Servlets & CGI

Introduction

One of the initial purposes of the Java language was to enable programmers to make Web pages more interactive by embedding programs called applets. When a browser loads a Web page containing an applet, the browser downloads the applet bytecode and executes it on the client machine. However, because of client compatibility, bandwidth, security and other issues, businesses needed an alternative solution where Web pages could be made to interact with server-side instead of client-side Java programs.

Server-side Java programming solves problems associated with applets. A servlet can be thought of as a server-side applet. However, when the code is executed on the server-side, there are no issues with browser compatibility or download times. The servlet bytecode runs entirely on the server and only sends information to the client in a form that the client can understand.

Similar to a CGI program, a servlet takes requests from a client such as a Web browser, accesses data, applies business logic, and returns the results. The servlet is loaded and executed by the Web server, and the client communicates with the servlet through the Web server using HTTP requests. This means that if your Web server is behind a firewall, your servlet is secure.

With isCOBOL Evolve, servlets can be written entirely in COBOL. The isCOBOL Compiler understands Object Oriented COBOL syntax and outputs pure Java classes, so there is never a requirement to program in the Java language. All features and benefits of servlet technology are automatically inherited by COBOL programmers when using isCOBOL Evolve.