Drools - Rete Alogrithm explanation

Quite recently I have found a very nice article about the Rete Algorithm.

New Too Much Coding repository!

Hi!

As you know there is a code repository of Too Much Coding sources here at Bitbucket. If you don't like it you can also find the Too Much Coding sources at GitHub!

Enjoy :)

Drools integration with Spring vs manual rules creation

Hi!

 Often in your work you can come across with issues related to business logic. Let us assume that you have dozens of rules (for the time being in our project we have more than 50 and I used to work on a project where we had hundreds of those rules) that you have to implement, divide into some classes, subclasses, abstractions and of course unit test. This can be difficult and timeconsuming to both write and support. There are many ways of dealing with this problem and I will show you one of them - JBoss Drools.

Drools is a library specifically created for such purposes like implementing rules. As presented in Wikipedia:

"Drools is a rule engine implementaion based on Charles Forgy's Rete Algorithm tailored for the Java language." 

It contains a rule engine that can process rules wirtten using the Drools language (you can also provide rules in Excel spreadsheets! - perfect for Business side to support and maintain).

In the following example we will take a look at the way one can integrate JBoss Drools with Spring and an example of solving a similar problem without Drools.

Very interesting article about XSD

A friend from my project (that will soon start his own blog ;) here is his blog ) has found a very interesting article about XSDs and namespaces.

 Tutorial about XSD and namespaces

Hamcrest Matchers, Guava Predicate and Builder design pattern

Hi coding addicts :)

Often, while coding we have to deal with some POJO objects that have dozens of fields in them. Many times we initialize those classes through a constructor having dozens of arguments which is terrible in any possibly imaginable way :) Apart from that the functions that use those constructors are hardly testable. Let's take a closer look at using a Builder to change that situation, together with Hamcrest matchers and Guava Predicates to unit test it.

Let's start off with taking a look at the POJO class.

Google Guava Cache with regular expression patterns

Hi! Merry Christmas everyone :) Quite recently I've seen a nice presentation about Google Guava and we came to the conclusion in our project that it could be really interesting to use the its Cache functionallity. Let us take a look at the regexp Pattern class and its compile function. Quite often in the code we can see that each time a regular expression is being used a programmer is repeatidly calling the aforementioned Pattern.compile() function with the same argument thus compiling the same regular expression over and over again. What could be done however is to cache the result of such compilations - let us take a look at the RegexpUtils utility class:

RegexpUtils.java

package pl.grzejszczak.marcin.guava.cache.utils;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

import java.util.concurrent.ExecutionException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import static java.lang.String.format;

public final class RegexpUtils {

    private RegexpUtils() {
        throw new UnsupportedOperationException("RegexpUtils is a utility class - don't instantiate it!");
    }

    private static final LoadingCache<String, Pattern> COMPILED_PATTERNS =
            CacheBuilder.newBuilder().build(new CacheLoader<String, Pattern>() {
                @Override
                public Pattern load(String regexp) throws Exception {
                    return Pattern.compile(regexp);
                }
            });

    public static Pattern getPattern(String regexp) {
        try {
            return COMPILED_PATTERNS.get(regexp);
        } catch (ExecutionException e) {
            throw new RuntimeException(format("Error when getting a pattern [%s] from cache", regexp), e);
        }
    }

    public static boolean matches(String stringToCheck, String regexp) {
        return doGetMatcher(stringToCheck, regexp).matches();
    }

    public static Matcher getMatcher(String stringToCheck, String regexp) {
        return doGetMatcher(stringToCheck, regexp);
    }

    private static Matcher doGetMatcher(String stringToCheck, String regexp) {
        Pattern pattern = getPattern(regexp);
        return pattern.matcher(stringToCheck);
    }

}

As you can see the Guava's LoadingCache with the CacheBuilder is being used to populate a cache with a new compiled pattern if one is not found. Due to caching the compiled pattern if a compilation has already taken place it will not be repeated ever again (in our case since we dno't have any expiry set). Now a simple test

GuavaCache.java

package pl.grzejszczak.marcin.guava.cache;


import com.google.common.base.Stopwatch;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import pl.grzejszczak.marcin.guava.cache.utils.RegexpUtils;

import java.util.regex.Pattern;

import static java.lang.String.format;

public class GuavaCache {
    private static final Logger LOGGER = LoggerFactory.getLogger(GuavaCache.class);
    public static final String STRING_TO_MATCH = "something";

    public static void main(String[] args) {
        runTestForManualCompilationAndOneUsingCache(1);
        runTestForManualCompilationAndOneUsingCache(10);
        runTestForManualCompilationAndOneUsingCache(100);
        runTestForManualCompilationAndOneUsingCache(1000);
        runTestForManualCompilationAndOneUsingCache(10000);
        runTestForManualCompilationAndOneUsingCache(100000);
        runTestForManualCompilationAndOneUsingCache(1000000);
    }

    private static void runTestForManualCompilationAndOneUsingCache(int firstNoOfRepetitions) {
        repeatManualCompilation(firstNoOfRepetitions);
        repeatCompilationWithCache(firstNoOfRepetitions);
    }

    private static void repeatManualCompilation(int noOfRepetitions) {
        Stopwatch stopwatch = new Stopwatch().start();
        compileAndMatchPatternManually(noOfRepetitions);
        LOGGER.debug(format("Time needed to compile and check regexp expression [%d] ms, no of iterations [%d]", stopwatch.elapsedMillis(), noOfRepetitions));
    }

    private static void repeatCompilationWithCache(int noOfRepetitions) {
        Stopwatch stopwatch = new Stopwatch().start();
        compileAndMatchPatternUsingCache(noOfRepetitions);
        LOGGER.debug(format("Time needed to compile and check regexp expression using Cache [%d] ms, no of iterations [%d]", stopwatch.elapsedMillis(), noOfRepetitions));
    }

    private static void compileAndMatchPatternManually(int limit) {
        for (int i = 0; i < limit; i++) {
            Pattern.compile("something").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something1").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something2").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something3").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something4").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something5").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something6").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something7").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something8").matcher(STRING_TO_MATCH).matches();
            Pattern.compile("something9").matcher(STRING_TO_MATCH).matches();
        }
    }


    private static void compileAndMatchPatternUsingCache(int limit) {
        for (int i = 0; i < limit; i++) {
            RegexpUtils.matches(STRING_TO_MATCH, "something");
            RegexpUtils.matches(STRING_TO_MATCH, "something1");
            RegexpUtils.matches(STRING_TO_MATCH, "something2");
            RegexpUtils.matches(STRING_TO_MATCH, "something3");
            RegexpUtils.matches(STRING_TO_MATCH, "something4");
            RegexpUtils.matches(STRING_TO_MATCH, "something5");
            RegexpUtils.matches(STRING_TO_MATCH, "something6");
            RegexpUtils.matches(STRING_TO_MATCH, "something7");
            RegexpUtils.matches(STRING_TO_MATCH, "something8");
            RegexpUtils.matches(STRING_TO_MATCH, "something9");
        }
    }

}

We are running a series of tests and checking the time of their execution. Note that the results of these tests are not precise due to the fact that the application is not being run in isolation so numerous conditions can affect the time of the execution. We are interested in showing some degree of the problem rather than showing the precise execution time. For a given number of iterations (1,10,100,1000,10000,100000,1000000) we are either compiling 10 regular expressions or using a Guava's cache to retrieve the compiled Pattern and then we match them against a string to match. These are the logs:

pl.grzejszczak.marcin.guava.cache.GuavaCache:34 Time needed to compile and check regexp expression [1] ms, no of iterations [1]
pl.grzejszczak.marcin.guava.cache.GuavaCache:40 Time needed to compile and check regexp expression using Cache [35] ms, no of iterations [1]
pl.grzejszczak.marcin.guava.cache.GuavaCache:34 Time needed to compile and check regexp expression [1] ms, no of iterations [10]
pl.grzejszczak.marcin.guava.cache.GuavaCache:40 Time needed to compile and check regexp expression using Cache [0] ms, no of iterations [10]
pl.grzejszczak.marcin.guava.cache.GuavaCache:34 Time needed to compile and check regexp expression [8] ms, no of iterations [100]
pl.grzejszczak.marcin.guava.cache.GuavaCache:40 Time needed to compile and check regexp expression using Cache [3] ms, no of iterations [100]
pl.grzejszczak.marcin.guava.cache.GuavaCache:34 Time needed to compile and check regexp expression [10] ms, no of iterations [1000]
pl.grzejszczak.marcin.guava.cache.GuavaCache:40 Time needed to compile and check regexp expression using Cache [10] ms, no of iterations [1000]
pl.grzejszczak.marcin.guava.cache.GuavaCache:34 Time needed to compile and check regexp expression [83] ms, no of iterations [10000]
pl.grzejszczak.marcin.guava.cache.GuavaCache:40 Time needed to compile and check regexp expression using Cache [33] ms, no of iterations [10000]
pl.grzejszczak.marcin.guava.cache.GuavaCache:34 Time needed to compile and check regexp expression [800] ms, no of iterations [100000]
pl.grzejszczak.marcin.guava.cache.GuavaCache:40 Time needed to compile and check regexp expression using Cache [279] ms, no of iterations [100000]
pl.grzejszczak.marcin.guava.cache.GuavaCache:34 Time needed to compile and check regexp expression [7562] ms, no of iterations [1000000]
pl.grzejszczak.marcin.guava.cache.GuavaCache:40 Time needed to compile and check regexp expression using Cache [3067] ms, no of iterations [1000000]

You can find the sources over here under the Guava/Cache directory or go to the url https://bitbucket.org/gregorin1987/too-much-coding/src

Google Guava

Some interesting link:

Very nice presentation about Google Guava, sources