Question

我正在尝试在crawler4j中使用Basic爬虫示例。我从crawler4j网站here获取了代码。

package edu.crawler;

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;
import java.util.List;
import java.util.regex.Pattern;
import org.apache.http.Header;

public class MyCrawler extends WebCrawler {

    private final static Pattern FILTERS = Pattern.compile(".*(\\.(css|js|bmp|gif|jpe?g" + "|png|tiff?|mid|mp2|mp3|mp4"
                    + "|wav|avi|mov|mpeg|ram|m4v|pdf" + "|rm|smil|wmv|swf|wma|zip|rar|gz))$");

    /**
     * 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();
            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) {
            int docid = page.getWebURL().getDocid();
            String url = page.getWebURL().getURL();
            String domain = page.getWebURL().getDomain();
            String path = page.getWebURL().getPath();
            String subDomain = page.getWebURL().getSubDomain();
            String parentUrl = page.getWebURL().getParentUrl();
            String anchor = page.getWebURL().getAnchor();

            System.out.println("Docid: " + docid);
            System.out.println("URL: " + url);
            System.out.println("Domain: '" + domain + "'");
            System.out.println("Sub-domain: '" + subDomain + "'");
            System.out.println("Path: '" + path + "'");
            System.out.println("Parent page: " + parentUrl);
            System.out.println("Anchor text: " + anchor);

            if (page.getParseData() instanceof HtmlParseData) {
                    HtmlParseData htmlParseData = (HtmlParseData) page.getParseData();
                    String text = htmlParseData.getText();
                    String html = htmlParseData.getHtml();
                    List<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());
            }

            Header[] responseHeaders = page.getFetchResponseHeaders();
            if (responseHeaders != null) {
                    System.out.println("Response headers:");
                    for (Header header : responseHeaders) {
                            System.out.println("\t" + header.getName() + ": " + header.getValue());
                    }
            }

            System.out.println("=============");
    }
}

以上是示例中抓取器类的代码。

public class Controller {

    public static void main(String[] args) throws Exception {
            String crawlStorageFolder = "../data/";
            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);
    }
}

以上是Web爬网程序的控制器类的类。当我尝试从IDE（Intellij）运行Controller类时，我收到以下错误：

Exception in thread "main" java.lang.UnsupportedClassVersionError: edu/uci/ics/crawler4j/crawler/CrawlConfig : Unsupported major.minor version 51.0

我应该知道找到here的maven配置吗？我必须使用其他版本吗？

Answer 1

问题不在于crawler4j。问题是我使用的Java版本与crawler4j中使用的Java的最新版本不同。我在更新到Java 7之前切换了版本，一切正常。我猜测将我的Java版本升级到7会产生同样的效果。

为什么crawler4j示例会出错？

1 个答案: