1.getOutputStream() has already been called for this response
报错的原因:
使用tomcat容器调用response.getOutputStream()方法的时候仅仅可以写二进制文件.
但调用requonse.getWriter()方法时,则仅仅可以在前台打印文本文件.
所以:
假设在jsp页面:
outPutStream.flush(); outPutStream.close(); outPutStream=null; response.flushBuffer(); out.clear(); out = pageContext.pushBody();
这里out和pageContext是jsp的内置对象;
假设在后台:
假设使用response.getWrter,那么前面仅仅能用response.setContentType("text/html");
假设想用二进制流的方式输出,那么就不都够使用response.setContentType("text/html");
假设是想传输文件,推荐:
response.setContentType("application/x-msdownload;charset=utf-8");
同一时候为了防止乱码,response.setCharacterEncoding("utf-8");
filename = URLEncoder.encode(filename, "utf-8");
文件下载的代码:
public void getDownLoadBook() throws IOException{ response.setCharacterEncoding("utf-8"); String filepath=request.getSession().getServletContext().getRealPath("\\") + "upload\\books\\"; //通过前台bookId,从数据库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("此电子书不存在!"); 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()+"不见了!"); 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(); //编码文件名称,防止乱码 filename = URLEncoder.encode(filename, "utf-8"); response.setHeader("Content-Disposition", "attachment; filename=" +filename); //得到输出流 javax.servlet.ServletOutputStream out = response.getOutputStream(); // 读取文件流 java.io.FileInputStream fileInputStream = new java.io.FileInputStream(file); // 下载文件, 设置响应头和下载保存的文件名称 filename=book.getOriginalName(); if (filename != null && filename.length() > 0) { if (fileInputStream != null) { int filelen = fileInputStream.available(); 文件太大时内存不能一次读出,要循环 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(); } }
时间: 2024-10-05 14:44:16