Servlet原理

Servlet原理

ServletContext

共享数据

  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//   this.getInitParameter(); 初始化参数
//   this.getServletConfig();Servlet配置
//   this.getServletContext();Servlet上下文
        ServletContext context = this.getServletContext();
        String username = "小王";//数据
        context.setAttribute("username",username);
        //将一个数据保存在ServletContext中，名字为：username值：username

    }

 

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String username = (String) context.getAttribute("username");
        resp.setContentType("text/html");
        resp.setCharacterEncoding("utf-8");  //设置显示字符和类型 否则网页会出现乱码
        resp.getWriter().print("名字"+username);
    }

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

 <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.kuang.servlet.HelloServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>getc</servlet-name>
        <servlet-class>com.kuang.servlet.GetServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getc</servlet-name>
        <url-pattern>/getc</url-pattern>
    </servlet-mapping>

 简单应用

 文件下载

1.获取下载文件的路径
2.下载文件名
3.设置浏览器下载文件（Content-Disposition）
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，使用OutputStream将缓冲区中的数据输出到客户端

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        1.获取下载文件的路径
        String realPath = "F:\\IDEA\\Javawebmaven\\javaweb-02-servlet\\servlet-02\\src\\main\\resources\\132231.jpg";
//        2.下载文件名
        String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
//        3.设置浏览器下载文件（Content-Disposition）
        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);
    }

 验证码

 

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //让浏览器自动刷新
        resp.setHeader("refresh","3");
        //在内存中创建图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_3BYTE_BGR);
        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();
        //设置图片背景颜色
        g.setColor(Color.BLUE);
        g.fillRect(0,0,80,20);
        //给图片数据
        g.setColor(Color.WHITE);
        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/jpg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("exprirs",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
        //把图片写给浏览器
        ImageIO.write(image,"jpg", resp.getOutputStream());


    }
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 7-num.length(); i++) {
            sb.append("0");
        }
        num= sb.toString() + num;
        return num;
    }

实现重定向

 

 

 登陆跳转页面重定向实现

  @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      //处理请求
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        System.out.println(username+":"+password);

        resp.sendRedirect("/s2/success.jsp");
    }

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

<form action="${pageContext.request.contextPath}/login" method="get">
    用户名：<input type="text" name="username"> <br>
    密码：<input type="password" name="password"> <br>
    <input type="submit">
</form>

 请求转发实现登陆页面跳转

 @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobbys = req.getParameterValues("hobbys");
        System.out.println("---------------------------");
        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobbys));
        System.out.println("---------------------------");
        //通过请求转发
        req.getRequestDispatcher("./success.jsp").forward(req,resp);
    }

                    <%--以post方式提交表单，提交到login请求--%>
    <form action="${pageContext.request.contextPath}/login" method="post">
        用户名：<input type="text" name="username"><br>
        密码： <input type="password" name="password"><br>
        爱好：
        <input type="checkbox" name="hobbys" value="女孩">女孩
        <input type="checkbox" name="hobbys" value="代码">代码
        <input type="checkbox" name="hobbys" value="游戏">游戏
        <input type="checkbox" name="hobbys" value="电影">电影
        <input type="submit">

    </form>

 Cookie

 

 

 

Session