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器上的路徑暴露了,並且還無法對文件下載進行其它的控制(如權限)。這個就不寫示例了。
2.在服務器端把文件轉換成輸出流,寫入到response,以response把文件帶到浏覽器,由浏覽器來提示用戶是否願意保存文件到本地。(示例如下)
<% response.setContentType(fileminitype); response.setHeader("Location",filename); response.setHeader("Cache-Control", "max-age=" + cacheTime); //filename應該是編碼後的(utf-8) response.setHeader("Content-Disposition", "attachment; filename=" + filename); 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發送來的數據流,並寫入到本地。
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(); //把文件路徑為srcFile的文件寫入outputStream中 popFile(srcFile, outputStream)) ; } catch (IOException e) { e.printStackTrace(); } }
JApplet端示例
URLConnection con; try { //url是被調用的SERVLET的網址 如 *.do con = url.openConnection(); 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, "正在從服務器下載文件內容", in); ProgressMonitor pMonitor = pmInputStream.getProgressMonitor(); pMonitor.setMillisToDecideToPopup(3); pMonitor.setMillisToPopup(3); //localfilepath本地路徑,localstr文件文件夾,filename本地文件名 String localfilepath = localstr + filename ; //方法saveFilsaveFilee是把輸入流pmInputStream寫到文件localfilepath中 if(saveFilsaveFilee(localfilepath,pmInputStream)){ 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是被調用的SERVLET的網址 如 *.do con.setUseCaches(false); con.setDoInput(true); con.setDoOutput(true); con.setRequestProperty("Content-Type","application/octet-stream"); OutputStream out = con.getOutputStream(); //localfilepath本地路徑,localstr文件文件夾,filename本地文件名 String localfilepath = localstr + filename; //文件getOutputStream是把文件localfilepath寫到輸出流out中 getOutputStream(localfilepath,out); 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(); //把輸入流inputStream保存到文件路徑為srcFile的文件中 writefile(srcFile, inputStream); } catch (IOException e) { e.printStackTrace(); } } // end service
總結: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來發送流和讀取流。以及把文件轉換成流或把流轉換成文件的操作。