source: other-projects/hathitrust/wcsa/extracted-features-solr/trunk/solr-ingest/src/main/java/org/hathitrust/extractedfeatures/WhitelistBloomFilter.java@ 31175

package org.hathitrust.extractedfeatures;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Stream;

import com.google.common.hash.BloomFilter;
import com.google.common.hash.Funnel;
import com.google.common.hash.Funnels;

public class WhitelistBloomFilter {
    
    protected String _dictionary_filename;
    protected BloomFilter<CharSequence> _bloomFilter;
    
    protected int FILL_FACTOR = 26;
    
    // http://stackoverflow.com/questions/453018/number-of-lines-in-a-file-in-java
        public static int countLines(String filename) throws IOException 
        {
            InputStream is = new BufferedInputStream(new FileInputStream(filename));
        
            try {
                byte[] c = new byte[1024];
                int count = 0;
                int readChars = 0;
                boolean empty = true;
                while ((readChars = is.read(c)) != -1) {
                    empty = false;
                    for (int i = 0; i < readChars; ++i) {
                        if (c[i] == '\n') {
                            ++count;
                        }
                    }
                }
                return (count == 0 && !empty) ? 1 : count;
            } finally {
                is.close();
            }
        }
        
        
    public WhitelistBloomFilter(String dictionary_filename) {
        System.out.println("Constructing: WhitelistBloomFilter");
    
        _dictionary_filename = dictionary_filename;
        
        System.out.println("Counting lines in: " + dictionary_filename);
        int num_lines;
        try {
            num_lines = countLines(dictionary_filename);
            
            Funnel<CharSequence> string_funnel = Funnels.stringFunnel(StandardCharsets.UTF_8);
            _bloomFilter = BloomFilter.create(string_funnel, FILL_FACTOR * num_lines,0.01);
            
        } catch (IOException e) {
            
            e.printStackTrace();
        }
    
    }
    
    public void storeEntries() 
    {
        System.out.println("Build Bloom filter ...");
        
        for (int i=0; i<FILL_FACTOR; i++) {
            
            char prefix = (char) ('a' + i);
            
            //read file into stream, try-with-resources
            try (Stream<String> stream = Files.lines(Paths.get(_dictionary_filename))) {

                stream.forEach(word -> {_bloomFilter.put(prefix+word);});
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        System.out.println("... done");

    }
    
    public boolean contains(String key)
    {
        return _bloomFilter.mightContain(key);
    }
}