基于crawler4j、jsoup、javacsv的爬虫实践
1. crawler4j基础
crawler4j是一个基于Java的爬虫开源项目,其官方地址如下:
http://code.google.com/p/crawler4j/
crawler4j的使用主要分为两个步骤:
- 实现一个继承自WebCrawler的爬虫类;
- 通过CrawlController调用实现的爬虫类。
WebCrawler是一个抽象类,继承它必须实现两个方法:shouldVisit和visit。其中:
- shouldVisit是判断当前的URL是否已经应该被爬取(访问);
- visit则是爬取该URL所指向的页面的数据,其传入的参数即是对该web页面全部数据的封装对象Page。
另外,WebCrawler还有其它一些方法可供覆盖,其方法的命名规则类似于Android的命名规则。如getMyLocalData方法可以返回WebCrawler中的数据;onBeforeExit方法会在该WebCrawler运行结束前被调用,可以执行一些资源释放之类的工作。
相对而言,CrawlController的调用就比较格式化了。一般地,它的调用代码如下:
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/~welling/"); controller.addSeed("http://www.ics.uci.edu/~lopes/"); 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);
CrawlController自带多线程功能,start方法中的第二个参数numberOfCrawlers即是同时开启的线程数。
另外,由于CrawlController对WebCrawler特殊的调用方式——反射(上述代码最后一行),因此WebCrawler的实现类必须拥有无参的构造方法,且有参的构造方法不会生效。对WebCrawler的实现类的私有成员的赋值需要通过静态方法来实现,示例参见crawler4j提供的例子:Image Crawler
更多信息请参见crawler4j的代码和示例。
2. jsoup基础
jsoup是一个基于Java的开源HTML解析器,其官网地址如下:
jsoup最大的特点,或者说,它比使用DOM4J进行HTML解析更好的原因,是它可以采用jQuery选择器的语法。
例如:
Document doc = Jsoup.connect("http://en.wikipedia.org/").get(); Elements newsHeadlines = doc.select("#mp-itn b a");
上述代码就是获取了http://en.wikipedia.org/页面中id为mp-itn的元素下的<b>标签中的<a>标签,与jQuery选择器的结果一致。
更多jsoup的使用方法请参见jsoup的示例(在主页的右侧Cookbook Content中)。
需要特别说明的是,jsoup中主要有三种操作对象:Document、Elements及Element。其中:
- Document继承自Element类,它包含页面中的全部数据,通过Jsoup类的静态方法获得;
- Elements是Element的集合类;
- Element是页面元素的实体类,包含了诸多操作页面元素的方法,其中除了类似于jQuery选择器的select方法外,还有大量类似于JS和jQuery的对DOM元素进行操作的方法,如getElementById,text,addClass,等等。
3. javacsv基础
javacsv是一个基于Java的开源CSV文件读写工具,其官方地址如下:
http://www.csvreader.com/java_csv.php
CSV文件的读写其实很简单,可以自己实现,网上也有诸多示例。使用javacsv的原因在于其代码简洁易用。
javacsv的使用示例参见其官方示例:
http://www.csvreader.com/java_csv_samples.php
需要说明的是,读写CSV文件时,若存在中文,请尽量使用FileReader(读)及FileWriter(写),而非FileInputStream和FileOutputStream,以免出现乱码。
4. 爬虫实践
下面的实践的目标是爬取搜车网的全部二手车信息,并作为CSV文件输出。代码如下:
Maven pom.xml
<dependency> <groupId>edu.uci.ics</groupId> <artifactId>crawler4j</artifactId> <version>3.5</version> <type>jar</type> <scope>compile</scope> </dependency> <dependency> <groupId>org.jsoup</groupId> <artifactId>jsoup</artifactId> <version>1.7.3</version> </dependency> <dependency> <groupId>net.sourceforge.javacsv</groupId> <artifactId>javacsv</artifactId> <version>2.0</version> </dependency>
MyCrawler.java
import java.io.File; import java.io.FileWriter; import java.io.IOException; import java.util.regex.Pattern; import org.jsoup.Jsoup; import org.jsoup.nodes.Document; import org.jsoup.nodes.Element; import org.jsoup.select.Elements; import com.csvreader.CsvWriter; import edu.uci.ics.crawler4j.crawler.Page; import edu.uci.ics.crawler4j.crawler.WebCrawler; import edu.uci.ics.crawler4j.parser.HtmlParseData; import edu.uci.ics.crawler4j.url.WebURL; public class MyCrawler extends WebCrawler { private final static Pattern FILTERS = Pattern .compile(".*(\\.(css|js|bmp|gif|jpe?g|ico" + "|png|tiff?|mid|mp2|mp3|mp4" + "|wav|avi|mov|mpeg|ram|m4v|pdf" + "|rm|smil|wmv|swf|wma|zip|rar|gz))$"); private final static String URL_PREFIX = "http://www.souche.com/pages/onsale/sale_car_list.html?"; private final static Pattern URL_PARAMS_PATTERN = Pattern .compile("carbrand=brand-\\d+(&index=\\d+)?"); private final static String CSV_PATH = "data/crawl/data.csv"; private CsvWriter cw; private File csv; public MyCrawler() throws IOException { csv = new File(CSV_PATH); if (csv.isFile()) { csv.delete(); } cw = new CsvWriter(new FileWriter(csv, true), ‘,‘); cw.write("title"); cw.write("brand"); cw.write("newPrice"); cw.write("oldPrice"); cw.write("mileage"); cw.write("age"); cw.write("stage"); cw.endRecord(); cw.close(); } /** * You should implement this function to specify whether the given url * should be crawled or not (based on your crawling logic). */ @Override public boolean shouldVisit(WebURL url) { String href = url.getURL().toLowerCase(); if (FILTERS.matcher(href).matches() || !href.startsWith(URL_PREFIX)) { return false; } String[] strs = href.split("\\?"); if (strs.length < 2) { return false; } if (!URL_PARAMS_PATTERN.matcher(strs[1]).matches()) { return false; } return true; } /** * 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(); if (page.getParseData() instanceof HtmlParseData) { HtmlParseData htmlParseData = (HtmlParseData) page.getParseData(); String html = htmlParseData.getHtml(); Document doc = Jsoup.parse(html); String brand = doc.select("div.choose_item").first().text(); Elements contents = doc.select("div.list_content"); if (contents.size() == 20 && !url.contains("index=")) { return; } else { System.out.println("URL: " + url); } for (Element c : contents) { Element info = c.select(".list_content_carInfo").first(); String title = info.select("h1").first().text(); Elements prices = info.select(".list_content_price div"); String newPrice = prices.get(0).text(); String oldPrice = prices.get(1).text(); Elements others = info.select(".list_content_other div"); String mileage = others.get(0).select("ins").first().text(); String age = others.get(1).select("ins").first().text(); String stage = "unknown"; if (c.select("i.car_tag_zhijian").size() != 0) { stage = c.select("i.car_tag_zhijian").text(); } else if (c.select("i.car_tag_yushou").size() != 0) { stage = "presell"; } try { cw = new CsvWriter(new FileWriter(csv, true), ‘,‘); cw.write(title); cw.write(brand); cw.write(newPrice.replaceAll("[¥万]", "")); cw.write(oldPrice.replaceAll("[¥万]", "")); cw.write(mileage); cw.write(age); cw.write(stage); cw.endRecord(); cw.close(); } catch (IOException e) { e.printStackTrace(); } } } } }
Controller.java
import edu.uci.ics.crawler4j.crawler.CrawlConfig; import edu.uci.ics.crawler4j.crawler.CrawlController; import edu.uci.ics.crawler4j.fetcher.PageFetcher; import edu.uci.ics.crawler4j.robotstxt.RobotstxtConfig; import edu.uci.ics.crawler4j.robotstxt.RobotstxtServer; 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/~welling/"); controller.addSeed("http://www.ics.uci.edu/~lopes/"); 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); } }
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