java 实现文件的下载功能-优快云博客

本文详细介绍了文件下载的四个关键步骤：设置文件ContentType类型、设置文件头、通过response获取ServletOutputStream对象并将其写入输出流。

我们就直接切入主题啦，文件下载只需要四步：

1.设置文件ContentType类型

2.设置文件头

3.通过response获取ServletOutputStream对象(out)

4.写到输出流(out)中

//文件下载
public String download() throws Exception {
    HttpServletRequest request = ServletActionContext.getRequest();
    HttpServletResponse response = ServletActionContext.getResponse();
    ActionBase actionBase = new ActionBase();
    String result =    actionBase.actionBegin(request);
    String fileName = ServletRequestUtils.getRequiredStringParameter(request,"fileName");

    if (fileName != null) {
        File file = new File("D:\\app\\cms\\tomcat\\webapps\\ROOT\\WEB-INF\\upload\\"+fileName);
        FileInputStream is = new FileInputStream(file);
        response.setContentType("application/octet-stream");
        response.addHeader("Content-Disposition", "attachment;filename="
                + new String(fileName.getBytes("gb2312"), "ISO8859_1"));
        OutputStream out = response.getOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while ((len = is.read(buffer)) != -1) {
            out.write(buffer, 0, len);
        }
        out.flush();
        out.close();
    } else {
        PrintWriter writer = response.getWriter();
        writer.write("设备系统配置文件不存在，请确认是否已经上传。");
        writer.close();
    }
    return null;
}