java EE : http 协议响应头部信息验证

一  location ：*****   302   重定向 

private void doWork(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         // 设置响应 code 
        resp.setStatus(302);
        // 设置响应 header 参数 ，通知浏览器进行重定向
        resp.setHeader("location", "index.jsp");
    }

二   refresh ：3;url=index.jsp  浏览器自动刷新

 protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 设置响应 header 参数，通知浏览器 3 秒后进行自动刷新，重定向至 url 指定地址
        resp.setHeader("refresh","3;url=index.jsp");

    }

三  content-type： image/png   告知浏览器调用哪个模块打开，比如：显示图片、显示 html 信息

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 设置 header 参数 ，告知浏览器调用何种模块打开
        resp.setHeader("content-type", "image/png");
        // 使用 IO 流返回图片字节信息
        InputStream inputStream = new FileInputStream("E:\\trunck\\chapter02\\servletTest2\\web\\test.png");
        int len = -1;
        byte[] bytes = new byte[1024];
        while ((len = inputStream.read(bytes)) != -1) {
            resp.getOutputStream().write(bytes, 0, len);
        }
        inputStream.close();

    }

四   Content-Disposition ：attachment;filename=文件名   通知浏览器下载该文件

   @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        File file=new File("E:\\trunck\\chapter02\\servletTest2\\web\\test.png");
        // 设置 header 参数，通知浏览器下载该文件
        resp.setHeader("Content-Disposition","attachment;filename="+file.getName());
        InputStream inputStream=new FileInputStream(file);
        int len = -1 ;
        byte[] bytes=new byte[1024];
        while ((len=inputStream.read(bytes))!=-1){
            resp.getOutputStream().write(bytes,0,len);
        }
        inputStream.close();
    }

五   content-encoding ： gzip（服务器端响应过来的压缩模式）    content-length ：字节长度

  Accept-Encoding: gzip, deflate （客户端通知服务端，浏览器所支持的压缩模式）

https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Headers/Content-Encoding

  @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String content = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
        System.out.println("字符串长度：" + content.length());
        System.out.println("字符串转数组长度：" + content.getBytes().length);

        // IO 流中 ByteArrayOutputStream 
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        GZIPOutputStream gzipOutputStream = new GZIPOutputStream(byteArrayOutputStream);
        gzipOutputStream.write(content.getBytes());
        gzipOutputStream.close();

        byte[] bytes = byteArrayOutputStream.toByteArray();
        System.out.println("压缩后数组长度：" + bytes.length);


        resp.setHeader("content-encoding", "gzip");
        resp.setHeader("content-length", bytes.length + "");
        resp.getOutputStream().write(bytes);

    }

六   expires ：-1（HTTP1.1的客户端和缓存必须将其他非法的日期格式（包括0）看作已经过期）    cache-control：no-cache pragma：no-cache  告知浏览器不进行缓存

  @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setHeader("expires", "-1");
        resp.setHeader("cache-control", "no-cache");
        resp.setHeader("pragma", "no-cache");

        resp.getWriter().write("abccc");
    }