Jersey REST服务将响应作为带有下载窗口的图像返回

Question

I have a D3 graph generated on client side. I send the SVG data to Jersey REST service convert the SVG data to image ( OutputStream ) using Transcoding . When I return the response from service I could see the data returned as binary stream in console.

What I want is a browser download window to popup as soon as the service returns the response.

Following is the code snippet:

@POST
@Path("downloadSVG")
@Produces("image/png")

public javax.ws.rs.core.Response downloadSVG(@Context HttpServletRequest request, @Context HttpServletResponse httpServletResponse,String values){

              LOGGER.info("Inside downloadSVG service.");

              javax.ws.rs.core.Response graphImage = null;
              JSONObject data = new JSONObject(values);
              String svgXML = data.get("svgURL").toString();
              try {

                     OutputStream os = httpServletResponse.getOutputStream();
                     JPEGTranscoder t = new JPEGTranscoder();
                     t.addTranscodingHint(JPEGTranscoder.KEY_QUALITY, new Float(.8));
                     InputStream is = new ByteArrayInputStream(svgXML.getBytes());
                     TranscoderInput input = new TranscoderInput(is);
                     TranscoderOutput output = new TranscoderOutput(os);
                     t.transcode(input, output);
                     LOGGER.info("Graph image generated. Trying to return it to client.");
                     graphImage = javax.ws.rs.core.Response.ok(os).header("Content-Disposition", "attachment;       
                filename=graph.png").type("image/png").build();
             os.flush();
                     os.close();
              } catch (IOException e1) {
                     e1.printStackTrace();
              } catch (TranscoderException e) {
                     e.printStackTrace();
              }
              return graphImage;
}

Once this service is called I get following Exception on server console:

SLF4J: This version of SLF4J requires log4j version 1.2.12 or later. See also http://www.slf4j.org/codes.html#log4j_version
Jan 03, 2014 3:21:32 PM com.sun.jersey.spi.container.ContainerResponse write
SEVERE: A message body writer for Java class org.apache.catalina.connector.CoyoteOutputStream, and Java type class org.apache.catalina.connector.CoyoteOutputStream, and MIME media type image/png was not found
Jan 03, 2014 3:21:32 PM com.sun.jersey.spi.container.ContainerResponse write
SEVERE: The registered message body writers compatible with the MIME media type are:
image/* ->
  com.sun.jersey.core.impl.provider.entity.RenderedImageProvider
*/* ->
  com.sun.jersey.core.impl.provider.entity.FormProvider
  com.sun.jersey.core.impl.provider.entity.MimeMultipartProvider
  com.sun.jersey.core.impl.provider.entity.StringProvider
.
.
Jan 03, 2014 3:21:32 PM com.sun.jersey.spi.container.ContainerResponse logException
SEVERE: Mapped exception to response: 500 (Internal Server Error)
javax.ws.rs.WebApplicationException: com.sun.jersey.api.MessageException: A message body writer for Java class org.apache.catalina.connector.CoyoteOutputStream, and Java type class org.apache.catalina.connector.CoyoteOutputStream, and MIME media type
image/png was not found
        at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:285)
        at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1448)
        at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1360)
.
.
.
Caused by: com.sun.jersey.api.MessageException: A message body writer for Java class org.apache.catalina.connector.CoyoteOutputStream, and Java type class org.apache.catalina.connector.CoyoteOutputStream, and MIME media type image/png was not found

... 56 more

I think I am missing some Jersey dependency.

Any pointers are highly appreciated. Thanks in advance.

Answer 1

I think I am missing some Jersey dependency.

No I don't think so... I believe the fundamental issue is that you can't directly manipulate the response OutputStream and return a Response from your downloadSVG method.

Any pointers are highly appreciated.

A cleaner approach would be to separate the logic that constructs the image from the logic that renders the image to the client. Check out MessageBodyWriter . It gives you access to the request OutputStream and allows you to manipulate the response headers.

Here's what I would do:

1) Create a new class (MyPNG). Modify your REST method to return MyPNG rather than Response and mark it with a @Produces tag.

@Produces("image/png")
public MyPNG downloadSVG(@Context HttpServletRequest request, @Context HttpServletResponse httpServletResponse,String values){

2) In your REST method, read the InputStream and create and return a new instance of MyPNG

3) Implement MessageBodyWriter and do something like this in the writeTo method:

public PNGMessageBodyWriter implements MessageBodyWriter<MyPNG> {
....
boolean isWriteable(java.lang.Class<?> type,
                java.lang.reflect.Type genericType,
                java.lang.annotation.Annotation[] annotations,
                MediaType mediaType)
{
    return mediaType.toString.equals("image/png");
}
....
void writeTo(MyJPEG instance, java.lang.Class<?> type, java.lang.reflect.Type genericType, java.lang.annotation.Annotation[] annotations, 
    MediaType mediaType, MultivaluedMap<java.lang.String,java.lang.Object> httpHeaders, java.io.OutputStream entityStream) throws java.io.IOException,
                    WebApplicationException
{
    JPEGTranscoder t = new JPEGTranscoder();
    t.addTranscodingHint(JPEGTranscoder.KEY_QUALITY, new Float(.8));
    InputStream is = new ByteArrayInputStream(instance.getBytes());
    TranscoderInput input = new TranscoderInput(is);
    TranscoderOutput output = new TranscoderOutput(entityStream);
    t.transcode(input, output);
    httpHeaders.put("Content-Disposition", ""attachment;filename=" + instance.getFilename());
    // and so on....
    httpHeaders.put("whatever else", "some other value");
}

4) Follow the instructions appropriate for your version of Jersey to register your MessageBodyWriter as a Provider.