什麼是文件下載
將服務器上的一個文件，通過流寫入到客戶端。
文件下載的方式：
- 使用超鏈接的方式實現文件下載
- 通過手動編寫代碼的方式實現文件下載
- 設置兩個頭和一個流
- Content-Type：文件的MIME類型
- Content-Disposition：瀏覽器支持該格式的文件，提示下載
- 設置代表該文件的輸入流（輸出流是固定的response.getOutputStream）
文件下載——超鏈接
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>文件下載：超鏈接</h1>
<h3><a href="${ pageContext.request.contextPath }/download/qwe.txt">qwe.txt</a></h3>
<h3><a href="${ pageContext.request.contextPath }/download/qweqweqwe.pptx">qwe.pptx</a></h3>
</body>
</html>
文件下載——手動編碼
- 文件下載頁面準備
<h1>文件下載：手動編碼</h1>
<h3><a href="${ pageContext.request.contextPath }/DownloadServlet?filename = qwe.txt">qwe.txt</a></h3>
<h3><a href="${ pageContext.request.contextPath }/DownloadServlet?filename = qweqweqwe.pptx">qwe.pptx</a></h3>
- 文件下載的Servlet
/**
* 文件下載的Servlet
*/
public class DownloadServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//接收參數
String filename = request.getParameter("filename");
//下載，設置兩個頭一個流
//1、設置Content-Type
String type = getServletContext().getMimeType(filename);
response.setContentType(type);
//2、設置Content-Disposition
response.setHeader("Content-Disposition", "attachment;filename="+filename);
//3、設置一個代表了文件的輸入流
String path = getServletContext().getRealPath("/download");
InputStream is = new FileInputStream(path+"/"+filename);
OutputStream os = response.getOutputStream();
//4、兩個流對接
int len =0;
byte[] b = new byte[1024];
while((len = is.read(b)) != -1) {
os.write(b,0,len);
}
is.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
中文文件下載
不同瀏覽器對中文文件下載的編碼不一樣。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//接收參數
String filename = new String(request.getParameter("filename").getBytes("ISO-8859-1"),"UTF-8");
//下載，設置兩個頭一個流
//1、設置Content-Type
String type = getServletContext().getMimeType(filename);
response.setContentType(type);
//2、設置Content-Disposition
response.setHeader("Content-Disposition", "attachment;filename="+filename);
//定義一個代表該文件的路徑：
String path = getServletContext().getRealPath("/download");
File file = new File(path+"/"+filename);
//判斷瀏覽器類型
String agent = request.getHeader("User-Agent");
if(agent.contains("Firefox")) {
//filename = base64的解碼方式
}else {
//ie或其他瀏覽器
filename = URLEncoder.encode(filename,"UTF-8");
}
//3、設置一個代表了文件的輸入流
InputStream is = new FileInputStream(file);
OutputStream os = response.getOutputStream();
//4、兩個流對接
int len =0;
byte[] b = new byte[1024];
while((len = is.read(b)) != -1) {
os.write(b,0,len);
}
is.close();
}
給定目錄下的文件下載
需求描述：
給定一個目錄，將這個路徑中的文件顯示到頁面上，在頁面上給每個文件都提供響應下載的鏈接，點擊鏈接下載。
文件列表顯示（樹形遍歷）（downlist.jsp）：
<%@page import="java.io.File"%>
<%@page import="java.util.LinkedList"%>
<%@page import="java.util.Queue"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>樹形遍歷</h1>
<%
//1、創建一個隊列
Queue<File> queue = new LinkedList<File>();
//2、先將根節點入隊
File root = new File("D://CloudMusic");
queue.offer(root);
//判斷這個隊列是否爲空，不爲空需要進行遍歷：
while(!queue.isEmpty()){
//將根節點出隊
File file = queue.poll();
//獲得根節點下的子節點
File[] files = file.listFiles();
//遍歷子節點
for(File f:files){
//判斷該節點是否爲葉子節點
if(f.isFile()){
%>
<h4><a href="${ pageContext.request.contextPath }/DownloadListServlet?filename = <%f.getCanonicalPath();%>"><%= f.getName() %></a></h4>
<%
}else{
queue.offer(f);
}
}
}
%>
</body>
</html>
文件下載（DownloadListServlet）：
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//接收參數
String path = request.getParameter("filename");
if(path != null) {
path = new String(path.getBytes("ISO-8859-1"),"UTF-8");
}
File file = new File(path);
//實現文件下載
//設置兩個頭一個流
//獲得文件名
String filename = file.getName();
response.setContentType(getServletContext().getMimeType(filename));
//設置另一個頭
String agent = request.getHeader("User-Agent");
if(agent.contains("Firefox")) {
//base64轉碼
}else {
filename = URLEncoder.encode(filename,"UTF-8"); //url編碼會將空格變成+
filename = filename.replace("+", " ");
}
response.setHeader("Content-Disposition", "attachment;filename="+filename);
//設置輸入流
InputStream is = new FileInputStream(file);
OutputStream os = response.getOutputStream();
//流對接
int len = 0;
byte[] b = new byte[1024];
while((len = is.read(b)) != -1) {
os.write(b,0,len);
}
is.close();
}