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在 Servlet 3.0 中处理 multipart/form-data 请求的两个辅助方法

Posted on 2010-04-24 11:59 蜀山兆孨龘 阅读(4329) 评论(0)  编辑  收藏 所属分类: Java EE
在 Servlet 3.0 中处理 multipart/form-data 请求的两个辅助方法 Two Assistant Methods for Dealing with multipart/form-data Request in Servlet 3.0
Servlet 3.0 引入了 javax.servlet.http.Part 接口，从而提供了对 multipart/form-data 类型的 HTTP 请求的直接支持，我们从此就可以摆脱诸如 Apache Commons FileUpload 之类的第三方依赖。然而，该支持太过单纯，所以还要多做点事情，以便能更有效地进行工作。我将在本文中介绍两个辅助方法。 Servlet 3.0 comes with out-of-the-box support for handling HTTP request of type multipart/form-data by introducing of javax.servlet.http .Part interface, freeing us from 3rd party dependencies such as Apache Commons FileUpload. However, the support so pure that we still need to do a little more work to get us work more effective. I'll demostrate two assistant methods in this article.
首先，Servlet 3.0 没有提供方法将 Part 对象专为字符串。multipart/form-data 请求也可能包含字符串参数。在这种情况下，我们可以写一个工具方法来从 Part 对象读取字节，然后将其解析为字符串。为了方便，还可以让这个方法能处理最常见的 application/x-www-form-urlencoded 请求： First, there's no method to translate a Part object to a string value in Servlet 3.0. A multipart/form-data request may also contain string parameters. In this case, we can wrtie a utility method to read bytes from the Part object and parse them to a string value. For convenience we also enable the method to handle the most common application/x-www-form-urlencoded request:
  1. /**
  2.  * Returns the value of a request parameter from the given {@code HttpServletRequest}
  3.  * as a {@code String}, or {@code null} if the parameter does not exist.
  4.  * This method can handle request of type both {@code application/x-www-form-urlencoded}
  5.  * and {@code multipart/form-data}.
  6.  * @param req The request object.
  7.  * @param name The name of the parameter.
  8.  * @param charset The name of charset for parsing bytes to string if the request
  9.  * if of type {@code multipart/form-data}. An improper charset might lead to
  10.  * messy code in the returned string.
  11.  * @return The velue of the parameter.
  12.  */
  13. public static String getParameter(HttpServletRequest req, String name,String charse) {
  14.     // First assume the request is of type application/x-www-form-urlencoded.
  15.     String value = req.getParameter(name);
  16.     if (value != null) {
  17.         return value;
  18.     }
  19.     // Trying to handle the request as a multipart/form-data type.
  20.     try {
  21.         Reader in = new InputStreamReader(part.getInputStream(), charset);
  22.         StringBuilder sb = new StringBuilder();
  23.         char[] buffer = new char[256];
  24.         int read = 0;
  25.         while ((read = in.read(buffer)) != -1) {
  26.             sb.append(buffer, 0, read);
  27.         }
  28.         in.close();
  29.         return sb.toString();
  30.     } catch (Exception ex) {
  31.         return null;
  32.     }
  33. }
类似地，可以写一个 getParameterValues 方法去处理名称相同的多个参数，所以就不在这里列出代码了。第二个辅助方法用于从 Part 对象获取文件名。Part 接口并没有提供这种方法，但我们可以容易地从头部提取出文件名： In the similar manner we can write a getParameterValues method to handle multiple parameter with the same name, so I'm not going to list the code here. The sencond assistant method is for getting the filename from a Part object. The Part interface doesn't provide such a method, but we can easily extract the filename from the header:
  1. private static final String FILENAME_KEY = "filename=\"";
  3. /**
  4.  * Gets the original filename of a {@code Part}. The filename is encoded in
  5.  * the {@code content-disposition} header of the {@code Part} as the value
  6.  * of {@code filename} parameter.
  7.  * @param part The {@code Part} object.
  8.  * @return The filename of the part, or {@code null} if the part doesn't
  9.  * contain a file.
  10.  */
  11. public static String getFileNameFromPart(Part part) {
  12.     String cdHeader = part.getHeader("content-disposition");
  13.     if (cdHeader == null) {
  14.         return null;
  15.     }
  16.     for (String s : cdHeader.split("; ")) {
  17.         if (s.startsWith(FILENAME_KEY)) {
  18.             // Some stupid browers, e.g. IE, put the full file path on the
  19.             // client machine as the value, so we have to extract the filename
  20.             // out from it.
  21.             String path = s.substring(FILENAME_KEY.length(),
  22.                     s.length() - 1).replaceAll("\\\\", "/");
  23.             return path.substring(path.lastIndexOf("/") + 1);
  24.         }
  25.     }
  26.     return null;
  27. }

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