標籤：檔案下載
11.1、檔案下載概述1、將響應的內容類型設定為檔案的內容類型。標題Content-type用來規定實體主體中的資料類型，包含媒體類型和子類型標識符。
2、添加一個名為Content-Disposition的HTTP回應標頭，給它賦值attachment；filename=filename，這裡的fileName是指在檔案下載對話方塊中顯示出來的預設檔案名稱。它通常與檔案名稱相同，但是也可以不同。
例如，以下就是將一個檔案發送到瀏覽器的代碼範例。
FileInputStream fis = new FileInputStream(file) ;
BufferedInputStream bis = new BufferedInputStream(fis) ;
byte[] bytes = new byte[bis.available()] ;
response.setContentType(contentType) ;
OutputStream os = response.getOutputStream() ;
bis.read(bytes) ;
os.write(bytes) ;
警告：一定要確保你沒有在無意中發送超出實際檔案內容以外的任何字元。這有可能在你毫不知情的情況下發生。例如，如果需要在JSP頁面中使用page指令，可以這麼寫：
<%@ page import=”java.io.FileInputStream”%>
<jsp:useBean id=”DBBeanId” scope=”page” class=”MyBean”>
在你毫不察覺的情況下，page指令後面的斷行符號分行符號就會被發送給瀏覽器。為了防止發送多餘的字元，需要像下面這樣編寫這個指令：
<%@ page import=”java.io.FileInputStream”
%><jsp:useBean id=”DBBeanId” scope=”page” class=”MyBean”>
11.2、範例1：隱藏資源
在下面這個程式中，我們用一個FileDownloadServlet servlet將secret.pdf檔案發送到瀏覽器。但是，只有授權使用者才能瀏覽。如果使用者沒有登入，應用程式就會跳轉到Login頁面。在這裡，使用者可以在表單中輸入使用者名稱和密碼，這些內容都將被提交給另一個Servlet：LoginServlet。
LoginServlet.java
package filedownloaded;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 = 1L;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");return ;}else{RequestDispatcher dispatcher = request.getRequestDispatcher("/login.jsp") ;dispatcher.forward(request, response);}}}
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <base href="<%=basePath%>"> <title>My JSP 'login.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><!--<link rel="stylesheet" type="text/css" href="styles.css">--> </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 name="password" type="password"/></td> </tr> <tr> <td colspan="2"> <input type="submit" value="login"/> </td> </tr> </table> </form> </body></html>FileDownloadServlet.java
package filedownloaded;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 = 1L;@Overridepublic void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {HttpSession session = req.getSession() ;if(session == null || session.getAttribute("loggedIn") == null){RequestDispatcher dispatcher = req.getRequestDispatcher("/login.jsp") ;dispatcher.forward(req, resp); return ;}String dataDirectory = req.getServletContext().getRealPath("/WEB-INF/data") ;File file = new File(dataDirectory, "secret.pdf") ;if(file.exists()){resp.setContentType("application/pdf");resp.addHeader("Content-Disposition", "attachment; filename=secret.pdf");byte[] buffer = new byte[1024] ;try(FileInputStream fis = new FileInputStream(file) ;BufferedInputStream bis = new BufferedInputStream(fis);OutputStream os = resp.getOutputStream()){int i = bis.read(buffer) ;while(i != -1){os.write(buffer, 0, i);i = bis.read(buffer) ;}}catch(IOException e){e.printStackTrace();}}}}
第十一章_檔案下載
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