聂永的博客

1. 需要添加MultipartConfig注解
2. 从request对象中获取Part文件对象

/**
 * 上传文件测试 location为临时文件保存路径
 * 
 * @author yongboy
 * @date 2011-1-13
 * @version 1.0
 */
@MultipartConfig(location = "/home/yongboy/tmp/", maxFileSize = 1024 * 1024 * 10)
@WebServlet("/upload")
public class UploadFileAction extends HttpServlet {
 private static final long serialVersionUID = 92166165626L;
 private static final Log log = LogFactory.getLog(UploadFileAction.class);
 // 得到注解信息
 private static final MultipartConfig config;

 static {
  config = UploadFileAction.class.getAnnotation(MultipartConfig.class);
 }

 protected void doGet(HttpServletRequest request,
   HttpServletResponse response) throws ServletException, IOException {
  request.getRequestDispatcher("/upload.jsp").forward(request, response);
 }

 protected void doPost(HttpServletRequest request,
   HttpServletResponse response) throws ServletException, IOException {
  // 为避免获取文件名称时出现乱码
  request.setCharacterEncoding("UTF-8");

  Part part = null;
  try {
   // <input name="file" size="50" type="file" />
   part = request.getPart("file");
  } catch (IllegalStateException ise) {
   // 上传文件超过注解所标注的maxRequestSize或maxFileSize值
   if (config.maxRequestSize() == -1L) {
    log.info("the Part in the request is larger than maxFileSize");
   } else if (config.maxFileSize() == -1L) {
    log.info("the request body is larger than maxRequestSize");
   } else {
    log.info("the request body is larger than maxRequestSize, or any Part in the request is larger than maxFileSize");
   }

   forwardErrorPage(request, response, "上传文件过大，请检查输入是否有误！");
   return;
  } catch (IOException ieo) {
   // 在接收数据时出现问题
   log.error("I/O error occurred during the retrieval of the requested Part");
  } catch (Exception e) {
   log.error(e.toString());
   e.printStackTrace();
  }

  if (part == null) {
   forwardErrorPage(request, response, "上传文件出现异常，请检查输入是否有误！");
   return;
  }
  
  // 得到文件的原始名称，eg ：测试文档.pdf
  String fileName = UploadUtils.getFileName(part);

  log.info("contentType : " + part.getContentType());
  log.info("fileName : " + fileName);
  log.info("fileSize : " + part.getSize());
  log.info("header names : ");
  for (String headerName : part.getHeaderNames()) {
   log.info(headerName + " : " + part.getHeader(headerName));
  }

  String saveName = System.currentTimeMillis() + "."
    + FilenameUtils.getExtension(fileName);

  log.info("save the file with new name : " + saveName);

  // 因在注解中指定了路径，这里可以指定要写入的文件名
  // 在未执行write方法之前，将会在注解指定location路径下生成一临时文件
  part.write(saveName);

  request.setAttribute("fileName", fileName);
  request.getRequestDispatcher("/uploadResult.jsp").forward(request,
    response);
 }

 private void forwardErrorPage(HttpServletRequest request,
   HttpServletResponse response, String errMsg)
   throws ServletException, IOException {
  request.setAttribute("errMsg", errMsg);

  request.getRequestDispatcher("/upload.jsp").forward(request, response);
 }
}

 /**
  * 如何得到上传的文件名, API没有提供直接的方法，只能从content-disposition属性中获取
  * 
  * @param part
  * @return
  */
 protected static String getFileName(Part part) {
  if (part == null)
   return null;

  String fileName = part.getHeader("content-disposition");
  if (StringUtils.isBlank(fileName)) {
   return null;
  }

  return StringUtils.substringBetween(fileName, "filename=\"", "\"");
 }

截图中可以看到Part包含content-disposition属性，可以很容易从值中抽取出文件名。临时生成的上传文件大都以 .tmp为后缀，大致如下：

让上传出现错误，就可以在保存路径下看到大致如上的临时文件。

一次上传多个文件的后台servlet示范：

/**
 * 多文件上传支持
 * @author yongboy
 * @date 2011-1-14
 * @version 1.0
 */
@MultipartConfig(
  location = "/home/yongboy/tmp/", 
  maxFileSize = 1024L * 1024L, // 每一个文件的最大值
  maxRequestSize = 1024L * 1024L * 10L // 一次上传最大值，若每次只能上传一个文件，则设置maxRequestSize意义不大
)
@WebServlet("/uploadFiles")
public class UploadFilesAction extends HttpServlet {
 private static final long serialVersionUID = 2304820820384L;
 private static final Log log = LogFactory.getLog(UploadFilesAction.class);

 protected void doGet(HttpServletRequest request,
   HttpServletResponse response) throws ServletException, IOException {
  request.getRequestDispatcher("/uploads.jsp").forward(request, response);
 }

 protected void doPost(HttpServletRequest request,
   HttpServletResponse response) throws ServletException, IOException {
  request.setCharacterEncoding("UTF-8");

  Collection parts = null;
  try {
   parts = request.getParts();
  } catch (IllegalStateException ise) {
   // 可能某个文件大于指定文件容量maxFileSize，或者提交数据大于maxRequestSize
   log.info("maybe the request body is larger than maxRequestSize, or any Part in the request is larger than maxFileSize");
  } catch (IOException ioe) {
   // 在获取某个文件时遇到拉IO异常错误
   log.error("an I/O error occurred during the retrieval of the Part components of this request");
  } catch (Exception e) {
   log.error("the request body is larger than maxRequestSize, or any Part in the request is larger than maxFileSize");
   e.printStackTrace();
  }

  if (parts == null || parts.isEmpty()) {
   doError(request, response, "上传文件为空！");
   return;
  }

  // 前端具有几个file组件，这里会对应几个Part对象
  List fileNames = new ArrayList();
  for (Part part : parts) {
   if (part == null) {
    continue;
   }
   // 这里直接以源文件名保存
   String fileName = UploadUtils.getFileName(part);

   if (StringUtils.isBlank(fileName)) {
    continue;
   }

   part.write(fileName);
   fileNames.add(fileName);
  }

  request.setAttribute("fileNames", fileNames);
  request.getRequestDispatcher("/uploadsResult.jsp").forward(request,
    response);
 }

 private void doError(HttpServletRequest request,
   HttpServletResponse response, String errMsg)
   throws ServletException, IOException {
  request.setAttribute("errMsg", errMsg);

  this.doGet(request, response);
 }
}

批量上传很简单，但也有风险，任一个文件若超过maxFileSize值，意味着整个上传都会失败。若不限大小，那就不存在以上忧虑了。

总之，在Servlet 3.0 中，无论是上传一个文件，或者多个批量上传都是非常简单，但要处理好异常，避免出错。