With the development and expansion of the Internet, the traditional application system model of "host/terminal" or "client/server" can no longer adapt to the new environment, so a new distributed application system has emerged. Accordingly, new development models have emerged, namely the so-called "browser/server" structure, "thin client" model. Application server is a core technology to realize this mode. [1]
Web applications reside on the Application Server. The application server provides a simple and manageable access mechanism to system resources for Web applications. It also provides low-level services, such as the implementation of HTTP protocol and database connection management. The servlet container is only part of the application server. In addition to the servlet container, the application server may also provide other Java EE (Enterprise Edition) components, such as EJB containers, JNDI servers, and JMS Server, etc. A variety of application servers are available in the market, including Apache Tomcat, IBM WebSphere Application Server, Caucho Technology Resin, and Macromedia JRun , NEC WebOTX Application Server, JBoss Application Server, WebLogic of Oracle (merged BEA), etc. Some of them, such as NEC WebOTX Application Server, WebLogic and WebSphere, are not only servlet containers, but also provide support for EJB (Enterprise JavaBeans), JMS (Java Message Service) and other Java EE technologies. Each type of application server has its own advantages, limitations and applicability. Generally, all documents can be divided into the following three categories according to the time when the document content is determined.
Static: A static Web document is a document stored on the Web The server File. The author of a static document determines the content of the document when writing. Since the content of the document will not change, every visit to a static document returns the same result. Dynamic: dynamic web documents do not exist in a predefined format, but access the web in the browser The server Is created when. When a request arrives, the web server runs an application to create Dynamic Document (dynamic documents), the server returns the output of the program as a response. Because a new document must be created for each visit, the content of a dynamic document changes. Activity: One Active Document Incompletely caused by The server At one end, it includes a program to calculate and display values. When the browser accesses the active document, the server returns a program that the browser can execute locally. When the program runs, it can interact with the user to execute and constantly change the display. In this way, the content of the active document is not fixed - as long as the user keeps the program running, it is always changing. The main advantages of static documents are their simplicity, reliability, and performance. Because static documents specify the format directly. It can be created by people who do not understand programming. More importantly, static documents are always correct after they have been created and tested. Finally, the browser can quickly access documents and speed up access to these documents in the future by putting them in the buffer on the local disk. The main disadvantage of static documents is inflexibility - documents must be redesigned when information changes. In addition, changes are time-consuming because they require manual modification of files. Therefore, static documents are not suitable for frequently changing reporting information. Dynamic Document The main advantage of is its ability to report current information. For example, a dynamic document can be used to report the stock market situation, weather forecast or concert ticket sales. When the browser requests information, The server Run an application, access the required information, and create a document. The server then returns the document to the browser. Dynamic documents place tasks on the server side, and browsers access dynamic documents in the same way as static documents. In fact, from a browser perspective. There is no difference between dynamic documents and static documents. Since both dynamic and static documents are written in HTML, the browser does not know whether the server gets the document from a disk file or a computer program. The main disadvantages of dynamic documents are increased costs and inability to display changing information. Similar to static documents, Dynamic Document It will not be changed after the browser gets the document. So after the information is sent to the browser, the document begins to become obsolete. For example, a dynamic document that reports stock market information will soon become obsolete when users access it because of the rapid changes in stock market information. Dynamic documents are more expensive to create and access than static documents. To create a dynamic document cost Higher, because the creator of a dynamic document must know how to write a program. In addition, the program must be carefully written and widely tested to ensure the legitimacy of the output. It is difficult to verify the correctness of such a program, because the input can contain multiple data from different sources. In addition to the high cost of creating dynamic documents, the hardware cost is also high because The server End needs more powerful computers. Finally, it takes a little more time to get the dynamic document, because the server needs extra time to run the program to create the document. Although when the application arrives Dynamic Document Is created, but the information may quickly become obsolete, Active Document The main advantage over dynamic documents is its ability to continuously change information. For example, only the active document can quickly change the display to show animation. More importantly, the active document can directly access the information source and continuously change the display. For example, an active document that displays stock market information can continuously read stock market information and automatically modify the display without user intervention. The main disadvantage of an active document is the additional costs , and lack of security. First, the display of active documents requires more complex browser software and a powerful computer browser. In addition, writing a correct active document requires more programming skills than writing other pictures, and the resulting document is more difficult to test. Also, because the active document must run on the client side instead of The server In the end, the program must solve the compatibility problem on different customers. Finally, there is a potential security problem with the active document, because the document inputs information and outputs information. Web documents can be divided into three categories according to the time when the information in the document changes. The information of a static document will change only when the author modifies it, Dynamic Document 's information in The server Change when the client receives the document application, Active Document The displayed information changes after the document is downloaded to the browser side. Since the responsibility for creating dynamic documents lies on the server side of document management, it is only necessary to modify the server to support dynamic documents. In fact, change means extension, and the server that manages dynamic documents also includes code to handle static documents. A Web server that processes dynamic documents requires three features. First, the server program must be extended to execute a separate application that creates documents when each request arrives. The server must be programmed to capture the output of the application and return the document to the browser.
Second, you must write a separate application for each dynamic document.
last, The server It must be configured to know which URL corresponds to Dynamic Document Which URL corresponds to the static document. For each dynamic document, the application generating the document must be described during configuration. Each application contains a URL corresponding to a dynamic or static document. The server uses the configuration information and the URL in the received request to decide how to handle it. If the configuration information indicates that the URL in the application corresponds to a static document, the server will retrieve the file as usual. If the URL in the application corresponds to a dynamic document, the server selects the application that generates the document, runs the program, and returns the output of the program to the browser as a document. Difference between application server and WEB server
Generally speaking, the Web server delivers pages so that the browser can browse, while the application server provides methods that client applications can call. To be exact, you can say that the Web server specializes in handling HTTP requests, but the application server provides business logic for applications through many protocols.
Let's go into details:
The Web Server can parse the HTTP protocol. When the Web server receives an HTTP request, it will return an HTTP response, such as an HTML page. To process a request, the Web server can respond to a static page or image, redirect the page, or delegate the generation of dynamic response to some other programs, such as CGI scripts and JSP (JavaServer Pages) scripts, Servlets, ASP (Active Server Pages) scripts, server side JavaScript, or some other server side technologies. Regardless of their purpose, these server side programs usually generate an HTML response for browsers to browse.
Enterprise WEB server is an information exchange platform for enterprise network users. WEB is used more and more in the process of enterprise production management. It is the entrance of information application. Some application systems are integrated on the WEB server. You should know that the proxy model of the Web server is very simple. When a request is sent to the Web server, it simply passes the request to a program that can handle the request well. The Web server only provides an environment that can execute the server side program and return the response (generated by the program), without going beyond the scope of functions. Server side programs usually have functions such as transaction processing, database connectivity, and messaging. [2]
Although the Web server does not support transaction processing or database connection pooling, it can configure various strategies to achieve fault tolerance and scalability, such as load balancing and caching. Clustering features are often mistaken for application server specific features. [3]
The Application Server
By definition, as an application server, it exposes business logic to client applications through various protocols, including HTTP. The Web server mainly handles sending HTML to the browser for browsing, while the application server provides access to business logic for client applications. Applications use this business logic just like you call a method (or a function in a procedural language) of an object.
The client of the application server (including the graphical user interface (GUI)) may run on a PC, a Web server, or even other application servers. Traveling information between the application server and its client is not limited to simple display tags. On the contrary, this information is program logic. It is precisely because this logic takes the form of data and method calls rather than static HTML that the client can use this exposed business logic at will.
In most cases, the application server exposes business logic (to client applications) through the application program interface (API) of the component, such as the EJB (Enterprise JavaBean) component model based on the J2EE (Java 2 Platform, Enterprise Edition) application server. In addition, the application server can manage its own resources, such as gate keeping duties, including security, transaction processing, resource pooling, and messaging. Just like the Web server, the application server is configured with a variety of scalability and fault tolerance technologies.
IMS network is an open system based on IP bearer and providing users with various multimedia services. AS (Application Server) is the top application layer device in IMS system. The AS network element interacts with CSCF through the standard SIP protocol to trigger and execute various network services.
Specifically, the application server AS in the IMS network provides the following business applications:
The basic services in the IMS network include point-to-point voice calls, video calls, and call exception prompts. The point-to-point finger calls can be between two IMS users, or between IMS users and users of other networks, such as PSTN fixed line users, mobile network GSM users, etc; Call exception prompt refers to voice and video calls under various conditions, such as busy callees, no response, empty numbers, and the caller is in arrears. It plays a notification tone to the caller; The supplementary services provided in the IMS network include number display, call transfer, call restriction, call completion and multi-party call services.
Multi party call is a network application built between at least three users, in which the voice of any one person can be heard by all other people in the conference. Multimedia conference provides video images on the basis of multi party call transmission of voice information, thus enriching the types of media for interaction between people.
Provide users with various communication methods and services on the Internet, such as IM (instant message), file and video sharing, etc.
In addition, the service functions provided by AS also include SMS gateway, standard attendant console, group service, etc., greatly enriching various applications of IMS network.
