详解Java文件下载的几种实现方式

public HttpServletResponse download(String path, HttpServletResponse response) {
    try {
      // path是指欲下载的文件的路径。
      File file = new File(path);
      // 取得文件名。
      String filename = file.getName();
      // 取得文件的后缀名。
      String ext = filename.substring(filename.lastIndexOf(".") + 1).toUpperCase();

      // 以流的形式下载文件。
      InputStream fis = new BufferedInputStream(new FileInputStream(path));
      byte[] buffer = new byte[fis.available()];
      fis.read(buffer);
      fis.close();
      // 清空response
      response.reset();
      // 设置response的Header
      response.addHeader("Content-Disposition", "attachment;filename=" + new String(filename.getBytes()));
      response.addHeader("Content-Length", "" + file.length());
      OutputStream toClient = new BufferedOutputStream(response.getOutputStream());
      response.setContentType("application/octet-stream");
      toClient.write(buffer);
      toClient.flush();
      toClient.close();
    } catch (IOException ex) {
      ex.printStackTrace();
    }
    return response;
  }

  public void downloadLocal(HttpServletResponse response) throws FileNotFoundException {
    // 下载本地文件
    String fileName = "Operator.doc".toString(); // 文件的默认保存名
    // 读到流中
    InputStream inStream = new FileInputStream("c:/Operator.doc");// 文件的存放路径
    // 设置输出的格式
    response.reset();
    response.setContentType("bin");
    response.addHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
    // 循环取出流中的数据
    byte[] b = new byte[100];
    int len;
    try {
      while ((len = inStream.read(b)) > 0)
        response.getOutputStream().write(b, 0, len);
      inStream.close();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

  public void downloadNet(HttpServletResponse response) throws MalformedURLException {
    // 下载网络文件
    int bytesum = 0;
    int byteread = 0;

    URL url = new URL("windine.blogdriver.com/logo.gif");

    try {
      URLConnection conn = url.openConnection();
      InputStream inStream = conn.getInputStream();
      FileOutputStream fs = new FileOutputStream("c:/abc.gif");

      byte[] buffer = new byte[1204];
      int length;
      while ((byteread = inStream.read(buffer)) != -1) {
        bytesum += byteread;
        System.out.println(bytesum);
        fs.write(buffer, 0, byteread);
      }
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

public void downLoad(String filePath, HttpServletResponse response, boolean isOnLine) throws Exception {
    File f = new File(filePath);
    if (!f.exists()) {
      response.sendError(404, "File not found!");
      return;
    }
    BufferedInputStream br = new BufferedInputStream(new FileInputStream(f));
    byte[] buf = new byte[1024];
    int len = 0;

    response.reset(); // 非常重要
    if (isOnLine) { // 在线打开方式
      URL u = new URL("file:///" + filePath);
      response.setContentType(u.openConnection().getContentType());
      response.setHeader("Content-Disposition", "inline; filename=" + f.getName());
      // 文件名应该编码成UTF-8
    } else { // 纯下载方式
      response.setContentType("application/x-msdownload");
      response.setHeader("Content-Disposition", "attachment; filename=" + f.getName());
    }
    OutputStream out = response.getOutputStream();
    while ((len = br.read(buf)) > 0)
      out.write(buf, 0, len);
    br.close();
    out.close();
  }