"Four" Applet program components and Ajax technology

1. Applet program components

1.1. Definition:

　　An applet is a small application written in the Java programming language that can be included in an HTML ( an application of the standard Universal Markup Language) page in much the same way that an image is included in a page. The HTML file code of the webpage containing Applet has a pair of tags such as <applet> and </applet>. When a web browser that supports Java encounters this pair of tags, it will download the corresponding applet code and store it locally. Execute the applet on the computer.

1.2. Working principle and advantages:

　　1.2.1 Java Applet can greatly improve the interactive ability and dynamic execution ability of Web pages. The applet is embedded in the web page in the form of code, which is marked with the tag <applet></applet>. When a web browser that supports Java encounters this pair of tags, it downloads the corresponding application code and executes the applet on the local computer. . An applet is a Java applet, which is downloaded and executed by a Java-enabled web browser by using the HTML file of the applet. It can also be run through the appletviewer of the java development tools. Applet programs are inseparable from the HTML files that use them.

　　1.2.2 Applet can improve the interactive ability and dynamic execution ability of Web pages.

1.3. Development steps:

The main steps of Applet program development are as follows:

　　1.3.1 Use tools such as EDIT or Windows Notepad as editors to create Java Applet source programs.

　　1.3.2 Convert the source program of the Applet into a bytecode file.

　　1.3.3 Compile HTML files using class. Put the necessary <OBJECT> statements inside the HTML file.

1.4. Security restrictions:

In order to prevent such problems, by default, most browsers are subject to many restrictions on Applet security, and almost cannot perform any "read" or "write" operations on the system:

　　1.4.1 Applet is not allowed to access the local file system

　　1.4.2 Applet cannot execute any program on the local computer

　　1.4.3 Applet is not allowed to try to open the socket of any system except the server that provides Applet

　　1.4.4 Applet is not allowed to access user name, email address and other information related to the local system

　　1.4.5 Some standard system properties in the Java environment are read-only for Applets

　　1.4.6 The applet cannot create or load the network connection of the applet machine

　　1.4.7 Applet cannot act as a network server, listening or receiving connection requests from remote systems

　　1.4.8 Applets are not allowed to load dynamic libraries or define native method calls

　　1.4.9 An applet cannot manipulate any thread that is not in its own thread group

　　1.4.10 Applet cannot shut down the JVM.

　　　　

　　Reference link: https://baike.baidu.com/item/Applet/2723730?fr=aladdin

　　　　　　　 http://www.cnblogs.com/xucong/p/Applet-AJAX.html

 

2、Ajax

2.1 Definitions:

　　Ajax stands for " A synchronous Javascript A nd X ML "  (  asynchronous JavaScript  and XML ), which refers to a web development technology for creating interactive web applications.

　　Ajax is a technique for creating fast and dynamic web pages. A technology that can update parts of a web page without reloading the entire web page.

　　Ajax enables web pages to be updated asynchronously by exchanging small amounts of data with the server in the background. This means that parts of a page can be updated without reloading the entire page. Traditional web pages (without using Ajax) must reload the entire web page if the content needs to be updated.

2.2 Function:

　　2.2.1 Ajax uses asynchronous data transfer (HTTP requests) between the browser and the web server, which enables web pages to request small amounts of information from the server instead of the entire page.

　　2.2.2 Ajax can make Internet applications smaller, faster and more friendly.

　　2.2.3 Ajax is a browser technology independent of Web server software.

　　2.2.4 The biggest advantage of using AJAX is to maintain data without updating the entire page. This makes Web applications more responsive to user actions and avoids sending unchanged information over the network.

2.3 Application:

　　2.3.1 Use XHTML+CSS to express information
　　2.3.2 Use JavaScript to manipulate DOM (Document Object Model) to run dynamic effects
　　2.3.3 Use XML and XSLT to manipulate data
　　2.3.4 Use XMLHttpRequest or the new Fetch API to asynchronously communicate with web servers Data Exchange
　　Note: AJAX is differentiated from RIA technologies such as Flash, Silverlight and Java Applet

      Reference link: https://baike.baidu.com/item/ajax/8425