMatch = request.getHeader("If-None-Match"); if (ifNoneMatch != null && matches(ifNoneMatch, eTag)) { response.setHeader("ETag", eTag); // Required in 304. response.sendError(HttpServletResponse.SC_NOT_MODIFIED); return; } // If-Modified-Since header should be greater than LastModified. If so, then return 304. // This header is ignored if any If-None-Match header is specified. long ifModifiedSince = request.getDateHeader("If-Modified-Since"); if (ifNoneMatch == null && ifModifiedSince != -1 && ifModifiedSince + 1000 > lastModified) { response.setHeader("ETag", eTag); // Required in 304. response.sendError(HttpServletResponse.SC_NOT_MODIFIED); return; } // Validate request headers for resume ---------------------------------------------------- // If-Match header should contain "*" or ETag. If not, then return 412. String ifMatch = request.getHeader("If-Match"); if (ifMatch != null && !matches(ifMatch, eTag)) { response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED); return; } // If-Unmodified-Since header should be greater than LastModified. If not, then return 412. long ifUnmodifiedSince = request.getDateHeader("If-Unmodified-Since"); if (ifUnmodifiedSince != -1 && ifUnmodifiedSince + 1000 <= lastModified) { response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED); return; } // Validate and process range ------------------------------------------------------------- // Prepare some variables. The full Range represents the complete file. Range full = new Range(0, length - 1, length); List<Range> ranges = new ArrayList<Range>(); // Validate and process Range and If-Range headers. String range = request.getHeader("Range"); if (range != null) { // Range header should match format "bytes=n-n,n-n,n-n...". If not, then return 416. if (!range.matches("^bytes=\\d*-\\d*(,\\d*-\\d*)*$")) { response.setHeader("Content-Range", "bytes */" + length); // Required in 416. response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE); return; } // If-Range header should either match ETag or be greater then LastModified. If not, // then return full file. String ifRange = request.getHeader("If-Range"); if (ifRange != null && !ifRange.equals(eTag)) { try { long ifRangeTime = request.getDateHeader("If-Range"); // Throws IAE if invalid. if (ifRangeTime != -1 && ifRangeTime + 1000 < lastModified) { ranges.add(full); } } catch (IllegalArgumentException ignore) { ranges.add(full); } } // If any valid If-Range header, then process each part of byte range. if (ranges.isEmpty()) { for (String part : range.substring(6).split(",")) { // Assuming a file with length of 100, the following examples returns bytes at: // 50-80 (50 to 80), 40- (40 to length=100), -20 (length-20=80 to length=100). long start = sublong(part, 0, part.indexOf("-")); long end = sublong(part, part.indexOf("-") + 1, part.length()); if (start == -1) { start = length - end; end = length - 1; } else if (end == -1 || end > length - 1) { end = length - 1; } // Check if Range is syntactically valid. If not, then return 416. if (start > end) { response.setHeader("Content-Range", "bytes */" + length); // Required in 416. response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE); return; } // Add range. ranges.add(new Range(start, end, length)); } } } // Prepare and initialize response -------------------------------------------------------- // Get content type by file name and set default GZIP support and content disposition. String contentType = getServletContext().getMimeType(fileName); boolean acceptsGzip = false; String disposition = "inline"; // If content type is unknown, then set the default value. // For all content types, see: http://www.w3schools.com/media/media_mimeref.asp // To add new content types, add new mime-mapping entry in web.xml. if (contentType == null) { contentType = "application/octet-stream"; } // If content type is text, then determine whether GZIP content encoding is supported by // the browser and expand content type with the one and right character encoding. // Else, expect for images, determine content disposition. If content type is supported by // the browser, then set to inline, else attachment which will pop a 'save as' dialogue. if (contentType.startsWith("text")) { String acceptEncoding = request.getHeader("Accept-Encoding"); acceptsGzip = acceptEncoding != null && accepts(acceptEncoding, "gzip"); contentType += ";charset=UTF-8"; } else if (!contentType.startsWith("image")) { String accept = request.getHeader("Accept"); disposition = accept != null && accepts(accept, contentType) ? "inline" : "attachment"; } // Initialize response. response.reset(); response.setBufferSize(DEFAULT_BUFFER_SIZE); response.setHeader("Content-Disposition", disposition + ";filename=\"" + fileName + "\""); response.setHeader("Accept-Ranges", "bytes"); response.setHeader("ETag", eTag); response.setDateHeader("Last-Modified", lastModified); response.setDateHeader("Expires", System.currentTimeMillis() + DEFAULT_EXPIRE_TIME); // Send requested file (part(s)) to client ------------------------------------------------ // Prepare streams. RandomAccessFile input = null; OutputStream output = null; try { // Open streams. input = new RandomAccessFile(file, "r"); output = response.getOutputStream(); if (ranges.isEmpty() || ranges.get(0) == full) { // Return full file. Range r = full; response.setContentType(contentType); response.setHeader("Content-Range", "bytes " + r.start + "-" + r.end + "/" + r.total); if (content) { if (acceptsGzip) { // The browser accepts GZIP, so GZIP the content. response.setHeader("Content-Encoding", "gzip"); output = new GZIPOutputStream(output, DEFAULT_BUFFER_SIZE); } else { // Content length is not directly predictable in case of GZIP. // So only add it if there is no means of GZIP, else browser will hang. response.setHeader("Content-Length", String.valueOf(r.length)); } // Copy full range. copy(input, output, r.start, r.length); } } else if (ranges.size() == 1) { // Return single part of file. Range r = ranges.get(0); response.setContentType(contentType); response.setHeader("Content-Range", "bytes " + r.start + "-" + r.end + "/" + r.total); response.setHeader("Content-Length", String.valueOf(r.length)); response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); // 206. if (content) { // Copy single part range. copy(input, output, r.start, r.length); } } else { // Return multiple parts of file. response.setContentType("multipart/byteranges; boundary=" + MULTIPART_BOUNDARY); response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); // 206. if (content) { // Cast back to ServletOutputStream to get the easy println methods. ServletOutputStream sos = (ServletOutputStream) output; // Copy multi part range. for (Range r : ranges) { // Add multipart boundary and header fields for every range. sos.println(); sos.println("--" + MULTIPART_BOUNDARY); sos.println("Content-Type: " + contentType); sos.println("Content-Range: bytes " + r.start + "-" + r.end + "/" + r.total); // Copy single part range of multi part range. copy(input, output, r.start, r.length); } // End with multipart boundary. sos.println(); sos.println("--" + MULTIPART_BOUNDARY + "--"); } } } finally { // Gently close streams. close(output); close(input); } } /** * Returns true if the given accept header accepts the given value. * * @param acceptHeader The accept header. * @param toAccept The value to be accepted. * @return True if the given accept header accepts the given value. */ private static boolean accepts(String acceptHeader, String toAccept) { String[] acceptValues = acceptHeader.split("\\s*(,|;)\\s*"); Arrays.sort(acceptValues); return Arrays.binarySearch(acceptValues, toAccept) > -1 || Arrays.binarySearch(acceptValues, toAccept.replaceAll("/.*$", "/*")) > -1 || Arrays.binarySearch(acceptValues, "*/*") > -1; } /** * Returns true if the given match header matches the given value. * * @param matchHeader The match header. * @param toMatch The value to be matched. * @return True if the given match header matches the given value. */ private static boolean matches(String matchHeader, String toMatch) { String[] matchValues = matchHeader.split("\\s*,\\s*"); Arrays.sort(matchValues); return Arrays.binarySearch(matchValues, toMatch) > -1 || Arrays.binarySearch(matchValues, "*") > -1; } /** * Returns a substring of the given string value from the given begin index to the given end index as a long. If the substring * is empty, then -1 will be returned * * @param value The string value to return a substring as long for. * @param beginIndex The begin index of the substring to be returned as long. * @param endIndex The end index of the substring to be returned as long. * @return A substring of the given string value as long or -1 if substring is empty. */ private static long sublong(String value, int beginIndex, int endIndex) { String substring = value.substring(beginIndex, endIndex); return (substring.length() > 0) ? Long.parseLong(substring) : -1; } /** * Copy the given byte range of the given input to the given output. * * @param input The input to copy the given range to the given output for. * @param output The output to copy the given range from the given input for. * @param start Start of the byte range. * @param length Length of the byte range. * @throws IOException If something fails at I/O level. */ private static void copy(RandomAccessFile input, OutputStream output, long start, long length) throws IOException { byte[] buffer = new byte[DEFAULT_BUFFER_SIZE]; int read; if (input.length() == length) { // Write full range. while ((read = input.read(buffer)) > 0) { output.write(buffer, 0, read); } } else { // Write partial range. input.seek(start); long toRead = length; while ((read = input.read(buffer)) > 0) { toRead = toRead - read; if (toRead > 0) { output.write(buffer, 0, read); } else { output.write(buffer, 0, (int) toRead + read); break; } } } } /** * Close the given resource. * * @param resource The resource to be closed. */ private static void close(Closeable resource) { if (resource != null) { try { resource.close(); } catch (IOException ignore) { // Ignore IOException. If you want to handle this anyway, it might be useful to know // that this will generally only be thrown when the client aborted the request. } } } // Inner classes ------------------------------------------------------------------------------ /** * This class represents a byte range. */ protected class Range { long start; long end; long length; long total; /** * Construct a byte range. * * @param start Start of the byte range. * @param end End of the byte range. * @param total Total length of the byte source. */ public Range(long start, long end, long total) { this.start = start; this.end = end; this.length = end - start + 1; this.total = total; } } }