java下载文件

文件下载不需要第三包就是靠文件流、字节输入输出流实现。

<table>
      <tr>
          <td align="right">
          <a href="download.jsp?path=<%=getServletContext().getRealPath("123.png") %>">下载</a></td>
      </tr>
      </table>

download.jsp

<%
        response.setCharacterEncoding("utf-8");
        String pathname = request.getParameter("path");
        pathname = new String(pathname.getBytes("iso-8859-1"));
        File file = new File(pathname);
        InputStream ins = new FileInputStream(file);
        OutputStream os = response.getOutputStream();
        BufferedInputStream bis = new BufferedInputStream(ins);
        BufferedOutputStream bos = new BufferedOutputStream(os);
        response.addHeader("Content-Disposition","attachment;filename="+new String(file.getName().getBytes("utf-8"),"iso-8859-1"));
        response.addHeader("Content-Length",file.length()+"");
        response.setContentType("application/octet-stream");
        int len = 0;
        byte[] bys = new byte[1024];
        while((len=ins.read(bys))!=-1){
            bos.write(bys);
            bos.flush();
        }
        out.clear();
        out = pageContext.pushBody();
        bos.close();
        bis.close();
     %>

上述代码中调用了out.clear()和pageContext.pushBody()方法，是因为在JSP页面中内置有out,再使用response.getOutStream()方法会抛出java.lang.IllegalStateException异常，不过上述代码中本人去掉这两行也没错。