java servlet download

####利用HttpServlet下载文件
利用原生HttpServlet下载文件，其实就是利用Response来生成下载响应，通过设置响应的`Content-Type`为`application/octet-stream`,并且设置响应头`Header`的`Content-Disposition`为`attachment; filename=xxx.xx`,其实filename就是下载文件的默认文件名.

<代码开始 lang=" java">
try {
    int length = 0;
    //通过ServletOuptStream以流的方式输出文件
    ServletOutputStream outStream = this.getResponse().getOutputStream();
    //设置响应类型
    this.getResponse().setContentType("application/octet-stream");
    //获取要下载的文件
    File f = new File("D:/下载.doc");
    //设置响应的长度
    this.getResponse().setContentLength((int) f.length());
    //设置强制下载的响应头
    this.getResponse().setHeader(
        "Content-Disposition",
        "attachment; filename=\""
        + java.net.URLEncoder.encode("下载.doc", "UTF-8") + "\"");
    byte[] byteBuffer = new byte[1024];
    //读取文件
    DataInputStream in = new DataInputStream(new FileInputStream(f));
    //把文件写入输出流
    while ((in != null) && ((length = in.read(byteBuffer)) != -1)) {
        outStream.write(byteBuffer, 0, length);
    }
    in.close();
    outStream.close();
} catch (IOException e) {
    e.printStackTrace();
}
</代码结束>

**`java.net.URLEncoder.encode`是用来让中文名称的文件不乱码**