Lucene is a high-performance, scalable information retrieval (IR) library. IR refers to the process of searching for documents, information within documents, or metadata about documents. Lucene lets you add searching capabilities to your applications. It’s a mature, free, open source project implemented in Java, and a project in the Apache Software Foundation, licensed under the liberal Apache Software License. As such, Lucene is currently, and has been for quite a few years, the most popular free IR library.
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