java - 使用 Servlet 将数据写入文件时出现问题

Question

我正在尝试读取 XML 文件并使用 HttpPost 发送到本地服务器。当在服务器端读取数据并写入文件时，总是会丢失最后几行。

客户端代码:

  HttpClient httpclient = new DefaultHttpClient();
  HttpPost httppost = new HttpPost("http://xxx.xxx.xxx.xxx:yyyy/FirstServlet/HelloWorldServlet");      
  InputStreamEntity reqEntity = new InputStreamEntity(
  new FileInputStream(dataFile), -1);
  reqEntity.setContentType("binary/octet-stream");

  // Send in multiple parts if needed
  reqEntity.setChunked(true);
  httppost.setEntity(reqEntity);
  HttpResponse response = httpclient.execute(httppost);
  int respcode =  response.getStatusLine().getStatusCode();

服务器代码:

    response.setContentType("binary/octet-stream");
    InputStream is = request.getInputStream();
    BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(new File("C:\\Files\\copyFile.xml")));
    byte[] buf = new byte[4096];
    for (int nChunk = is.read(buf); nChunk!=-1; nChunk = is.read(buf))
    {
        bos.write(buf, 0, nChunk);
    } 

我也尝试使用 BufferedReader，但出现同样的问题。

    BufferedReader in = new BufferedReader(  
            new InputStreamReader(request.getInputStream()));
    response.setContentType("binary/octet-stream");  
    String line = null;  
         BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(new File("C:\\Files\\copyFile.xml")));
         while((line = in.readLine()) != null) {
             line = in.readLine();
             bos.write((line + "\n").getBytes());
    }  

我也尝试过使用扫描仪。在这种情况下，只有当我使用 StringBuilder 并将值再次传递到 BufferedOutputStream 时，它才能正常工作。

    response.setContentType("binary/octet-stream");
    StringBuilder stringBuilder = new StringBuilder(2000);
    Scanner scanner = new Scanner(request.getInputStream());
    BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(new File("C:\\Files\\copyFile.xml")));
    while (scanner.hasNextLine()) {
        stringBuilder.append(scanner.nextLine() + "\n");
    }
    String tempStr = stringBuilder.toString();
    bos.write(tempStr.getBytes());

我无法使用上述逻辑来处理非常大的 XML，因为转换为字符串值会引发 Java 堆空间错误。

请告诉我代码有什么问题？

提前致谢!

Answer 1

flush()和 close()你的输出流。发生的情况是您没有刷新，最后几行保留在某个内部缓冲区中并且没有写出。

所以在你的服务器代码中:

response.setContentType("binary/octet-stream");
InputStream is = request.getInputStream();
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(new File("C:\\Files\\copyFile.xml")));
byte[] buf = new byte[4096];
for (int nChunk = is.read(buf); nChunk!=-1; nChunk = is.read(buf)) {
   bos.write(buf, 0, nChunk);
}
bos.flush();
bos.close();