被空字节损坏的Java代理输出流

Question

我们有一个JSP，它应该从内部URL中获取一个PDF，并将这个PDF传递给客户机(就像一个代理)。

由此产生的下载已损坏。在大约18'400字节之后，我们只能得到00字节直到结尾。有趣的是，下载的大小(以字节为单位)是完全正确的。

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    // Get the download
    URL url = new URL(url);
    HttpURLConnection req = (HttpURLConnection)url.openConnection();
    req.setDoOutput(true);
    req.setRequestMethod("GET");

    // Get Binary Response
    int contentLength = req.getContentLength();
    byte ba[] = new byte[contentLength];
    req.getInputStream().read(ba);
    ByteArrayInputStream in = new ByteArrayInputStream(ba);

    // Prepare Reponse Headers
    response.setContentType(req.getContentType());
    response.setContentLength(req.getContentLength());
    response.setHeader("Content-Disposition", "attachment; filename=download.pdf");

    // Stream to Response
    OutputStream output = response.getOutputStream();
    //OutputStream output = new FileOutputStream("c:\\temp\\op.pdf");
    int count;
    byte[] buffer = new byte[8192];
    while ((count = in.read(buffer)) > 0) output.write(buffer, 0, count);

    in.close();
    output.close();

    req.disconnect();

更新1:我不是唯一一个看到Java以4379字节(链接)停止流的人。

更新2:如果每次写完后执行output.flush，我会得到更多的数据，14599字节，然后是空值。必须与tomcat的输出缓冲区限制有关。

Answer 1

int contentLength = req.getContentLength();
byte ba[] = new byte[contentLength];
req.getInputStream().read(ba);
ByteArrayInputStream in = new ByteArrayInputStream(ba);

// Prepare Reponse Headers
response.setContentType(req.getContentType());
response.setContentLength(req.getContentLength());
response.setHeader("Content-Disposition", "attachment; filename=download.pdf");

// Stream to Response
OutputStream output = response.getOutputStream();
//OutputStream output = new FileOutputStream("c:\\temp\\op.pdf");
int count;
byte[] buffer = new byte[8192];
while ((count = in.read(buffer)) > 0) output.write(buffer, 0, count);

这些代码都是胡说八道。您忽略了第一个read()的结果，也浪费了ByteArrayInputStream的时间和空间。你只需要这样：

int contentLength = req.getContentLength();

// Prepare Reponse Headers
response.setContentType(req.getContentType());
response.setHeader("Content-Disposition", "attachment; filename=download.pdf");

// Stream to Response
InputStream in = req.getInputStream();
OutputStream output = response.getOutputStream();
int count;
byte[] buffer = new byte[8192];
while ((count = in.read(buffer)) > 0) output.write(buffer, 0, count);

注意，内容长度已经为您设置好了。