人工智能（Artificial Intelligence，简称AI）是计算机科学的一个分支，它试图理解和构建智能实体

人工智能（Artificial Intelligence，简称AI）是计算机科学的一个分支，它试图理解和构建智能实体。在人工智能领域，有几个关键技术特别重要：

1. 机器学习（Machine Learning）：这是AI的一个核心领域，它使计算机能够通过数据学习模式和做出决策，而无需明确编程。机器学习算法可以分为监督学习、无监督学习和强化学习等类型。

2. 深度学习（Deep Learning）：这是机器学习的一个子集，它使用神经网络模拟人脑处理信息的方式。深度学习特别适合于处理大量复杂的数据，如图像和声音识别任务。

3. 自然语言处理（Natural Language Processing，简称NLP）：这是AI的另一个关键领域，它涉及让计算机理解、解释和生成人类语言。NLP技术使得机器可以执行翻译、情感分析、文本摘要等任务。

这些技术共同推动了AI的发展，使其能够在医疗、金融、教育等多个行业中得到应用。

《Key Technologies Primer》是一本关于关键技术的入门书籍，它涵盖了多个领域的核心技术和概念。这本书的目的是帮助读者了解并掌握这些关键技术，以便在各自的领域内进行创新和发展。

书中的内容包括但不限于以下几个方面：

1. 计算机科学：包括算法、数据结构、编程语言、操作系统等基础知识。
2. 人工智能：介绍了机器学习、深度学习、自然语言处理等人工智能领域的关键技术。
3. 大数据：讲解了数据采集、存储、处理和分析的方法和技术。
4. 云计算：介绍了云服务的基本概念、架构和应用场景。
5. 物联网：讲述了物联网的原理、技术和应用领域。
6. 网络安全：讨论了网络安全的基本概念、威胁和防护措施。
7. 区块链：介绍了区块链技术的原理、应用和发展趋势。
8. 虚拟现实与增强现实：探讨了这两种技术的基本原理和应用案例。

通过阅读这本书，读者可以了解到各个技术领域的基础知识和最新进展，为进一步深入学习和研究打下坚实的基础。

“The time has come,” the Walrus said, “To talk of many things: Of shoes – and ships – and sealing-wax – Of cabbages – and kings – And why the sea is boiling hot – And whether pigs have wings.”

Intention
Key Technologies
    What you need to know
    General starting points
    HTTP, HTML and User Agents
    The HTTP Request/Response cycle
    The Java Language and Application Frameworks
        Reflection and Introspection
        Properties Files and ResourceBundles
        Threads
    JavaScript, AJAX, and SOAP
    Servlets, Filters, and Web Containers
    Sessions
    Web Applications
    Security
    JavaServer Pages, JSP Tag Libraries, and JavaServer Faces
    Extensible Markup Language (XML)
    Model View Controller (MVC)
Business Logic Frameworks
Data Access Frameworks

Intention

If you would like to get started with Apache Struts you most likely want to know what technologies you need to learn. This document shall give you a brief overview what you need to successfully run a Struts project.

If you still can’t decide if Struts is for you or if you have any questions, feel free to contact us via the Struts user mailinglist.
Key Technologies
What you need to know

The framework documentation is written for active web developers and assumes a working knowledge about how Java web applications are built. Before getting started, you should understand the basics of several key technologies:

HTTP and HTML
The HTTP Request/Response Cycle
The Java Language and Application Frameworks
JavaScript, AJAX, and SOAP
Properties Files and ResourceBundles
Servlets, Filters and Web Containers
Sessions
JavaServer Pages and JSP Tag Libraries
Extensible Markup Language (XML)
JAAS
Model View Controller

This primer briefly defines each of these technologies but does not describe them in detail. For your convenience, links to further information are often provided where it makes sense.
General starting points

If you are not familiar with the Java language generally,then the best starting point is the Java Tutorial.

If you are familiar with Java, but not the mentioned technologies, the best overall starting point is the Java EE Tutorial.

If you’ve created web applications for other platforms, you may be able to follow along and visit the other references as needed. The core technologies used by Struts are also used by most other Java web development products, so the background information will be useful in any Java project.
HTTP, HTML and User Agents

The World Wide Web was built over the Hypertext Transfer Protocol (HTTP) and the Hypertext Markup Language (HTML). A User Agent, like a web browser, uses HTTP to request a HTML document. The browser then formats and displays the document to its user. HTTP is used to transport more the HTML, HTML from the browser to render the view.

If you would like to learn HTML, we recommend Getting started with HTML by Dave Raggett.
The HTTP Request/Response cycle

A very important part of HTTP for the web developer is the request/response cycle. To use HTTP you have to make a request. An HTTP server, like a web server, is then obliged to respond. When you build your web application, you design it to react to an HTTP request by returning an HTTP response. Frameworks often abstract much of these nuts and bolts, but it is important to understand what is happening behind the scenes.

If you are not familiar with the HTTP request/response you should learn about it. There is a lot of help available in the internet, like How does the Internet work?
The Java Language and Application Frameworks

Struts is written in the Java programming language. Java is an object-orientated language, and the framework makes good use of many object-orientated techniques. A good understanding of Java, and especially object-orientated programming (OOP) and threading, will help you get the most out of Struts.
Reflection and Introspection

Reflection is the process of determining which member fields and methods are available on an object. Introspection is a specialized form of reflection used by the JavaBean API. Using Introspection, we can determine which methods of a Object are intended to be accessed by other objects. The getters and the setters, for example.

Struts uses Introspection to convert HTTP parameters into JavaBean properties and to populate HTML fields from JavaBean properties. This technique makes it easy to “roundtrip” properties between HTML forms and JavaBeans.

While it is not necessary to have a deep understanding of these concepts when you start with Apache Struts, it will help you when your application grows and becomes more complex.
Properties Files and ResourceBundles

Java applications, including web applications, are often configured using Properties files. Properties files are the basis for the ResourceBundles that the framework uses to provide message resources to an application.

The Java Tutorials provide a great introduction to Properties.

Java ResourceBundles use one or more Properties files to provide internationalized messages to users based their Locale. Support for localizing an application was built into the framework from the ground-up.

Again the Java Tutorials provide more information.
Threads

With Struts 1 you were required to know a lot about how to write code which can run in a multi-threaded environment. With Struts 2 this is no longer necessary. In an Struts 2 environment each action caused by a HTTP request is a plain old Java object which is instanced for each request.
JavaScript, AJAX, and SOAP

With HTTP and HTML you can already provide static web pages. Today this is much often not longer enough and your application users might expect a interactive user interface. Web developers often resort to JavaScript to make web applications more interesting.

AJAX is a technology often used by JavaScript programmers to create web applications that are as interactive and responsive as desktop applications. It is possible, to load a view parts of the website or just the data from the (Struts) application instead of regenerating the whole view.

Apache Struts provides plugins to easily work with AJAX and even JavaScript. Where Struts can’t provide the necessary functionality, third parties provide extensions for the required behavior.

Another technology that can enhance the HTTP request/response cycle is SOAP. Using SOAP, an application can access data and invoke business logic on another server using HTTP as transfer layer. Using AJAX and SOAP together is becoming a popular way for page to submit finely-grained requests directly to a remote server, while still retaining a separation of concerns between the the business logic and the page markup. Depending on your applications need, it might be not necessary for you to learn about SOAP.
Servlets, Filters, and Web Containers

Since Java is an object-orientated language, the Java Servlet platform strives to cast HTTP into an object-orientated form. This strategy makes it easier for Java developers to concentrate on what they need their application to do – rather than the mechanics of HTTP.

A Java-aware HTTP server can pass a request to a servlet container. The container can fulfill the request or it can pass the request back to the HTTP server. The container decides whether it can handle the request by checking its list of servlets. If there is a servlet registered for the request, the container passes the request to the servlet.

When a request comes in, the container checks to see if there is a servlet registered for that request. If there is a match, the request is given to the servlet. If not, the request is returned to the HTTP server.

It’s the container’s job to manages the servlet lifecycle. The container creates the servlets, invokes the servlets, and ultimately disposes the servlets.

The old Struts 1 version relied heavily on servlets and good knowledge about it usually helped a lot with developing web applications.

With Struts 2, you’ll need only a basic understanding of Servlets. Struts actually uses a so called ServletFilter to “make things work”. In general you are not required to write Servlets when using Struts 2. It still helps to know what Servlets, Filters and Containers are.

Filters let you compose a set of components that will process a request or response. Filters are aggregated into a chain in which each filter has a chance to process the request and response before and after it is processed by subsequent filters (and the servlet that is ultimately called).
Sessions

One of the key characteristics of HTTP is that it is stateless. In other words, there is nothing built in to HTTP that identifies a subsequent request from the same user as being related to a previous request from that user. This makes building an application that wants to engage in a conversation with the user over several requests to be somewhat difficult.

To alleviate this difficulty, the servlet API provides a programmatic concept called a session, represented as an object that implements the javax.servlet.http.HttpSession interface. The servlet container will use one of two techniques (cookies or URL rewriting) to ensure that the next request from the same user will include the session id for this session, so that state information saved in the session can be associated with multiple requests. This state information is stored in session attributes (in JSP, they are known as “session scope beans”).

To avoid occupying resources indefinitely when a user fails to complete an interaction, sessions have a configurable timeout interval. If the time gap between two requests exceeds this interval, the session will be timed out, and all session attributes removed. You define a default session timeout in your web application deployment descriptor.

It is important to know that Session data most often occupies RAM memory of your server. Depending on your container you may have different options to bypass this.

Struts 2 provides easy ways to create and access a session.
Web Applications

Just as a HTTP server can be used to host several distinct websites, a servlet container can be used to host more than one web application. The Java servlet platform provides a well-defined mechanism for organizing and deploying web applications. Each application runs in its own namespace so that they can be developed and deployed separately. A web application can be assembled into a Web Application Archive, or WAR file. The single WAR can be uploaded to the server and automatically deployed.

You definitely need to learn how you can build a war file from your Struts application and deploy it to your server. This might require knowledge of build tools like Maven and addition reading in the documentation of your server vendor.
Security

One detail that can be configured in the Web application deployment descriptor is container-managed security. Declarative security can be used to protect requests for URIs that match given patterns. Pragmatic security can be used to fine-tune security make authorization decisions based on the time of day, the parameters of a call, or the internal state of a Web component. It can also be used to restrict authentication based on information in a database.

For more about security, you should read the Java EE tutorial. Other projects, like Apache Shiro or Spring Security might also help you to secure your web application.
JavaServer Pages, JSP Tag Libraries, and JavaServer Faces

If you write a classic web app, you might need a view component. One of the first of its kind was JSP.

While still powerful and fully supported by Struts, people might prefer other technologies like Velocity and Freemarker. Both are also first class citizens for Struts.

All have in common that you would start writing HTML markup and add dynamic features using JSP tags (same goes for Velocity and Freemarker). While it is not recommended, JSP even supports adding plain Java to the markup. Reading about the JSTL or, even better, the Unified expression language is recommended.

That said, you can easily access your data model from the view. And render it appropriate. If you would like to use a more modern approach, you will love to hear Struts 2 provides features to return JSON, which usually fuels AJAX driven webpages. With that it is easily possible to use jQuery or AngularJS as a front end layer and even completely discard JSP.

As mentioned, aside from Java Server Pages, there are several other presentation technologies available to Struts:

Freemarker
iText (PDF)
JasperReports
Velocity
XSLT

Extensible Markup Language (XML)

The features provided by the framework rely on a number of objects that are sometimes deployed using a configuration file written in Extensible Markup Language. XML is also used to configure Java web applications; so, this is yet another familiar approach.

Luckily Struts 2 reduces the need for XML to almost zero. While a basic knowledge on XML is always good, it is no longer crucial to write long XML documents to create a Struts application. If you would like to read more about it, please visit the page of the Convention plugin.
Model View Controller (MVC)

Web applications based on JavaServer Pages sometimes commingle database code, page design code, and control flow code. In practice, we find that unless these concerns are separated, larger applications become difficult to maintain.

One way to separate concerns in a software application is to use a Model-View-Controller (MVC) architecture. The Model represents the business or database code, the View represents the page design code, and the Controller represents the navigational code.

The term “MVC” originated with the SmallTalk Model-View-Controller framework. In Smalltalk MVC, the View updates itself from the Model, via the “Observer” pattern. The original MVC pattern is like a closed loop: The View talks to the Controller, which talks to the Model, which talks to the View.

But, a direct link between the Model and the View is not practical for web applications, and we modify the classic MVC arrangement so that it would look less like a loop and more like a horseshoe with the controller in the middle.

In the MVC/Model 2 design pattern, application flow is mediated by a central Controller. The Controller delegates requests - in our case, HTTP requests - to an appropriate handler. The handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an application’s business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and Model, which can make applications significantly easier to create and maintain.

While MVC is a convenient paradigm, many workers find that applications may utilize more than three layers. For example, within the Model, there is often distinct business logic and data access layers.

The framework provides the control layer for a Model 2 web applications. Developers can use this layer with other standard technologies to build the business, data access, and presentation layers.

For more about MVC, see

Smalltalk MVC framework.
Wikipedia - MVC

Business Logic Frameworks

Most teams still roll their own business logic layer using plain old JavaBeans (POJOs). Though, business layer frameworks are beginning to emerge, and now include:

Spring
Google Guice
Commons Chain of Responsiblity
or you can rely on features of the bundled Struts XWork

Data Access Frameworks

Most often, the business layer is seen to be distinct from the data access layer. Some teams roll their own data access objects (DAOs), but more and more teams are turning to one of the many data access frameworks. Some popular data access frameworks include:

Apache Cayenne
Enterprise Java Beans
Hibernate
myBATIS

“现在是时候了，”海象说，“谈论很多事情了：鞋子、轮船、密封蜡、卷心菜、国王，还有为什么海水滚烫，猪有没有翅膀。”
意图
关键技术
你需要知道的
一般起点
HTTP、HTML和用户代理
HTTP请求/响应周期
Java语言与应用框架
反思与反思
属性文件和资源包
螺纹
JavaScript、AJAX和SOAP
servlet、过滤器和Web容器
会议
Web应用程序
安全
JavaServer页面、JSP标记库和JavaServer面
可扩展标记语言（XML）
模型视图控制器（MVC）
业务逻辑框架
数据访问框架
意图
如果你想开始使用Apache Struts，你很可能想知道你需要学习哪些技术。本文将简要概述成功运行Struts项目所需的内容。
如果您仍然无法决定Struts是否适合您，或者您有任何问题，请随时通过Struts用户邮件列表与我们联系。
关键技术
你需要知道的
框架文档是为活跃的web开发人员编写的，它假定您了解如何构建javaweb应用程序。在开始之前，您应该了解几个关键技术的基本知识：
HTTP和HTML
HTTP请求/响应周期
Java语言与应用框架
JavaScript、AJAX和SOAP
属性文件和资源包
servlet、过滤器和Web容器
会议
JavaServer页面和JSP标记库
可扩展标记语言（XML）
贾斯
模型视图控制器

本入门书简要地定义了这些技术中的每一种，但没有详细描述它们。为了您的方便，通常会在有意义的地方提供进一步信息的链接。
一般起点
如果您一般不熟悉Java语言，那么最好的起点是Java教程。
如果您熟悉Java，但不熟悉上述技术，那么最好的总体起点是Java EE教程。
如果您已经为其他平台创建了web应用程序，则可以根据需要跟踪并访问其他引用。Struts使用的核心技术也被大多数其他Java web开发产品所使用，因此背景信息在任何Java项目中都是有用的。
HTTP、HTML和用户代理
万维网是建立在超文本传输协议（HTTP）和超文本标记语言（HTML）之上的。用户代理和web浏览器一样，使用HTTP来请求HTML文档。浏览器随后格式化文档并将其显示给用户。HTTP用来传输更多的HTML，HTML从浏览器中呈现视图。
如果你想学习HTML，我们建议你从Dave Raggett的HTML开始。
HTTP请求/响应周期
对于web开发人员来说，HTTP的一个非常重要的部分是请求/响应周期。要使用HTTP，必须发出请求。一个HTTP服务器，就像一个web服务器，必须做出响应。当您构建web应用程序时，您可以通过返回HTTP响应来设计它来响应HTTP请求。框架通常会抽象出其中的大部分细节，但是理解幕后发生的事情很重要。
如果您不熟悉HTTP请求/响应，您应该了解它。因特网上有很多帮助，比如因特网是如何工作的？
Java语言与应用框架
Struts是用Java编程语言编写的。Java是一种面向对象的语言，该框架充分利用了多种面向对象的技术。对Java，特别是面向对象编程（OOP）和线程的良好理解将帮助您充分利用Struts。
反思与反思
反射是确定对象上哪些成员字段和方法可用的过程。内省是JavaBeanAPI使用的一种特殊的反射形式。使用内省，我们可以确定对象的哪些方法要被其他对象访问。例如，getter和setter。
Struts使用内省将HTTP参数转换为JavaBean属性，并从JavaBean属性填充HTML字段。这种技术使得在HTML表单和JavaBeans之间“往返”属性变得很容易。
当您开始使用Apache Struts时，不必深入理解这些概念，但当您的应用程序增长并变得更加复杂时，它将帮助您。
属性文件和资源包

Java教程提供了对属性的很好的介绍。
Java ResourceBundles使用一个或多个属性文件向用户提供基于其语言环境的国际化消息。对本地化应用程序的支持从一开始就构建在框架中。
Java教程同样提供了更多信息。
螺纹
使用Struts 1，您需要知道如何编写可以在多线程环境中运行的代码。对于Struts 2，这不再是必要的。在Struts2环境中，由HTTP请求引起的每个操作都是一个普通的旧Java对象，它为每个请求实例化。
JavaScript、AJAX和SOAP
使用HTTP和HTML，您已经可以提供静态web页面。现在，这通常还不够长，应用程序用户可能希望有一个交互式用户界面。Web开发人员经常使用JavaScript来使Web应用程序更有趣。
AJAX是JavaScript程序员经常使用的一种技术，它创建的web应用程序与桌面应用程序一样具有交互性和响应性。可以加载网站的视图部分，或者只加载（Struts）应用程序中的数据，而不是重新生成整个视图。
Apache Struts提供了插件，可以轻松地使用AJAX甚至JavaScript。当Struts不能提供必要的功能时，第三方为所需的行为提供扩展。
另一种可以增强HTTP请求/响应周期的技术是SOAP。使用SOAP，应用程序可以访问数据并使用HTTP作为传输层调用另一台服务器上的业务逻辑。将AJAX和SOAP结合使用正在成为页面直接向远程服务器提交细粒度请求的流行方式，同时仍然保持业务逻辑和页面标记之间的关注点分离。根据您的应用程序需要，您可能不需要了解SOAP。
servlet、过滤器和Web容器
由于Java是一种面向对象的语言，Java Servlet平台努力将HTTP转换成面向对象的形式。这种策略使Java开发人员更容易集中精力于他们需要应用程序做的事情，而不是HTTP的机制。
支持Java的HTTP服务器可以将请求传递给servlet容器。容器可以完成请求，也可以将请求传递回HTTP服务器。容器通过检查其servlet列表来决定是否可以处理该请求。如果有为请求注册的servlet，则容器将请求传递给servlet。
当请求进入时，容器检查是否有为该请求注册的servlet。如果存在匹配项，则将请求提供给servlet。否则，请求将返回到HTTP服务器。
容器的工作是管理servlet生命周期。容器创建servlet，调用servlet，并最终处理servlet。
旧的Struts 1版本在很大程度上依赖于servlets，而对它的良好了解通常有助于开发web应用程序。
使用Struts 2，您只需要对servlet有一个基本的了解。Struts实际上使用一个所谓的ServletFilter来“让事情正常工作”。通常，在使用Struts 2时不需要编写servlet。它仍然有助于了解什么是servlet、过滤器和容器。
过滤器允许您组合一组将处理请求或响应的组件。过滤器被聚合成一个链，在这个链中，每个过滤器都有机会在后续过滤器（以及最终调用的servlet）处理请求和响应之前和之后处理请求和响应。
会议
HTTP的一个关键特性是它是无状态的。换言之，在HTTP中没有任何内置内容可以将来自同一用户的后续请求标识为与来自该用户的先前请求相关。这使得构建一个希望与用户就多个请求进行对话的应用程序有些困难。
为了缓解这个困难，ServletAPI提供了一个称为会话的编程概念，表示为实现javax.servlet.http.http session接口的对象。servlet容器将使用两种技术（cookies或URL重写）之一，以确保来自同一用户的下一个请求将包含此会话的会话id，以便保存在会话中的状态信息可以与多个请求相关联。这个状态信息存储在会话属性中（在JSP中，它们被称为“会话作用域bean”）。

为了避免在用户无法完成交互时无限期占用资源，会话具有可配置的超时间隔。如果两个请求之间的时间间隔超过此间隔，则会话将超时，并删除所有会话属性。在web应用程序部署描述符中定义默认会话超时。
重要的是要知道会话数据通常占用服务器的RAM内存。根据容器的不同，您可以有不同的选项来绕过此问题。
Struts 2提供了创建和访问会话的简单方法。
Web应用程序
正如HTTP服务器可以用来托管多个不同的网站一样，servlet容器也可以用来托管多个web应用程序。JavaServlet平台为组织和部署web应用程序提供了一种定义良好的机制。每个应用程序在其自己的命名空间中运行，以便可以分别开发和部署它们。web应用程序可以组装成web应用程序归档文件或WAR文件。单个WAR可以上传到服务器并自动部署。
您肯定需要学习如何从Struts应用程序构建war文件并将其部署到服务器。这可能需要了解Maven之类的构建工具，并阅读服务器供应商的文档。
安全
可以在Web应用程序部署描述符中配置的一个细节是容器管理的安全性。声明性安全性可用于保护与给定模式匹配的uri请求。实用安全性可用于微调安全性，根据一天中的时间、调用的参数或Web组件的内部状态做出授权决策。它还可以用于根据数据库中的信息限制身份验证。
有关安全性的更多信息，您应该阅读Java EE教程。其他项目，如Apache Shiro或Spring Security也可以帮助您保护web应用程序。
JavaServer页面、JSP标记库和JavaServer面
如果你写一个经典的web应用，你可能需要一个视图组件。第一种是JSP。
尽管Struts仍然强大且完全支持，但人们可能更喜欢其他技术，如Velocity和Freemarker。他们都是Struts的一等公民。
所有这些都有一个共同点，就是您可以开始编写HTML标记，并使用JSP标记添加动态特性（Velocity和Freemarker也是如此）。虽然不建议这样做，但JSP甚至支持将纯Java添加到标记中。阅读JSTL，或者更好的是，推荐使用统一表达式语言。
也就是说，您可以从视图轻松访问数据模型。并使之适当。如果您想使用更现代的方法，您会喜欢Struts 2提供返回JSON的特性，JSON通常是AJAX驱动的网页的燃料。这样就很容易使用jQuery或AngularJS作为前端层，甚至完全放弃JSP。
如前所述，除了Java服务器页面之外，Struts还提供了其他几种表示技术：
模板引擎
文本（PDF）
贾斯珀报告
速度
XSLT
可扩展标记语言（XML）
框架提供的特性依赖于一些对象，这些对象有时使用可扩展标记语言编写的配置文件进行部署。XML还用于配置Java web应用程序；因此，这是另一种常见的方法。
幸运的是，Struts 2将对XML的需求几乎降到了零。虽然XML的基本知识总是很好的，但是编写长的XML文档来创建Struts应用程序已经不再是关键。如果你想了解更多，请访问会议插件的页面。
模型视图控制器（MVC）
基于JavaServer页面的Web应用程序有时混合了数据库代码、页面设计代码和控制流代码。在实践中，我们发现，除非将这些关注点分开，否则更大的应用程序就很难维护。

虽然MVC是一种方便的范例，但许多工作人员发现应用程序可能使用三个以上的层。例如，在模型中，通常有不同的业务逻辑和数据访问层。
框架为Model2 web应用程序提供了控制层。开发人员可以将此层与其他标准技术一起使用来构建业务、数据访问和表示层。
有关MVC的更多信息，请参见
Smalltalk MVC框架。
维基百科-MVC
业务逻辑框架
大多数团队仍然使用普通的旧JavaBeans（pojo）滚动自己的业务逻辑层。不过，业务层框架开始出现，现在包括：
春天
谷歌Guice
公共责任链
或者您可以依赖捆绑StrutsXWork的特性
数据访问框架
通常，业务层与数据访问层是不同的。一些团队推出自己的数据访问对象（dao），但越来越多的团队转向众多数据访问框架之一。一些流行的数据访问框架包括：
阿帕奇卡宴
企业级Java bean
冬眠
马巴蒂斯
AJAX，全称是"Asynchronous JavaScript and XML"（异步JavaScript和XML），是一种在不重新加载整个网页的情况下，仅更新部分页面内容的技术。通过在后台与服务器进行少量数据交换，AJAX使得网页能够实现局部刷新，提高了用户体验。这种技术的核心在于使用JavaScript在客户端与服务器端进行异步通信，这意味着用户操作可以立即得到响应，而不需要等待整个页面的加载。

AJAX的主要优点包括：

1. 提高用户体验：由于只有需要更新的数据被传输和处理，用户不需要等待整个页面重新加载，这大大加快了应用程序的响应速度。
2. 减少服务器压力：因为只传输必要的数据而不是整个页面，所以可以减少服务器的负载和带宽使用。
3. 增强交互性：AJAX允许开发者创建更动态、更互动的web应用，比如实时聊天、自动完成表单输入等。

AJAX（Asynchronous JavaScript and XML）是一种用于创建动态网页应用的技术。它允许网页在不重新加载整个页面的情况下，异步地与服务器交换数据和更新部分内容。

AJAX的工作原理如下：

1. 触发事件：用户在浏览器中执行某个操作，例如点击按钮或填写表单。
2. JavaScript发送请求：JavaScript创建一个XMLHttpRequest对象，并使用该对象向服务器发送HTTP请求。这个请求可以是GET、POST等类型，并且可以携带数据。
3. 服务器处理请求：服务器接收到请求后，处理相应的逻辑，生成响应数据。
4. 接收服务器响应：JavaScript负责接收服务器返回的数据，这通常是以JSON、XML或纯文本格式返回。
5. 更新页面内容：JavaScript根据接收到的数据，动态更新网页的部分内容，而不需要刷新整个页面。
6. 完成交互：用户看到页面内容的更新，从而完成了一次AJAX交互。

AJAX的核心优势在于提升用户体验，因为它可以在后台与服务器进行通信，不会打断用户的当前操作。