爬蟲架構分類
1. 分布式爬蟲
Nutch
2. Java單機爬蟲
Crawler4j、WebMagic、WebCollector
3. 非Java單機爬蟲
Scrapy
開發思路
根據業務需求選擇合适的爬蟲架構
根據網站規則及業務需求抽取資料,儲存到中間庫
資料清洗/格式化,儲存到目标庫
基于Crawler4j + jsoup實作爬蟲
用Crawler4j建構多線程的web爬蟲來抓取頁面内容。Crawler4j的使用分為兩個步驟:
(1) 實作一個繼承自WebCrawler的爬蟲類
需要覆寫兩個主要方法:
shouldVisit:這個方法決定了要抓取的URL及其内容。
visit:當URL下載下傳完成會調用這個方法。使用jsoup解析HTML,可以采用jQuery選擇器的文法。
(2) 通過CrawController調用實作的爬蟲類。
指定抓取的種子(seed)、中間資料存儲的檔案夾、并發線程的數目等資訊,實作控制器類。
示例代碼
pom.xml中依賴包設定
<dependency>
<groupId>edu.uci.ics</groupId>
<artifactId>crawler4j</artifactId>
<version>4.2</version>
</dependency>
<dependency>
<groupId>org.jsoup</groupId>
<artifactId>jsoup</artifactId>
<version>1.10.1</version>
</dependency>
代碼
(1) 爬蟲類
public class MyCrawler extends WebCrawler {
private final static Pattern FILTERS = Pattern.compile(".*(\\.(css|js|gif|jpg"
+ "|png|mp3|mp3|zip|gz))$");
/**
* This method receives two parameters. The first parameter is the page
* in which we have discovered this new url and the second parameter is
* the new url. You should implement this function to specify whether
* the given url should be crawled or not (based on your crawling logic).
* In this example, we are instructing the crawler to ignore urls that
* have css, js, git, ... extensions and to only accept urls that start
* with "http://www.ics.uci.edu/". In this case, we didn't need the
* referringPage parameter to make the decision.
*/
@Override
public boolean shouldVisit(Page referringPage, WebURL url) {
String href = url.getURL().toLowerCase();
return !FILTERS.matcher(href).matches()
&& href.startsWith("http://www.ics.uci.edu/");
}
/**
* This function is called when a page is fetched and ready
* to be processed by your program.
*/
@Override
public void visit(Page page) {
String url = page.getWebURL().getURL();
System.out.println("URL: " + url);
if (page.getParseData() instanceof HtmlParseData) {
HtmlParseData htmlParseData = (HtmlParseData) page.getParseData();
String text = htmlParseData.getText();
String html = htmlParseData.getHtml();
Set<WebURL> links = htmlParseData.getOutgoingUrls();
System.out.println("Text length: " + text.length());
System.out.println("Html length: " + html.length());
System.out.println("Number of outgoing links: " + links.size());
}
}
}
(2) Controller調用
public class Controller {
public static void main(String[] args) throws Exception {
String crawlStorageFolder = "/data/crawl/root";
int numberOfCrawlers = 7;
CrawlConfig config = new CrawlConfig();
config.setCrawlStorageFolder(crawlStorageFolder);
/*
* Instantiate the controller for this crawl.
*/
PageFetcher pageFetcher = new PageFetcher(config);
RobotstxtConfig robotstxtConfig = new RobotstxtConfig();
RobotstxtServer robotstxtServer = new RobotstxtServer(robotstxtConfig, pageFetcher);
CrawlController controller = new CrawlController(config, pageFetcher, robotstxtServer);
/*
* For each crawl, you need to add some seed urls. These are the first
* URLs that are fetched and then the crawler starts following links
* which are found in these pages
*/
controller.addSeed("http://www.ics.uci.edu/~lopes/");
controller.addSeed("http://www.ics.uci.edu/~welling/");
controller.addSeed("http://www.ics.uci.edu/");
/*
* Start the crawl. This is a blocking operation, meaning that your code
* will reach the line after this only when crawling is finished.
*/
controller.start(MyCrawler.class, numberOfCrawlers);
}
}