如果需要在多次请求中(间隔请求)的信息,可以存放在session中携带,例如之前的银行系统中的username,就可以在最开始存入session中

    1. if("登陆成功".equals(result)){
    2. HttpSession session=req.getSession();
    3. session.setAttribute("username",username);
    4. RequestDispatcher rd= req.getRequestDispatcher("welcome.jsp");
    5. rd.forward(req,resp);
    6. }
    1. protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    2. req.setCharacterEncoding("UTF-8");
    3. HttpSession session = req.getSession();
    4. String username = (String) session.getAttribute("username");
    5. AtmService atmService = MySpring.getJavaBean("service.AtmService");
    6. Float balance = atmService.inquire(username);
    7. //request对象中有两个map集合,Object value=request.getAttribute("key");
    8. req.setAttribute("balance", balance);
    9. req.getRequestDispatcher("showBalance.jsp").forward(req, resp);
    10. }

    setMaxInactiveInterval(秒**)**方法用于设置session最大活跃时间,超出时间session对象不活跃但对象还在;默认的最大活跃时间为30分钟;
    session.invalidate()**方法设置session对象失效
    session.getid(),返回值为String

    ServletContext application 全局上下文对象
    对比于session,若我们换一个浏览器请求同样的信息,session失效,因为它是一次会话,而application是全局上下文对象不会失效

    方法 返回值
    application.removeAttribute(“key”)
    application.setAttribute(“key”,Object)
    application.getAttribute(“key”) Object
    application.getAttributeNames() Enumeration
    application.getInitParameter(“key”) String
    application.getInitParameterNames() Enumeration
    application.getRealPath() String

    image.png
    index.jsp

    1. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    2. <html>
    3. <head>
    4. </head>
    5. <body>
    6. <%
    7. String value= application.getInitParameter("keyParam");//注意此处
    8. System.out.println("我是"+value);
    9. %>
    10. <form action="test.jsp" method="post">
    11. 测试数据:<input type="text" name="test" value=""><br>
    12. <input type="submit" value="submit">
    13. </form>
    14. </body>
    15. </html>

    JSPWriter out write(); println();
    Object page(等于this,当前页对象) 例如index_jsp.java这个类的对象
    PageContext pageContext 页面对象上下文

    作用域对象:
    pageContext 只在当前页作用域中可以访问(例如index_jsp.java这个类的范围内)
    request 一次请求的范围之内
    session 一次会话范围内
    application 全局范围内(好多个session可以共享)

    ServletConfig config

    方法 返回值
    config.getServletContext() ServletContext(application)
    config.getInitParameter(“key”) String
    config.getInitParameterNames() Enumeration
    config.getServletName() String


    Exception exception

    error.jsp

    1. <%@ page contentType="text/html;charset=UTF-8" language="java" isErrorPage="true" %>
    2. <html>
    3. <head>
    4. </head>
    5. <body>
    6. 异常(*^▽^*)
    7. </body>
    8. </html>
    1. <%@ page contentType="text/html;charset=UTF-8" language="java" errorPage="error.jsp" %>

    注意:404没有找到资源不是异常
    **