google pagerank

In this example, we will show you how to get Google PageRank (PR) in Java. To request a PageRank for “mkyong.com”, you just need to send following HTTP request :

http://toolbarqueries.google.com/tbr?client=navclient-auto&hl=en&ch=6236440745
&ie=UTF-8&oe=UTF-8&features=Rank&q=info:mkyong.com

P.S Above URL is used by Google toolbar plugin.

The tricky part is following hashing value :

ch=6236440745

Google is using Bob Jenkins hashing algorithm [1][2] to hash the URL and generate above “ch” value.

1. PageRank (PR) + Java Example

Get Google PR for website “mkyong.com”.

GoogleSeoHelper.java
package com.mkyong;
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;
import com.mkyong.hash.JenkinsHash;
 
public class GoogleSeoHelper {
 
  public static void main(String[] args) {
 
	GoogleSeoHelper obj = new GoogleSeoHelper();
	System.out.println(obj.getPR("mkyong.com"));
 
  }
 
  public int getPR(String domain) {
 
	String result = "";
 
	JenkinsHash jenkinsHash = new JenkinsHash();
	long hash = jenkinsHash.hash(("info:" + domain).getBytes());
 
	//Append a 6 in front of the hashing value.
	String url = "http://toolbarqueries.google.com/tbr?client=navclient-auto&hl=en&"
	   + "ch=6" + hash + "&ie=UTF-8&oe=UTF-8&features=Rank&q=info:" + domain;
 
	System.out.println("Sending request to : " + url);
 
	try {
		URLConnection conn = new URL(url).openConnection();
 
		BufferedReader br = new BufferedReader(new InputStreamReader(
			conn.getInputStream()));
 
		String input;
		while ((input = br.readLine()) != null) {
 
			// What Google returned? Example : Rank_1:1:9, PR = 9
			System.out.println(input);
 
			result = input.substring(input.lastIndexOf(":") + 1);
		}
 
	} catch (Exception e) {
		System.out.println(e.getMessage());
	}
 
	if ("".equals(result)) {
		return 0;
	} else {
		return Integer.valueOf(result);
	}
 
  }
 
}

Output – The URL “mkyong.com” has PageRank of 5!

Sending request to : http://toolbarqueries.google.com/tbr?client=navclient-auto
&hl=en&ch=6236440745&ie=UTF-8&oe=UTF-8&features=Rank&q=info:mkyong.com
Rank_1:1:5
5

2. Jenkins Perfect Hashing Algorithm

Here’s the Jenkins hash Java port example.

JenkinsHash.java
package com.mkyong.hash;
 
/**
 * Hash algorithm by Bob Jenkins, 1996.
 * 
 * You may use this code any way you wish, private, educational, or commercial.
 * It's free. See: http://burtleburtle.net/bob/hash/doobs.html
 * 
 */
public class JenkinsHash {
 
	// max value to limit it to 4 bytes
	private static final long MAX_VALUE = 0xFFFFFFFFL;
 
	// internal variables used in the various calculations
	long a;
	long b;
	long c;
 
	/**
	 * Convert a byte into a long value without making it negative.
	 */
	private long byteToLong(byte b) {
		long val = b & 0x7F;
		if ((b & 0x80) != 0) {
			val += 128;
		}
		return val;
	}
 
	/**
	 * Do addition and turn into 4 bytes.
	 */
	private long add(long val, long add) {
		return (val + add) & MAX_VALUE;
	}
 
	/**
	 * Do subtraction and turn into 4 bytes.
	 */
	private long subtract(long val, long subtract) {
		return (val - subtract) & MAX_VALUE;
	}
 
	/**
	 * Left shift val by shift bits and turn in 4 bytes.
	 */
	private long xor(long val, long xor) {
		return (val ^ xor) & MAX_VALUE;
	}
 
	/**
	 * Left shift val by shift bits. Cut down to 4 bytes.
	 */
	private long leftShift(long val, int shift) {
		return (val << shift) & MAX_VALUE;
	}
 
	/**
	 * Convert 4 bytes from the buffer at offset into a long value.
	 */
	private long fourByteToLong(byte[] bytes, int offset) {
	    return (byteToLong(bytes[offset + 0])
		+ (byteToLong(bytes[offset + 1]) << 8)
		+ (byteToLong(bytes[offset + 2]) << 16) + (byteToLong(bytes[offset + 3]) << 24));
	}
 
	/**
	 * Mix up the values in the hash function.
	 */
	private void hashMix() {
		a = subtract(a, b);
		a = subtract(a, c);
		a = xor(a, c >> 13);
		b = subtract(b, c);
		b = subtract(b, a);
		b = xor(b, leftShift(a, 8));
		c = subtract(c, a);
		c = subtract(c, b);
		c = xor(c, (b >> 13));
		a = subtract(a, b);
		a = subtract(a, c);
		a = xor(a, (c >> 12));
		b = subtract(b, c);
		b = subtract(b, a);
		b = xor(b, leftShift(a, 16));
		c = subtract(c, a);
		c = subtract(c, b);
		c = xor(c, (b >> 5));
		a = subtract(a, b);
		a = subtract(a, c);
		a = xor(a, (c >> 3));
		b = subtract(b, c);
		b = subtract(b, a);
		b = xor(b, leftShift(a, 10));
		c = subtract(c, a);
		c = subtract(c, b);
		c = xor(c, (b >> 15));
	}
 
	/**
	 * Hash a variable-length key into a 32-bit value. Every bit of the key
	 * affects every bit of the return value. Every 1-bit and 2-bit delta
	 * achieves avalanche. The best hash table sizes are powers of 2.
	 * 
	 * @param buffer
	 *            Byte array that we are hashing on.
	 * @param initialValue
	 *            Initial value of the hash if we are continuing from a previous
	 *            run. 0 if none.
	 * @return Hash value for the buffer.
	 */
	public long hash(byte[] buffer, long initialValue) {
		int len, pos;
 
		// set up the internal state
		// the golden ratio; an arbitrary value
		a = 0x09e3779b9L;
		// the golden ratio; an arbitrary value
		b = 0x09e3779b9L;
		// the previous hash value
 
		//c = initialValue;
		c = 0x0E6359A60L;
 
		// handle most of the key
		pos = 0;
		for (len = buffer.length; len >= 12; len -= 12) {
			a = add(a, fourByteToLong(buffer, pos));
			b = add(b, fourByteToLong(buffer, pos + 4));
			c = add(c, fourByteToLong(buffer, pos + 8));
			hashMix();
			pos += 12;
		}
 
		c += buffer.length;
 
		// all the case statements fall through to the next on purpose
		switch (len) {
		case 11:
			c = add(c, leftShift(byteToLong(buffer[pos + 10]), 24));
		case 10:
			c = add(c, leftShift(byteToLong(buffer[pos + 9]), 16));
		case 9:
			c = add(c, leftShift(byteToLong(buffer[pos + 8]), 8));
			// the first byte of c is reserved for the length
		case 8:
			b = add(b, leftShift(byteToLong(buffer[pos + 7]), 24));
		case 7:
			b = add(b, leftShift(byteToLong(buffer[pos + 6]), 16));
		case 6:
			b = add(b, leftShift(byteToLong(buffer[pos + 5]), 8));
		case 5:
			b = add(b, byteToLong(buffer[pos + 4]));
		case 4:
			a = add(a, leftShift(byteToLong(buffer[pos + 3]), 24));
		case 3:
			a = add(a, leftShift(byteToLong(buffer[pos + 2]), 16));
		case 2:
			a = add(a, leftShift(byteToLong(buffer[pos + 1]), 8));
		case 1:
			a = add(a, byteToLong(buffer[pos + 0]));
			// case 0: nothing left to add
		}
		hashMix();
 
		return c;
	}
 
	/**
	 * See hash(byte[] buffer, long initialValue)
	 * 
	 * @param buffer
	 *            Byte array that we are hashing on.
	 * @return Hash value for the buffer.
	 */
	public long hash(byte[] buffer) {
		return hash(buffer, 0);
	}
}

References

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