Java EE Development Technology Course Week fifth (applet program components and AJAX technology)

1, applet program components 1.1. Definition:

Applets are small applications written in the Java programming language, which can be contained in HTML ( an application of the Standard Universal Markup Language ) page, in much the same way as the page contains images. The HTML file code of the Web page containing the applet has a pair of tags such as <applet> and </applet>, when a Java-enabled web browser encounters this pair of tags, The appropriate applet code is downloaded and executed on the local computer.

1.2. Working principle and advantages:

1.2.1 Java applets can greatly improve the interactivity of Web pages and the ability to execute dynamically. The applet is embedded in the Web page as code, labeled <applet></applet> labeled, and when the Java-enabled web browser encounters this pair of tags, it downloads the appropriate application code and executes the applet on the local computer. An applet is a Java applet that is downloaded and run by a Java-enabled web browser by using the applet's HTML file. It can also be run through the appletviewer of Java development tools. The applet program cannot be separated from the HTML file that uses it.

1.2.2 applets can improve the interactivity of Web pages and the ability to execute dynamically.

1.3. Development Steps: Applet program development Main steps are as follows: 1.3.1 use tools such as edit or Windows Notepad to create Java applet source programs as editors.　　1.3.2 Converts the applet's source program to a bytecode file. 1.3.3 The HTML file using class. Put the necessary <OBJECT> statements inside the HTML file.   1.4. Security restrictions: In order to prevent such problems, in the default case, most browsers are subject to many restrictions on the security of applets, almost no "read" or "write" operation of the system: 1.4.1 does not allow applets to access the local file system 1.4.2 Applets cannot perform any program on the local computer 1.4.3 does not allow applets to attempt to open sockets for any system other than the server that provides the applet 1.4.4 does not allow applets to access user names, e-mail addresses, and other local system-related information 1.4.5 for Applet, some standard system properties in the Java environment are read-only 1.4.6 applets cannot create or load the network connection of the applet's machine 1.4.7 applet cannot act as a network server, listening to or receiving connection requests from remote systems 1.4.8 not allowed APPL　　　　　　The ET loads a dynamic library or defines a local method call 1.4.9 applet cannot manipulate any thread that is not in its own thread group 1.4.10 applets cannot shut down the JVM. Reference Links: Https://baike.baidu.com/item/Applet/2723730?fr=aladdin http://www.cnblogs.com/xucong/p/Applet-AJAX.html 2, Ajax2.1 definition: Ajax is " A Synchronous J avascript And X ML"(Asynchronous JavaScript and XML) is a web development technique that creates an interactive Web application. Ajax is a technique for creating fast, Dynamic Web pages.　　The ability to update parts of a Web page without reloading the entire page. Ajax enables Web pages to be updated asynchronously by exchanging small amounts of data in the background with the server. This means that you can update a part of a webpage without reloading the entire page. Traditional Web pages (without Ajax) if you need to update the content, you must reload the entire page page. 2.2 Effects:

2.2.1 Ajax uses asynchronous data transfer (HTTP requests) between the browser and the Web server, which allows the Web page to request a small amount of information from the server, rather than the entire page.

2.2.2 Ajax makes Internet applications smaller, faster and friendlier.

2.2.3 Ajax is a browser technology that is independent of WEB server software.

2.2.4 The biggest advantage of using AJAX is to maintain the data without updating the entire page. This allows Web applications to respond more quickly to user actions and avoid sending information that is not changed on the network.

2.3 Application:

2.3.1 Use XHTML+CSS to express information
2.3.2 using JavaScript to manipulate the DOM (Document Object Model) to run dynamic effects
2.3.3 using XML and XSLT to manipulate data
2.3.4 Asynchronous data exchange with a Web server using XMLHttpRequest or a new fetch API
　　Note: Ajax is distinguished from RIA technologies such as Flash, Silverlight, and Java applets

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

Java EE Development Technology Course Week fifth (applet program components and AJAX technology)