Java applets can create interfaces that go beyond the capability of HTML form tags, Javascript and VBScript. However, Java applets are limited in their capability of doing practical things such as connecting to databases, sending email, etc. The JavaCGIBridge project leverages the strengths of using Perl to connect to databases and perform application logic while using Java's superior GUI building facilities to provide a more user-friendly front-end to CGI/Perl scripts.

Problems with CGI/Perl alone

HTML forms have a minimal interface

• not interactive (JavaScript does not solve the whole problem)
• cannot be extended natively

Hard to maintain state between forms

Redundant data frequently needs to be re-retrieved between HTML forms

• A new interface must be recreated everytime info is sent to the server

Problems with Java alone

Bloated Applet Problem

• Placing all application code on the applet makes for a huge download

Java is hard!

• Browser Incompatibilities
• Complicated maze of class libraries to learn

Security "Sandbox" restricts what applets can do

• cannot read/write local files
• cannot open sockets to non-originating server (RDBMS problem)

Problems with Java Applets

• No good, easy connectivity options
• JDBC requires lax firewall for talking to DBMS directly or complex middleware
• RMI is not supported by browsers
• CORBA is not supported by all browsers

JavaCGIBridge Solution

CGI/Perl advantages

• CGI/Perl can provide database connectivity more easily
• Application related "business-rules" are centrally maintained and executed in CGI/Perl scripts
• Browsers that don't support Java can still use the application
• Leverage existing "legacy" CGI/Perl code
• Many Internet Service Providers only allow CGI/Perl access (no daemons)

Java advantages

• Java applet becomes a truly thin client
  - only requires GUI code and GUI logic
  - JavaCGIBridge class adds ~5k overhead
  - No need to learn the entire Java class library.
  - You can get by with AWT (Forms) and some utility classes
• Java applet can maintain state between all CGI script calls
• Java applet can cache retrieved data
  - eliminates the need to constantly get redundant data from the server

Nuts And Bolts

CGI/Perl Specs

• Data to be returned should be identified
• Top separator ()
• Bottom Separator ()
• Pipe delimited fields
• Set up form variable to tell script to send data using separators defined above (javacgibridge=on)

Java Specs

• Instantiate JavaCGIBridge class
• Set up form variable, form value pairs inside Hashtable
• Set up URL by instantiating URL class
• Get parsed data back using the URL and form variable Hashtable as a Vector of Vectors (otherwise known as an array of arrays in Perl 5)

Discussion Forum

JavaCGIBridge Discussion Forum among other Selena Sol Scripts Archive Forums.

Working Examples

These two examples are included in the distribution. They show the CGI application as well as the JAVA front end. The Applets were built using the JavaCGIBridge and the existing CGI.

ReverseString

Power of Two

Source Code

	javacgibridge.tar
	javacgibridge_tar.gz
	readme.installation
	readme.usage
	COM.Extropia.net.JavaCGIBridge
	COM.Extropia.net.JavaCGIBridgeTimeOutException
	JavaCGIBridge Documentation (JavaDOC)

O'Reilly Perl Conference Presentation August 1997

JavaCGIBridge Overview talk given at Perl97 in PowerPoint 95 Format (zipped).

JavaCGIBridge Overview talk in Adobe PDF Format. Use Adobe Acrobat to read this document.