How to enable resumable GET requests with Jersey?

I am creating a RESTful web service using Jersey. Some of the resources are binary files that I get from somewhere else on demand; such files are potentially big (hundreds of Mbytes).

I want browsers to GET those resources, so I have a @GET-annotated method returning a StreamingOutput, like in this answer.

I have two questions:

• Is StreamingOutput the proper way of returning files?
• What should I do in the server side to make it possi开发者_如何学JAVAble for browsers to resume an interrupted file transfer?

Just use the range-relevant HTTP headers, taking care w.r.t. caching. First, advertise that you can resume by setting the Accept-Ranges header. Secondly, check the Range and If-Range headers, and send the appropriate responses.

Note that you will probably need to construct your own Response and set the needed headers and result code by hand.

For the same purpose I've built a ContainerResponseFilter to intercept requests with a Range header and mangle the response accordingly[1].

This is the ContainerResponseFilter which will use encapsulate the output stream in a RangedOutputStream (see below):

public class RangeResponseFilter implements ContainerResponseFilter {

    private static final String RANGE = "Range";

    private static final String ACCEPT_RANGES = "Accept-Ranges";

    @Override
    public void filter(ContainerRequestContext requestContext, ContainerResponseContext responseContext)
            throws IOException {
        if (requestContext.getHeaders().containsKey(RANGE)) {
            String rangeHeader = requestContext.getHeaderString(RANGE);
            String contentType = responseContext.getMediaType().toString();
            OutputStream originOutputStream = responseContext.getEntityStream();
            RangedOutputStream rangedOutputStream = new RangedOutputStream(originOutputStream, rangeHeader, contentType, responseContext.getHeaders());
            responseContext.setStatus(Status.PARTIAL_CONTENT.getStatusCode());
            responseContext.getHeaders().putSingle(ACCEPT_RANGES, rangedOutputStream.getAcceptRanges());
            responseContext.setEntityStream(rangedOutputStream);
        }
    }

}

And here's the RangedOutputStream:

public class RangedOutputStream extends OutputStream {

    public class Range extends OutputStream {

        private ByteArrayOutputStream outputStream;

        private Integer from;

        private Integer to;

        public Range(Integer from, Integer to) {
            this.outputStream = new ByteArrayOutputStream();
            this.from = from;
            this.to = to;
        }

        public boolean contains(Integer i) {
            if (this.to == null) {
                return (this.from <= i);
            }
            return (this.from <= i && i <= this.to);
        }

        public byte[] getBytes() {
            return this.outputStream.toByteArray();
        }

        public Integer getFrom() {
            return this.from;
        }

        public Integer getTo(Integer ifNull) {
            return this.to == null ? ifNull : this.to;
        }

        @Override
        public void write(int b) throws IOException {
            this.outputStream.write(b);
        }

    }

    private final static char[] MULTIPART_CHARS = "-_1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
            .toCharArray();

    private static final String BOUNDARY_LINE_FORMAT = "--%s";

    private static final String CONTENT_TYPE_LINE_FORMAT = "Content-Type: %s";

    private static final String CONTENT_RANGE_FORMAT = "%s %d-%d/%d";

    private static final String CONTENT_RANGE_LINE_FORMAT = "Content-Range: " + CONTENT_RANGE_FORMAT;

    private static final String EMPTY_LINE = "\r\n";

    private OutputStream outputStream;

    private String boundary;

    private String accept;

    private String contentType;

    private boolean multipart;

    private boolean flushed = false;

    private int pos = 0;

    List<Range> ranges;

    MultivaluedMap<String, Object> headers;

    public RangedOutputStream(OutputStream outputStream, String ranges, String contentType, MultivaluedMap<String, Object> headers) {
        this.outputStream = outputStream;
        this.ranges = new ArrayList<>();
        String[] acceptRanges = ranges.split("=");
        this.accept = acceptRanges[0];
        for (String range : acceptRanges[1].split(",")) {
            String[] bounds = range.split("-");
            this.ranges.add(new Range(Integer.valueOf(bounds[0]), bounds.length == 2 ? Integer.valueOf(bounds[1]) : null ));
        }
        this.headers = headers;
        this.contentType = contentType;
        this.multipart = this.ranges.size() > 1;
        this.boundary = this.generateBoundary();
    }

    private String generateBoundary() {
        StringBuilder buffer = new StringBuilder();
        Random rand = new Random();
        int count = rand.nextInt(11) + 30;
        for (int i = 0; i < count; i++) {
            buffer.append(MULTIPART_CHARS[rand.nextInt(MULTIPART_CHARS.length)]);
        }
        return buffer.toString();
    }

    public boolean isMultipart() {
        return this.multipart;
    }

    public String getBoundary() {
        return this.boundary;
    }

    public String getAcceptRanges() {
        return this.accept;
    }

    public String getContentRange(int index) {
        Range range = this.ranges.get(index);
        return String.format(CONTENT_RANGE_LINE_FORMAT, this.accept, range.getFrom(), range.getTo(this.pos), this.pos);
    }

    @Override
    public void write(int b) throws IOException {
        for (Range range : this.ranges) {
            if (range.contains(this.pos)) {
                range.write(b);
            }
        }
        this.pos++;
    }

    @Override
    public void flush() throws IOException {
        if (this.flushed) {
            return;
        }
        if (this.multipart) {
            this.headers.putSingle(HttpHeaders.CONTENT_TYPE, String.format("multipart/byteranges; boundary=%s", this.boundary));
            for (Range range : this.ranges) {
                this.outputStream.write(String.format(BOUNDARY_LINE_FORMAT + EMPTY_LINE, this.boundary).getBytes());
                this.outputStream.write(String.format(CONTENT_TYPE_LINE_FORMAT + EMPTY_LINE, this.contentType).getBytes());
                this.outputStream.write(
                        String.format(CONTENT_RANGE_LINE_FORMAT + EMPTY_LINE, this.accept, range.getFrom(), range.getTo(this.pos), this.pos)
                                .getBytes());
                this.outputStream.write(EMPTY_LINE.getBytes());
                this.outputStream.write(range.getBytes());
                this.outputStream.write(EMPTY_LINE.getBytes());
            }
            this.outputStream.write(String.format(BOUNDARY_LINE_FORMAT, this.boundary + "--").getBytes());
        } else {
            Range range = this.ranges.get(0);
            this.headers.putSingle("Content-Range", String.format(CONTENT_RANGE_FORMAT, this.accept, range.getFrom(), range.getTo(this.pos), this.pos));
            this.outputStream.write(range.getBytes());
        }
        this.flushed = true;
    }

}

[1] https://github.com/heruan/jersey-range-filter