惠州如何使用Lucene索引文本文件？_北大青鸟IT学校

Java是现在非常主流的编程语言之一，很多人想转行学习Java。那么，如何使用Lucene索引文本文件？下面就让我们一起来看看惠州北大青鸟老师是怎么回答的。

实例

以下代码显示了如何使用Lucene索引文本文件。

/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.LongField;
import org.apache.lucene.document.StringField;
import org.apache.lucene.document.TextField;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig.OpenMode;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.Term;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.util.Version;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.Date;

/** Index all text files under a directory.
* <p>
* This is a command-line application demonstrating simple Lucene indexing.
* Run it with no command-line arguments for usage information.
*/public class Main {  
 private Main() {}

 /** Index all text files under a directory. */  public static void main(String[] args) {
   String usage = "java IndexFiles"
                + " [-index INDEX_PATH] [-docs DOCS_PATH] [-update]\n\n"
                + "This indexes the documents in DOCS_PATH, creating a Lucene index"
                + "in INDEX_PATH that can be searched with SearchFiles";
   String indexPath = "index";
   String docsPath = null;
   boolean create = true;    for(int i=0;i<args.length;i++) {      if ("-index".equals(args[i])) {
       indexPath = args[i+1];
       i++;
     } else if ("-docs".equals(args[i])) {
       docsPath = args[i+1];
       i++;
     } else if ("-update".equals(args[i])) {
       create = false;
     }
   }    if (docsPath == null) {
     System.err.println("Usage: " + usage);
     System.exit(1);
   }    final File docDir = new File(docsPath);    if (!docDir.exists() || !docDir.canRead()) {
     System.out.println("Document directory "" +docDir.getAbsolutePath()+ "" does not exist or is not readable, please check the path");
     System.exit(1);
   }
   
   Date start = new Date();    try {
     System.out.println("Indexing to directory "" + indexPath + ""...");

     Directory dir = FSDirectory.open(new File(indexPath));
     // :Post-Release-Update-Version.LUCENE_XY:
     Analyzer analyzer = new StandardAnalyzer(Version.LUCENE_4_10_0);
     IndexWriterConfig iwc = new IndexWriterConfig(Version.LUCENE_4_10_0, analyzer);      if (create) {
       // Create a new index in the directory, removing any
       // previously indexed documents:
       iwc.setOpenMode(OpenMode.CREATE);
     } else {
       // Add new documents to an existing index:
       iwc.setOpenMode(OpenMode.CREATE_OR_APPEND);
     }

     // Optional: for better indexing performance, if you
     // are indexing many documents, increase the RAM
     // buffer.  But if you do this, increase the max heap
     // size to the JVM (eg add -Xmx512m or -Xmx1g):
     //
     // iwc.setRAMBufferSizeMB(256.0);

     IndexWriter writer = new IndexWriter(dir, iwc);
     indexDocs(writer, docDir);

     // NOTE: if you want to maximize search performance,
     // you can optionally call forceMerge here.  This can be
     // a terribly costly operation, so generally it"s only
     // worth it when your index is relatively static (ie
     // you"re done adding documents to it):
     //
     // writer.forceMerge(1);

     writer.close();

     Date end = new Date();
     System.out.println(end.getTime() - start.getTime() + " total milliseconds");

   } catch (IOException e) {
     System.out.println(" caught a " + e.getClass() +       "\n with message: " + e.getMessage());
   }
 }

 /**
  * Indexes the given file using the given writer, or if a directory is given,
  * recurses over files and directories found under the given directory.
  *
  * NOTE: This method indexes one document per input file.  This is slow.  For good
  * throughput, put multiple documents into your input file(s).  An example of this is
  * in the benchmark module, which can create "line doc" files, one document per line,
  * using the
  * <a href="../../../../../contrib-benchmark/org/apache/lucene/benchmark/byTask/tasks/WriteLineDocTask.html"
  * >WriteLineDocTask</a>.
  *  
  * @param writer Writer to the index where the given file/dir info will be stored
  * @param file The file to index, or the directory to recurse into to find files to index
  * @throws IOException If there is a low-level I/O error
  */  static void indexDocs(IndexWriter writer, File file)
   throws IOException {
   // do not try to index files that cannot be read    if (file.canRead()) {      if (file.isDirectory()) {
       String[] files = file.list();
       // an IO error could occur        if (files != null) {          for (int i = 0; i < files.length; i++) {
           indexDocs(writer, new File(file, files[i]));
         }
       }
     } else {

       FileInputStream fis;        try {
         fis = new FileInputStream(file);
       } catch (FileNotFoundException fnfe) {
         // at least on windows, some temporary files raise this exception with an "access denied" message
         // checking if the file can be read doesn"t help
         return;
       }        try {

         // make a new, empty document
         Document doc = new Document();

         // Add the path of the file as a field named "path".  Use a
         // field that is indexed (i.e. searchable), but don"t tokenize
         // the field into separate words and don"t index term frequency
         // or positional information:
         Field pathField = new StringField("path", file.getPath(), Field.Store.YES);
         doc.add(pathField);

         // Add the last modified date of the file a field named "modified".
         // Use a LongField that is indexed (i.e. efficiently filterable with
         // NumericRangeFilter).  This indexes to milli-second resolution, which
         // is often too fine.  You could instead create a number based on
         // year/month/day/hour/minutes/seconds, down the resolution you require.
         // For example the long value 2011021714 would mean
         // February 17, 2011, 2-3 PM.
         doc.add(new LongField("modified", file.lastModified(), Field.Store.NO));

         // Add the contents of the file to a field named "contents".  Specify a Reader,
         // so that the text of the file is tokenized and indexed, but not stored.
         // Note that FileReader expects the file to be in UTF-8 encoding.
         // If that"s not the case searching for special characters will fail.
         doc.add(new TextField("contents", new BufferedReader(new InputStreamReader(fis, StandardCharsets.UTF_8))));          if (writer.getConfig().getOpenMode() == OpenMode.CREATE) {
           // New index, so we just add the document (no old document can be there):
           System.out.println("adding " + file);
           writer.addDocument(doc);
         } else {
           // Existing index (an old copy of this document may have been indexed) so
           // we use updateDocument instead to replace the old one matching the exact
           // path, if present:
           System.out.println("updating " + file);
           writer.updateDocument(new Term("path", file.getPath()), doc);
         }
         
       } finally {
         fis.close();
       }
     }
   }
 }
}

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