uk.co.smr.slf4j.logonce.strategy.BloomFilterStrategy.java Source code

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Here is the source code for uk.co.smr.slf4j.logonce.strategy.BloomFilterStrategy.java

Source

package uk.co.smr.slf4j.logonce.strategy;

import java.nio.charset.Charset;

import uk.co.smr.slf4j.logonce.MatchingStrategy;

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

/**
 * A space efficient BloomFilter is used to filter logged messages. 
 * It will occasionally result in false positives. That is, sometimes
 * messages will be logged more than once.
 * 
 * <p>This class is <b>not</b> thread safe.
 * 
 * @author Peter Lappo (smr.co.uk)
 * 
 * @see <a href="https://github.com/smr-co-uk/java-logonce/blob/master/LICENSE">License and Warranty</a>
 *
 */

public class BloomFilterStrategy implements MatchingStrategy {
    private final BloomFilter<CharSequence> filter;

    public BloomFilterStrategy() {
        this(2000, 0.03);
    }

    /**
     * @see BloomFilter
     * 
     * @param expectedInsertions the number of expected insertions to the constructed
     * @param fpp false positive probability must be positive, decimal fraction, eg. 0.03 for 3%
     */
    public BloomFilterStrategy(int expectedInsertions, double fpp) {
        filter = BloomFilter.create(Funnels.stringFunnel(Charset.defaultCharset()), expectedInsertions, fpp);
    }

    @Override
    public boolean add(String msg) {
        boolean logmsg = false;
        if (!filter.mightContain(msg)) {
            filter.put(msg);
            logmsg = true;
        }
        return logmsg;
    }

}