The first step is to implement LinkQueue and filter and store urls.
import java.util.ArrayList; import java.util.Collections; import java.util.HashSet; import java.util.List; import java.util.Set; public class LinkQueue { // Accessed url collection private static Set<String> visitedUrl = Collections.synchronizedSet(new HashSet<String>()); // Unaccessed url private static List<String> unVisitedUrl = Collections.synchronizedList(new ArrayList<String>()); // Unvisited URLs are out of the queue public static String unVisitedUrlDeQueue() { if (unVisitedUrl.size() > 0) { String url = unVisitedUrl.remove(0); visitedUrl.add(url); return url; } return null; } // Verify when a new url is added, ensuring that it is only added once public static void addUnvisitedUrl(String url) { if (url != null && !url.trim().equals("") && !visitedUrl.contains(url) && !unVisitedUrl.contains(url)) unVisitedUrl.add(url); } // Determine whether the unvisited URL queue is empty public static boolean unVisitedUrlsEmpty() { return unVisitedUrl.isEmpty(); } }The second step is to collect the links under each URL and filter to generate new links.
import java.util.HashSet; import java.util.Set; import org.htmlparser.Node; import org.htmlparser.NodeFilter; import org.htmlparser.Parser; import org.htmlparser.filters.NodeClassFilter; import org.htmlparser.filters.OrFilter; import org.htmlparser.tags.LinkTag; import org.htmlparser.util.NodeList; import org.htmlparser.util.ParserException; /** * Filter http's url to get urls that can comply with the rules * @author Administrator * */ public class ParserHttpUrl { // Get a link on a website, filter is used to filter links public static Set<String> extracLinks(String url, LinkFilter filter) { Set<String> links = new HashSet<String>(); try { Parser parser = new Parser(url); // Filter the filter of the <frame> tag to extract the link represented by the src attribute in the frame tag NodeFilter frameFilter = new NodeFilter() { public boolean accept(Node node) { if (node.getText().startsWith("frame src=")) { return true; } else { return false; } } } }; // OrFilter to set filtering <a> tags, and <frame> tags OrFilter linkFilter = new OrFilter(new NodeClassFilter( LinkTag.class), frameFilter); // Get all filtered tags NodeList list = parser.extractAllNodesThatMatch(linkFilter); for (int i = 0; i < list.size(); i++) { Node tag = list.elementAt(i); if (tag instanceof LinkTag)// <a> Tag { LinkTag link = (LinkTag) tag; String linkUrl = link.getLink();// url if (filter.accept(linkUrl)) links.add(linkUrl); } else// <frame> Tag { // Extract the link to the src attribute in the frame, such as <frame src="test.html"/> String frame = tag.getText(); int start = frame.indexOf("src="); frame = frame.substring(start); int end = frame.indexOf(" "); if (end == -1) end = frame.indexOf(">"); String frameUrl = frame.substring(5, end - 1); if (filter.accept(frameUrl)) links.add(frameUrl); } } catch (ParserException e) { e.printStackTrace(); } return links; } }Step 3: Implement the image download function
import java.io.File; import java.io.FileOutputStream; import java.io.InputStream; import java.net.URL; import java.net.URLConnection; import java.util.ArrayList; import java.util.List; import java.util.regex.Matcher; import java.util.regex.Pattern; /*** * java crawl network pictures* * @author swinglife * */ public class DownloadPic { // Encoding private static final String ECODING = "UTF-8"; // Get the img tag regular private static final String IMGURL_REG = "<img.*src=(.*?)[^>]*?>"; // Get the regular private static final String IMGSRC_REG = "http:/"?(.*?)(/"|>|//s+)"; public static void downloadPic(String url) { // Get the html text content String HTML = null; try { HTML = DownloadPic.getHTML(url); } catch (Exception e) { e.printStackTrace(); } if (null != HTML && !"".equals(HTML)) { // Get the image tag List<String> imgUrl = DownloadPic.getImageUrl(HTML); // Get the image src address List<String> imgSrc = DownloadPic.getImageSrc(imgUrl); // Download the image DownloadLoadPic.download(imgSrc); } } /*** * Get HTML content* * @param url * @return * @throws Exception */ private static String getHTML(String url) throws Exception { URL uri = new URL(url); URLConnection connection = uri.openConnection(); InputStream in = connection.getInputStream(); byte[] buf = new byte[1024]; int length = 0; StringBuffer sb = new StringBuffer(); while ((length = in.read(buf, 0, buf.length)) > 0) { sb.append(new String(buf, ECODING)); } in.close(); return sb.toString(); } /*** * Get ImageUrl address* * @param HTML * @return */ private static List<String> getImageUrl(String HTML) { Matcher matcher = Pattern.compile(IMGURL_REG).matcher(HTML); List<String> listImgUrl = new ArrayList<String>(); while (matcher.find()) { listImgUrl.add(matcher.group()); } return listImgUrl; } /*** * Get ImageSrc address* * @param listImageUrl * @return */ private static List<String> getImageSrc(List<String> listImageUrl) { List<String> listImgSrc = new ArrayList<String>(); for (String image : listImageUrl) { Matcher matcher = Pattern.compile(IMGSRC_REG).matcher(image); while (matcher.find()) { listImgSrc.add(matcher.group().substring(0, matcher.group().length() - 1)); } } return listImgSrc; } /*** * Download image* * @param listImgSrc */ private static void download(List<String> listImgSrc) { for (String url : listImgSrc) { try { String imageName = url.substring(url.lastIndexOf("/") + 1, url.length()); URL uri = new URL(url); InputStream in = uri.openStream(); FileOutputStream fo = new FileOutputStream(new File(imageName)); byte[] buf = new byte[1024]; int length = 0; while ((length = in.read(buf, 0, buf.length)) != -1) { fo.write(buf, 0, length); } in.close(); fo.close(); } catch (Exception e) { e.printStackTrace(); } } } }Real Filter interface, define filter interface:
public interface Filter { public boolean accept(String url); }Step 4: Implementation of filtering rules:
public class Crawler { /** * Crawl process* * @return * @param seeds */ public void crawling(String url) { // Define filter Filter filter = new Filter() { public boolean accept(String url) { //The filtering rules here are changed according to the rules of the websites that need to be crawled. It is recommended to use regular implementation. I am crawling Douban website if(url.indexOf("douban.com/group/topic") != -1 || url.indexOf("douban.com/group/haixiuzu/discussion?start") != -1 ) return true; else return false; } }; // Initialize URL queue LinkQueue.addUnvisitedUrl(url); // Loop condition, the link to be crawled is not empty while (!LinkQueue.unVisitedUrlsEmpty()) { // The header URL exits the queue String visitUrl = (String) LinkQueue.unVisitedUrlDeQueue(); if (visitUrl == null) continue; DownloadLoadPic.downloadPic(visitUrl); // Extract the URL from the downloaded web page Set<String> links = ParserHttpUrl.extracLinks(visitUrl, filter); // New unvisited URL enqueue for (String link : links) { LinkQueue.addUnvisedUrl(link); } } } // main method entry public static void main(String[] args) { Crawler crawler = new Crawler(); crawler.crawling("http://www.douban.com/group/haixiuzu/discussion?start=0"); } }Summarize
The above is the example code for Java implementation of crawling website pictures introduced by the editor. I hope it will be helpful to everyone. If you have any questions, please leave me a message and the editor will reply to everyone in time. Thank you very much for your support to Wulin.com website!