JSP: Library — Zhiheng Lin's Second Brain

JSP

20th August 2020 at 2:19pm

JSP 是一种 HTML + Java 揉在一起的东西，类似带 Java 解释器的模板语言。在 Web 开发中，主要有两种用法：

纯 JSP 实现一切逻辑，输出 HTML 给用户
搭配 Servlets，由 Servlets 做逻辑，再把数据传给 JSP 做模板输出

第一种的例子：

<html>
   <head>
      <title>Reading Cookies</title>
   </head>
   
   <body>
      <center>
         <h1>Reading Cookies</h1>
      </center>
      <%
         Cookie cookie = null;
         Cookie[] cookies = null;
         
         // Get an array of Cookies associated with the this domain
         cookies = request.getCookies();
         
         if( cookies != null ) {
            out.println("<h2> Found Cookies Name and Value</h2>");
            
            for (int i = 0; i < cookies.length; i++) {
               cookie = cookies[i];
               out.print("Name : " + cookie.getName( ) + ",  ");
               out.print("Value: " + cookie.getValue( )+" <br/>");
            }
         } else {
            out.println("<h2>No cookies founds</h2>");
         }
      %>
   </body>
</html>

第二种的例子：

// Servlet
package jsp.GuestJsp;

import java.io.*;
import java.util.*;

import javax.servlet.*;
import javax.servlet.http.*;

/**
 * GuestJsp is a servlet controlling user
 * interaction with the guest book.
 */
public class GuestJsp extends HttpServlet {
  /**
   * doGet handles GET requests
   */
  public void doGet(HttpServletRequest req,
                    HttpServletResponse res)
    throws ServletException, IOException
  {
    // Save the message in the request for login.jsp
    req.setAttribute("message", "Hello, world");

    // get the application object
    ServletContext app = getServletContext();

    // select login.jsp as the template
    RequestDispatcher disp;
    disp = app.getRequestDispatcher("login.jsp");

    // forward the request to the template
    disp.forward(req, res);
  }
}

// JSP
<%@ page language=javascript %>

<head>
<title><%= request.attribute.message %></title>
</head>

<body bgcolor='white'>
<h1><%= request.attribute.message %></h1>
</body>

看 request.attribute 携带了从 Servlet 传过来的数据。

现在 JSP 应该没什么人用了。大概懂它当年做什么就好。