JSP学习笔记(四十七)：以文件流方式读取文件，并且强制下载

本文代码以servlet方式实现，其他方式可以做适当调整：

public class MyClass extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        // 输入流 FileInputStream
        FileInputStream inputStream = new FileInputStream("c:/myapp.rar");

        // 输出流 ByteArrayOutputStream
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

        // 下面5行代码实现从输入流 FileInputStream 到 输出流 ByteArrayOutputStream 写入的过程
        byte[] buffer = new byte[1024];
        int iLength = 0;
        while ((iLength = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, iLength);
        }

        // 通知response的输出类型，输出方式及输出内容
        resp.addHeader("Content-Disposition", "attachment; filename=myapp.rar");
        resp.setContentType("application/octet-stream");
        resp.setContentLength(outputStream.size());

        ServletOutputStream out = resp.getOutputStream();
        outputStream.writeTo(out);
        out.flush();

        inputStream.close();
        outputStream.close();
    }
}