一个文件下载的Servlet

转载自：http://www.cnblogs.com/mingzi/archive/2009/03/09/1406810.html

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 = "";

    /**

     * 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();

            }

        }

    }

web.xml

    <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>