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java爬虫代码怎么实现 java实现爬虫技术( 三 )

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Java网络爬虫怎么实现？网络爬虫是一个自动提取网页java爬虫代码怎么实现的程序java爬虫代码怎么实现 ， 它为搜索引擎从万维网上下载网页java爬虫代码怎么实现 ， 是搜索引擎的重要组成 。\x0d\x0a传统爬虫从一个或若干初始网页的URL开始，获得初始网页上的URL ， 在抓取网页的过程中，不断从当前页面上抽取新的URL放入队列，直到满足系统的一定停止条件 。对于垂直搜索来说，聚焦爬虫 ， 即有针对性地爬取特定主题网页的爬虫 ， 更为适合 。\x0d\x0a\x0d\x0a以下是一个使用java实现的简单爬虫核心代码java爬虫代码怎么实现：\x0d\x0apublic void crawl() throws Throwable {\x0d\x0awhile (continueCrawling()) {\x0d\x0aCrawlerUrl url = getNextUrl(); //获取待爬取队列中的下一个URL\x0d\x0aif (url != null) {\x0d\x0aprintCrawlInfo();\x0d\x0aString content = getContent(url); //获取URL的文本信息\x0d\x0a\x0d\x0a//聚焦爬虫只爬取与主题内容相关的网页，这里采用正则匹配简单处理\x0d\x0aif (isContentRelevant(content, this.regexpSearchPattern)) {\x0d\x0asaveContent(url, content); //保存网页至本地\x0d\x0a\x0d\x0a//获取网页内容中的链接，并放入待爬取队列中\x0d\x0aCollection urlStrings = extractUrls(content, url);\x0d\x0aaddUrlsToUrlQueue(url, urlStrings);\x0d\x0a} else {\x0d\x0aSystem.out.println(url + " is not relevant ignoring ...");\x0d\x0a}\x0d\x0a\x0d\x0a//延时防止被对方屏蔽\x0d\x0aThread.sleep(this.delayBetweenUrls);\x0d\x0a}\x0d\x0a}\x0d\x0acloseOutputStream();\x0d\x0a}\x0d\x0aprivate CrawlerUrl getNextUrl() throws Throwable {\x0d\x0aCrawlerUrl nextUrl = null;\x0d\x0awhile ((nextUrl == null)(!urlQueue.isEmpty())) {\x0d\x0aCrawlerUrl crawlerUrl = this.urlQueue.remove();\x0d\x0a//doWeHavePermissionToVisitjava爬虫代码怎么实现：是否有权限访问该URL ， 友好的爬虫会根据网站提供的"Robot.txt"中配置的规则进行爬取\x0d\x0a//isUrlAlreadyVisited：URL是否访问过 ， 大型的搜索引擎往往采用BloomFilter进行排重，这里简单使用HashMap\x0d\x0a//isDepthAcceptable：是否达到指定的深度上限 。爬虫一般采取广度优先的方式 。一些网站会构建爬虫陷阱（自动生成一些无效链接使爬虫陷入死循环），采用深度限制加以避免\x0d\x0aif (doWeHavePermissionToVisit(crawlerUrl)\x0d\x0a(!isUrlAlreadyVisited(crawlerUrl))\x0d\x0aisDepthAcceptable(crawlerUrl)) {\x0d\x0anextUrl = crawlerUrl;\x0d\x0a// System.out.println("Next url to be visited is " + nextUrl);\x0d\x0a}\x0d\x0a}\x0d\x0areturn nextUrl;\x0d\x0a}\x0d\x0aprivate String getContent(CrawlerUrl url) throws Throwable {\x0d\x0a//HttpClient4.1的调用与之前的方式不同\x0d\x0aHttpClient client = new DefaultHttpClient();\x0d\x0aHttpGet httpGet = new HttpGet(url.getUrlString());\x0d\x0aStringBuffer strBuf = new StringBuffer();\x0d\x0aHttpResponse response = client.execute(httpGet);\x0d\x0aif (HttpStatus.SC_OK == response.getStatusLine().getStatusCode()) {\x0d\x0aHttpEntity entity = response.getEntity();\x0d\x0aif (entity != null) {\x0d\x0aBufferedReader reader = new BufferedReader(\x0d\x0anew InputStreamReader(entity.getContent(), "UTF-8"));\x0d\x0aString line = null;\x0d\x0aif (entity.getContentLength()0) {\x0d\x0astrBuf = new StringBuffer((int) entity.getContentLength());\x0d\x0awhile ((line = reader.readLine()) != null) {\x0d\x0astrBuf.append(line);\x0d\x0a}\x0d\x0a}\x0d\x0a}\x0d\x0aif (entity != null) {\x0d\x0ansumeContent();\x0d\x0a}\x0d\x0a}\x0d\x0a//将url标记为已访问\x0d\x0amarkUrlAsVisited(url);\x0d\x0areturn strBuf.toString();\x0d\x0a}\x0d\x0apublic static boolean isContentRelevant(String content,\x0d\x0aPattern regexpPattern) {\x0d\x0aboolean retValue = https://www.04ip.com/post/false;/x0d/x0aif (content != null) {/x0d/x0a//是否符合正则表达式的条件/x0d/x0aMatcher m = regexpPattern.matcher(content.toLowerCase());/x0d/x0aretValue = m.find();/x0d/x0a}/x0d/x0areturn retValue;/x0d/x0a}/x0d/x0apublic List extractUrls(String text, CrawlerUrl crawlerUrl) {/x0d/x0aMap urlMap = new HashMap();/x0d/x0aextractHttpUrls(urlMap, text);/x0d/x0aextractRelativeUrls(urlMap, text, crawlerUrl);/x0d/x0areturn new ArrayList(urlMap.keySet());/x0d/x0a}/x0d/x0aprivate void extractHttpUrls(Map urlMap, String text) {/x0d/x0aMatcher m = (text);/x0d/x0awhile (m.find()) {/x0d/x0aString url = m.group();/x0d/x0aString[] terms = url.split("a href=https://www.04ip.com/"");\x0d\x0afor (String term : terms) {\x0d\x0a// System.out.println("Term = " + term);\x0d\x0aif (term.startsWith("http")) {\x0d\x0aint index = term.indexOf("\"");\x0d\x0aif (index0) {\x0d\x0aterm = term.substring(0, index);\x0d\x0a}\x0d\x0aurlMap.put(term, term);\x0d\x0aSystem.out.println("Hyperlink: " + term);\x0d\x0a}\x0d\x0a}\x0d\x0a}\x0d\x0a}\x0d\x0aprivate void extractRelativeUrls(Map urlMap, String text,\x0d\x0aCrawlerUrl crawlerUrl) {\x0d\x0aMatcher m = relativeRegexp.matcher(text);\x0d\x0aURL textURL = crawlerUrl.getURL();\x0d\x0aString host = textURL.getHost();\x0d\x0awhile (m.find()) {\x0d\x0aString url = m.group();\x0d\x0aString[] terms = url.split("a href=https://www.04ip.com/"");\x0d\x0afor (String term : terms) {\x0d\x0aif (term.startsWith("/")) {\x0d\x0aint index = term.indexOf("\"");\x0d\x0aif (index0) {\x0d\x0aterm = term.substring(0, index);\x0d\x0a}\x0d\x0aString s = //" + host + term;\x0d\x0aurlMap.put(s, s);\x0d\x0aSystem.out.println("Relative url: " + s);\x0d\x0a}\x0d\x0a}\x0d\x0a}\x0d\x0a\x0d\x0a}\x0d\x0apublic static void main(String[] args) {\x0d\x0atry {\x0d\x0aString url = "";\x0d\x0aQueue urlQueue = new LinkedList();\x0d\x0aString regexp = "java";\x0d\x0aurlQueue.add(new CrawlerUrl(url, 0));\x0d\x0aNaiveCrawler crawler = new NaiveCrawler(urlQueue, 100, 5, 1000L,\x0d\x0aregexp);\x0d\x0a// boolean allowCrawl = crawler.areWeAllowedToVisit(url);\x0d\x0a// System.out.println("Allowed to crawl: " + url + " " +\x0d\x0a// allowCrawl);\x0d\x0acrawler.crawl();\x0d\x0a} catch (Throwable t) {\x0d\x0aSystem.out.println(t.toString());\x0d\x0at.printStackTrace();\x0d\x0a}\x0d\x0a}

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