html与jsp小节

1.html与jsp的区别：html是静态的网页，而jsp是动态的。jsp就是一个servlet以及servlet显示所需要的html代码构成，所有能在servlet中生成的动态数据都可以在jsp中实现，同样的能在jsp中实现的内容也都可以在servlet中使用纯java代码实现。jsp在运行的时候会自动先转换为java代码及servlet再实现。如在以下代码中：

protected void service(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("gbk");
		response.setCharacterEncoding("gbk");

		HttpSession session = request.getSession();
		String s = (String) session.getAttribute("userName");
		if (s != null) {
			String sql = "select s_c.score,course.name from s_c,student,course where student.name='"
					+ s
					+ "' and student.id=s_c.student_id and course.id=s_c.course_id;";
			ConnLJ cn = new ConnLJ();
			System.out.println("执行了sql");
			PrintWriter pw = response.getWriter();
			pw.write("欢迎回来！！！" + s);
			pw.write("<br>");
			List<show> show = cn.showScore(sql);
			for (int i = 0; i < show.size(); i++) {
				show a = show.get(i);
				String score = a.getScore();
				String name = a.getName();

				pw.write("你" + name + "课程的成绩是" + score);
				pw.write("<br>");

			}
		} else {
			response.sendRedirect("error.html");
			return;
		}
	}

将会在浏览器上显示用户的课程名和成绩，这段代码将可以以jsp的形式实现：

<%
          //HttpSession session = request.getSession();
		   String s = (String) session.getAttribute("userName");
		if (s != null) {
			String sql = "select s_c.score,course.name from s_c,student,course where student.name='"
					+ s
					+ "' and student.id=s_c.student_id and course.id=s_c.course_id;";
			ConnLJ cn = new ConnLJ();
			System.out.println("执行了sql");
			
			out.write("欢迎回来！！！" + s);
			out.print("<br>");
			List<show> show = cn.showScore(sql);
			for (int i = 0; i < show.size(); i++) {
				show a = show.get(i);
				String score = a.getScore();
				String name = a.getName();

				out.print("你" + name + "课程的成绩是" + score);
				out.print("<br>");

			}
		} else {
			response.sendRedirect("error.html");
			return;
		}
	%>

 2：jsp常用的隐式对象：application，out，request，response，session。

    out引用jsp页面的输出流，如上面代码中直接用out打印出语句

    session：可以在jsp中直接得到应用的会话对象

    application引用执行jsp所在web应用程序的环境

    request引用传递给_jspService方法的当前请求

    response引用发送给用户的响应