Java Applets

Publicado em: 06 Fevereiro 2017
no canal de: World Gurukul way of Learning Values and Wisdom

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A Java applet is a small application which is written in Java,
Compiled to Java bytecode and
Executed when user launches the Java applet from a web page, within a Java Virtual Machine (JVM).
Java applets are executed in a sandbox by most web browsers, preventing them from accessing local data like the clipboard or file system. The code of the applet is downloaded from a web server, after which the browser either embeds the applet into a web page or opens a new window showing the applet's user interface.
An applet is placed in an HTML document using the applet or object tag. The applet tag has three attributes set: code=“TestApplet.class" specifies the name of the Applet class
Applets may also be embedded in HTML using either the object or embed element, although support for these elements by web browsers is inconsistent.
However, the applet tag is deprecated, so the object tag is preferred where supported.
The host application, typically a Web browser, instantiates the TestApplet and creates an AppletContext for the applet. Once the applet has initialized itself, it is added to the AWT display hierarchy.
Java applets are programs that are embedded in other applications, typically in a Web page displayed in a web browser.
The import statements direct the Java compiler to include the javax.swing.JApplet and java.awt.Graphics classes in the compilation. The import statement allows these classes to be referenced in the source code using the simple class name (i.e. JApplet) instead of the fully qualified class name (FQCN, i.e. javax.swing.JApplet).
Java rich internet applications (RIA) are applications that have traits similar to desktop applications, but are deployed via the Internet. Java RIAs may be developed and deployed as Java applets or Java Web Start applications.
• Java applets
• Java Web Start applications
Advantages
• Applets are supported by most web browsers
• The same applet can work on "all" installed versions of Java at the same time.
• Web browsers cache applets to quick to load.
• Make web solutions more scalable.
• Supports the changing user state.
• Developers can develop and debug an applet directly.
• Applets are secure.
• Java applets are fast
• Provide interactive features to web applications.
• Applets like news tickers or WYSIWYG editors are popular
Disadvantages
• Java applets depend on a JRE and requires a plug-in for the web browser.
• Some mobile browsers on Apple iOS or Android, do not run Java applets.
• Unlike the older applet tag, the object tag is complex.
• Security restrictions to run for an untrusted applet to achieve the desired goals.
Applet Security
• There are two applet types signed applets and unsigned applets.
• Applets are encouraged to be signed with a trusted certificate,
• Unsigned applets are blocked by default and they can be run by creating an exception in the Java Control Panel.
Signed/Unsigned applets
Signed
• A signed applet contains a signature that the browser should verify independent certificate authority server.
• Once the signature is verified, and the user of the current machine also approves, a signed applet can get more rights.
• This approach allows applets to be used for many tasks.
Self-signed
• Self-signed applets, which are applets signed by the developer themselves, may potentially pose a security risk;
• Such self-signed certificates are used during development prior to release
• As of 2014, For deploying java applets have to acquire trusted certificates from commercial sources.

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