在 Jersey 2 中流式传输多部分答案

【问题标题】：Streaming a multipart in Jersey 2在 Jersey 2 中流式传输多部分
【发布时间】：2015-03-25 17:30:50
【问题描述】：

我目前有 Jersey REST 代码来流式传输单个文件，效果很好：

StreamingOutput stream = new StreamingOutput() {
    @Override
    public void write(OutputStream out)
    throws IOException {
        final BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(out);

        // Stream is filled with data in this method.
        restDAO.readData(bufferedOutputStream);
        bufferedOutputStream.flush();
        bufferedOutputStream.close();
    }
};

return Response.ok(body, mimeType).header("filename", getFileName()).build();

但是，我想流式传输包含大文件和 JSON 的多部分文件，执行以下操作：

FormDataMultiPart multiPart = new FormDataMultiPart();
multiPart.bodyPart(jsonObject, MediaType.APPLICATION_JSON_TYPE);
String mimeType = "application/octet-stream";

StreamingOutput stream = new StreamingOutput() {
    @Override
    public void write(OutputStream out)
    throws IOException {
        final BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(out);

        // Stream is filled with data in this method.
        restDAO.readData(bufferedOutputStream);
        bufferedOutputStream.flush();
        bufferedOutputStream.close();
    }
};
multiPart.bodyPart(stream, MediaTypeUtil.stringToMediaType(mimeType));

return Response.ok(multiPart, MediaType.MULTIPART_FORM_DATA).build();

但是，上面的代码不起作用。运行时出现此错误：javax.ws.rs.BadRequestException: HTTP 400 Bad Request

是否可以以类似的方式流式传输 multiPart？我看到的主要问题是进入多部分的文件来自流本身。

【问题讨论】：

标签： java json jersey streaming multipart

【解决方案1】：

为了正确地流式传输多部分，我最终使用了 PipedInputStream 和 PipedOutputStream 以及一个线程：

PipedOutputStream pipedOutputStream = new PipedOutputStream();
PipedInputStream pipedInputStream = new PipedInputStream(pipedOutputStream);
final BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(pipedOutputStream);

FormDataMultiPart multiPart = new FormDataMultiPart();
multiPart.bodyPart(jsonObject, MediaType.APPLICATION_JSON_TYPE);
String mimeType = "application/octet-stream";

// Multipart streaming.
// Write to the PipedOutputStream in a separate thread
Runnable runnable = new Runnable() {
    public void run() {
        try {
            restDAO.readData(bufferedOutputStream);
            bufferedOutputStream.flush();
            bufferedOutputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
};

Thread fileThread = new Thread(runnable, "MultiPartFileStreamer");
fileThread.start();
final StreamDataBodyPart streamDataBodyPart = new StreamDataBodyPart(
    "file", pipedInputStream, data.getContentFileName(), 
    MediaUtils.stringToMediaType(mimeType));
multiPart.bodyPart(streamDataBodyPart);

return Response.ok(multiPart, MediaType.MULTIPART_FORM_DATA).build();

【讨论】：