127 lines
3.7 KiB
Java
127 lines
3.7 KiB
Java
/*
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* The MIT License (MIT)
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*
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* Copyright © 2021 xrv <xrv@live.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package io.github.ehlxr.util;
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import java.util.BitSet;
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/**
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* @author ehlxr
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* @since 2021-12-16 09:36.
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*/
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public class MyBloomFilter {
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/**
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* 一个长度为10 亿的比特位
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*/
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private static final int DEFAULT_SIZE = 256 << 22;
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/**
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* 为了降低错误率，使用加法hash算法，所以定义一个8个元素的质数数组
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*/
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private static final int[] SEEDS = {3, 5, 7, 11, 13, 31, 37, 61};
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/**
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* 相当于构建 8 个不同的hash算法
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*/
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private static final HashFunction[] HASH_FUNCS = new HashFunction[SEEDS.length];
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/**
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* 初始化布隆过滤器的 bitmap
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*/
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private static final BitSet BIT_SET = new BitSet(DEFAULT_SIZE);
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/**
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* 添加数据
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*
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* @param value 需要加入的值
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*/
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public static void add(String value) {
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if (value != null) {
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for (HashFunction f : HASH_FUNCS) {
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//计算 hash 值并修改 bitmap 中相应位置为 true
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BIT_SET.set(f.hash(value), true);
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}
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}
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}
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/**
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* 判断相应元素是否存在
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*
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* @param value 需要判断的元素
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* @return 结果
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*/
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public static boolean contains(String value) {
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if (value == null) {
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return false;
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}
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boolean ret = true;
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for (HashFunction f : HASH_FUNCS) {
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ret = BIT_SET.get(f.hash(value));
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//一个 hash 函数返回 false 则跳出循环
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if (!ret) {
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break;
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}
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}
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return ret;
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}
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/**
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* 模拟用户是不是会员，或用户在不在线。。。
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*/
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public static void main(String[] args) {
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for (int i = 0; i < SEEDS.length; i++) {
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HASH_FUNCS[i] = new HashFunction(DEFAULT_SIZE, SEEDS[i]);
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}
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// 添加1亿数据
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for (int i = 0; i < 1_0000_0000; i++) {
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add(String.valueOf(i));
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}
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String id = "123456789";
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add(id);
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System.out.println(contains(id)); // true
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System.out.println("" + contains("234567890")); //false
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}
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}
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class HashFunction {
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private final int size;
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private final int seed;
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public HashFunction(int size, int seed) {
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this.size = size;
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this.seed = seed;
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}
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public int hash(String value) {
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int result = 0;
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int len = value.length();
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for (int i = 0; i < len; i++) {
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result = seed * result + value.charAt(i);
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}
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int r = (size - 1) & result;
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return (size - 1) & result;
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}
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} |