---
uid: Lucene.Net
summary: *content
---

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Apache Lucene is a high-performance, full-featured text search engine library. Here's a simple example how to use Lucene for indexing and searching (using JUnit to check if the results are what we expect):

<!-- =   Java2Html Converter 5.0 [2006-03-04] by Markus Gebhard  markus@jave.de   = -->

        Analyzer analyzer = new StandardAnalyzer(Version.LUCENE_CURRENT);
    
    // Store the index in memory:
        Directory directory = new RAMDirectory();
        // To store an index on disk, use this instead:
        //Directory directory = FSDirectory.open("/tmp/testindex");
        IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_CURRENT, analyzer);
        IndexWriter iwriter = new IndexWriter(directory, config);
        Document doc = new Document();
        String text = "This is the text to be indexed.";
        doc.add(new Field("fieldname", text, TextField.TYPE_STORED));
        iwriter.addDocument(doc);
        iwriter.close();

        // Now search the index:
        DirectoryReader ireader = DirectoryReader.open(directory);
        IndexSearcher isearcher = new IndexSearcher(ireader);
        // Parse a simple query that searches for "text":
        QueryParser parser = new QueryParser(Version.LUCENE_CURRENT, "fieldname", analyzer);
        Query query = parser.parse("text");
        ScoreDoc[] hits = isearcher.search(query, null, 1000).scoreDocs;
        assertEquals(1, hits.length);
        // Iterate through the results:
        for (int i = 0; i < hits.length;="" i++)="" {="" document="" hitdoc="isearcher.doc(hits[i].doc);" assertequals("this="" is="" the="" text="" to="" be="" indexed.",="" hitdoc.get("fieldname"));="" }="" ireader.close();="">

The Lucene API is divided into several packages:

*   __<xref:Lucene.Net.Analysis>__
defines an abstract [Analyzer](xref:Lucene.Net.Analysis.Analyzer)
API for converting text from a {@link java.io.Reader}
into a [TokenStream](xref:Lucene.Net.Analysis.TokenStream),
an enumeration of token [Attribute](xref:Lucene.Net.Util.Attribute)s. 
A TokenStream can be composed by applying [TokenFilter](xref:Lucene.Net.Analysis.TokenFilter)s
to the output of a [Tokenizer](xref:Lucene.Net.Analysis.Tokenizer). 
Tokenizers and TokenFilters are strung together and applied with an [Analyzer](xref:Lucene.Net.Analysis.Analyzer). 
[analyzers-common](../analyzers-common/overview-summary.html) provides a number of Analyzer implementations, including 
[StopAnalyzer](../analyzers-common/org/apache/lucene/analysis/core/StopAnalyzer.html)
and the grammar-based [StandardAnalyzer](../analyzers-common/org/apache/lucene/analysis/standard/StandardAnalyzer.html).


*   __<xref:Lucene.Net.Codecs>__
provides an abstraction over the encoding and decoding of the inverted index structure,
as well as different implementations that can be chosen depending upon application needs.


*   __<xref:Lucene.Net.Documents>__
provides a simple [Document](xref:Lucene.Net.Documents.Document)
class.  A Document is simply a set of named [Field](xref:Lucene.Net.Documents.Field)s,
whose values may be strings or instances of {@link java.io.Reader}.


*   __<xref:Lucene.Net.Index>__
provides two primary classes: [IndexWriter](xref:Lucene.Net.Index.IndexWriter),
which creates and adds documents to indices; and <xref:Lucene.Net.Index.IndexReader>,
which accesses the data in the index.


*   __<xref:Lucene.Net.Search>__
provides data structures to represent queries (ie [TermQuery](xref:Lucene.Net.Search.TermQuery)
for individual words, [PhraseQuery](xref:Lucene.Net.Search.PhraseQuery) 
for phrases, and [BooleanQuery](xref:Lucene.Net.Search.BooleanQuery) 
for boolean combinations of queries) and the [IndexSearcher](xref:Lucene.Net.Search.IndexSearcher)
which turns queries into [TopDocs](xref:Lucene.Net.Search.TopDocs).
A number of [QueryParser](../queryparser/overview-summary.html)s are provided for producing
query structures from strings or xml.


*   __<xref:Lucene.Net.Store>__
defines an abstract class for storing persistent data, the [Directory](xref:Lucene.Net.Store.Directory),
which is a collection of named files written by an [IndexOutput](xref:Lucene.Net.Store.IndexOutput)
and read by an [IndexInput](xref:Lucene.Net.Store.IndexInput). 
Multiple implementations are provided, including [FSDirectory](xref:Lucene.Net.Store.FSDirectory),
which uses a file system directory to store files, and [RAMDirectory](xref:Lucene.Net.Store.RAMDirectory)
which implements files as memory-resident data structures.


*   __<xref:Lucene.Net.Util>__
contains a few handy data structures and util classes, ie [OpenBitSet](xref:Lucene.Net.Util.OpenBitSet)
and [PriorityQueue](xref:Lucene.Net.Util.PriorityQueue).

To use Lucene, an application should:

1.  Create [Document](xref:Lucene.Net.Documents.Document)s by
adding
[Field](xref:Lucene.Net.Documents.Field)s;


2.  Create an [IndexWriter](xref:Lucene.Net.Index.IndexWriter)
and add documents to it with [AddDocument](xref:Lucene.Net.Index.IndexWriter#methods);


3.  Call [QueryParser.parse()](../queryparser/org/apache/lucene/queryparser/classic/QueryParserBase.html#parse(java.lang.String))
to build a query from a string; and


4.  Create an [IndexSearcher](xref:Lucene.Net.Search.IndexSearcher)
and pass the query to its [Search](xref:Lucene.Net.Search.IndexSearcher#methods)
method.

Some simple examples of code which does this are:

*    [IndexFiles.java](../demo/src-html/org/apache/lucene/demo/IndexFiles.html) creates an
index for all the files contained in a directory.


*    [SearchFiles.java](../demo/src-html/org/apache/lucene/demo/SearchFiles.html) prompts for
queries and searches an index.

