Java + Spring：如果我有没有HttpRequest的路径，我可以上传文件吗？

Question

我真的这样做

protected ModelAndView onSubmit(HttpServletRequest request, 
     HttpServletResponse response, Object command, BindException errors) 
     throws Exception { 
    MultipartFile multipartFile = null; 
    File destFile = new File(
      "/home/stas/eclipse/" + request.getParameter("fileName")); 
multipartFile.transferTo(destFile); 

但我有例外

27.03.2012 20:39:45 org.apache.catalina.core.StandardWrapperValve invoke 
SEVERE: Servlet.service() for servlet [springapp] in context with 
    path [/springapp] threw exception [Request processing failed; 
    nested exception is java.lang.NullPointerException] with root cause 
    java.lang.NullPointerException 

Answer 1

的NullPointerException是相当明显的：

MultipartFile multipartFile = null; 
File destFile = new File("/home/stas/eclipse/"+request.getParameter("fileName")); 
multipartFile.transferTo(destFile); <-----Exception 

multipartFile变量从未被初始化，并抛出NPE被第一次访问时。

你可以从要求所有上传的文件使用：

public ModelAndView onSubmit(HttpServletRequest request, /*...*/) { 
    MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest)request; 
    Map<String, MultipartFile> files = multipartRequest.getFileMap();