jsoup - Grundlegendes Beispiel für Web-Crawler

        
            org.jsoup
            jsoup
            1.10.2
        

package com.example.basicwebcrawler;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import java.io.IOException;
import java.util.HashSet;

public class BasicWebCrawler {

    private HashSet links;

    public BasicWebCrawler() {
        links = new HashSet();
    }

    public void getPageLinks(String URL) {
        //4. Check if you have already crawled the URLs
        //(we are intentionally not checking for duplicate content in this example)
        if (!links.contains(URL)) {
            try {
                //4. (i) If not add it to the index
                if (links.add(URL)) {
                    System.out.println(URL);
                }

                //2. Fetch the HTML code
                Document document = Jsoup.connect(URL).get();
                //3. Parse the HTML to extract links to other URLs
                Elements linksOnPage = document.select("a[href]");

                //5. For each extracted URL... go back to Step 4.
                for (Element page : linksOnPage) {
                    getPageLinks(page.attr("abs:href"));
                }
            } catch (IOException e) {
                System.err.println("For '" + URL + "': " + e.getMessage());
            }
        }
    }

    public static void main(String[] args) {
        //1. Pick a URL from the frontier
        new BasicWebCrawler().getPageLinks("http://www.example.com/");
    }

}

http://www.example.com/
Android Tutorial

Android Tutorial

Java I/O Tutorial

Java I/O Tutorial

Java XML Tutorial

Java XML Tutorial

Java JSON Tutorial

Java JSON Tutorial

Java Regular Expression Tutorial

Java Regular Expression Tutorial

JDBC Tutorial

...(+ many more links)

package com.example.depthwebcrawler;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import java.io.IOException;
import java.util.HashSet;

public class WebCrawlerWithDepth {
    private static final int MAX_DEPTH = 2;
    private HashSet links;

    public WebCrawlerWithDepth() {
        links = new HashSet<>();
    }

    public void getPageLinks(String URL, int depth) {
        if ((!links.contains(URL) && (depth < MAX_DEPTH))) {
            System.out.println(">> Depth: " + depth + " [" + URL + "]");
            try {
                links.add(URL);

                Document document = Jsoup.connect(URL).get();
                Elements linksOnPage = document.select("a[href]");

                depth++;
                for (Element page : linksOnPage) {
                    getPageLinks(page.attr("abs:href"), depth);
                }
            } catch (IOException e) {
                System.err.println("For '" + URL + "': " + e.getMessage());
            }
        }
    }

    public static void main(String[] args) {
        new WebCrawlerWithDepth().getPageLinks("http://www.example.com/", 0);
    }
}

...
>> Depth: 1 [https://docs.gradle.org/current/userguide/userguide.html]
>> Depth: 1 [http://hibernate.org/orm/]
>> Depth: 1 [https://jax-ws.java.net/]
>> Depth: 1 [http://tomcat.apache.org/tomcat-8.0-doc/index.html]
>> Depth: 1 [http://www.javacodegeeks.com/]
For 'http://www.javacodegeeks.com/': HTTP error fetching URL
>> Depth: 1 [http://beust.com/weblog/]
>> Depth: 1 [https://dzone.com]
>> Depth: 1 [https://wordpress.org/]
>> Depth: 1 [http://www.liquidweb.com/?RID=example]
>> Depth: 1 [http://www.example.com/privacy-policy/]

package com.example.extractor;

package com.example;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

public class Extractor {
    private HashSet links;
    private List> articles;

    public Extractor() {
        links = new HashSet<>();
        articles = new ArrayList<>();
    }

    //Find all URLs that start with "http://www.example.com/page/" and add them to the HashSet
    public void getPageLinks(String URL) {
        if (!links.contains(URL)) {
            try {
                Document document = Jsoup.connect(URL).get();
                Elements otherLinks = document.select("a[href^=\"http://www.example.com/page/\"]");

                for (Element page : otherLinks) {
                    if (links.add(URL)) {
                        //Remove the comment from the line below if you want to see it running on your editor
                        System.out.println(URL);
                    }
                    getPageLinks(page.attr("abs:href"));
                }
            } catch (IOException e) {
                System.err.println(e.getMessage());
            }
        }
    }

    //Connect to each link saved in the article and find all the articles in the page
    public void getArticles() {
        links.forEach(x -> {
            Document document;
            try {
                document = Jsoup.connect(x).get();
                Elements articleLinks = document.select("h2 a[href^=\"http://www.example.com/\"]");
                for (Element article : articleLinks) {
                    //Only retrieve the titles of the articles that contain Java 8
                    if (article.text().matches("^.*?(Java 8|java 8|JAVA 8).*$")) {
                        //Remove the comment from the line below if you want to see it running on your editor,
                        //or wait for the File at the end of the execution
                        //System.out.println(article.attr("abs:href"));

                        ArrayList temporary = new ArrayList<>();
                        temporary.add(article.text()); //The title of the article
                        temporary.add(article.attr("abs:href")); //The URL of the article
                        articles.add(temporary);
                    }
                }
            } catch (IOException e) {
                System.err.println(e.getMessage());
            }
        });
    }

    public void writeToFile(String filename) {
        FileWriter writer;
        try {
            writer = new FileWriter(filename);
            articles.forEach(a -> {
                try {
                    String temp = "- Title: " + a.get(0) + " (link: " + a.get(1) + ")\n";
                    //display to console
                    System.out.println(temp);
                    //save to file
                    writer.write(temp);
                } catch (IOException e) {
                    System.err.println(e.getMessage());
                }
            });
            writer.close();
        } catch (IOException e) {
            System.err.println(e.getMessage());
        }
    }

    public static void main(String[] args) {
        Extractor bwc = new Extractor();
        bwc.getPageLinks("http://www.example.com");
        bwc.getArticles();
        bwc.writeToFile("Java 8 Articles");
    }
}