Servlet实现文件下载功能

public class DownloadServlet extends HttpServlet {  private String contentType = "application/x-msdownload";  private String enc = "utf-8";  private String fileRoot = "";  /**   * 初始化contentType，enc，fileRoot   */  public void init(ServletConfig config) throws ServletException {    String tempStr = config.getInitParameter("contentType");    if (tempStr != null && !tempStr.equals("")) {      contentType = tempStr;    }    tempStr = config.getInitParameter("enc");    if (tempStr != null && !tempStr.equals("")) {      enc = tempStr;    }    tempStr = config.getInitParameter("fileRoot");    if (tempStr != null && !tempStr.equals("")) {      fileRoot = tempStr;    }  }  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {    String filepath = request.getParameter("filepath");    String fullFilePath = fileRoot + filepath;    /*读取文件*/    File file = new File(fullFilePath);    /*如果文件存在*/    if (file.exists()) {      String filename = URLEncoder.encode(file.getName(), enc);      response.reset();      response.setContentType(contentType);      response.addHeader("Content-Disposition", "attachment; filename=/"" + filename + "/"");      int fileLength = (int) file.length();      response.setContentLength(fileLength);      /*如果文件长度大于0*/      if (fileLength != 0) {        /*创建输入流*/        InputStream inStream = new FileInputStream(file);        byte[] buf = new byte[4096];        /*创建输出流*/        ServletOutputStream servletOS = response.getOutputStream();        int readLength;        while (((readLength = inStream.read(buf)) != -1)) {          servletOS.write(buf, 0, readLength);        }        inStream.close();        servletOS.flush();        servletOS.close();      }    }  }

  <servlet>    <servlet-name>downloadservlet-name>    <servlet-class>org.mstar.servlet.DownloadServletservlet-class>    <init-param>      <param-name>fileRootparam-name>      <param-value>d:/tempparam-value>    init-param>    <init-param>      <param-name>contentTypeparam-name>      <param-value>application/x-msdownloadparam-value>    init-param>    <init-param>      <param-name>encparam-name>      <param-value>utf-8param-value>    init-param>  servlet>  <servlet-mapping>    <servlet-name>downloadservlet-name>    <url-pattern>/downurl-pattern>  servlet-mapping>