DATABASE SYSTEMS AND THE WEB - Database Design and Development: An Essential Guide for IT Professionals - page 609

Some Limitations Usually, a special cookie file stores cookies on the user's com-
puter system. Therefore, cookies are vulnerable to the whims of the user's actions.
Accidentally or willfully, the user may delete the cookie file. Again, if the cookie file
is not large enough or if the browser imposes restrictions on the size and number
of cookie files, older cookies may be overwritten with later ones. Also, if you switch
browsers, the cookies stored by the earlier browser will be lost.
Another drawback relates to name and password information stored in a cookie
file. This information is usually not encrypted and therefore could cause serious
problems. As a user, you are not aware of the cookies being stored on your com-
puter's hard drive. Some browsers may be configured to alert users when cookies
are being stored. Some browsers allow you to prevent any cookies from being set
on your computer system at all.

Use of Java Applications

As most IT professionals know, Java is a proprietary programming language
developed by Sun Microsystems. Java has been designed and developed to be
completely portable. It is a “write-once, run anywhere” language. A few attributes
of Java are that it is simple, object-oriented, distributed, interpreted, robust,
secure,

architecture-neutral, portable, high-performance, multithreaded, and

dynamic.
Java's portability represents its greatest strength. It is machine-independent. For
most programming languages, first you need to establish the processor and operat-
ing system on which the completed program will be running. After compiling, the
linker must prepare the executable object file with components from the operating
system libraries. The whole process is different for a Java program.
The Java compiler generates a file of bytecodes, called a class file. These
are instructions of the Java Virtual Machine (JVM). JVM does not physically
exist; however, JVM (interpreter and runtime system) may be ported to any
kind of computer. You can load a class file to any computer with JVM. The Java
program will run on the JVM of that computer. Therefore, a Java program is
totally portable. Figure 19-8 presents the components of the Java programming
environment.
Well, what has the portability of Java to do with Web computing? Currently, all
available browsers have embedded JVM. Therefore, a Java program can run any
computer with a browser. That includes an enormous number of and many types of
computer systems. Java is generally accepted as the preferred programming lan-
guage for applications on the Web. Using Java, you can build Web applications,
called applets, and server applications, known as servlets.

Applets. These are Java programs that are embedded in an HTML page. A
Java-enabled browser executes an applet. The browser applies its own JVM inter-
preter to execute the bytecode of an applet. Applets are generally written to
enhance the user interface and add dynamic content to HTML pages.

Servlets. These add functionality to Web servers. Whereas an applet executes on
the browser, a servlet runs on the server. A servlet may connect to database servers,
process the application, and return the results in a web page.