布隆过滤

import java.util.BitSet;public class BloomFilter {private static int defaultSize = 2 << 24;private static int basic = defaultSize - 1;private static BitSet bits;private static BloomFilter bf = new BloomFilter();public BloomFilter() {bits = new BitSet(defaultSize);}public static boolean contains(String url) {if (url == null) {return true;}int pos1 = hash1(url);int pos2 = hash2(url);int pos3 = hash3(url);if (bits.get(pos1) && bits.get(pos2) && bits.get(pos3)) {return true;}return false;}public static void add(String url) {if (url == null) {return;}int pos1 = hash1(url);int pos2 = hash2(url);int pos3 = hash3(url);bits.set(pos1);bits.set(pos2);bits.set(pos3);}private static int hash3(String line) {int h = 0;int len = line.length();for (int i = 0; i < len; i++) {h = 37 * h + line.charAt(i);}return check(h);}private static int hash2(String line) {int h = 0;int len = line.length();for (int i = 0; i < len; i++) {h = 33 * h + line.charAt(i);}return check(h);}private static int hash1(String line) {int h = 0;int len = line.length();for (int i = 0; i < len; i++) {h = 31 * h + line.charAt(i);}return check(h);}private static int check(int h) {return basic & h;}}