j2ee,jsp,servlet文件下載server端
阿新 • • 發佈：2017-07-01
filepath cati 方法 exce line article position book spa
1.getOutputStream() has already been called for this response
報錯的原因:
使用tomcat容器調用response.getOutputStream()方法的時候僅僅可以寫二進制文件.
但調用requonse.getWriter()方法時，則僅僅可以在前臺打印文本文件.
所以:
假設在jsp頁面:
outPutStream.flush(); outPutStream.close(); outPutStream=null; response.flushBuffer(); out.clear(); out = pageContext.pushBody();
假設在後臺:
假設使用response.getWrter,那麽前面僅僅能用response.setContentType("text/html");
假設想用二進制流的方式輸出,那麽就不都夠使用response.setContentType("text/html");
假設是想傳輸文件,推薦:
response.setContentType("application/x-msdownload;charset=utf-8");
同一時候為了防止亂碼,response.setCharacterEncoding("utf-8");
filename = URLEncoder.encode(filename, "utf-8");
文件下載的代碼:
public void getDownLoadBook() throws IOException{
response.setCharacterEncoding("utf-8");
String filepath=request.getSession().getServletContext().getRealPath("\\") + "upload\\books\\";
//通過前臺bookId,從數據庫中取出文件保存的信息
Book book=this.getBookService().getBook(bookId);
if(book==null)
{ response.setContentType("text/html");
PrintWriter writer=response.getWriter();
writer.write("<html><body>");
writer.write("此電子書不存在!");
writer.write("</body></html>");
writer.flush();
writer.close();
return;
}
String filename=book.getSaveName()+"";
java.io.File file = new java.io.File(filepath + filename);
if (!file.exists()) {
response.setContentType("text/html");
PrintWriter writer=response.getWriter();
writer.write("<html><body>");
writer.write("文件不存在!<br/>"+file.getAbsolutePath()+book.getOriginalName()+"不見了!");
writer.write("</body></html>");
writer.flush();
writer.close();
return;
}
response.setContentType("application/x-msdownload;charset=utf-8");
response.setCharacterEncoding("utf-8");
response.setContentLength((int) file.length());
filename=book.getOriginalName();
//編碼文件名稱,防止亂碼
filename = URLEncoder.encode(filename, "utf-8");
response.setHeader("Content-Disposition", "attachment; filename=" +filename);
//得到輸出流
javax.servlet.ServletOutputStream out = response.getOutputStream();
// 讀取文件流
java.io.FileInputStream fileInputStream = new java.io.FileInputStream(file);
// 下載文件, 設置響應頭和下載保存的文件名稱
filename=book.getOriginalName();
if (filename != null && filename.length() > 0) {
if (fileInputStream != null) {
int filelen = fileInputStream.available();
文件太大時內存不能一次讀出,要循環
int i=4096;
do{
byte a[] = new byte[4096];
i=fileInputStream.read(a);
out.write(a, 0, i);
}while(i>=4096);
}
fileInputStream.close();
out.flush();
out.close();
}
}
j2ee,jsp,servlet文件下載server端