One of the things that I think is particularly nice about the UnboundID LDAP SDK for Java is the way that it allows you to perform a search and have it collect the matching entries in a list that is available in the search result. However, this is really only well suited for cases in which you’re sure that you won’t get a huge number of entries returned because otherwise the need to hold all of the matching entries at once can cause significant memory problems.

However, if you are going to be dealing with large search result sets, then the LDAP SDK provides a couple of additional APIs that may be of use. The SearchResultListener interface defines methods that can be invoked whenever an entry or reference is returned by the server that allows you to act on that entry or reference as soon as it is received. I’ve had a number of people ask for an example of how to use this interface, so I’ve created a simple program, WriteAttrToFileUsingListener.java, that you can use to accomplish this. It’s a pretty simple program that performs a search to retrieve all entries containing a specified attribute, and then writes all of the values for that attribute to a specified output file. It’s a little more complex than it absolutely needs to be in order to demonstrate just the SearchResultListener interface, but it also serves as a nice example of the LDAPCommandLineTool API that you can use to easily write command-line utilities that need to talk to a directory server.

We also have another class, LDAPEntrySource, which can be used to make dealing with large result sets easier. This class provides an implementation of the EntrySource API (which makes it easy to iterate across entries in a common way regardless of how they were obtained, like returned as search results or read from an LDIF file), and you can treat it kind of like an iterator across search entries. I’ve created another version of the example program, WriteAttrToFileUsingEntrySource.java, that demonstrates how to use the LDAPEntrySource as an alternative to SearchResultListener to achieve the same result.