Free Java Libraries and Source Code

OpenMap - Open Systems Mapping Technology
OpenMap is an open source JavaBeans toolkit that allows you to "build applications and applets that access data from legacy databases and applications" (quoted from their website). Note that you should read their licence agreement before you blindly use the package, since it is not one of the standard open source licences. (At the time I looked at it, I got the impression that if you make a derivative work from their toolkit, you are also giving them the permission to make a derivative work from your program. But it's best you read the licence agreement yourself.)
Sun's JavaMail API
Sun's JavaMail API provides you a set of abstract classes that helps you to build mail and messenging applications. This reference implementation is royalty free (but only provided in binary form). You need the JavaBeans Activation Framework to use this (see elsewhere on this page).
Sun's JavaBeans Activation Framework (JAF)
The JavaBeans Activation Framework, or JAF, to quote verbatim from their website, allow you to use standard services "to determine the type of an arbitrary piece of data, encapsulate access to it, discover the operations available on it, and to instantiate the appropriate bean to perform said operation(s)". This reference implementation is royalty free, and provided only in binary form.
Java SNMP Package
The Java SNMP Package implements the SNMP protocol with support for the SNMP client and agent operations in SNMP versions 1 and 2 (except the security model of version 2).
GNU Getopt (Java port)
As is obvious from the name, this is a Java port of the GNU getopt() command line parser.
QFLib
This Java library is compatible with JDK 1.1, 1.2 and above. The library supports the following: a logging system, GUI stuff, "especially a JTable extension that supports sorting and filtering with only a few lines of code", and a collection of miscellaneous utilities (command line parser, thread pool, etc).
ObjectDB for Java/JDO Free Database Edition
ObjectDB for Java/JDO is an Object Database Management System (ODBMS) written in Java. It is JDO compliant (Java Data Objects), allows your application to query the database using JDO Query (JDOQL), allows you to have up to 5,000 Java objects per database, uses a single file database, etc. The free edition may only be used for personal, non-commercial purposes.
Cyrus SASL
To quote, "the Cyrus SASL library is a generic library for SASL authentication, as used in SMTP and IMAP protocols. It's used for authentication by the Cyrus IMAP server as well as the Sendmail 8.10 release." It also includes a Java SASL library. Note that the link above is to an FTP directory. Look for a file like "cyrus-sasl-1.5.20.tar.gz" (the numbers may change when newer versions are released).
GNU Classpath
This is a free replacement for Sun's proprietary class libraries. It is still currently under development. The intention is for the released version to be fully compatibile with Java 1.1 and mostly compatible with 1.2.
Biss AWT
According to its web site, this Java framework provides approximately 150 classes for building graphical applications. Unlike java.awt which uses the native operative system's look and feel, this one has its own appearance. Source code is provided. It has support for pop-up menus, notebooks, hierachial lists, etc, without the need for a JDK 1.1 native library.