BinaryData ComplexObs FileDownload Servlet

This servlet helps to download complexObs from the server to client web browser. Specially the servlet supports resume downloads. (which helps in use cases like video stream for players/file download using download-managers)
References: http://balusc.blogspot.com/2009/02/fileservlet-supporting-resume-and.html
package org.openmrs.module.patientnarratives.web.servlet;

import org.apache.commons.io.FileUtils;
import org.openmrs.Obs;
import org.openmrs.api.context.Context;
import org.openmrs.obs.ComplexData;
import org.openmrs.util.OpenmrsConstants;
import org.springframework.util.SerializationUtils;

import java.io.*;
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 File tempMergedVideoFile = null;
    // Actions ------------------------------------------------------------------------------------

    /**
     * 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 ------------------------------------------------------------

        tempMergedVideoFile = File.createTempFile("downloadVideoFile", ".flv");
        String requestedFile = tempMergedVideoFile.getCanonicalPath();

        Integer videoObsId = Integer.parseInt(request.getParameter("videoObsId"));
        Obs complexObs = Context.getObsService().getComplexObs(videoObsId, OpenmrsConstants.RAW_VIEW);
        ComplexData complexData = complexObs.getComplexData();
        byte[] videoObjectData = ((byte[]) complexData.getData());
        FileUtils.writeByteArrayToFile(new File(requestedFile), videoObjectData);

        // 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(requestedFile);

        // 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;
        long expires = System.currentTimeMillis() + DEFAULT_EXPIRE_TIME;


        // 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.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            response.setHeader("ETag", eTag); // Required in 304.
            response.setDateHeader("Expires", expires); // Postpone cache with 1 week.
            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.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            response.setHeader("ETag", eTag); // Required in 304.
            response.setDateHeader("Expires", expires); // Postpone cache with 1 week.
            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", expires);


        // 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);
            tempMergedVideoFile.delete();
        }
    }

    // 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;
        }

    }

}