Java Jar Catalog

This essay is about a suggested student project in Java programming. This essay gives a rough overview of how it might work. It does not describe an actual complete program. I have no source, object, specifications, file layouts or anything else useful to implementing this project. Everything I have to say to help you with this project is written below. I am not prepared to help you implement it; I have too many other projects of my own.

I do contract work for a living, which could include writing a program such as this. However, I don’t do people’s homework for them. That just robs them of an education.

You have my full permission to implement this project any way you please.

Introduction

This project is similar to the NoClassDefFound Amanuensis. This student project searches your entire hard disk for *.jar files and makes a catalog of their *.class contents, sorted by path, and classname.

You could then examine or search this file using high quality text editor such as SlickEdit.

Why would you want such a thing? When you get a NoClassDefFoundError you would then have a clue as to which jars need to put on the classpath. You could detect potential for getting a class from the wrong jar.

You could extend this to search *.zip and *.war files, and look for *.java source, image resources (*.gif, *.jpg, *.png etc.) You might even include all files, not just container files.

Database

As you include more types of container file and more types of contents, the need for more sophisticated searching and sorting presents itself. I suggest exporting the list to an SQL database. You can then do ad-hoc queries from the command line, or cook up some simple app to do checkbox selected queries.

One type of query you could do is provide a classpath, and then see which version of each class on that classpath would actually be selected if it were loaded. It might note duplicates that would be ignored, a potential source of trouble.

A tool you would want is a method to dump the classpath of a running program in a form that can be imported as for a query.

A report you would want is a list by package, listing which jars each package appears in, and by jar, listing which packages are represented in each jar. This gives you a bird’s eye view of the entire jar system.

You might make your database available to the web, so that other without your enormous jar collection could look up where missing classes come from. For that you need to track the original source of each jar as well.

Implementation

The basic tool is the java.util.zip.ZipFile class and its subclass java.util.jar.JarFile.

To make this easy, just scan the entire disk periodically and rebuild the catalog. Don’t try to monitor changes on the fly. You could of course avoid rescanning jars if their dates have not changed.

You could set his up with MySQL — a free database that you can also distribute freely.

Interface Finder: find classes on classpath implementing a given inteface
jar
jar verifier Project
JarCheck
JarLook
Path and Classpath tool project
Which and What Project: path and classpath analysis

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