How to return a PNG image from Jersey REST service method to the browser

I'm not convinced its a good idea to return image data in a REST service. It ties up your application server's memory and IO bandwidth. Much better to delegate that task to a proper web server that is optimized for this kind of transfer. You can accomplish this by sending a redirect to the image resource (as a HTTP 302 response with the URI of the image). This assumes of course that your images are arranged as web content.

Having said that, if you decide you really need to transfer image data from a web service you can do so with the following (pseudo) code:

@Path("/whatever")@Produces("image/png")public Response getFullImage(...) {    BufferedImage image = ...;    ByteArrayOutputStream baos = new ByteArrayOutputStream();    ImageIO.write(image, "png", baos);    byte[] imageData = baos.toByteArray();    // uncomment line below to send non-streamed    // return Response.ok(imageData).build();    // uncomment line below to send streamed    // return Response.ok(new ByteArrayInputStream(imageData)).build();}

Add in exception handling, etc etc.

I built a general method for that with following features:

• returning "not modified" if the file hasn't been modified locally, a Status.NOT_MODIFIED is sent to the caller. Uses Apache Commons Lang
• using a file stream object instead of reading the file itself

Here the code:

import org.apache.commons.lang3.time.DateUtils;import org.slf4j.Logger;import org.slf4j.LoggerFactory;private static final Logger logger = LoggerFactory.getLogger(Utils.class);@GET@Path("16x16")@Produces("image/png")public Response get16x16PNG(@HeaderParam("If-Modified-Since") String modified) {    File repositoryFile = new File("c:/temp/myfile.png");    return returnFile(repositoryFile, modified);}/** *  * Sends the file if modified and "not modified" if not modified * future work may put each file with a unique id in a separate folder in tomcat *   * use that static URL for each file *   * if file is modified, URL of file changes *   * -> client always fetches correct file  *  *     method header for calling method public Response getXY(@HeaderParam("If-Modified-Since") String modified) { *  * @param file to send * @param modified - HeaderField "If-Modified-Since" - may be "null" * @return Response to be sent to the client */public static Response returnFile(File file, String modified) {    if (!file.exists()) {        return Response.status(Status.NOT_FOUND).build();    }    // do we really need to send the file or can send "not modified"?    if (modified != null) {        Date modifiedDate = null;        // we have to switch the locale to ENGLISH as parseDate parses in the default locale        Locale old = Locale.getDefault();        Locale.setDefault(Locale.ENGLISH);        try {            modifiedDate = DateUtils.parseDate(modified, org.apache.http.impl.cookie.DateUtils.DEFAULT_PATTERNS);        } catch (ParseException e) {            logger.error(e.getMessage(), e);        }        Locale.setDefault(old);        if (modifiedDate != null) {            // modifiedDate does not carry milliseconds, but fileDate does            // therefore we have to do a range-based comparison            // 1000 milliseconds = 1 second            if (file.lastModified()-modifiedDate.getTime() < DateUtils.MILLIS_PER_SECOND) {                return Response.status(Status.NOT_MODIFIED).build();            }        }    }            // we really need to send the file    try {        Date fileDate = new Date(file.lastModified());        return Response.ok(new FileInputStream(file)).lastModified(fileDate).build();    } catch (FileNotFoundException e) {        return Response.status(Status.NOT_FOUND).build();    }}/*** copied from org.apache.http.impl.cookie.DateUtils, Apache 2.0 License ***//** * Date format pattern used to parse HTTP date headers in RFC 1123 format. */public static final String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";/** * Date format pattern used to parse HTTP date headers in RFC 1036 format. */public static final String PATTERN_RFC1036 = "EEEE, dd-MMM-yy HH:mm:ss zzz";/** * Date format pattern used to parse HTTP date headers in ANSI C * <code>asctime()</code> format. */public static final String PATTERN_ASCTIME = "EEE MMM d HH:mm:ss yyyy";public static final String[] DEFAULT_PATTERNS = new String[] {    PATTERN_RFC1036,    PATTERN_RFC1123,    PATTERN_ASCTIME};

Note that the Locale switching does not seem to be thread-safe. I think, it's better to switch the locale globally. I am not sure about the side-effects though...

in regard of answer from @Perception, its true to be very memory-consuming when working with byte arrays, but you could also simply write back into the outputstream

@Path("/picture")public class ProfilePicture {  @GET  @Path("/thumbnail")  @Produces("image/png")  public StreamingOutput getThumbNail() {    return new StreamingOutput() {      @Override      public void write(OutputStream os) throws IOException, WebApplicationException {        //... read your stream and write into os      }    };  }}