１。最直接最簡單的，方式是把文件地址直接放到html頁面的一個鏈接中。這樣做的缺點是把文件在服務(wù)器上的路徑暴露了，并且還無法對文件下載進行其它的控制（如權(quán)限）。這個就不寫示例了。
２。在服務(wù)器端把文件轉(zhuǎn)換成輸出流，寫入到response，以response把文件帶到瀏覽器，由瀏覽器來提示用戶是否愿意保存文件到本地。（示例如下）
<%
?response.setContentType(fileminitype);
?response.setHeader("Location",filename);
?response.setHeader("Cache-Control",?"max-age="?+?cacheTime);
?response.setHeader("Content-Disposition",?"attachment;?filename="?+?filename);?//filename應(yīng)該是編碼后的(utf-8)
?response.setContentLength(filelength);
?OutputStream?outputStream?=?response.getOutputStream();
?InputStream?inputStream?=?new?FileInputStream(filepath);
?byte[]?buffer?=?new?byte[1024];
?int?i?=?-1;
?while?((i?=?inputStream.read(buffer))?!=?-1)?{
??outputStream.write(buffer,?0,?i);
??}
?outputStream.flush();
?outputStream.close();
?inputStream.close();
?outputStream?=?null;
%>
３。既然是JSP的話，還有一種方式就是用Applet來實現(xiàn)文件的下載。不過客戶首先得信任你的這個Applet小程序，由這個程序來接受由servlet發(fā)送來的數(shù)據(jù)流，并寫入到本地。
servlet端示例
????public?void?service(HttpServletRequest?req,?HttpServletResponse?res)
????????????throws?ServletException,?IOException?{
????????res.setContentType("?text/plain?");
????????OutputStream?outputStream?=?null;
????????try?{
????????????outputStream?=?res.getOutputStream();
????????????popFile(srcFile,?outputStream))?;//把文件路徑為srcFile的文件寫入到outputStream中。
????????}?catch?(IOException?e)?{
????????????e.printStackTrace();
????????}
????}?
JApplet端示例
???URLConnection?con;
????????try?{
????????????con?=?url.openConnection();//url是被調(diào)用的SERVLET的網(wǎng)址?如http://localhost:8080/sendDateSevlet.do??
????????????con.setUseCaches(false);
????????????con.setDoInput(true);
????????????con.setDoOutput(true);
????????????con.setRequestProperty("Content-Type",
????????????????"application/octet-stream");
????????????InputStream?in?=?con.getInputStream();
????????????ProgressMonitorInputStream?pmInputStream?=?new?ProgressMonitorInputStream(
????????????????????pane,?"正在從服務(wù)器下載文件內(nèi)容",?in);
????????????ProgressMonitor?pMonitor?=?pmInputStream
????????????????????.getProgressMonitor();
????????????pMonitor.setMillisToDecideToPopup(3);
????????????pMonitor.setMillisToPopup(3);
????????????String?localfilepath?=?localstr?+?filename?;//localfilepath本地路徑,localstr文件文件夾，filename本地文件名
??? if(saveFilsaveFilee(localfilepath,pmInputStream)){ //方法saveFilsaveFilee是把輸入流pmInputStream寫到文件localfilepath中。????????????????????
openLocalFile(localfilepath);
????????????}
４。順便把JApplet上傳文件的代碼也貼上來.
JApplet端示例
URLConnection?con;
????????try?{
????????????con?=?url.openConnection();//url是被調(diào)用的SERVLET的網(wǎng)址?如http://localhost:8080/sendDateSevlet.do?????????
???con.setUseCaches(false);
????????????con.setDoInput(true);
????????????con.setDoOutput(true);
????????????con.setRequestProperty("Content-Type",
????????????????"application/octet-stream");
????????????
????????????OutputStream?out?=?con.getOutputStream();
????????????String?localfilepath?=?localstr?+?filename;?//localfilepath本地路徑,localstr文件文件夾，filename本地文件名
????????????getOutputStream(localfilepath,out);//文件getOutputStream是把文件localfilepath寫到輸出流out中。
????????????InputStream?in?=?con.getInputStream();
????????????return?true;
????????}catch?(IOException?e)?{
???????????????System.out.println("文件上傳出錯！");
????????????e.printStackTrace();
????????}
servlet端代碼示例
????public?void?service(HttpServletRequest?req,?HttpServletResponse?res)
????????????throws?ServletException,?IOException?{
????????res.setContentType("?text/plain?");
????????InputStream?inputStream?=?null;
????????try?{
????????????inputStream?=?res.getInputStream();
????????????writefile(srcFile,?inputStream);//把輸入流inputStream保存到文件路徑為srcFile的文件中
????????}?catch?(IOException?e)?{
????????????e.printStackTrace();
????????}
????}?//?end?service
?總結(jié)：在文件的傳輸中是流的形式存在的，在硬盤上是文件的形式存在的。我們要做的只是通過HttpServletRequest和HttpServletResponse，或者是response和request來發(fā)送流和讀取流。以及把文件轉(zhuǎn)換成流或把流轉(zhuǎn)換成文件的操作。
posted on 2007-02-13 11:20
aaabbb 閱讀(225)
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