如何将PNG图像从Jersey REST服务方法返回到浏览器

I have a web server running with Jersey REST resources up and I wonder how to get an image/png reference for the browsers img tag; after submitting a Form or getting an Ajax response. The image processing code for adding graphics is working, just need to return it somehow.

我有一个运行Jersey REST资源的Web服务器，我想知道如何获取浏览器img标签的image / png参考;提交表单或获得Ajax响应后。用于添加图形的图像处理代码正常工作，只需要以某种方式返回它。

Code:

码：

@POST
@Path("{fullsize}")
@Consumes(MediaType.MULTIPART_FORM_DATA)
@Produces("image/png")
// Would need to replace void
public void getFullImage(@FormDataParam("photo") InputStream imageIS,
                         @FormDataParam("submit") String extra) {

      BufferedImage image = ImageIO.read(imageIS);

      // .... image processing
      //.... image processing

      return ImageIO.  ..  ?

}

Cheers

干杯

4 个解决方案

#1

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.

我不相信在REST服务中返回图像数据是个好主意。它占用了应用服务器的内存和IO带宽。将该任务委派给适合此类传输的适当Web服务器要好得多。您可以通过向图像资源发送重定向来实现此目的（作为带有图像URI的HTTP 302响应）。当然，这假定您的图像被安排为Web内容。

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:

话虽如此，如果您确定需要从Web服务传输图像数据，您可以使用以下（伪）代码执行此操作：

@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.

添加异常处理等。

#2

I built a general method for that with following features:

我为此构建了一个通用方法，具有以下功能：

• returning "not modified" if the file hasn't been modified locally, a Status.NOT_MODIFIED is sent to the caller. Uses Apache Commons Lang
• 如果文件尚未在本地修改，则返回“未修改”，将Status.NOT_MODIFIED发送给调用者。使用Apache Commons Lang
• using a file stream object instead of reading the file itself
• 使用文件流对象而不是读取文件本身

Here the code:

这里的代码：

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...

请注意，Locale切换似乎不是线程安全的。我认为，最好全局切换语言环境。我不确定副作用...

#3

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

关于来自@Perception的回答，它在处理字节数组时非常耗费内存，但你也可以简单地写回输出流

@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
      }
    };
  }
}

#4

If you have a number of image resource methods, it is well worth creating a MessageBodyWriter to output the BufferedImage:

如果您有许多图像资源方法，那么创建MessageBodyWriter以输出BufferedImage非常值得：

@Produces({ "image/png", "image/jpg" })
@Provider
public class BufferedImageBodyWriter implements MessageBodyWriter<BufferedImage>  {
  @Override
  public boolean isWriteable(Class<?> type, Type type1, Annotation[] antns, MediaType mt) {
    return type == BufferedImage.class;
  }

  @Override
  public long getSize(BufferedImage t, Class<?> type, Type type1, Annotation[] antns, MediaType mt) {
    return -1; // not used in JAX-RS 2
  }

  @Override
  public void writeTo(BufferedImage image, Class<?> type, Type type1, Annotation[] antns, MediaType mt, MultivaluedMap<String, Object> mm, OutputStream out) throws IOException, WebApplicationException {
    ImageIO.write(image, mt.getSubtype(), out);
  } 
}

This MessageBodyWriter will be used automatically if auto-discovery is enabled for Jersey, otherwise it needs to be returned by a custom Application sub-class. See JAX-RS Entity Providers for more info.

如果为Jersey启用了自动发现，则将自动使用此MessageBodyWriter，否则需要由自定义Application子类返回。有关详细信息，请参阅JAX-RS实体提供程序。

Once this is set up, simply return a BufferedImage from a resource method and it will be be output as image file data:

设置完成后，只需从资源方法返回一个BufferedImage，它将作为图像文件数据输出：

@Path("/whatever")
@Produces({"image/png", "image/jpg"})
public Response getFullImage(...) {
  BufferedImage image = ...;
  return Response.ok(image).build();
}

A couple of advantages to this approach:

这种方法有两个优点：

• It writes to the response OutputSteam rather than an intermediary BufferedOutputStream
• 它写入响应OutputSteam而不是中间BufferedOutputStream
• It supports both png and jpg output (depending on the media types allowed by the resource method)
• 它支持png和jpg输出（取决于资源方法允许的媒体类型）