Servlet实现文件下载功能

本文实例为大家分享了Servlet实现文件下载的具体代码，供大家参考，具体内容如下

把文件目录直接暴露给用户是很不安全的。所以要用Servlet来做，而且这样做，文件的存储方式就更丰富了，可以是从文件系统上取来的，也可以是数据库中经过计算生成的，或者从其它什么稀奇古怪的地方取来的。

public class DownloadServlet extends httpservlet {  private String contentType = "application/x-msdownload";  private String enc = "utf-8";  private String 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;        File file = new File(fullFilePath);        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);            if (fileLength != 0) {                InputStream inStream = new FileInputStream(file);        byte[] buf = new byte[4096];                ServletOutputStream servletOS = response.getOutputStream();        int readLength;        while (((readLength = inStream.read(buf)) != -1)) {          servletOS.write(buf, 0, readLength);        }        inStream.close();        servletOS.flush();        servletOS.close();      }    }  }