几个JSP应用模板

来源：Linux-cn.com 作者：Webmaster 时间：2007-05-05 点击： [收藏] [投稿]

引论
样板的框架: Hello, World
Servlet 评论
展示留言板
留言板的模式
作为应用属性的留言板
留言板的逻辑
结论

引论

　　JSP的强大优势在于把一种应用的商务逻辑和它的介绍分离开来。用 Smalltalk的面向对象的术语来说， JSP鼓励MVC

　　(model-view-controller)的web应用。JSP的classes 或 beans 是模型, JSP 是这个视图, 而Servlet是控制器。

　　这个例子是一个简单的留言板。用户登录和留言。 It is also available in the Resin demos


Role Implementation 
Model A GuestBook of Guests. 
View login.jsp for new users 
add.jsp for logged-in users. 
Controller GuestJsp, a servlet to manage the state.

　　样板的框架: Hello, World

　　GuestJsp的框架把 "Hello, World" 这个字符串传给login.jsp页面。这个框架为留言板设立结构。具体细节将在下面补充。

　　这个例子被编译后可以浏览到：http://localhost:8080/servlet/jsp.GuestJsp

　　你可以看到这样的页面:

Hello, world

　　JSP模板是以Servlet的处理开始然后把处理结果传给JSP页进行格式化。

　　Forwarding uses a Servlet 2.1 feature of the ServletContext, getRequestDispatcher().

　　The request dispatcher lets servlets forward and include any subrequests on the server.

　　It's a more flexible replacements for SSI includes. The RequestDispatcher can include the results of any page, servlet, or JSP page in a servlet's page.

　　GuestJsp will use dispatcher.forward() to pass control to the JSP page for formatting.


GuestJsp.java: Skeleton 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); 
} 
}

　　The servlet and the jsp page communicate with attributes in the HttpRequest object.

　　The skeleton stores "Hello, World" in the "message" attribute.

　　When login.jsp starts, it will grab the string and print it.

　　Since Resin's JavaScript understands extended Bean patterns,

　　it translates the request.getAttribute("message") into the J

　　avaScript equivalent request.attribute.message.


login.jsp: Skeleton <%@ page language=javascript %> 

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

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

Servlet Review

　　For those coming to JSP from an ASP or CGI background, Servlets replace CGI scripts taking advantage of

　　Java's strength in dynamic class loading. A servlet is just a Java class which extends Servlet or HttpServlet and

　　placed in the proper directory. Resin will automatically load the servlet and execute it.

doc

　　index.html

　　add.jsp

　　WEB-INF

　　classes

　　jsp

　　GuestJsp.class

　　GuestBook.class

　　Guest.class

　　The url /servlet/classname forwards the request to the Servlet Invoker.

　　The Invoker will dynamically load the Java class classname from doc/WEB-INF/classes and try to execute the Servlet's service method.

　　Resin checks the class file periodically to see if the class has changed.

　　If so, it will replace the old servlet with the new servlet.

Displaying the Guest Book

　　The next step, after getting the basic framework running, is to create the model.

　　The GuestBook model

　　The guest book is straightforward so I've just included the API here. It conforms to Bean patterns to simplify the JavaScript.

　　The same API will work for HashMap, file-based, and database implementations.

　　JSP files only have access to public methods. So a JSP file cannot create a new GuestBook and it can't add a new guest.

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