How do you Programmatically Download a Webpage in

问题:

I would like to be able to fetch a web page\'s html and save it to a String, so I can do some processing on it. Also, how could I handle various types of compression.

How would I go about doing that using Java?

回答1:

Here\'s some tested code using Java\'s URL class. I\'d recommend do a better job than I do here of handling the exceptions or passing them up the call stack, though.

public static void main(String[] args) {
    URL url;
    InputStream is = null;
    BufferedReader br;
    String line;

    try {
        url = new URL(\"http://stackoverflow.com/\");
        is = url.openStream();  // throws an IOException
        br = new BufferedReader(new InputStreamReader(is));

        while ((line = br.readLine()) != null) {
            System.out.println(line);
        }
    } catch (MalformedURLException mue) {
         mue.printStackTrace();
    } catch (IOException ioe) {
         ioe.printStackTrace();
    } finally {
        try {
            if (is != null) is.close();
        } catch (IOException ioe) {
            // nothing to see here
        }
    }
}

回答2:

I\'d use a decent HTML parser like Jsoup. It\'s then as easy as:

String html = Jsoup.connect(\"http://stackoverflow.com\").get().html();

It handles GZIP and chunked responses and character encoding fully transparently. It offers more advantages as well, like HTML traversing and manipulation by CSS selectors like as jQuery can do. You only have to grab it as Document, not as a String.

Document document = Jsoup.connect(\"http://google.com\").get();

You really don\'t want to run basic String methods or even regex on HTML to process it.

See also:

• What are the pros and cons of leading HTML parsers in Java?

回答3:

Bill\'s answer is very good, but you may want to do some things with the request like compression or user-agents. The following code shows how you can various types of compression to your requests.

URL url = new URL(urlStr);
HttpURLConnection conn = (HttpURLConnection) url.openConnection(); // Cast shouldn\'t fail
HttpURLConnection.setFollowRedirects(true);
// allow both GZip and Deflate (ZLib) encodings
conn.setRequestProperty(\"Accept-Encoding\", \"gzip, deflate\");
String encoding = conn.getContentEncoding();
InputStream inStr = null;

// create the appropriate stream wrapper based on
// the encoding type
if (encoding != null && encoding.equalsIgnoreCase(\"gzip\")) {
    inStr = new GZIPInputStream(conn.getInputStream());
} else if (encoding != null && encoding.equalsIgnoreCase(\"deflate\")) {
    inStr = new InflaterInputStream(conn.getInputStream(),
      new Inflater(true));
} else {
    inStr = conn.getInputStream();
}

To also set the user-agent add the following code:

conn.setRequestProperty ( \"User-agent\", \"my agent name\");

回答4:

Well, you could go with the built-in libraries such as URL and URLConnection, but they don\'t give very much control.

Personally I\'d go with the Apache HTTPClient library.
Edit: HTTPClient has been set to end of life by Apache. The replacement is: HTTP Components

回答5:

All the above mentioned approaches do not download the web page text as it looks in the browser. these days a lot of data is loaded into browsers through scripts in html pages. none of above mentioned techniques supports scripts, they just downloads the html text only. HTMLUNIT supports the javascripts. so if you are looking to download the web page text as it looks in the browser then you should use HTMLUNIT.

回答6:

Here is an example of a download html file from a https web page. In the following example, the html file is being saved into c:\\temp\\filename.html Enjoy!

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;

import javax.net.ssl.HttpsURLConnection;

/**
 * <b>Get the Html source from the secure url </b>
 */
public class HttpsClientUtil {
    public static void main(String[] args) throws Exception {
        String httpsURL = \"https://stackoverflow.com\";
        String FILENAME = \"c:\\\\temp\\\\filename.html\";
        BufferedWriter bw = new BufferedWriter(new FileWriter(FILENAME));
        URL myurl = new URL(httpsURL);
        HttpsURLConnection con = (HttpsURLConnection) myurl.openConnection();
        con.setRequestProperty ( \"User-Agent\", \"Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:63.0) Gecko/20100101 Firefox/63.0\" );
        InputStream ins = con.getInputStream();
        InputStreamReader isr = new InputStreamReader(ins, \"Windows-1252\");
        BufferedReader in = new BufferedReader(isr);
        String inputLine;

        // Write each line into the file
        while ((inputLine = in.readLine()) != null) {
            System.out.println(inputLine);
            bw.write(inputLine);
        }
        in.close(); 
        bw.close();
    }
}

回答7:

On a Unix/Linux box you could just run \'wget\' but this is not really an option if you\'re writing a cross-platform client. Of course this assumes that you don\'t really want to do much with the data you download between the point of downloading it and it hitting the disk.

回答8:

Try using the jsoup library.

import java.io.IOException;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;


public class ParseHTML {

    public static void main(String args[]) throws IOException{
        Document doc = Jsoup.connect(\"https://www.wikipedia.org/\").get();
        String text = doc.body().text();

        System.out.print(text);
    }
}

You can download the jsoup library here.

回答9:

Jetty has an HTTP client which can be use to download a web page.

package com.zetcode;

import org.eclipse.jetty.client.HttpClient;
import org.eclipse.jetty.client.api.ContentResponse;

public class ReadWebPageEx5 {

    public static void main(String[] args) throws Exception {

        HttpClient client = null;

        try {

            client = new HttpClient();
            client.start();

            String url = \"http://www.something.com\";

            ContentResponse res = client.GET(url);

            System.out.println(res.getContentAsString());

        } finally {

            if (client != null) {

                client.stop();
            }
        }
    }
}

The example prints the contents of a simple web page.

In a Reading a web page in Java tutorial I have written six examples of dowloading a web page programmaticaly in Java using URL, JSoup, HtmlCleaner, Apache HttpClient, Jetty HttpClient, and HtmlUnit.

回答10:

Get help from this class it get code and filter some information.

public class MainActivity extends AppCompatActivity {

    EditText url;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.activity_main );

        url = ((EditText)findViewById( R.id.editText));
        DownloadCode obj = new DownloadCode();

        try {
            String des=\" \";

            String tag1= \"<div class=\\\"description\\\">\";
            String l = obj.execute( \"http://www.nu.edu.pk/Campus/Chiniot-Faisalabad/Faculty\" ).get();

            url.setText( l );
            url.setText( \" \" );

            String[] t1 = l.split(tag1);
            String[] t2 = t1[0].split( \"</div>\" );
            url.setText( t2[0] );

        }
        catch (Exception e)
        {
            Toast.makeText( this,e.toString(),Toast.LENGTH_SHORT ).show();
        }

    }
                                        // input, extrafunctionrunparallel, output
    class DownloadCode extends AsyncTask<String,Void,String>
    {
        @Override
        protected String doInBackground(String... WebAddress) // string of webAddress separate by \',\'
        {
            String htmlcontent = \" \";
            try {
                URL url = new URL( WebAddress[0] );
                HttpURLConnection c = (HttpURLConnection) url.openConnection();
                c.connect();
                InputStream input = c.getInputStream();
                int data;
                InputStreamReader reader = new InputStreamReader( input );

                data = reader.read();

                while (data != -1)
                {
                    char content = (char) data;
                    htmlcontent+=content;
                    data = reader.read();
                }
            }
            catch (Exception e)
            {
                Log.i(\"Status : \",e.toString());
            }
            return htmlcontent;
        }
    }
}

回答11:

I used the actual answer to this post (url) and writing the output into a file.

package test;

import java.net.*;
import java.io.*;

public class PDFTest {
    public static void main(String[] args) throws Exception {
    try {
        URL oracle = new URL(\"http://www.fetagracollege.org\");
        BufferedReader in = new BufferedReader(new InputStreamReader(oracle.openStream()));

        String fileName = \"D:\\\\a_01\\\\output.txt\";

        PrintWriter writer = new PrintWriter(fileName, \"UTF-8\");
        OutputStream outputStream = new FileOutputStream(fileName);
        String inputLine;

        while ((inputLine = in.readLine()) != null) {
            System.out.println(inputLine);
            writer.println(inputLine);
        }
        in.close();
        } catch(Exception e) {

        }

    }
}