Lucene example source code file (Lookup.java)

This example Lucene source code file (Lookup.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Lucene tags/keywords

io, ioexception, ioexception, iterator, lookup, lookuppriorityqueue, lookuppriorityqueue, lookupresult, lookupresult, object, override, priorityqueue, string, termfreqiterator, termfreqiterator, util

The Lucene Lookup.java source code

package org.apache.lucene.search.suggest;

import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;

import org.apache.lucene.search.spell.Dictionary;
import org.apache.lucene.search.spell.TermFreqIterator;
import org.apache.lucene.util.PriorityQueue;

public abstract class Lookup {
  /**
   * Result of a lookup.
   */
  public static final class LookupResult implements Comparable<LookupResult> {
    public final String key;
    public final float value;
    
    public LookupResult(String key, float value) {
      this.key = key;
      this.value = value;
    }
    
    @Override
    public String toString() {
      return key + "/" + value;
    }

    /** Compare alphabetically. */
    public int compareTo(LookupResult o) {
      return this.key.compareTo(o.key);
    }
  }
  
  public static final class LookupPriorityQueue extends PriorityQueue<LookupResult> {
    
    public LookupPriorityQueue(int size) {
      initialize(size);
    }

    @Override
    protected boolean lessThan(LookupResult a, LookupResult b) {
      return a.value < b.value;
    }
    
    public LookupResult[] getResults() {
      int size = size();
      LookupResult[] res = new LookupResult[size];
      for (int i = size - 1; i >= 0; i--) {
        res[i] = pop();
      }
      return res;
    }
  }
  
  /** Build lookup from a dictionary. Some implementations may require sorted
   * or unsorted keys from the dictionary's iterator - use
   * {@link SortedTermFreqIteratorWrapper} or
   * {@link UnsortedTermFreqIteratorWrapper} in such case.
   */
  public void build(Dictionary dict) throws IOException {
    Iterator<String> it = dict.getWordsIterator();
    TermFreqIterator tfit;
    if (it instanceof TermFreqIterator) {
      tfit = (TermFreqIterator)it;
    } else {
      tfit = new TermFreqIterator.TermFreqIteratorWrapper(it);
    }
    build(tfit);
  }
  
  public abstract void build(TermFreqIterator tfit) throws IOException;
  
  /**
   * Persist the constructed lookup data to a directory. Optional operation.
   * @param storeDir directory where data can be stored.
   * @return true if successful, false if unsuccessful or not supported.
   * @throws IOException when fatal IO error occurs.
   */
  public abstract boolean store(File storeDir) throws IOException;

  /**
   * Discard current lookup data and load it from a previously saved copy.
   * Optional operation.
   * @param storeDir directory where lookup data was stored.
   * @return true if completed successfully, false if unsuccessful or not supported.
   * @throws IOException when fatal IO error occurs.
   */
  public abstract boolean load(File storeDir) throws IOException;
  
  /**
   * Look up a key and return possible completion for this key.
   * @param key lookup key. Depending on the implementation this may be
   * a prefix, misspelling, or even infix.
   * @param onlyMorePopular return only more popular results
   * @param num maximum number of results to return
   * @return a list of possible completions, with their relative weight (e.g. popularity)
   */
  public abstract List<LookupResult> lookup(String key, boolean onlyMorePopular, int num);

  /**
   * Modify the lookup data by recording additional data. Optional operation.
   * @param key new lookup key
   * @param value value to associate with this key
   * @return true if new key is added, false if it already exists or operation
   * is not supported.
   */
  public abstract boolean add(String key, Object value);
  
  /**
   * Get value associated with a specific key.
   * @param key lookup key
   * @return associated value
   */
  public abstract Object get(String key);  
}