Servlet文件下载的常用实例1

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范例一：隐藏资源

1.功能描述：对于登录成功的用户，保存会话，然后可以下载资源文件。

2.目的：不允许直接访问某些静态资源文件，从而达到保护静态资源文件的目的

3.实现步骤：

（1）创建一个FileDownloadServlet、一个LoginServlet、一个login.jsp页面

（2）在FileDownloadServlet中的业务逻辑：

1）根据httpSession进行判断,如果成功，则进行下载。否则，跳转到登录页面

（3）在LoginServlet中的业务逻辑：

1）如果用户登录成功，则保存会话，跳转到FileDownloadServlet

2）如果登录失败，则跳转到login.jsp页面

4.源代码：

import java.io.BufferedInputStream;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.OutputStream;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;@WebServlet(urlPatterns = { "/download" })public class FileDownloadServlet extends HttpServlet {    private static final long serialVersionUID = 7583L;    public void doGet(HttpServletRequest request,            HttpServletResponse response) throws ServletException,            IOException {        HttpSession session = request.getSession();        if (session == null ||                 session.getAttribute("loggedIn") == null) {            RequestDispatcher dispatcher =                     request.getRequestDispatcher("/login.jsp");            dispatcher.forward(request, response);            // must return after dispatcher.forward(). Otherwise,              // the code below will be executed            return;         }        String dataDirectory = request.                getServletContext().getRealPath("/WEB-INF/data");        File file = new File(dataDirectory, "secret.pdf");        if (file.exists()) {            response.setContentType("application/pdf");            response.addHeader("Content-Disposition",                     "attachment; filename=secret.pdf");            byte[] buffer = new byte[1024];            FileInputStream fis = null;            BufferedInputStream bis = null;            // if you're using Java 7, use try-with-resources            try {                fis = new FileInputStream(file);                bis = new BufferedInputStream(fis);                OutputStream os = response.getOutputStream();                int i = bis.read(buffer);                while (i != -1) {                    os.write(buffer, 0, i);                    i = bis.read(buffer);                }            } catch (IOException ex) {                System.out.println (ex.toString());            } finally {                if (bis != null) {                    bis.close();                }                if (fis != null) {                    fis.close();                }            }        }    }}

import java.io.IOException;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;@WebServlet(urlPatterns = { "/login" })public class LoginServlet extends HttpServlet {    private static final long serialVersionUID = -920L;    public void doPost(HttpServletRequest request,            HttpServletResponse response) throws ServletException,            IOException {        String userName = request.getParameter("userName");        String password = request.getParameter("password");        if (userName != null && userName.equals("ken")                 && password != null && password.equals("secret")) {            HttpSession session = request.getSession(true);            session.setAttribute("loggedIn", Boolean.TRUE);            response.sendRedirect("download");            // must call return or else the code after this if             // block, if any, will be executed            return;        } else {            RequestDispatcher dispatcher =                     request.getRequestDispatcher("/login.jsp");            dispatcher.forward(request, response);        }    }}

<html><head><title>Login</title></head><body><form action="login" method="post">    <table>    <tr>        <td>User Name:</td>        <td><input name="userName"/></td>    </tr>    <tr>        <td>Password:</td>        <td><input type="password" name="password"/></td>    </tr>    <tr>        <td colspan="2">            <input type="submit" value="Login"/>        </td>    </tr>    </table></form></body></html>

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