如何通过表单上传文件并让 Java 将其作为输入流处理？

Question

我有一个 Java 类，它接受 InputStream 并对传入的数据进行编码。如何才能让某些东西能够接受用户上传的文件，但将其视为流，而不先将整个文件保存到磁盘并使用 FileInputStream？

基本上，我正在寻找一些 Java 中的轻量级 Web 框架，它可以让我获取用户作为数据流上传的文件。

Answer 1

如果尚未完成，请安装 Web 服务器/servlet 容器，例如 Apache Tomcat。

如果您选择 Tomcat 6.x，则使用 Apache Commons FileUpload 获取上传的文件作为 输入流。如果您选择 Tomcat 7.x (Servlet 3.0)，则使用 HttpServletRequest#getPart() 然后 Part#getInputStream() 获取上传的文件作为 InputStream< /代码>。

Answer 2

import org.apache.commons.fileupload.FileItemStream;
 import org.apache.commons.fileupload.FileItemIterator;
 import org.apache.commons.fileupload.servlet.ServletFileUpload;

 import java.io.InputStream;
 import java.io.IOException;
 import java.util.logging.Logger;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 public class FileUpload extends HttpServlet {
   private static final Logger log =
       Logger.getLogger(FileUpload.class.getName());

   public void doPost(HttpServletRequest req, HttpServletResponse res)
       throws ServletException, IOException {
     try {
       ServletFileUpload upload = new ServletFileUpload();
       res.setContentType("text/plain");

       FileItemIterator iterator = upload.getItemIterator(req);
       while (iterator.hasNext()) {
         FileItemStream item = iterator.next();
         InputStream stream = item.openStream();

         if (item.isFormField()) {
           log.warning("Got a form field: " + item.getFieldName());
         } else {
           log.warning("Got an uploaded file: " + item.getFieldName() +
                       ", name = " + item.getName());

           // You now have the filename (item.getName() and the
           // contents (which you can read from stream).  Here we just
           // print them back out to the servlet output stream, but you
           // will probably want to do something more interesting (for
           // example, wrap them in a Blob and commit them to the
           // datastore).
           int len;
           byte[] buffer = new byte[8192];
           while ((len = stream.read(buffer, 0, buffer.length)) != -1) {
             res.getOutputStream().write(buffer, 0, len);
           }
         }
       }
     } catch (Exception ex) {
       throw new ServletException(ex);
     }
   }
 }

该示例是从 Google App Engine 文档中提取的，因为 GAE 也不允许应用程序在磁盘上写入文件。原始示例可以在此处找到