Java网络爬虫怎么实现？ java 网络爬虫怎么实现
java \u7f51\u7edc\u722c\u866b\u600e\u4e48\u5b9e\u73b0\uff1f1\u3001\u5728\u6253\u5f00\u7684ie\u6d4f\u89c8\u5668\u7a97\u53e3\u53f3\u4e0a\u65b9\u70b9\u51fb\u9f7f\u8f6e\u56fe\u6807\uff0c\u9009\u62e9\u201cInternet\u9009\u9879\u201d\uff0c\u5982\u4e0b\u56fe\u6240\u793a\uff1a
2\u3001\u5728\u6253\u5f00\u7684Internet\u9009\u9879\u7a97\u53e3\u4e2d\uff0c\u5207\u6362\u5230\u5b89\u5168\u680f\uff0c\u5728\u5b89\u5168\u9009\u5361\u4e2d\u70b9\u51fb\u201c\u81ea\u5b9a\u4e49\u7ea7\u522b\u201d\uff0c\u5982\u4e0b\u56fe\u6240\u793a\uff1a
3\u3001\u5728\u201c\u5b89\u5168\u8bbe\u7f6e-Internet \u533a\u57df\u201d\u754c\u9762\u627e\u5230\u201cJava \u5c0f\u7a0b\u5e8f\u811a\u672c\u201d\u3001\u201c\u6d3b\u52a8\u811a\u672c\u201d\uff0c\u5e76\u5c06\u8fd9\u4e24\u4e2a\u9009\u9879\u90fd\u9009\u62e9\u4e3a\u201c\u7981\u7528\u201d\uff0c\u7136\u540e\u70b9\u51fb\u786e\u5b9a,\u5982\u4e0b\u56fe\u6240\u793a\uff1a
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\u3000\u3000\u4ee5\u4e0b\u662f\u4e00\u4e2a\u4f7f\u7528java\u5b9e\u73b0\u7684\u7b80\u5355\u722c\u866b\u6838\u5fc3\u4ee3\u7801\uff1a\u3000\u3000
public void crawl() throws Throwable {
while (continueCrawling()) {
CrawlerUrl url = getNextUrl(); //\u83b7\u53d6\u5f85\u722c\u53d6\u961f\u5217\u4e2d\u7684\u4e0b\u4e00\u4e2aURL
if (url != null) {
printCrawlInfo();
String content = getContent(url); //\u83b7\u53d6URL\u7684\u6587\u672c\u4fe1\u606f
//\u805a\u7126\u722c\u866b\u53ea\u722c\u53d6\u4e0e\u4e3b\u9898\u5185\u5bb9\u76f8\u5173\u7684\u7f51\u9875\uff0c\u8fd9\u91cc\u91c7\u7528\u6b63\u5219\u5339\u914d\u7b80\u5355\u5904\u7406
if (isContentRelevant(content, this.regexpSearchPattern)) {
saveContent(url, content); //\u4fdd\u5b58\u7f51\u9875\u81f3\u672c\u5730
//\u83b7\u53d6\u7f51\u9875\u5185\u5bb9\u4e2d\u7684\u94fe\u63a5\uff0c\u5e76\u653e\u5165\u5f85\u722c\u53d6\u961f\u5217\u4e2d
Collection urlStrings = extractUrls(content, url);
addUrlsToUrlQueue(url, urlStrings);
} else {
System.out.println(url + " is not relevant ignoring ...");
}
//\u5ef6\u65f6\u9632\u6b62\u88ab\u5bf9\u65b9\u5c4f\u853d
Thread.sleep(this.delayBetweenUrls);
}
}
closeOutputStream();
}
private CrawlerUrl getNextUrl() throws Throwable {
CrawlerUrl nextUrl = null;
while ((nextUrl == null) && (!urlQueue.isEmpty())) {
CrawlerUrl crawlerUrl = this.urlQueue.remove();
//doWeHavePermissionToVisit\uff1a\u662f\u5426\u6709\u6743\u9650\u8bbf\u95ee\u8be5URL\uff0c\u53cb\u597d\u7684\u722c\u866b\u4f1a\u6839\u636e\u7f51\u7ad9\u63d0\u4f9b\u7684"Robot.txt"\u4e2d\u914d\u7f6e\u7684\u89c4\u5219\u8fdb\u884c\u722c\u53d6
//isUrlAlreadyVisited\uff1aURL\u662f\u5426\u8bbf\u95ee\u8fc7\uff0c\u5927\u578b\u7684\u641c\u7d22\u5f15\u64ce\u5f80\u5f80\u91c7\u7528BloomFilter\u8fdb\u884c\u6392\u91cd\uff0c\u8fd9\u91cc\u7b80\u5355\u4f7f\u7528HashMap
//isDepthAcceptable\uff1a\u662f\u5426\u8fbe\u5230\u6307\u5b9a\u7684\u6df1\u5ea6\u4e0a\u9650\u3002\u722c\u866b\u4e00\u822c\u91c7\u53d6\u5e7f\u5ea6\u4f18\u5148\u7684\u65b9\u5f0f\u3002\u4e00\u4e9b\u7f51\u7ad9\u4f1a\u6784\u5efa\u722c\u866b\u9677\u9631\uff08\u81ea\u52a8\u751f\u6210\u4e00\u4e9b\u65e0\u6548\u94fe\u63a5\u4f7f\u722c\u866b\u9677\u5165\u6b7b\u5faa\u73af\uff09\uff0c\u91c7\u7528\u6df1\u5ea6\u9650\u5236\u52a0\u4ee5\u907f\u514d
if (doWeHavePermissionToVisit(crawlerUrl)
&& (!isUrlAlreadyVisited(crawlerUrl))
&& isDepthAcceptable(crawlerUrl)) {
nextUrl = crawlerUrl;
// System.out.println("Next url to be visited is " + nextUrl);
}
}
return nextUrl;
}
private String getContent(CrawlerUrl url) throws Throwable {
//HttpClient4.1\u7684\u8c03\u7528\u4e0e\u4e4b\u524d\u7684\u65b9\u5f0f\u4e0d\u540c
HttpClient client = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url.getUrlString());
StringBuffer strBuf = new StringBuffer();
HttpResponse response = client.execute(httpGet);
if (HttpStatus.SC_OK == response.getStatusLine().getStatusCode()) {
HttpEntity entity = response.getEntity();
if (entity != null) {
BufferedReader reader = new BufferedReader(
new InputStreamReader(entity.getContent(), "UTF-8"));
String line = null;
if (entity.getContentLength() > 0) {
strBuf = new StringBuffer((int) entity.getContentLength());
while ((line = reader.readLine()) != null) {
strBuf.append(line);
}
}
}
if (entity != null) {
nsumeContent();
}
}
//\u5c06url\u6807\u8bb0\u4e3a\u5df2\u8bbf\u95ee
markUrlAsVisited(url);
return strBuf.toString();
}
public static boolean isContentRelevant(String content,
Pattern regexpPattern) {
boolean retValue = false;
if (content != null) {
//\u662f\u5426\u7b26\u5408\u6b63\u5219\u8868\u8fbe\u5f0f\u7684\u6761\u4ef6
Matcher m = regexpPattern.matcher(content.toLowerCase());
retValue = m.find();
}
return retValue;
}
public List extractUrls(String text, CrawlerUrl crawlerUrl) {
Map urlMap = new HashMap();
extractHttpUrls(urlMap, text);
extractRelativeUrls(urlMap, text, crawlerUrl);
return new ArrayList(urlMap.keySet());
}
private void extractHttpUrls(Map urlMap, String text) {
Matcher m = (text);
while (m.find()) {
String url = m.group();
String[] terms = url.split("a href=\"");
for (String term : terms) {
// System.out.println("Term = " + term);
if (term.startsWith("http")) {
int index = term.indexOf("\"");
if (index > 0) {
term = term.substring(0, index);
}
urlMap.put(term, term);
System.out.println("Hyperlink: " + term);
}
}
}
}
private void extractRelativeUrls(Map urlMap, String text,
CrawlerUrl crawlerUrl) {
Matcher m = relativeRegexp.matcher(text);
URL textURL = crawlerUrl.getURL();
String host = textURL.getHost();
while (m.find()) {
String url = m.group();
String[] terms = url.split("a href=\"");
for (String term : terms) {
if (term.startsWith("/")) {
int index = term.indexOf("\"");
if (index > 0) {
term = term.substring(0, index);
}
String s = //" + host + term;
urlMap.put(s, s);
System.out.println("Relative url: " + s);
}
}
}
}
public static void main(String[] args) {
try {
String url = "";
Queue urlQueue = new LinkedList();
String regexp = "java";
urlQueue.add(new CrawlerUrl(url, 0));
NaiveCrawler crawler = new NaiveCrawler(urlQueue, 100, 5, 1000L,
regexp);
// boolean allowCrawl = crawler.areWeAllowedToVisit(url);
// System.out.println("Allowed to crawl: " + url + " " +
// allowCrawl);
crawler.crawl();
} catch (Throwable t) {
System.out.println(t.toString());
t.printStackTrace();
}
}
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。
以下是一个使用java实现的简单爬虫核心代码：
public void crawl() throws Throwable {
while (continueCrawling()) {
CrawlerUrl url = getNextUrl(); //获取待爬取队列中的下一个URL
if (url != null) {
printCrawlInfo();
String content = getContent(url); //获取URL的文本信息
//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
if (isContentRelevant(content, this.regexpSearchPattern)) {
saveContent(url, content); //保存网页至本地
//获取网页内容中的链接，并放入待爬取队列中
Collection urlStrings = extractUrls(content, url);
addUrlsToUrlQueue(url, urlStrings);
} else {
System.out.println(url + " is not relevant ignoring ...");
}
//延时防止被对方屏蔽
Thread.sleep(this.delayBetweenUrls);
}
}
closeOutputStream();
}
private CrawlerUrl getNextUrl() throws Throwable {
CrawlerUrl nextUrl = null;
while ((nextUrl == null) && (!urlQueue.isEmpty())) {
CrawlerUrl crawlerUrl = this.urlQueue.remove();
//doWeHavePermissionToVisit：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
//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
//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
if (doWeHavePermissionToVisit(crawlerUrl)
&& (!isUrlAlreadyVisited(crawlerUrl))
&& isDepthAcceptable(crawlerUrl)) {
nextUrl = crawlerUrl;
// System.out.println("Next url to be visited is " + nextUrl);
}
}
return nextUrl;
}
private String getContent(CrawlerUrl url) throws Throwable {
//HttpClient4.1的调用与之前的方式不同
HttpClient client = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url.getUrlString());
StringBuffer strBuf = new StringBuffer();
HttpResponse response = client.execute(httpGet);
if (HttpStatus.SC_OK == response.getStatusLine().getStatusCode()) {
HttpEntity entity = response.getEntity();
if (entity != null) {
BufferedReader reader = new BufferedReader(
new InputStreamReader(entity.getContent(), "UTF-8"));
String line = null;
if (entity.getContentLength() > 0) {
strBuf = new StringBuffer((int) entity.getContentLength());
while ((line = reader.readLine()) != null) {
strBuf.append(line);
}
}
}
if (entity != null) {
nsumeContent();
}
}
//将url标记为已访问
markUrlAsVisited(url);
return strBuf.toString();
}
public static boolean isContentRelevant(String content,
Pattern regexpPattern) {
boolean retValue = false;
if (content != null) {
//是否符合正则表达式的条件
Matcher m = regexpPattern.matcher(content.toLowerCase());
retValue = m.find();
}
return retValue;
}
public List extractUrls(String text, CrawlerUrl crawlerUrl) {
Map urlMap = new HashMap();
extractHttpUrls(urlMap, text);
extractRelativeUrls(urlMap, text, crawlerUrl);
return new ArrayList(urlMap.keySet());
}
private void extractHttpUrls(Map urlMap, String text) {
Matcher m = (text);
while (m.find()) {
String url = m.group();
String[] terms = url.split("a href=\"");
for (String term : terms) {
// System.out.println("Term = " + term);
if (term.startsWith("http")) {
int index = term.indexOf("\"");
if (index > 0) {
term = term.substring(0, index);
}
urlMap.put(term, term);
System.out.println("Hyperlink: " + term);
}
}
}
}
private void extractRelativeUrls(Map urlMap, String text,
CrawlerUrl crawlerUrl) {
Matcher m = relativeRegexp.matcher(text);
URL textURL = crawlerUrl.getURL();
String host = textURL.getHost();
while (m.find()) {
String url = m.group();
String[] terms = url.split("a href=\"");
for (String term : terms) {
if (term.startsWith("/")) {
int index = term.indexOf("\"");
if (index > 0) {
term = term.substring(0, index);
}
String s = //" + host + term;
urlMap.put(s, s);
System.out.println("Relative url: " + s);
}
}
}
}
public static void main(String[] args) {
try {
String url = "";
Queue urlQueue = new LinkedList();
String regexp = "java";
urlQueue.add(new CrawlerUrl(url, 0));
NaiveCrawler crawler = new NaiveCrawler(urlQueue, 100, 5, 1000L,
regexp);
// boolean allowCrawl = crawler.areWeAllowedToVisit(url);
// System.out.println("Allowed to crawl: " + url + " " +
// allowCrawl);
crawler.crawl();
} catch (Throwable t) {
System.out.println(t.toString());
t.printStackTrace();
}
}
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