Response用处

一---HttpServletResponse

web服务器接收到客户端的请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse。我们实际上就是操作这两个对象。

   如果要获取我们客户端请求过来的参数：找HttpServletRequest

   如果要给客户端响应一些信息：找HttpServletResponse

1）简单分类

 负责向浏览器发送数据的方法

ServletOutputStream getOutputStream() throws IOException; // 写平常的流

PrintWriter getWriter() throws IOException; // 写中文用这个 

负责向浏览器发送一些响应头的方法

    void setCharacterEncoding(String var1);

    void setContentLength(int var1);

    void setContentLengthLong(long var1);

    void setContentType(String var1);

8       void setDateHeader(String var1, long var2);

       void addDateHeader(String var1, long var2);
 
       void setHeader(String var1, String var2);

       void addHeader(String var1, String var2);

       void setIntHeader(String var1, int var2);

       void addIntHeader(String var1, int var2);

响应的状态码：

int SC_CONTINUE = 100;
    int SC_SWITCHING_PROTOCOLS = 101;
    int SC_OK = 200;
    int SC_CREATED = 201;
    int SC_ACCEPTED = 202;
    int SC_NON_AUTHORITATIVE_INFORMATION = 203;
    int SC_NO_CONTENT = 204;
    int SC_RESET_CONTENT = 205;
    int SC_PARTIAL_CONTENT = 206;
    int SC_MULTIPLE_CHOICES = 300;
    int SC_MOVED_PERMANENTLY = 301;
    int SC_MOVED_TEMPORARILY = 302;
    int SC_FOUND = 302;
    int SC_SEE_OTHER = 303;
    int SC_NOT_MODIFIED = 304;
    int SC_USE_PROXY = 305;
    int SC_TEMPORARY_REDIRECT = 307;
    int SC_BAD_REQUEST = 400;
    int SC_UNAUTHORIZED = 401;
    int SC_PAYMENT_REQUIRED = 402;
    int SC_FORBIDDEN = 403;
    int SC_NOT_FOUND = 404;
    int SC_METHOD_NOT_ALLOWED = 405;
    int SC_NOT_ACCEPTABLE = 406;
    int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
    int SC_REQUEST_TIMEOUT = 408;
    int SC_CONFLICT = 409;
    int SC_GONE = 410;
    int SC_LENGTH_REQUIRED = 411;
    int SC_PRECONDITION_FAILED = 412;
    int SC_REQUEST_ENTITY_TOO_LARGE = 413;
    int SC_REQUEST_URI_TOO_LONG = 414;
    int SC_UNSUPPORTED_MEDIA_TYPE = 415;
    int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
    int SC_EXPECTATION_FAILED = 417;
    int SC_INTERNAL_SERVER_ERROR = 500;
    int SC_NOT_IMPLEMENTED = 501;
    int SC_BAD_GATEWAY = 502;
    int SC_SERVICE_UNAVAILABLE = 503;
    int SC_GATEWAY_TIMEOUT = 504;
    int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

2）下载文件

 1：向浏览器输出消息

  2：下载文件

    1：要获取下载文件的路径

    2：下载的文件名

    3：想办法让浏览器能够支持我们需要下载的东西

    4：获取下载文件的输入流

    5：创建缓冲区

    6：获取OutputStream对象

    7：将FileOutputStream流写入到buffer缓冲区

    8：使用OutputStream流对象将缓冲区中的数据输出到客户端

public class FileSeeervlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1：要获取下载文件的路径
        String realPath = "D:\\java31\\javaweb-02-servlet\\response\\src\\main\\resources\\尹雄.png";
        System.out.println("路径" + realPath);
        // 2：下载的文件名
        String filename = realPath.substring(realPath.lastIndexOf("\\") + 1);
        // 3：想办法让浏览器能够支持我们需要下载的东西,中文文件名用URLEncoder.encode(filename,"utf-8")编码，否则有可能乱码
        resp.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(filename,"utf-8"));
        // 4：获取下载文件的输入流
        FileInputStream in = new FileInputStream(realPath);
        // 5：创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        // 6：获取OutputStream对象
        ServletOutputStream out = resp.getOutputStream();
        // 7：将FileOutputStream流写入到buffer缓冲区
        // 使用OutputStream流对象将缓冲区中的数据输出到客户端
        while((len = in.read(buffer)) > 0) {
            out.write(buffer, 0, len);
        }

        in.close();
        out.close();

    }

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

3.验证码功能

验证怎么来的?

1)前端实现

2）后端实现，需要用到java的图片类，生成一个图片

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 如何让浏览器5秒自动刷新一次;
        resp.setHeader("refresh","3");
        // 在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        // 得到图片
        Graphics2D g =(Graphics2D) image.getGraphics(); // g是一支2D的笔
        // 设置图片的背景颜色
        g.setColor(Color.WHITE);
        g.fillRect(0,0,80,20);
        // 给图片写数据
        g.setColor(Color.BLUE);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNum(),0,20);

        // 告诉浏览器这个请求用图片的方式打开
        resp.setContentType("image/jpeg");
        // 网站是有缓存的，我们不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Progma","no-cache");

        //把图片写给浏览器
        boolean write = ImageIO.write(image,"jpg", resp.getOutputStream());
    }

    // 生成随机数
    private String makeNum () {
        Random random = new Random();
        String num = random.nextInt(99999999) + "";
        StringBuffer sb = new StringBuffer();
        // 保证都是7位数
        for (int i = 0; i < 7 - num.length() ;  i++) {
            sb.append("0");
        }
        String s = sb.toString() + num;
        return num;
    }




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