Java开发工程师必备技能：了解搜索引擎如何展示结果

一、搜索引擎结果展示的基本原理

搜索引擎的主要功能是根据用户输入的关键词，从众多网页中筛选出最相关的内容，并将这些内容显示在搜索结果页面上。这个过程可以分为三个基本步骤：

1、爬虫抓取：搜索引擎利用爬虫程序（也称为蜘蛛）从互联网上抓取网页。

public class Spider {

    private static final int MAX_PAGES_TO_SEARCH = 10;

    private Set pagesVisited = new HashSet();
    private List pagesToVisit = new LinkedList();

    /**
     * Our main launching point for the Spider's functionality. Internally it creates spider legs
     * that make an HTTP request and parse the response (the web page).
     * 
     * @param url
     *            - The starting point of the spider
     * @param searchWord
     *            - The word or string that you are searching for
     */
    public void search(String url, String searchWord)
    {
        while(this.pagesVisited.size() < MAX_PAGES_TO_SEARCH)
        {
            String currentUrl;
            SpiderLeg leg = new SpiderLeg();
            if(this.pagesToVisit.isEmpty())
            {
                currentUrl = url;
                this.pagesVisited.add(url);
            }
            else
            {
                currentUrl = this.nextUrl();
            }
            leg.crawl(currentUrl); // Lots of stuff happening here. Look at the crawl method in
                                   // SpiderLeg
            boolean success = leg.searchForWord(searchWord);
            if(success)
            {
                System.out.println(String.format("**Success** Word %s found at %s", searchWord, currentUrl));
                break;
            }
            this.pagesToVisit.addAll(leg.getLinks());
        }
        System.out.println(String.format("**Done** Visited %s web page(s)", this.pagesVisited.size()));
    }

    /**
     * Returns the next URL to visit (in the order that they were found). We also do a check to
     * make sure this method doesn't return a URL that has already been visited.
     * 
     * @return
     */
    private String nextUrl()
    {
        String nextUrl;
        do
        {
            nextUrl = this.pagesToVisit.remove(0);
        } while(this.pagesVisited.contains(nextUrl));
        this.pagesVisited.add(nextUrl);
        return nextUrl;
    }
}

2、索引处理：搜索引擎将爬虫抓取到的网页存储进索引库中，同时对网页的主要内容进行索引处理。索引处理的目的是能够快速准确地找到包含关键字的网页，这个过程主要是通过计算TF-IDF等算法来实现。

public class Indexer {

    private WebCrawler spider;

    private Map frequencyToUrlMap;
    private Map<String, Map> wordUrlsMap;

    public Indexer(WebCrawler spider) {
        this.spider = spider;
        frequencyToUrlMap = new HashMap();
        wordUrlsMap = new HashMap<String, Map>();
    }

    /**
     * Index a page by its URL
     * 
     * @param url
     *            - The URL of the page to be indexed
     */
    public void indexPage(String url) {
        System.out.println("Indexing " + url);
        Document document = spider.getDocument(url);
        String text = document.text();
        List words = spider.getWordsFromDocument(text);

        // Count frequency of web pages
        for (String word : words) {
            if (!wordUrlsMap.containsKey(word)) {
                wordUrlsMap.put(word, new HashMap());
            }
            Map urlToCountMap = wordUrlsMap.get(word);
            if (!urlToCountMap.containsKey(url)) {
                urlToCountMap.put(url, 0);
            }
            urlToCountMap.put(url, urlToCountMap.get(url) + 1);
        }

        // Map frequency to URL
        int frequency = 0;
        for (Map.Entry<String, Map> entry : wordUrlsMap.entrySet()) {
            String word = entry.getKey();
            Map urlToCountMap = entry.getValue();
            frequency = 0;
            for (Map.Entry urlEntry : urlToCountMap.entrySet()) {
                frequency += urlEntry.getValue();
            }

            // TODO: implement sorting by frequency
            frequencyToUrlMap.put(word, url);

            System.out.println("indexing " + word + ", " + url);
        }
    }
}

3、结果展示：当用户输入关键字之后，搜索引擎会将包含关键字的网页内容展示在搜索结果页面上，同时还会对这些网页进行排名，将最相关的网页排名靠前。

二、搜索引擎结果展示的主要形式

搜索引擎结果通常有以下几种主要形式：

1、蓝色链接+标题+描述：这是搜索结果最常见的展示形式，用户在搜索后会看到一系列链接，每个链接后面跟着网页的标题和描述信息，让用户可以对结果进行初步筛选。

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2、图文结果：对于一些特定的搜索，搜索引擎也会展示图文结果，包括图片、视频、新闻等信息。这种展示形式更加直观且易于用户理解。

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