Question

我在客户端生成了D3图表。我将SVG数据发送到Jersey REST服务，使用SVG将OutputStream数据转换为图片（Transcoding）。当我从服务返回响应时，我可以在控制台中看到作为二进制流返回的数据。

我想要的是一旦服务返回响应就会弹出一个浏览器下载窗口。

以下是代码段：

@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;
}

调用此服务后，我会在服务器控制台上关注Exception：

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

我想我错过了一些泽西岛的依赖。

任何指针都非常感谢。提前谢谢。

Answer 1

我想我错过了一些泽西岛的依赖。

不，我不这么认为......我认为根本问题是你不能直接操作响应OutputStream并从你的downloadSVG方法返回一个响应。

任何指针都受到高度赞赏。

更简洁的方法是将构建图像的逻辑与将图像呈现给客户端的逻辑分开。查看MessageBodyWriter。它使您可以访问请求OutputStream，并允许您操作响应头。

这就是我要做的事情：

1）创建一个新类（MyPNG）。修改您的REST方法以返回MyPNG而不是Response，并使用@Produces标记对其进行标记。

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

2）在REST方法中，读取InputStream并创建并返回MyPNG的新实例

3）实现MessageBodyWriter并在writeTo方法中执行类似的操作：

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）按照适用于您的Jersey版本的说明将MessageBodyWriter注册为提供者。

Jersey REST服务将响应作为带有下载窗口的图像返回

1 个答案: