AJAX, JSP, can someone fully explain the specific meaning?

AJAX is called "asynchronous JavaScript and XML", which refers to a web development technology for creating interactive web applications.

It mainly includes the following technologies.

Definition of Ajax (asynchronous JavaScript+XML)

XHTML+CSS representation based on web standard representation;

Use DOM (Document Object Model) for dynamic display and interaction;

Use XML and XSLT for data exchange and related operations;

Asynchronous data query and retrieval using XMLHttpRequest;

Use JavaScript to bind everything together. See the original text of jesse james Garrett, the originator of Ajax.

Similar to DHTML or LAMP, AJAX does not refer to a single technology, but uses a series of related technologies organically. In fact, some AJAX-based "derivative/composite" technologies are emerging, such as "AFLAX".

The application of AJAX uses a web browser supporting the above technology as the running platform. These browsers currently include Mozilla, Firefox, Internet Explorer, Opera, Konqueror and Safari. But Opera does not support XSL format objects, nor does it support XSLT.

Compared with the traditional web application

Traditional web applications allow users to fill in forms and send requests to the web server when submitting the forms. The server receives and processes the incoming form, and then returns a new web page. This practice wastes a lot of bandwidth, because most of the HTML codes on the front and back pages are often the same. Because every application interaction needs to send a request to the server, the response time of the application depends on the response time of the server. This causes the user interface to respond much more slowly than the local application.

Unlike this, AJAX applications can only send and retrieve necessary data to the server. It uses SOAP or some other XML-based web service interfaces, and uses JavaScript on the client to handle the response from the server. Because the data exchanged between the server and the browser is greatly reduced, we can see more responsive applications. At the same time, a lot of processing work can be done on the requesting client, so the processing time of the Web server is also reduced.

The advantages of Ajax applications are:

1. Improve the user experience through asynchronous mode.

2. Optimize the transmission between the browser and the server, reduce unnecessary data round trip and reduce bandwidth occupation.

3.Ajax engine runs on the client, taking on part of the work originally undertaken by the server, thus reducing the load of the server with a large number of users.

phylogeny

This technology was applied around 1998. The first component that allows client scripts to send HTTP requests (XMLHTTP) was written by the Outlook Web Access team. This component originally belonged to Microsoft Exchange Server and soon became a part of Internet Explorer 4.0 [3]. Some observers believe that Outlook Web Access is the first successful commercial application using Ajax technology, and it has become the leader of many products, including Oddpost's webmail product. However, at the beginning of 2005, many events made Ajax accepted by the public. Google uses asynchronous communication in its famous interactive applications, such as Google discussion groups, Google maps, Google search suggestions, Gmail and so on. The word Ajax:web coined by Ajax: a new method of web application. The rapid spread of this article has raised people's awareness of using this technology. In addition, the support of Mozilla/Gecko makes the technology more mature and easier to use.

merits and demerits

The biggest advantage of using Ajax is that you can maintain data without updating the whole page. This enables Web applications to respond to user actions more quickly and avoid sending unchanged information on the network.

Ajax doesn't need any browser plug-ins, but it needs users to allow JavaScript to execute on the browser. Just like DHTML applications, Ajax applications must undergo rigorous testing on many different browsers and platforms. With the maturity of Ajax, some libraries that simplify the use of Ajax came out one after another. Similarly, another auxiliary programming technology has emerged, providing an alternative function for users who do not support JavaScript.

The main criticism of Ajax applications is that it may break the normal behavior of the browser back button [4]. In the case of dynamically updating the page, the user cannot return to the previous page state, because the browser can only record static pages in history. The difference between a completely read-in page and a dynamically modified page is very subtle; Users usually want to click the back button to cancel the previous operation, but in Ajax applications, this is impossible. However, developers have proposed various methods to solve this problem, most of which are to reproduce the changes on the page by creating or using a hidden IFRAME when the user clicks the back button to access the history. (For example, when a user clicks Back in Google Maps, it will search in a hidden IFRAME and then reflect the search results on Ajax elements, thus restoring the application state to the current state. )

A related point of view is that using dynamic page updates makes it difficult for users to save specific status to favorites. Solutions to this problem have also emerged, mostly using URL fragment identifiers (usually called anchor points, that is, the part after # in the URL) for tracking, allowing users to return to the specified application state. (Many browsers allow JavaScript to dynamically update the anchor point, which enables Ajax applications to update the anchor point while updating the display content. These solutions also solve many arguments about not supporting the back button.

When developing Ajax, you need to carefully consider the network delay-that is, the interval between the user request and the server response. Failure to give users a clear response [5], lack of appropriate pre-reading data [6], or improper handling of XMLHttpRequest [7] will make users feel delayed, which users don't want to see and they can't understand [8]. The usual solution is to use visual components to tell users that the system is running in the background and reading data and content.

Some handheld devices (such as mobile phones, PDA, etc. ) Ajax is not well supported.

Ajax engine with JavaScript, JavaScript compatibility and debugging are all headaches;

Ajax's no-refresh overload, because the page change is not as obvious as the refresh overload, is easy to cause trouble to users-users are not sure whether the current data is new or updated; The existing solutions include: prompting at relevant locations, designing obvious data update areas, and prompting users after data update.

Support for streaming media is not as good as FLASH and Java applets;

ASP is the abbreviation of dynamic server page:

Active server pags (ASP for short) is included in Internet information.

Server (IIS) provides a server-side scripting environment for generating and executing dynamic, interactive and efficient site server applications.

You don't have to worry about whether the browser can execute the active server page you designed. Your site server will automatically interpret the code of the dynamic server page as the home page content in standard HTML format and display it on the browser sent to the client. A client can browse the contents of a homepage designed by a dynamic server page by using a conventional browser capable of executing HTML code.

Active Server Pages features:

One: no compilation: easy to generate and can be executed without compilation or linking.

Second: You can design it by using a regular text editor, such as Windows Notepad.

Third, browser independence: As long as the client uses a regular browser that can execute HTML, it can browse the homepage content designed by Active Server Pages.

Scripting languages (VbScript, Jscript) are executed on the site server (server side), and users do not need to execute these scripting languages.

Four: object-oriented.

Fifth, you can extend the function through ActiveX server components.

ActiveX server components can be implemented in visual basic, Java, visual c++, cobol and other languages.

Six: Active Server Pages is compatible with any AcTiveX scripting language. Besides VBscript or JScript, other scripting languages provided by third parties, such as REXX, perl, Tcl, etc. , which can be used for design. The script engine is a COM (Component Object Model) object that processes scripts.

Seven: The source code of Active server Pages will not be transmitted to the user's browser, so it can protect the hard-written source code from overflowing. What is passed to the user's browser is the regular HTML code of the execution result of the active server page.

Eight: Use server-side scripts to generate client-side scripts. You can use ASP code to execute a scripting language (VBscript or Jscript) on the site server to generate or change the scripting language executed on the client.