基于PHP的布隆过滤器实现网页爬虫去重技术介绍

class BloomFilter {
    private $bitArray;
    private $hashFunctions;
    
    public function __construct($size, $hashFunctions) {
        $this->bitArray = new SplFixedArray($size);
        $this->bitArray->setSize($size);
        $this->hashFunctions = $hashFunctions;
    }
    
    public function add($value) {
        foreach ($this->hashFunctions as $function) {
            $index = $function($value) % count($this->bitArray);
            $this->bitArray[$index] = true;
        }
    }
    
    public function contains($value) {
        foreach ($this->hashFunctions as $function) {
            $index = $function($value) % count($this->bitArray);
            if (!$this->bitArray[$index]) {
                return false;
            }
        }
        return true;
    }
}

$hashFunctions = [
    function($value) { return crc32($value); },
    function($value) { return crc32(md5($value)); }
];

$bloomFilter = new BloomFilter(10000, $hashFunctions);

function crawlPage($url) {
    global $bloomFilter;
    
    if ($bloomFilter->contains($url)) {
        return; // 已经被爬取过
    }
    
    // 爬取网页并处理
    
    $bloomFilter->add($url); // 将爬取过的网页添加到布隆过滤器中
}