I'm writing a little crawler. What is the best way to download a web page's source html? I'm currently using little piece of code below but some times the result is just half of the page's source!!! I don't know what's the problem. Some people suggested that I should use Jsoup but using .get.html() function from Jsoup also returns half of the page's source if it's too long. Since I'm writing a crawler, it's very important that the method support unicode (UTF-8) and the efficiency is also very important. I wanted to know the best modern way to do it so I asked you guys since I'm new to Java. Thanks.
Code:
public static String downloadPage(String url)
{
try
{
URL pageURL = new URL(url);
StringBuilder text = new StringBuilder();
Scanner scanner = new Scanner(pageURL.openStream(), "utf-8");
try {
while (scanner.hasNextLine()){
text.append(scanner.nextLine() + NL);
}
}
finally{
scanner.close();
}
return text.toString();
}
catch(Exception ex)
{
return null;
}
}
I use commons-io String html = IOUtils.toString(url.openStream(), "utf-8");
Personally, I'm very pleased with the Apache HTTP library http://hc.apache.org/httpcomponents-client-ga/. If you're writing a web crawler, which I am also, you may greatly appreciate the control it gives over things like cookies and client sharing and the like.
Related
I am doing an assignment for one of my classes.
I am supposed to write a webcrawler that download files and images from a website given a specified crawl depth.
I am allowed to use third party parsing api so I am using Jsoup. I've also tried htmlparser. Both nice softwares but they are not perfect.
I used the default java URLConnection to check content type before processing the url but it becomes really slow as the number of links grows.
Question : Anyone know any specialized parser api for images and links ?
I could start writing mine using Jsoup but am being lazy. Besides why reinvent the wheel if there could be a working solution out there? Any help would be appreciated.
i need to check contentType while looping through the links to check if the link is to a file, in an effective way but Jsoup does not have what i need. Heres what i have:
**
HttpConnection mimeConn =null;
Response mimeResponse = null;
for(Element link: links){
String linkurl =link.absUrl("href");
if(!linkurl.contains("#")){
if(DownloadRepository.curlExists(link.absUrl("href"))){
continue;
}
mimeConn = (HttpConnection) Jsoup.connect(linkurl);
mimeConn.ignoreContentType(true);
mimeConn.ignoreHttpErrors(true);
mimeResponse =(Response) mimeConn.execute();
WebUrl webUrl = new WebUrl(linkurl,currentDepth+1);
String contentType = mimeResponse.contentType();
if(contentType.contains("html")){
page.addToCrawledPages(new WebPage(webUrl));
}else if(contentType.contains("image")){
page.addToImages(new WebImage(webUrl));
}else{
page.addToFiles(new WebFile(webUrl));
}
DownloadRepository.addCrawledURL(linkurl);
}**
UPDATE
Based on Yoshi's answer, I was able to get my code to work right. Here's the link:
https://github.com/unekwu/cs_nemesis/blob/master/crawler/crawler/src/cu/cs/cpsc215/project1/parser/Parser.java
Use jSoup i think this API is good enough for your purpose. Also you can find good Cookbook on this site.
Several steps:
Jsoup: how to get an image's absolute url?
how to download image from any web page in java
You can write your own recursion method which walk through links on page which contains nesessary domain name or relative links. Use this way to grab all links and find all images on it. Write it yourself it's not bad practice.
You don't need to use URLConnection class, jSoup have wrapper for it.
e.g
You can use only one line of code to get DOM object:
Document doc = Jsoup.connect("http://en.wikipedia.org/").get();
Instead of this code:
URL oracle = new URL("http://www.oracle.com/");
URLConnection yc = oracle.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(
yc.getInputStream()));
String inputLine;
while ((inputLine = in.readLine()) != null)
System.out.println(inputLine);
in.close();
Update1
try to add in your code next lines:
Connection.Response res = Jsoup.connect("http://en.wikipedia.org/").execute();
String pageContentType = res.contentType();
I have a problem once again where I cant find the source code because its hidden or something... When my java program indexes the page it finds everything but the info i need... I assume its hidden for a reason but is there anyway around this?
Its just a bunch of tr/td tags that show up in firebug but dont show up when viewing the page source or when i do below
URL url = new URL("my url");
URLConnection yc = url.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(yc.getInputStream()));
String inputLine;
while ((inputLine = in.readLine()) != null) {
I really have no idea how to attempt to get the info that i need...
The reason for this behavior is because probably those tags are dynamically injected into the DOM using javascript and are not part of the initial HTML which is what you can fetch with an URLConnection. They might even be created using AJAX. You will need a javascript interpreter on your server if you want to fetch those.
If they don't show up in the page source, they're likely being added dynamically by Javascript code. There's no way to get them from your server-side script short of including a javascript interpreter, which is rather high-overhead.
The information in the tags is presumably coming from somewhere, though. Why not track that down and grab it straight from there?
Try Using Jsoup.
Document doc = doc=Jsoup.parse("http:\\",10000);
System.out.print(doc.toString());
Assuming that the issue is that the "missing" content is being injected using javascript, the following SO Question is pertinent:
What's a good tool to screen-scrape with Javascript support?
i'm trying to get an entire WebPage through a URLConnection.
What's the most efficient way to do this?
I'm doing this already:
URL url = new URL("http://www.google.com/");
URLConnection connection;
connection = url.openConnection();
InputStream in = connection.getInputStream();
BufferedReader bf = new BufferedReader(new InputStreamReader(in));
StringBuffer html = new StringBuffer();
String line = bf.readLine();
while(line!=null){
html.append(line);
line = bf.readLine();
}
bf.close();
html has the entire HTML page.
I think this is the best way. The size of the page is fixed ("it is what it is"), so you can't improve on memory. Perhaps you can compress the contents once you have them, but they aren't very useful in that form. I would imagine that eventually you'll want to parse the HTML into a DOM tree.
Anything you do to parallelize the reading would overly complicate the solution.
I'd recommend using a StringBuilder with a default size of 2048 or 4096.
Why are you thinking that the code you posted isn't sufficient? You sound like you're guilty of premature optimization.
Run with what you have and sleep at night.
What do you want to do with the obtained HTML? Parse it? It may be good to know that a bit decent HTML parser can already have a constructor or method argument which takes straight an URL or InputStream so that you don't need to worry about streaming performance like that.
Assuming that all you want to do is described in your previous question, with for example Jsoup you could obtain all those news links extraordinary easy like follows:
Document document = Jsoup.connect("http://news.google.com.ar/nwshp?hl=es&tab=wn").get();
Elements newsLinks = document.select("h2.title a:eq(0)");
for (Element newsLink : newsLinks) {
System.out.println(newsLink.attr("href"));
}
This yields the following after only a few seconds:
http://www.infobae.com/mundo/541259-100970-0-Pinera-confirmo-que-el-rescate-comenzara-las-20-y-durara-24-y-48-horas
http://www.lagaceta.com.ar/nota/403112/Argentina/Boudou-disculpo-con-DAIA-pero-volvio-cuestionar-medios.html
http://www.abc.es/agencias/noticia.asp?noticia=550415
http://www.google.com/hostednews/epa/article/ALeqM5i6x9rhP150KfqGJvwh56O-thi4VA?docId=1383133
http://www.abc.es/agencias/noticia.asp?noticia=550292
http://www.univision.com/contentroot/wirefeeds/noticias/8307387.shtml
http://noticias.terra.com.ar/internacionales/ecuador-apoya-reclamo-argentino-por-ejercicios-en-malvinas,3361af2a712ab210VgnVCM4000009bf154d0RCRD.html
http://www.infocielo.com/IC/Home/index.php?ver_nota=22642
http://www.larazon.com.ar/economia/Cristina-Fernandez-Censo-indispensable-pais_0_176100098.html
http://www.infobae.com/finanzas/541254-101275-0-Energeticas-llevaron-la-Bolsa-portena-ganancias
http://www.telam.com.ar/vernota.php?tipo=N&idPub=200661&id=381154&dis=1&sec=1
http://www.ambito.com/noticia.asp?id=547722
http://www.canal-ar.com.ar/noticias/noticiamuestra.asp?Id=9469
http://www.pagina12.com.ar/diario/cdigital/31-154760-2010-10-12.html
http://www.lanacion.com.ar/nota.asp?nota_id=1314014
http://www.rpp.com.pe/2010-10-12-ganador-del-pulitzer-destaca-nobel-de-mvll-noticia_302221.html
http://www.lanueva.com/hoy/nota/b44a7553a7/1/79481.html
http://www.larazon.com.ar/show/sdf_0_176100096.html
http://www.losandes.com.ar/notas/2010/10/12/batista-siento-comodo-dieron-respaldo-520595.asp
http://deportes.terra.com.ar/futbol/los-rumores-empiezan-a-complicar-la-vida-de-river-y-vuelve-a-sonar-gallego,a24483b8702ab210VgnVCM20000099f154d0RCRD.html
http://www.clarin.com/deportes/futbol/Exigieron-Roman-regreso-Huracan_0_352164993.html
http://www.el-litoral.com.ar/leer_noticia.asp?idnoticia=146622
http://www.nuevodiarioweb.com.ar/nota/181453/Locales/C%C3%A1ncer_mama:_200_casos_a%C3%B1o_Santiago.html
http://www.ultimahora.com/notas/367322-Funcionarios-sanitarios-capacitaran-sobre-cancer-de-mama
http://www.lanueva.com/hoy/nota/65092f2044/1/79477.html
http://www.infobae.com/policiales/541220-101275-0-Se-suspendio-la-declaracion-del-marido-Fernanda-Lemos
http://www.clarin.com/sociedad/educacion/titulo_0_352164863.html
Did someone already said that regex is absolutely the wrong tool to parse HTML? ;)
See also:
Pros and cons of HTML parsers in Java
Your approach looks pretty good, however you can make it somewhat more efficient by avoiding the creation of intermediate String objects for each line.
The way to do this is to read directly into a temporary char[] buffer.
Here is a slightly modified version of your code that does this (minus all the error checking, exception handling etc. for clarity):
URL url = new URL("http://www.google.com/");
URLConnection connection;
connection = url.openConnection();
InputStream in = connection.getInputStream();
BufferedReader bf = new BufferedReader(new InputStreamReader(in));
StringBuffer html = new StringBuffer();
char[] charBuffer = new char[4096];
int count=0;
do {
count=bf.read(charBuffer, 0, 4096);
if (count>=0) html.append(charBuffer,0,count);
} while (count>0);
bf.close();
For even more performance, you can of course do little extra things like pre-allocating the character array and StringBuffer if this code is going to be called frequently.
You can try using commons-io from apache (http://commons.apache.org/io/api-release/org/apache/commons/io/IOUtils.html)
new String(IOUtils.toCharArray(connection.getInputStream()))
There are some technical considerations. You may wish to use HTTPURLConnection instead of URLConnection.
HTTPURLConnection supports chunked transfer encoding, which allows you to process the data in chunks, rather than buffering all of the content before you start doing work. This can lead to an improved user experience.
Also, HTTPURLConnection supports persistent connections. Why close that connection if you're going to request another resource right away? Keeping the TCP connection open with the web server allows your application to quickly download multiple resources without spending the overhead (latency) of establishing a new TCP connection for each resource.
Tell the server that you support gzip and wrap a BufferedReader around GZIPInputStream if the response header says the content is compressed.
I am using HTML Parser to develop an application.
The code below is not able to get the entire set of tags in the page.
There are some tags which are missed out and the attributes and text body of them are also missed out.
Please help me to explain why is this happening.....or suggest me other way....
URL url = new URL("...");
PrintWriter pw=new PrintWriter(new FileWriter("HTMLElements.txt"));
URLConnection connection = url.openConnection();
InputStream is = connection.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
HTMLEditorKit htmlKit = new HTMLEditorKit();
HTMLDocument htmlDoc = (HTMLDocument)htmlKit.createDefaultDocument();
HTMLEditorKit.Parser parser = new ParserDelegator();
HTMLEditorKit.ParserCallback callback = htmlDoc.getReader(0);
parser.parse(br, callback, true);
ElementIterator iterator = new ElementIterator(htmlDoc);
Element element;
while ((element = iterator.next()) != null)
{
AttributeSet attributes = element.getAttributes();
Enumeration e=attributes.getAttributeNames();
pw.println("Element Name :"+element.getName());
while(e.hasMoreElements())
{
Object key=e.nextElement();
Object val=attributes.getAttribute(key);
int startOffset = element.getStartOffset();
int endOffset = element.getEndOffset();
int length = endOffset - startOffset;
String text=htmlDoc.getText(startOffset, length);
pw.println("Key :"+key.toString()+" Value :"+val.toString()+"\r\n"+"Text :"+text+"\r\n");
}
}
}
I am doing this fairly reliably with HTML Parser, (provided that the HTML document does not change its structure). A web service with a stable API is much better, but sometimes we just do not have one.
General idea:
You first have to know in what tags (div, meta, span, etc) the information you want are in, and know the attributes to identify those tags. Example :
<span class="price"> $7.95</span>
if you are looking for this "price", then you are interested in span tags with class "price".
HTML Parser has a filter-by-attribute functionality.
filter = new HasAttributeFilter("class", "price");
When you parse using a filter, you will get a list of Nodes that you can do a instanceof operation on them to determine if they are of the type you are interested in, for span you'd do something like
if (node instanceof Span) // or any other supported element.
See list of supported tags here.
An example with HTML Parser to grab the meta tag that has description about a site:
Tag Sample :
<meta name="description" content="Amazon.com: frankenstein: Books"/>
Code:
import org.htmlparser.Node;
import org.htmlparser.Parser;
import org.htmlparser.util.NodeList;
import org.htmlparser.util.ParserException;
import org.htmlparser.filters.HasAttributeFilter;
import org.htmlparser.tags.MetaTag;
public class HTMLParserTest {
public static void main(String... args) {
Parser parser = new Parser();
//<meta name="description" content="Some texte about the site." />
HasAttributeFilter filter = new HasAttributeFilter("name", "description");
try {
parser.setResource("http://www.youtube.com");
NodeList list = parser.parse(filter);
Node node = list.elementAt(0);
if (node instanceof MetaTag) {
MetaTag meta = (MetaTag) node;
String description = meta.getAttribute("content");
System.out.println(description);
// Prints: "YouTube is a place to discover, watch, upload and share videos."
}
} catch (ParserException e) {
e.printStackTrace();
}
}
}
As per the comments:
actually i want to extract information such as product name,price etc of all products listed in an online shopping site such as amazon.com How should i go about it???
Step 1: read their robots file. It's usually found on the root of the site, for example http://amazon.com/robots.txt. If the URL you're trying to access is covered by a Disallow on an User-Agent of *, then stop here. Contact them, explain them in detail what you're trying to do and ask them for ways/alternatives/webservices which can provide you the information you need. Else you're violating the laws and you may risk to get blacklisted by the site and/or by your ISP or worse. If not, then proceed to step 2.
Step 2: check if the site in question hasn't already a public webservice available which is much more easy to use than parsing a whole HTML page. Using a webservice, you'll get exactly the information you're looking for in a concise format (JSON or XML) based on a simple set of parameters. Look around or contact them for details about any webservices. If there's no way, proceed to step 3.
Step 3: learn how HTML/CSS/JS work, learn how to work with webdeveloper tools like Firebug, learn how to interpret the HTML/CSS/JS source you see by rightclick > View Page Source. My bet that the site in question uses JS/Ajax to load/populate the information you'd like to gather. In that case, you'll need to use a HTML parser which is capable of parsing and executing JS as well (the one you're using namely doesn't do that). This isn't going to be an easy job, so I won't explain it in detail until it's entirely clear what you're trying to achieve and if that is allowed and if there aren't more-easy-to-use webservices available.
You seemed to use the Swing HtmlDocument. It may not be the smartest idea ever.
I believe you would have better results using, as an example, NekoHtml.
Or another simple library you can use is jtidy that can clean up your html before parsing it.
Hope this helps.
http://sourceforge.net/projects/jtidy/
Ciao!
I have 30000 dictionary words. In that I want to to search each word in Google and want to find hits of each word using Java program. Is it possible?
Look up <estimatedTotalResultsCount> using Google's SOAP search API.
You'll be limited to 1000 queries per day though. This limit is removed if you use their AJAX API.
Since your duplicate post is closed, I'll post my answer here as well:
Whether this is possible or not doesn't really matter: Google doesn't want you to do that. They have a public AJAX-search API developers can use: http://code.google.com/apis/ajaxsearch/web.html
Here is a Sun tutorial on Reading to and Writing from an URLConnection.
The simplest URL I can see to make a Google search is like:
http://www.google.com/#q=wombat
Reading from a url with java is pretty straight forward. A basic working example is as follows
public Set<String> readUrl(String url) {
String line;
Set<String> lines = new HashSet<String>();
try {
URL url = new URL(url);
URLConnection page = url.openConnection();
BufferedReader in = new BufferedReader( new InputStreamReader(page.getInputStream()));
while ((line = in.readLine()) != null) {
lines.add(line);
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return lines;
}
I'd recommend separating your problem into pieces. Get each one working, then marry them together for the solution you want.
You have a few things going on here:
Downloading text from a URL
Scanning a stream of characters and breaking it up into words
Iterating through a list of words and tallying up the hits from your dictionary
Computer science is all about taking large problems and decomposing them into smaller ones. I'd recommend that you start learning how to do that now.