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jsfeng/FileServlet.java

Created May 7, 2012 19:31
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  1. jsfeng created this gist May 7, 2012.
    498 changes: 498 additions & 0 deletions FileServlet.java
    View file
    Original file line number Diff line number Diff line change
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    /*
    * 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 net.balusc.webapp;

    import java.io.Closeable;
    import java.io.File;
    import java.io.IOException;
    import java.io.OutputStream;
    import java.io.RandomAccessFile;
    import java.net.URLDecoder;
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;
    import java.util.zip.GZIPOutputStream;

    import javax.servlet.ServletException;
    import javax.servlet.ServletOutputStream;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;

    /**
    * A file servlet supporting resume of downloads and client-side caching and GZIP of text content.
    * This servlet can also be used for images, client-side caching would become more efficient.
    * This servlet can also be used for text files, GZIP would decrease network bandwidth.
    *
    * @author BalusC
    * @link http://balusc.blogspot.com/2009/02/fileservlet-supporting-resume-and.html
    */
    public class FileServlet 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";

    // Properties ---------------------------------------------------------------------------------

    private String basePath;

    // Actions ------------------------------------------------------------------------------------

    /**
    * Initialize the servlet.
    * @see HttpServlet#init().
    */
    public void init() throws ServletException {

    // Get base path (path to get all resources from) as init parameter.
    this.basePath = getServletContext().getRealPath(getInitParameter("basePath"));

    // Validate base path.
    if (this.basePath == null) {
    throw new ServletException("FileServlet init param 'basePath' is required.");
    } else {
    File path = new File(this.basePath);
    if (!path.exists()) {
    throw new ServletException("FileServlet init param 'basePath' value '"
    + this.basePath + "' does actually not exist in file system.");
    } else if (!path.isDirectory()) {
    throw new ServletException("FileServlet init param 'basePath' value '"
    + this.basePath + "' is actually not a directory in file system.");
    } else if (!path.canRead()) {
    throw new ServletException("FileServlet init param 'basePath' value '"
    + this.basePath + "' is actually not readable in file system.");
    }
    }
    }

    /**
    * Process HEAD request. This returns the same headers as GET request, but without content.
    * @see HttpServlet#doHead(HttpServletRequest, HttpServletResponse).
    */
    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).
    */
    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.
    */
    private void processRequest
    (HttpServletRequest request, HttpServletResponse response, boolean content)
    throws IOException
    {
    // Validate the requested file ------------------------------------------------------------

    // Get requested file by path info.
    String requestedFile = request.getPathInfo();

    // Check if file is actually supplied to the request URL.
    if (requestedFile == null) {
    // Do your thing if the file is not supplied to the request URL.
    // Throw an exception, or send 404, or show default/warning page, or just ignore it.
    response.sendError(HttpServletResponse.SC_NOT_FOUND);
    return;
    }

    // URL-decode the file name (might contain spaces and on) and prepare file object.
    File file = new File(basePath, URLDecoder.decode(requestedFile, "UTF-8"));

    // Check if file actually exists in filesystem.
    if (!file.exists()) {
    // Do your thing if the file appears to be non-existing.
    // Throw an exception, or send 404, or show default/warning page, or just ignore it.
    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.
    if (contentType.startsWith("text")) {
    String acceptEncoding = request.getHeader("Accept-Encoding");
    acceptsGzip = acceptEncoding != null && accepts(acceptEncoding, "gzip");
    contentType += ";charset=UTF-8";
    }

    // 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.
    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);
    }
    }

    // Helpers (can be refactored to public utility class) ----------------------------------------

    /**
    * 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) {
    if ((toRead -= read) > 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;
    }

    }
    }

    <servlet>
    <servlet-name>fileServlet</servlet-name>
    <servlet-class>net.balusc.webapp.FileServlet</servlet-class>
    <init-param>
    <param-name>basePath</param-name>
    <param-value>/WEB-INF/resources</param-value>
    </init-param>
    </servlet>

    <servlet-mapping>
    <servlet-name>fileServlet</servlet-name>
    <url-pattern>/resources/*</url-pattern>
    </servlet-mapping>