英文原文:Lucene in 5 minutes
更新:下面的代码使用 Lucene 4.0 版本!
Lucene 大大简化了在应用中集成全文搜索的功能。但实际上 Lucene 十分简单,我可以在五分钟之内向你展示如何使用 Lucene。
1. 建立索引
为了简单起见,我们下面为一些字符串创建内存索引:
StandardAnalyzer analyzer = new StandardAnalyzer (Version.LUCENE_40); Directory index = new RAMDirectory (); IndexWriterConfig config = new IndexWriterConfig (Version.LUCENE_40, analyzer); IndexWriter w = new IndexWriter (index, config); addDoc (w, "Lucene in Action", "193398817"); addDoc (w, "Lucene for Dummies", "55320055Z"); addDoc (w, "Managing Gigabytes", "55063554A"); addDoc (w, "The Art of Computer Science", "9900333X"); w.close ();
addDoc ()方法把文档(译者注:这里的文档是 Lucene 中的 Document 类的实例)添加到索引中。
private static void addDoc (IndexWriter w, String title, String isbn) throws IOException { Document doc = new Document (); doc.add (new TextField ("title", title, Field.Store.YES)); doc.add (new StringField ("isbn", isbn, Field.Store.YES)); w.addDocument (doc); }
注意,对于需要分词的内容我们使用 TextField,对于像 id 这样不需要分词的内容我们使用 StringField。
2. 搜索请求
我们从标准输入(stdin)中读入搜索请求,然后对它进行解析,最后创建一个 Lucene 中的 Query 对象。
String querystr = args.length > 0 ? args[0] : "lucene"; Query q = new QueryParser (Version.LUCENE_40, "title", analyzer) .parse (querystr);
3. 搜索
我们创建一个 Searcher 对象并且使用上面创建的 Query 对象来进行搜索,匹配到的前 10 个结果封装在 TopScoreDocCollector 对象里返回。
int hitsPerPage = 10; IndexReader reader = IndexReader.open (index); IndexSearcher searcher = new IndexSearcher (reader); TopScoreDocCollector collector = TopScoreDocCollector.create (hitsPerPage, true); searcher.search (q, collector); ScoreDoc[] hits = collector.topDocs () .scoreDocs;
4. 展示
现在我们得到了搜索结果,我们需要想用户展示它。
System.out.println ("Found " + hits.length + " hits."); for(int i=0;i<hits.length;++i) { int docId = hits[i].doc; Document d = searcher.doc (docId); System.out.println ((i + 1) + ". " + d.get("isbn") + "\t" + d.get("title")); }
这里是这个小应用的完整代码。下载 HelloLucene.java。
import org.apache.lucene.analysis.standard.StandardAnalyzer; import org.apache.lucene.document.Document; import org.apache.lucene.document.Field; import org.apache.lucene.document.StringField; import org.apache.lucene.document.TextField; import org.apache.lucene.index.DirectoryReader; import org.apache.lucene.index.IndexReader; import org.apache.lucene.index.IndexWriter; import org.apache.lucene.index.IndexWriterConfig; import org.apache.lucene.queryparser.classic.ParseException; import org.apache.lucene.queryparser.classic.QueryParser; import org.apache.lucene.search.IndexSearcher; import org.apache.lucene.search.Query; import org.apache.lucene.search.ScoreDoc; import org.apache.lucene.search.TopScoreDocCollector; import org.apache.lucene.store.Directory; import org.apache.lucene.store.RAMDirectory; import org.apache.lucene.util.Version; import java.io.IOException; public class HelloLucene { public static void main (String[] args) throws IOException, ParseException { // 0. Specify the analyzer for tokenizing text. // The same analyzer should be used for indexing and searching StandardAnalyzer analyzer = new StandardAnalyzer (Version.LUCENE_40); // 1. create the index Directory index = new RAMDirectory (); IndexWriterConfig config = new IndexWriterConfig (Version.LUCENE_40, analyzer); IndexWriter w = new IndexWriter (index, config); addDoc (w, "Lucene in Action", "193398817"); addDoc (w, "Lucene for Dummies", "55320055Z"); addDoc (w, "Managing Gigabytes", "55063554A"); addDoc (w, "The Art of Computer Science", "9900333X"); w.close (); // 2. query String querystr = args.length > 0 ? args[0] : "lucene"; // the "title" arg specifies the default field to use // when no field is explicitly specified in the query. Query q = new QueryParser (Version.LUCENE_40, "title", analyzer) .parse (querystr); // 3. search int hitsPerPage = 10; IndexReader reader = DirectoryReader.open (index); IndexSearcher searcher = new IndexSearcher (reader); TopScoreDocCollector collector = TopScoreDocCollector.create (hitsPerPage, true); searcher.search (q, collector); ScoreDoc[] hits = collector.topDocs () .scoreDocs; // 4. display results System.out.println ("Found " + hits.length + " hits."); for(int i=0;i<hits.length;++i) { int docId = hits[i].doc; Document d = searcher.doc (docId); System.out.println ((i + 1) + ". " + d.get ("isbn") + "\t" + d.get ("title")); } // reader can only be closed when there // is no need to access the documents any more. reader.close (); } private static void addDoc (IndexWriter w, String title, String isbn) throws IOException { Document doc = new Document (); doc.add (new TextField ("title", title, Field.Store.YES)); // use a string field for isbn because we don't want it tokenized doc.add (new StringField ("isbn", isbn, Field.Store.YES)); w.addDocument (doc); } }
可以直接在命令行中使用这个小应用,键入java HelloLucene 。
下面可以做什么?
一些与 Lucene 和搜索相关的书籍
Github 上的基于 maven 的库
Mac Luq 在 Github 上的基于 maven 的库:
https://github.com/macluq/helloLucene
用下面这条命令下载它:
git clone https://github.com/macluq/helloLucene.git
PS:如果你是 Java 新手的话,试试下面的命令:
wget http://repo1.maven.org/maven2/org/apache/lucene/lucene-core/4.0.0/lucene-core-4.0.0.jar
wget http://repo1.maven.org/maven2/org/apache/lucene/lucene-analyzers-common/4.0.0/lucene-analyzers-common-4.0.0.jar
wget http://repo1.maven.org/maven2/org/apache/lucene/lucene-queryparser/4.0.0/lucene-queryparser-4.0.0.jar
wget http://www.lucenetutorial.com/code/HelloLucene.java
javac -classpath .:lucene-core-4.0.0.jar:lucene-analyzers-common-4.0.0.jar:lucene-queryparser-4.0.0.jar HelloLucene.java java -classpath .:lucene-core-4.0.0.jar:lucene-analyzers-common-4.0.0.jar:lucene-queryparser-4.0.0.jar HelloLucene
你会得到下面的结果:
Found 2 hits.
1. Lucene
in
Action
2. Lucene
for
Dummies
Erik,一个可能对你有所帮助的读者抱怨到:
编译过程还算顺利,但是我不能正常运行这段代码。在网上搜索并且自己尝试了以后发现 Lucene 的 jar 文件必须在 classpath 中,否则运行不起来。这可能对很多像我这样的 java 初学者很多帮助。
安装 Lucene
PS:我发现一些初学者在安装 Lucene 时有些困难。
你应该先下载 Lucene,然后把它解压到一个你用于编程的目录。
如果你使用 Netbeans,你也可以这么做:
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