布隆过滤器的java实现

package com.kaikeba.data.jobspider.util;

import java.util.BitSet;

public class Bloomfilter {

private static final int DEFAULT_SIZE = 2 << 29;//布隆过滤器的比特长度

private static final int[] seeds = {3,5,7, 11, 13, 31, 37, 61};//这里要选取质数，能很好的降低错误率

private BitSet bits = new BitSet(DEFAULT_SIZE);

private SimpleHash[] func = new SimpleHash[seeds.length];

public Bloomfilter()

{

for (int i = 0; i < seeds.length; i++) {

func[i] = new SimpleHash(DEFAULT_SIZE, seeds[i]);

}

}

private void addValue(String value)

{

for(SimpleHash f : func)//将字符串value哈希为8个或多个整数，然后在这些整数的bit上变为1

bits.set(f.hash(value),true);

}

public void add(String value)

{

if(value != null) addValue(value);

}

public boolean contains(String value)

{

if(value == null) return false;

boolean ret = true;

for(SimpleHash f : func)//这里其实没必要全部跑完，只要一次ret==false那么就不包含这个字符串

ret = ret && bits.get(f.hash(value));

return ret;

}

// /**

// *初始化过滤器.

// *

// * @param

// */

// public void init(String file) {

// for (int i = 0; i < seeds.length; i++) {

// func[i] = new SimpleHash(DEFAULT_SIZE, seeds[i]);

// }

//// BufferedReader reader = null;

//// try {

//// reader = new BufferedReader(new FileReader(file));

//// String line = reader.readLine();

//// while (line != null && line.length() > 0) {

//// this.put(line);

//// line = reader.readLine();

//// }

//// } catch (Exception e) {

//// e.printStackTrace();

//// } finally {

//// try {

//// if (reader != null)

//// reader.close();

//// } catch (IOException e) {

//// e.printStackTrace();

//// }

//// }

// }

// public static void main(String[] args) {

// String value = "xkeyideal@gmail.com";

//

// add(value);

// System.out.println(contains(value));

// }

}

class SimpleHash {//这玩意相当于C++中的结构体

private int cap;

private int seed;

public SimpleHash(int cap, int seed) {

this.cap = cap;

this.seed = seed;

}

public int hash(String value) {//字符串哈希，选取好的哈希函数很重要

int result = 0;

int len = value.length();

for (int i = 0; i < len; i++) {

result = seed * result + value.charAt(i);

}

return (cap - 1) & result;

}

}