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Updated February 2003 (Originally Published June 2002)
This article describes a J2EE design pattern, the DataListHandler, that represents a substantial improvement over traditional methods for efficiently processing Internet searches and quickly displaying the results to the user. The DataListHandler design pattern addresses the problem of processing Internet search queries that return large result sets in an efficient manner. It provides a set of interfaces, DataListHandler, DataList, and DataListIterator, that insulate the client from the underlying details of the search and retrieval implementation.
A central component of the Relational Database Access
Strategy of the Data List Handler pattern is the
retention of database connections across requests and
the use of scrollable JDBC ResultSets. The original
version of the pattern, published in June 2002, did not provide a detailed
strategy for addressing the overhead of long-lived
open database connections. The pattern has been
updated to include a new strategy for expiring idle
database connections and re-establishing them
transparently as needed. The strategy also handles
failover of Data List Handler instances to another JVM
in an distributed application server environment.
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