package com.yyz.response;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//文件下載
public class ResponseDemo extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String realpath = this.getServletContext().getRealPath("/download/1.gif");
String filename = realpath.substring(realpath.lastIndexOf("
//")+1);
response.setHeader("content-disposition", "attachment;filename="+filename);
//服務器通過這個頭，告訴瀏覽器以下載方式打開數據
FileInputStream in = new FileInputStream(realpath);
int len = 0;
byte buffer[]=new byte[1024];
OutputStream out = response.getOutputStream();
while((len = in.read(buffer))>0){
out.write(buffer, 0, len);
}
in.close();
//out不用close，response在銷毀的時候服務器會自動關閉與response相關的流。
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
}
讓我們增加一點難度，我們要下載的文件是一個中文名字的文件。由于在http協議中頭文件中的東西只能是ASCII字符，因而通過上述方式（直接將 String realpath = this.getServletContext().getRealPath("/download/1.gif");改為 String realpath = this.getServletContext().getRealPath("/download/圖片.gif");）直接拿文件，
package com.yyz.response;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//中文文件下載時，中文文件名要經過URL編碼。
public class ResponseDemo extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String realpath = this.getServletContext().getRealPath("/download/圖片.gif");
String filename = realpath.substring(realpath.lastIndexOf("
//")+1);
response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(filename,"UTF-8"));
//本函數將字符串以 URL 編碼
FileInputStream in = new FileInputStream(realpath);
int len = 0;
byte buffer[]=new byte[1024];
OutputStream out = response.getOutputStream();
while((len = in.read(buffer))>0){
out.write(buffer, 0, len);
}
in.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request,response);
}
}
不能用FileReader代替FileInputStream。用FileReader會丟失數據，原因是這樣的：FileReader是字符流，而圖片，媒體文件等的數據都是以01的方式存儲，用FileReader讀的時候需要查閱一個編碼表，如果未指定一種編碼，則使用相應平臺的默認編碼。如在中國的電腦就會去查GB2312。當讀到GB2312碼表中不存在的編碼時，會將該數據編碼成'？'，結束后數據就變成中文和'？'的混合。發到客戶端后顯示時再次查閱碼表，將所有的'?'替換成'?'的編碼，就會丟失數據。向這種細節只需要記住一點：字節流可以處理任意類型的數據，字符流只能處理字符數據。
