What is an application server?

Application server

Application server refers to a program that exposes business logic to clients through various protocols. It provides access to business logic for use by client applications. The application server uses this business logic just like calling a method on an object.

Basic information

Chinese name

Application server

Provides

access to business logic

Implementation

Dynamic web page technology

Contents

Definition

With the development and growth of the Internet, "host/terminal" Or the traditional application system model of "client/server" can no longer adapt to the new environment, so new distributed application systems have emerged. Correspondingly, new development models have also emerged, the so-called "browser/server" Server" structure, "thin client" mode. The application server is a core technology that implements this model. [1]

Web applications reside on the application server (Application Server). Application servers provide Web applications with a simple and manageable access mechanism to system resources. It also provides low-level services, such as HTTP protocol implementation and database connection management. The servlet container is just a 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 servers.

A variety of application servers are available on the market, including Apache's Tomcat, IBM's WebSphere Application Server, Caucho Technology's Resin, Macromedia's JRun, NEC WebOTX Application Server, JBoss Application Server, Oracle (acquired BEA's WebLogic, etc. Some of them, such as NEC WebOTX Application Server, WebLogic, and WebSphere, are not just Servlet containers. They 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.

Classification

Usually, all documents can be divided into the following three categories according to the time when the content of the document is determined.

Static

Static: A static Web document is a file stored on a Web server. The author of a static document determines the document's content at the time of writing. Because the document content does not change, each access to a static document returns the same results.

Dynamic

Dynamic: Dynamic web documents do not exist in a predefined format, but are created when the browser accesses the web server. When a request arrives, the web server runs an application to create dynamic documents, and the server returns the program's output as a response. Since a new document is created every time it is accessed, the content of the dynamic document changes.

Activity

Activity: An activity document is not fully specified by the server side, but includes a program that calculates and displays values. When the browser accesses the active document, the server returns a program that the browser can execute locally. When the program is running, it can interact with the user and continuously change the display. In this way, the content of the active document is not fixed - it is constantly changing as long as the user keeps the program running. The main advantages of static documents are its simplicity, reliability and performance.

Because static documents specify the format directly. It can be created by people who don't know programming. What's more, static documents are always correct after they have been created and tested. Finally, the browser can quickly access documents and speed up future access to those documents by placing them in a buffer on the local disk. The main disadvantage of static documents is their inflexibility - the document must be redesigned when information changes. Additionally, changes are time-consuming as it requires manual modification of files. Therefore, static documents are not suitable for frequently changing reporting information. The main advantage of a dynamic document is its ability to report current information. For example, a dynamic document could be used to report on stock market conditions, weather forecasts, or concert ticket sales. When the browser requests information, the server runs an application, accesses the required information, and creates a document, which the server then returns to the browser. Dynamic documents place the task on the server side, and the browser accesses dynamic documents in the same way as static documents. Actually, from the browser's perspective. There is no difference between dynamic documents and static documents. Because both dynamic and static documents are written in HTML, the browser does not know whether the server obtained the document from a disk file or a computer program. The main disadvantages of dynamic documents are increased cost and the inability to display changing information. Similar to static documents, dynamic documents do not change after the browser obtains the document. So after the information is sent to the browser, the document becomes outdated. For example, a dynamic document reporting stock market information. Since stock market information changes rapidly, the document will quickly become outdated when users access it. Dynamic documents are more expensive to create and access than static documents. Creating dynamic documents is more expensive because the creator of dynamic documents must know how to write programs. Additionally, programs must be carefully written and extensively tested to ensure the legality of the output. Verifying the correctness of such a program is difficult because the input can contain multiple types of data from different sources. In addition to the high cost of creating dynamic documents, the hardware cost is also higher because the server side requires a more powerful computer. In the end, it takes slightly more time to retrieve the dynamic document, because the server needs extra time to run the program to create the document. Although dynamic documents are created when the application arrives, the information can quickly become outdated, and the main advantage of active documents over dynamic documents is its ability to continuously change information. For example, only active documents can quickly change the display to show animations. What's more, active documents have the ability to directly access information sources 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 disadvantages of active documents are the additional cost required to create and run such documents, and the lack of security. First, the display of active documents requires more sophisticated browser software and a powerful computer to run the browser. In addition, writing correct activity documentation requires more programming skills than writing other screens, and the resulting documentation is more difficult to test. Moreover, because Active Documents must run on the client rather than the server, the program must address compatibility issues on different clients. Finally, Active Documents have potential security issues because they both input and output information.