java下載檔案案例（帶原始碼）
阿新 • • 發佈：2019-01-03
前言：
web開發中上傳和下載是最基本的內容了。前幾天寫了一篇上傳的案例，今天總結一下下載。案例說明：
1.本案例是使用myeclipse編寫
2.需要下載的檔案存放的 /download_demo/WebRoot/WEB-INF/attachment 目錄下面---這裡我只是放進去了測試檔案
下載檔案思路：
1.得到伺服器上面的檔案File
2.得到輸入流，將檔案流化
3.得到servlet輸出流，將檔案已流的方式寫到客戶端看懂案例中的需要的知識點：
1.servlet的配置
2.filter的配置
3.java檔案的基礎知識
4.java流的知識前臺頁面程式碼：一、index.jsp頁面
功能：點選按鈕，進入下載檔案頁面
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML>
<html>
<head> 前臺頁面：二、download.jsp 頁面
作用：下載檔案介面：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML>
<html>
<head>
<base href="<%=basePath%>">
<title>download demo</title>
<meta charset="UTF-8">
<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">
-->
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.2.1.js"></script>
</head>
<body>
<!-- 遍歷檔案 -->
<c:forEach var="file" items="${files}" varStatus="status">
<span>${file.name}</span><a href="download/downloadfile?fileName=${file.name}">下載</a>
<br>
</c:forEach>
</body>
</html>
後端程式碼：一、下載控制器（servlet） —核心程式碼
package cn.cupcat.controller;
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DownloadController extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = 1L;
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("我進入了post方法！");
/*測試開始*/
/*
String uri = request.getRequestURI();// /download_demo/download/show
StringBuffer url = request.getRequestURL();//http://127.0.0.1:8080/download_demo/download/show
String servletPath = request.getServletPath();// /download
String serverName = request.getServerName();// 127.0.0.1
String servletPath = request.getPathInfo();// /show
*/
/*測試結束*/
String servletPath = request.getPathInfo();// /show
String relativePath = File.separatorChar + "WEB-INF"+ File.separatorChar + "attachment";
String absolutePath = request.getServletContext().getRealPath(relativePath);
if(servletPath.equalsIgnoreCase("/show")){
File file = new File(absolutePath);
if(file.exists()){
if(file.isDirectory()){
File[] files = file.listFiles();
request.setAttribute("files", files);
}
}
request.getRequestDispatcher("/download.jsp").forward(request, response);
}else if(servletPath.equalsIgnoreCase("/downloadfile")){
String fileName = request.getParameter("fileName");
String fileAbosultePath = absolutePath +File.separatorChar+ fileName;
File file = new File(fileAbosultePath);
if(file.exists()){//file存在
if(file.isFile()){//file是一個檔案
FileInputStream fis = new FileInputStream(file);
BufferedInputStream bis = new BufferedInputStream(fis);
byte[] buff = new byte[4096];
int readSize ;
ServletOutputStream outputStream = response.getOutputStream();
while((readSize = bis.read(buff)) != -1){
outputStream.write(buff, 0, readSize);
}
//1.設定檔案ContentType型別，這樣設定，會自動判斷下載檔案型別
response.setContentType("multipart/form-data");
//2.設定檔案頭：最後一個引數是設定下載檔名(假如我們叫a.pdf)
response.setHeader("Content-Disposition", "attachment;fileName="+ URLEncoder.encode(file.getName(), "UTF-8"));
bis.close();
outputStream.close();
}
}
}else{
System.out.println("沒有用到！");
}
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
System.out.println("我進入了get方法！");
this.doPost(req, resp);
}
}
後端程式碼：二、過濾器（filter） —同一編碼
package cn.cupcat.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class UnicodeFilter implements Filter{
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest arg0, ServletResponse arg1,
FilterChain arg2) throws IOException, ServletException {
if(arg0 instanceof HttpServletRequest){
System.out.println("進入了過濾器");
HttpServletRequest request = (HttpServletRequest)arg0;
request.setCharacterEncoding("UTF-8"); //設定編碼，防止後臺得到中文亂碼
}
if (arg1 instanceof HttpServletResponse){
HttpServletResponse response = (HttpServletResponse)arg1;
response.setCharacterEncoding("UTF-8");//設定編碼，防止返回客戶端亂碼
}
arg2.doFilter(arg0, arg1);
}
@Override
public void init(FilterConfig arg0) throws ServletException {
}
}配置檔案：web.xml —配置servlet、filter
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
<display-name>download_demo</display-name>
<!-- 下載servlet開始 -->
<servlet>
<servlet-name>download</servlet-name>
<servlet-class>cn.cupcat.controller.DownloadController</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>download</servlet-name>
<url-pattern>/download/*</url-pattern>
</servlet-mapping>
<!-- 下載servlet結束 -->
<!-- 同一編碼 過濾器開始 -->
<filter>
<filter-name>unicode</filter-name>
<filter-class>cn.cupcat.filter.UnicodeFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>unicode</filter-name>
<!-- 這裡指定filter只對servlet的name為upload生效 -->
<url-pattern>/*</url-pattern>
</filter-mapping>
<!-- 同一編碼 過濾器結束 -->
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
</web-app>注意：
//1.設定檔案ContentType型別，這樣設定，會自動判斷下載檔案型別
response.setContentType("multipart/form-data");
//2.設定檔案頭：最後一個引數是設定下載檔名(假如我們叫a.pdf)
response.setHeader("Content-Disposition", "attachment;fileName="+ URLEncoder.encode(file.getName(), "UTF-8"));
說明：
1.第一句是設定返回客戶端的二進位制檔案，客戶端可以直接下載
2.第二句是設定返下載後的檔名
專案原始碼下載地址：
http://download.csdn.net/detail/xinghuo0007/9858034