如何通過表單上傳文件並讓Java將其作爲InputStream處理？

Question

我有一個Java類，它接受InputStream並對進入的數據進行編碼。如何獲得可接受來自用戶的文件上傳的工作，但將其視爲流而不是先保存整個磁盤並使用的FileInputStream？

基本上我正在尋找一些Java中的輕量級web框架，它只是讓我獲取用戶上傳的文件作爲數據流。

Answer 1

如果尚未完成，請安裝一個webserver/servletcontainer，如Apache Tomcat。

如果您選擇Tomcat 6.x，然後使用Apache Commons FileUpload將上傳的文件作爲InputStream。如果您選擇Tomcat 7.x（Servlet 3.0），然後使用HttpServletRequest#getPart()，然後使用Part#getInputStream()獲取上傳的文件，作爲InputStream。

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); 
    } 
    } 
} 

該示例是從Google App Engine文檔中提取的，因爲GAE也不允許應用程序在磁盤上寫入文件。原始示例可以發現here