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?

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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.

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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