yaz4j is a toolkit for Java which includes a wrapper for the ZOOM API of YAZ. This allows developers to write Z39.50/SRU clients in Java. yaz4j supports both search and scan. See the javadoc for details.
For a tutorial on how to use yaz4j in a servlet environment please see Building Simple HTTP-Z3950 gateway using yaz4j and Tomcat.
For Windows users: yaz4j is now part of the YAZ Windows installer and this is the recommended way of obtaining yaz4j on that platform.