This file consists of a listing of problems I've encountered while working on Lab assignment #3 for the Distributed Java class at De Anza College, and solutions to those problems which I've found to make progress possible. In most cases I haven't found a proper decent solution because the instructor for the class knows next to nothing about Linux, and none of the other students in the class are using Linux either, so I mostly have to find solutions myself, even if they are hacks to bypass the roadblock. A hack to get around a problem, no matter how ugly, is better than total defeat. But still I'd like to eventually find out how to do things correctly, and then clean up my code accordingly.

Table of contents, for my Java programming problems with solutions:
• Runtime validation of class against interface:
  • For print/println (one-of-a-kind code)
  • For HttpServletRequest etc. (refactored to be general)
• Printing data objects in s-expression format for debugging.
• Not yet finished: Parser for such s-expressions to allow easy input of test data into test rigs.

Unresolved problems:
• Insufficient instructions in tutorial for configuring bookstore1
• How to call Servlet via JSP?
• How to call Servlet directly from URL?
  Update:
  • I was able to deploy the 'hello1' sample program, which has direct call of Servlet, but then when I made a slight change (added one word within some text, nothing else whatsoever changed) and re-deployed it, attempt to refresh WebPage caused servlet exception
• How to get Application Client to work with EJB?

If you see a typo here, even a trivial spelling error, please let me know. Unlike newsgroups, and traditional print publishing, where you post or publish something and then never have a chance to fix anything you typed incorrectly, with Web pages there's never a deadline for corrections, and my goal is the same as Knuth's policy with his books, eventual 100% accuracy if I get the cooperation of readers to spot typos I missed. One difference from Knuth, however: Nobody ever pays me money for my work, so I have no money even for food or paying off credit-card bills, so there's absolutely no money to pay proofreaders.

Runtime validation of class against interface (one-of-a-kind)

Source code for MyPrintableI.java
Sample source code for the interface against which MyPrintableI effectively verifies a Java class (not yet tested, since I haven't yet converted MyPrintableI to use MyPrintable.class, instead it still has ad hoc hand-coded tests).

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Runtime validation of class against interface (flexible)

My initial alternate plan was to write my own class that implements the javax.servlet.http.HttpServletRequest interface. But then I looked at it, and there are 49 (fourty-nine) different methods that must be implemented!! There's no way I can figure out what all that code is supposed to do, much less actually implement it in time to finish my lab assignment by the due date. So I thought of this minimal alternate plan:

I'll define a much smaller interface that contains just the methods my HttpServlets will actually use. Unfortunately, with compile-time checking of interfaces for both my own code and code I must use from other sources, it'll be impossible to force that "other" code, whose source I don't have, to implement my minimal interface. This was a roadblock until early this morning (2005.May.15) when I thought of this idea while lying in bed:

I'll invent run-time class/interface validation, just like I did a few days ago for output streams capable of doing print and println even though they have no superclass (except Object) or common interface in the Java API, except this time I'll do it the right way, by actually creating an in interface and compiling it and then using the Reflection API to collect the methods it specifies and compare them against the methods actually implemented in a regular class file. (The print/println runtime interface was one-of-a-kind, hand-coded to know specifically that void print(String) and void println(String) are the only methods required. But it was a good warm-up exercise before this done-right version today.) So I did it today (2995.May.15), and already have it finished and working. Here's the code! And here's a sample interface and a sample class that doesn't quite implement it (download all three files and try it yourself).

By comparison, here's the older MyPrintableI class (not yet uploaded). At some point I should refactor the MyPrintableI to just call the new CompareIntCls. Maybe tomorrow... or maybe after this lab assignment is done.

How to invoke HttpServlet via JSP or URL?

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