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

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:
/**  * Returns the value of a request parameter from the given {@code HttpServletRequest}  * as a {@code String}, or {@code null} if the parameter does not exist.  * This method can handle request of type both {@code application/x-www-form-urlencoded}  * and {@code multipart/form-data}.  * @param req The request object.  * @param name The name of the parameter.  * @param charset The name of charset for parsing bytes to string if the request  * if of type {@code multipart/form-data}. An improper charset might lead to  * messy code in the returned string.  * @return The velue of the parameter.  */ public static String getParameter(HttpServletRequest req, String name,String charse) {     // First assume the request is of type application/x-www-form-urlencoded.     String value = req.getParameter(name);     if (value != null) {         return value;     }     // Trying to handle the request as a multipart/form-data type.     try {         Reader in = new InputStreamReader(part.getInputStream(), charset);         StringBuilder sb = new StringBuilder();         char[] buffer = new char[256];         int read = 0;         while ((read = in.read(buffer)) != -1) {             sb.append(buffer, 0, read);         }         in.close();         return sb.toString();     } catch (Exception ex) {         return null;     } }
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:
private static final String FILENAME_KEY = "filename=\""; /**  * Gets the original filename of a {@code Part}. The filename is encoded in  * the {@code content-disposition} header of the {@code Part} as the value  * of {@code filename} parameter.  * @param part The {@code Part} object.  * @return The filename of the part, or {@code null} if the part doesn't  * contain a file.  */ public static String getFileNameFromPart(Part part) {     String cdHeader = part.getHeader("content-disposition");     if (cdHeader == null) {         return null;     }     for (String s : cdHeader.split("; ")) {         if (s.startsWith(FILENAME_KEY)) {             // Some stupid browers, e.g. IE, put the full file path on the             // client machine as the value, so we have to extract the filename             // out from it.             String path = s.substring(FILENAME_KEY.length(),                     s.length() - 1).replaceAll("\\\\", "/");             return path.substring(path.lastIndexOf("/") + 1);         }     }     return null; }