Mega Code Archive
Determines probability that text contains Spam
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// Revised from apache james
import java.util.Map;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Collection;
import java.util.ArrayList;
import java.io.Reader;
import java.io.StreamTokenizer;
import java.io.StringReader;
/**
* <P>Determines probability that text contains Spam.</P>
*
* <P>Based upon Paul Grahams' <a href="http://www.paulgraham.com/spam.html">A Plan for Spam</a>.
* Extended to Paul Grahams' <a href="http://paulgraham.com/better.html">Better Bayesian Filtering</a>.</P>
*
* <P>Sample method usage:</P>
*
* <P>Use:
* void addHam(Reader)
* and
* void addSpam(Reader)
*
* methods to build up the Maps of ham & spam tokens/occurrences.
* Both addHam and addSpam assume they're reading one message at a time,
* if you feed more than one message per call, be sure to adjust the
* appropriate message counter: hamMessageCount or spamMessageCount.
*
* Then...</P>
*
* <P>Use:
* void buildCorpus()
*
* to build the final token/probabilities Map.
*
* Use your own methods for persistent storage of either the individual
* ham/spam corpus & message counts, and/or the final corpus.
*
* Then you can...</P>
*
* <P>Use:
* double computeSpamProbability(Reader)
*
* to determine the probability that a particular text contains spam.
* A returned result of 0.9 or above is an indicator that the text was
* spam.</P>
*
* <P>If you use persistent storage, use:
* void setCorpus(Map)
*
* before calling computeSpamProbability.</P>
*
* @version CVS $Revision: $ $Date: $
* @since 2.3.0
*/
public class BayesianAnalyzer {
/**
* Number of "interesting" tokens to use to compute overall
* spamminess probability.
*/
private final static int MAX_INTERESTING_TOKENS = 15;
/**
* Minimum probability distance from 0.5 to consider a token "interesting" to use to compute overall
* spamminess probability.
*/
private final static double INTERESTINGNESS_THRESHOLD = 0.46;
/**
* Default token probability to use when a token has not been
* encountered before.
*/
private final static double DEFAULT_TOKEN_PROBABILITY = 0.4;
/**
* Map of ham tokens and their occurrences.
*
* String key
* Integer value
*/
private Map hamTokenCounts = new HashMap();
/**
* Map of spam tokens and their occurrences.
*
* String key
* Integer value
*/
private Map spamTokenCounts = new HashMap();
/**
* Number of ham messages analyzed.
*/
private int hamMessageCount = 0;
/**
* Number of spam messages analyzed.
*/
private int spamMessageCount = 0;
/**
* Final token/probability corpus.
*
* String key
* Double value
*/
private Map corpus = new HashMap();
/**
* Inner class for managing Token Probability Strengths during the
* computeSpamProbability phase.
*
* By probability <i>strength</i> we mean the absolute distance of a
* probability from the middle value 0.5.
*
* It implements Comparable so that it's sorting is automatic.
*/
private class TokenProbabilityStrength
implements Comparable {
/**
* Message token.
*/
String token = null;
/**
* Token's computed probability strength.
*/
double strength = Math.abs(0.5 - DEFAULT_TOKEN_PROBABILITY);
/**
* Force the natural sort order for this object to be high-to-low.
*
* @param anotherTokenProbabilityStrength A TokenProbabilityStrength instance to compare
* this instance with.
*
* @return The result of the comparison (before, equal, after).
*/
public final int compareTo(Object anotherTokenProbabilityStrength) {
int result = (int) ((((TokenProbabilityStrength) anotherTokenProbabilityStrength).strength - strength) * 1000000);
if (result == 0) {
return this.token.compareTo(((TokenProbabilityStrength) anotherTokenProbabilityStrength).token);
} else {
return result;
}
}
/**
* Simple toString () implementation mostly for debugging purposes.
*
* @return String representation of this object.
*/
public String toString() {
StringBuffer sb = new StringBuffer(30);
sb.append(token)
.append("=")
.append(strength);
return sb.toString();
}
}
/**
* Basic class constructor.
*/
public BayesianAnalyzer() {
}
/**
* Public setter for the hamTokenCounts Map.
*
* @param hamTokenCounts The new ham Token counts Map.
*/
public void setHamTokenCounts(Map hamTokenCounts) {
this.hamTokenCounts = hamTokenCounts;
}
/**
* Public getter for the hamTokenCounts Map.
*/
public Map getHamTokenCounts() {
return this.hamTokenCounts;
}
/**
* Public setter for the spamTokenCounts Map.
*
* @param spamTokenCounts The new spam Token counts Map.
*/
public void setSpamTokenCounts(Map spamTokenCounts) {
this.spamTokenCounts = spamTokenCounts;
}
/**
* Public getter for the spamTokenCounts Map.
*/
public Map getSpamTokenCounts() {
return this.spamTokenCounts;
}
/**
* Public setter for spamMessageCount.
*
* @param spamMessageCount The new spam message count.
*/
public void setSpamMessageCount(int spamMessageCount) {
this.spamMessageCount = spamMessageCount;
}
/**
* Public getter for spamMessageCount.
*/
public int getSpamMessageCount() {
return this.spamMessageCount;
}
/**
* Public setter for hamMessageCount.
*
* @param hamMessageCount The new ham message count.
*/
public void setHamMessageCount(int hamMessageCount) {
this.hamMessageCount = hamMessageCount;
}
/**
* Public getter for hamMessageCount.
*/
public int getHamMessageCount() {
return this.hamMessageCount;
}
/**
* Clears all analysis repositories and counters.
*/
public void clear() {
corpus.clear();
tokenCountsClear();
hamMessageCount = 0;
spamMessageCount = 0;
}
/**
* Clears token counters.
*/
public void tokenCountsClear() {
hamTokenCounts.clear();
spamTokenCounts.clear();
}
/**
* Public setter for corpus.
*
* @param corpus The new corpus.
*/
public void setCorpus(Map corpus) {
this.corpus = corpus;
}
/**
* Public getter for corpus.
*/
public Map getCorpus() {
return this.corpus;
}
/**
* Builds the corpus from the existing ham & spam counts.
*/
public void buildCorpus() {
//Combine the known ham & spam tokens.
Set set = new HashSet(hamTokenCounts.size() + spamTokenCounts.size());
set.addAll(hamTokenCounts.keySet());
set.addAll(spamTokenCounts.keySet());
Map tempCorpus = new HashMap(set.size());
//Iterate through all the tokens and compute their new
//individual probabilities.
Iterator i = set.iterator();
while (i.hasNext()) {
String token = (String) i.next();
tempCorpus.put(token, new Double(computeProbability(token)));
}
setCorpus(tempCorpus);
}
/**
* Adds a message to the ham list.
* @param stream A reader stream on the ham message to analyze
* @throws IOException If any error occurs
*/
public void addHam(Reader stream)
throws java.io.IOException {
addTokenOccurrences(stream, hamTokenCounts);
hamMessageCount++;
}
/**
* Adds a message to the spam list.
* @param stream A reader stream on the spam message to analyze
* @throws IOException If any error occurs
*/
public void addSpam(Reader stream)
throws java.io.IOException {
addTokenOccurrences(stream, spamTokenCounts);
spamMessageCount++;
}
/**
* Computes the probability that the stream contains SPAM.
* @param stream The text to be analyzed for Spamminess.
* @return A 0.0 - 1.0 probability
* @throws IOException If any error occurs
*/
public double computeSpamProbability(Reader stream)
throws java.io.IOException {
//Build a set of the tokens in the Stream.
Set tokens = parse(stream);
// Get the corpus to use in this run
// A new corpus may be being built in the meantime
Map workCorpus = getCorpus();
//Assign their probabilities from the Corpus (using an additional
//calculation to determine spamminess).
SortedSet tokenProbabilityStrengths = getTokenProbabilityStrengths(tokens, workCorpus);
//Compute and return the overall probability that the
//stream is SPAM.
return computeOverallProbability(tokenProbabilityStrengths, workCorpus);
}
/**
* Parses a stream into tokens, and updates the target Map
* with the token/counts.
*
* @param stream
* @param target
*/
private void addTokenOccurrences(Reader stream, Map target)
throws java.io.IOException {
String token;
String header = "";
//Update target with the tokens/count encountered.
while ((token = nextToken(stream)) != null) {
boolean endingLine = false;
if (token.length() > 0 && token.charAt(token.length() - 1) == '\n') {
endingLine = true;
token = token.substring(0, token.length() - 1);
}
if (token.length() > 0 && header.length() + token.length() < 90 && !allDigits(token)) {
if (token.equals("From:")
|| token.equals("Return-Path:")
|| token.equals("Subject:")
|| token.equals("To:")
) {
header = token;
if (!endingLine) {
continue;
}
}
token = header + token;
Integer value = null;
if (target.containsKey(token)) {
value = new Integer(((Integer) target.get(token)).intValue() + 1);
} else {
value = new Integer(1);
}
target.put(token, value);
}
if (endingLine) {
header = "";
}
}
}
/**
* Parses a stream into tokens, and returns a Set of
* the unique tokens encountered.
*
* @param stream
* @return Set
*/
private Set parse(Reader stream)
throws java.io.IOException {
Set tokens = new HashSet();
String token;
String header = "";
//Build a Map of tokens encountered.
while ((token = nextToken(stream)) != null) {
boolean endingLine = false;
if (token.length() > 0 && token.charAt(token.length() - 1) == '\n') {
endingLine = true;
token = token.substring(0, token.length() - 1);
}
if (token.length() > 0 && header.length() + token.length() < 90 && !allDigits(token)) {
if (token.equals("From:")
|| token.equals("Return-Path:")
|| token.equals("Subject:")
|| token.equals("To:")
) {
header = token;
if (!endingLine) {
continue;
}
}
token = header + token;
tokens.add(token);
}
if (endingLine) {
header = "";
}
}
//Return the unique set of tokens encountered.
return tokens;
}
private String nextToken(Reader reader) throws java.io.IOException {
StringBuffer token = new StringBuffer();
int i;
char ch, ch2;
boolean previousWasDigit = false;
boolean tokenCharFound = false;
if (!reader.ready()) {
return null;
}
while ((i = reader.read()) != -1) {
ch = (char) i;
if (ch == ':') {
String tokenString = token.toString() + ':';
if (tokenString.equals("From:")
|| tokenString.equals("Return-Path:")
|| tokenString.equals("Subject:")
|| tokenString.equals("To:")
) {
return tokenString;
}
}
if (Character.isLetter(ch)
|| ch == '-'
|| ch == '$'
|| ch == '\u20AC' // the EURO symbol
|| ch == '!'
|| ch == '\''
) {
tokenCharFound = true;
previousWasDigit = false;
token.append(ch);
} else if (Character.isDigit(ch)) {
tokenCharFound = true;
previousWasDigit = true;
token.append(ch);
} else if (previousWasDigit && (ch == '.' || ch == ',')) {
reader.mark(1);
previousWasDigit = false;
i = reader.read();
if (i == -1) {
break;
}
ch2 = (char) i;
if (Character.isDigit(ch2)) {
tokenCharFound = true;
previousWasDigit = true;
token.append(ch);
token.append(ch2);
} else {
reader.reset();
break;
}
} else if (ch == '\r') {
// cr found, ignore
} else if (ch == '\n') {
// eol found
tokenCharFound = true;
previousWasDigit = false;
token.append(ch);
break;
} else if (tokenCharFound) {
break;
}
}
if (tokenCharFound) {
// System.out.println("Token read: " + token);
return token.toString();
} else {
return null;
}
}
/**
* Compute the probability that "token" is SPAM.
*
* @param token
* @return The probability that the token occurs within spam.
*/
private double computeProbability(String token) {
double hamFactor = 0;
double spamFactor = 0;
boolean foundInHam = false;
boolean foundInSpam = false;
double minThreshold = 0.01;
double maxThreshold = 0.99;
if (hamTokenCounts.containsKey(token)) {
foundInHam = true;
}
if (spamTokenCounts.containsKey(token)) {
foundInSpam = true;
}
if (foundInHam) {
hamFactor = 2 *((Integer) hamTokenCounts.get(token)).doubleValue();
if (!foundInSpam) {
minThreshold = (hamFactor > 20) ? 0.0001 : 0.0002;
}
}
if (foundInSpam) {
spamFactor = ((Integer) spamTokenCounts.get(token)).doubleValue();
if (!foundInHam) {
maxThreshold = (spamFactor > 10) ? 0.9999 : 0.9998;
}
}
if ((hamFactor + spamFactor) < 5) {
//This token hasn't been seen enough.
return 0.4;
}
double spamFreq = Math.min(1.0, spamFactor / spamMessageCount);
double hamFreq = Math.min(1.0, hamFactor / hamMessageCount);
return Math.max(minThreshold, Math.min(maxThreshold, (spamFreq / (hamFreq + spamFreq))));
}
/**
* Returns a SortedSet of TokenProbabilityStrength built from the
* Corpus and the tokens passed in the "tokens" Set.
* The ordering is from the highest strength to the lowest strength.
*
* @param tokens
* @param workCorpus
* @return SortedSet of TokenProbabilityStrength objects.
*/
private SortedSet getTokenProbabilityStrengths(Set tokens, Map workCorpus) {
//Convert to a SortedSet of token probability strengths.
SortedSet tokenProbabilityStrengths = new TreeSet();
Iterator i = tokens.iterator();
while (i.hasNext()) {
TokenProbabilityStrength tps = new TokenProbabilityStrength();
tps.token = (String) i.next();
if (workCorpus.containsKey(tps.token)) {
tps.strength = Math.abs(0.5 - ((Double) workCorpus.get(tps.token)).doubleValue());
}
else {
//This token has never been seen before,
//we'll give it initially the default probability.
Double corpusProbability = new Double(DEFAULT_TOKEN_PROBABILITY);
tps.strength = Math.abs(0.5 - DEFAULT_TOKEN_PROBABILITY);
boolean isTokenDegeneratedFound = false;
Collection degeneratedTokens = buildDegenerated(tps.token);
Iterator iDegenerated = degeneratedTokens.iterator();
String tokenDegenerated = null;
double strengthDegenerated;
while (iDegenerated.hasNext()) {
tokenDegenerated = (String) iDegenerated.next();
if (workCorpus.containsKey(tokenDegenerated)) {
Double probabilityTemp = (Double) workCorpus.get(tokenDegenerated);
strengthDegenerated = Math.abs(0.5 - probabilityTemp.doubleValue());
if (strengthDegenerated > tps.strength) {
isTokenDegeneratedFound = true;
tps.strength = strengthDegenerated;
corpusProbability = probabilityTemp;
}
}
}
// to reduce memory usage, put in the corpus only if the probability is different from (stronger than) the default
if (isTokenDegeneratedFound) {
synchronized(workCorpus) {
workCorpus.put(tps.token, corpusProbability);
}
}
}
tokenProbabilityStrengths.add(tps);
}
return tokenProbabilityStrengths;
}
private Collection buildDegenerated(String fullToken) {
ArrayList tokens = new ArrayList();
String header;
String token;
// look for a header string termination
int headerEnd = fullToken.indexOf(':');
if (headerEnd >= 0) {
header = fullToken.substring(0, headerEnd);
token = fullToken.substring(headerEnd);
} else {
header = "";
token = fullToken;
}
int end = token.length();
do {
if (!token.substring(0, end).equals(token.substring(0, end).toLowerCase())) {
tokens.add(header + token.substring(0, end).toLowerCase());
if (header.length() > 0) {
tokens.add(token.substring(0, end).toLowerCase());
}
}
if (end > 1 && token.charAt(0) >= 'A' && token.charAt(0) <= 'Z') {
tokens.add(header + token.charAt(0) + token.substring(1, end).toLowerCase());
if (header.length() > 0) {
tokens.add(token.charAt(0) + token.substring(1, end).toLowerCase());
}
}
if (token.charAt(end - 1) != '!') {
break;
}
end--;
tokens.add(header + token.substring(0, end));
if (header.length() > 0) {
tokens.add(token.substring(0, end));
}
} while (end > 0);
return tokens;
}
/**
* Compute the spamminess probability of the interesting tokens in
* the tokenProbabilities SortedSet.
*
* @param tokenProbabilities
* @param workCorpus
* @return Computed spamminess.
*/
private double computeOverallProbability(SortedSet tokenProbabilityStrengths, Map workCorpus) {
double p = 1.0;
double np = 1.0;
double tempStrength = 0.5;
int count = MAX_INTERESTING_TOKENS;
Iterator iterator = tokenProbabilityStrengths.iterator();
while ((iterator.hasNext()) && (count-- > 0 || tempStrength >= INTERESTINGNESS_THRESHOLD)) {
TokenProbabilityStrength tps = (TokenProbabilityStrength) iterator.next();
tempStrength = tps.strength;
// System.out.println(tps);
double theDoubleValue = DEFAULT_TOKEN_PROBABILITY; // initialize it to the default
Double theDoubleObject = (Double) workCorpus.get(tps.token);
// if either the original token or a degeneration was found use the double value, otherwise use the default
if (theDoubleObject != null) {
theDoubleValue = theDoubleObject.doubleValue();
}
p *= theDoubleValue;
np *= (1.0 - theDoubleValue);
// System.out.println("Token:" + tps.token + ", p=" + theDoubleValue + ", overall p=" + p / (p + np));
}
return (p / (p + np));
}
private boolean allSameChar(String s) {
if (s.length() < 2) {
return false;
}
char c = s.charAt(0);
for (int i = 1; i < s.length(); i++) {
if (s.charAt(i) != c) {
return false;
}
}
return true;
}
private boolean allDigits(String s) {
for (int i = 0; i < s.length(); i++) {
if (!Character.isDigit(s.charAt(i))) {
return false;
}
}
return true;
}
}
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