package sample;import java.util.ArrayList;import java.util.List;import org.drools.KnowledgeBase;import org.drools.builder.ResourceType;import org.drools.logger.KnowledgeRuntimeLogger;import org.drools.logger.KnowledgeRuntimeLoggerFactory;import org.drools.runtime.StatefulKnowledgeSession;import sample.helper.KnowledgeBaseHelper;import sample.model.PI;import sample.model.RuleResource;public class CalcPI {    public static void main(String[] args) {                try {            // load up the knowledge base            KnowledgeBase kbase = readKnowledgeBase();            StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();            KnowledgeRuntimeLogger logger = KnowledgeRuntimeLoggerFactory.newFileLogger(ksession, "test");            // go !            PI pi = new PI();            pi.setIterStrategy(PI.IterStrategySetting.ballardMethod.getStrategy());            ksession.insert(pi);            ksession.fireAllRules();                System.out.println("PI: " + pi.getPi());            logger.close();        } catch (Throwable t) {            t.printStackTrace();        }                        }            private static KnowledgeBase readKnowledgeBase() throws Exception {        List<RuleResource> resources = new ArrayList<RuleResource>();        resources.add(new RuleResource("rules/CalcPI.drl", ResourceType.DRL));        return KnowledgeBaseHelper.readKnowledgeBase(resources);    }}

package sample.model;import java.math.BigDecimal;/** * @author qin.shuq * @see http://zh.wikipedia.org/wiki/%E5%9C%93%E5%91%A8%E7%8E%87 */public class PI {        private BigDecimal pi;    // PI 值        private int   iterValue;   // 迭代值        private IterStrategy iterStrategy ;   // 迭代策略        public PI() {        iterStrategy = IterStrategySetting.WallisMethod.getStrategy();        this.pi = BigDecimal.valueOf(IterStrategySetting.WallisMethod.getInitPi());        this.iterValue =http://www.mamicode.com/ IterStrategySetting.WallisMethod.getInitIterValue();    }    public PI(IterStrategy strategy) {        this.iterStrategy = strategy;        this.pi = BigDecimal.valueOf(IterStrategySetting.toEnum(this.iterStrategy).getInitPi());        this.iterValue = http://www.mamicode.com/IterStrategySetting.toEnum(this.iterStrategy).getInitIterValue();    }        private static final IterStrategy leibnizStrategy = new LeibnizIterStrategy();    private static final IterStrategy wallisStrategy = new WallisIterStrategy();    private static final IterStrategy arctanStrategy = new ArctanIterStrategy();    private static final IterStrategy ballardStrategy = new BallardIterStrategy();        /**     * 迭代一次的计算     */    public void iterOne() {        iterStrategy.iterCalcOne(this);    }        public BigDecimal getPi() {        return pi;    }    public void setPi(BigDecimal pi) {        this.pi = pi;    }    public int getIterValue() {        return iterValue;    }    public void setIterValue(int iterValue) {        this.iterValue =http://www.mamicode.com/ iterValue;    }    public void setIterStrategy(IterStrategy iterStrategy) {        this.iterStrategy = iterStrategy;        this.pi = BigDecimal.valueOf(IterStrategySetting.toEnum(this.iterStrategy).getInitPi());        this.iterValue = http://www.mamicode.com/IterStrategySetting.toEnum(this.iterStrategy).getInitIterValue();    }    public enum IterStrategySetting {        LeibnizMethod(leibnizStrategy, 4, 1),   //  PI: 3.141590653589692    iterValue: 1000000        WallisMethod(wallisStrategy, 2, 1),     //  PI: 3.141591082795387    iterValue: 1000000                // PI: 3.141592653589793057092897568389359        //       021087492184878678890301622544682        //       870922262624376585084262078791652        //       664665170934387960240111985365743        //       816329749380749612568341860137676        //       992899578827196104523046458933737        //       232212198503616995641765457187290        //       803101355648406923221343642309071        //       354773081438421905649763339659738        //       095339778728962929492812141689849872323987745         // iterValue: 183        ArctanMethod(arctanStrategy, 4*((double)44/57+(double)7/239-(double)12/682+(double)24/12943), 1),                ballardMethod(ballardStrategy, 0.015625*(-32-(double)1/3+256-(double)64/3-0.8-(double)4/7+(double)1/9), 0);                private IterStrategy strategy;        private double initPi;        private int    initIterValue;                private IterStrategySetting(IterStrategy strategy, double initPi, int initIterValue) {            this.strategy = strategy;            this.initPi = initPi;            this.initIterValue =http://www.mamicode.com/ initIterValue;        }                public double getInitPi() {            return initPi;        }        public int getInitIterValue() {            return initIterValue;        }        public void setStrategy(IterStrategy strategy) {            this.strategy = strategy;        }                public IterStrategy getStrategy() {            return strategy;        }        public static IterStrategySetting toEnum(IterStrategy strategy) {            for (IterStrategySetting s: IterStrategySetting.values()) {                if (strategy.equals(s.getStrategy())) {                    return s;                }            }            return null;        }            }    }interface IterStrategy {    void iterCalcOne(PI pi);}class LeibnizIterStrategy implements IterStrategy {    public void iterCalcOne(PI pi) {        /**         * according to formula :         * PI/4 = (1-1/3+1/5-1/7+1/9-...)         */        int iterValue = http://www.mamicode.com/pi.getIterValue()+2;        pi.setIterValue(iterValue);        int sign = (iterValue % 4 == 3) ? -1 : 1;        pi.setPi(BigDecimal.valueOf(pi.getPi().doubleValue() + (double) 4 * sign / iterValue));    }    }class WallisIterStrategy implements IterStrategy {    public void iterCalcOne(PI pi) {        /**         * according to formula :         * PI/2 = (2/1 * 2/3) * (4/3 * 4/5) * (6/5 * 6/7) ...         */        long iterValue =http://www.mamicode.com/ pi.getIterValue();        double newpi = pi.getPi().doubleValue() * (1 + (double)1/(iterValue*(iterValue+2)));        pi.setPi(BigDecimal.valueOf(newpi));        pi.setIterValue((int)(iterValue+2));    }    }/** * PI: 3.141592653589793    iterValue: 183 */class ArctanIterStrategy implements IterStrategy {    public void iterCalcOne(PI pi) {        /**         * according to formula :         *  PI/4 = 44arctan(1/57) + 7arctan(1/239) - 12arctan(1/682) + 24arctan(1/12943)         *  arctan(x) = x - 1/3*x^3 + 1/5*x^5 - 1/7*x^7          */        long iterValue = http://www.mamicode.com/pi.getIterValue() + 2;        int sign = (iterValue % 4 == 3) ? -1 : 1;        BigDecimal part1 = BigDecimal.valueOf((double)44*Math.pow((double)1/57, iterValue));        BigDecimal part2 = BigDecimal.valueOf((double)7*Math.pow((double)1/239, iterValue));        BigDecimal part3 = BigDecimal.valueOf((double)12*Math.pow((double)1/682, iterValue));        BigDecimal part4 = BigDecimal.valueOf((double)24*Math.pow((double)1/12943, iterValue));        BigDecimal incre = BigDecimal.valueOf(4*sign*((double)1/iterValue)).multiply(                           part1.add(part2).subtract(part3).add(part4));        pi.setPi(pi.getPi().add(incre));        pi.setIterValue((int)iterValue);    }    }class BallardIterStrategy implements IterStrategy {    /**     * PI = 0.015625* SUM(0-n) {(-1)^n/2^(10*n)*(-32/(4n+1)-1/(4n+3)+256/(10n+1)-64/(10n+3)-4/(10n+5)-4/(10n+7)+1/(10n+9)))}     */    public void iterCalcOne(PI pi) {        int iterValue = http://www.mamicode.com/pi.getIterValue()+1;        int sign = (iterValue % 2 == 0) ? 1: -1;        BigDecimal part1 = BigDecimal.valueOf(-32/(double)(4*iterValue+1));        BigDecimal part2 = BigDecimal.valueOf(-1/(double)(4*iterValue+3));        BigDecimal part3 = BigDecimal.valueOf(256/(double)(10*iterValue+1));        BigDecimal part4 = BigDecimal.valueOf(-64/(double)(10*iterValue+3));        BigDecimal part5 = BigDecimal.valueOf(-4/(double)(10*iterValue+5));        BigDecimal part6 = BigDecimal.valueOf(-4/(double)(10*iterValue+7));        BigDecimal part7 = BigDecimal.valueOf(1/(double)(10*iterValue+9));        BigDecimal incre = BigDecimal.valueOf(0.015625*sign/Math.pow(2, 10*iterValue)).multiply(                part1.add(part2).add(part3).add(part4).add(part5).add(part6).add(part7));        pi.setPi(pi.getPi().add(incre));        System.out.println(iterValue);        pi.setIterValue((int)iterValue);    }    }

package sample.model;import org.drools.builder.ResourceType;public class RuleResource {        private String ruleResourceFile;    private ResourceType resType;        public RuleResource(String ruleResourceFile, ResourceType resType) {        this.ruleResourceFile = ruleResourceFile;        this.resType = resType;    }        public String getRuleResourceFile() {        return ruleResourceFile;    }    public void setRuleResourceFile(String ruleResourceFile) {        this.ruleResourceFile = ruleResourceFile;    }    public ResourceType getResType() {        return resType;    }    public void setResType(ResourceType resType) {        this.resType = resType;    }}

package sample.helper;import java.util.List;import org.drools.KnowledgeBase;import org.drools.KnowledgeBaseFactory;import org.drools.builder.KnowledgeBuilder;import org.drools.builder.KnowledgeBuilderError;import org.drools.builder.KnowledgeBuilderErrors;import org.drools.builder.KnowledgeBuilderFactory;import org.drools.io.ResourceFactory;import sample.model.RuleResource;public class KnowledgeBaseHelper {        private KnowledgeBaseHelper() {}        public static KnowledgeBase readKnowledgeBase(List<RuleResource> resources) {        KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();        for (RuleResource res: resources) {            try {                kbuilder.add(ResourceFactory.newClassPathResource(res.getRuleResourceFile()), res.getResType());            } catch (Exception ex) {                kbuilder.add(ResourceFactory.newFileResource(res.getRuleResourceFile()), res.getResType());            }        }        KnowledgeBuilderErrors errors = kbuilder.getErrors();        if (errors.size() > 0) {            for (KnowledgeBuilderError error: errors) {                System.err.println(error);            }            throw new IllegalArgumentException("Could not parse knowledge.");        }        KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();        kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());        return kbase;    }}

#created on: 2011-1-12package mymathimport sample.model.PI;rule "CalcPI"    no-loop false        when        pi: PI(iterValue<183)    then         System.out.println("exec rule CalcPI ... ");         System.out.println("PI: " + pi.getPi() + "    iterValue: " + pi.getIterValue());         pi.iterOne();         update(pi);end

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">  <modelVersion>4.0.0</modelVersion>  <groupId>drools-study</groupId>  <artifactId>drools-study</artifactId>  <version>1.0</version>  <name>drools-study</name>  <description>a project for learning drools5.1.1</description>    <dependencies>      <dependency>        <groupId>org.drools</groupId>        <artifactId>drools-compiler</artifactId>        <version>5.1.1</version>    </dependency>            <dependency>        <groupId>org.drools</groupId>        <artifactId>drools-core</artifactId>        <version>5.1.1</version>    </dependency>        <dependency>        <groupId>org.drools</groupId>        <artifactId>drools-api</artifactId>        <version>5.1.1</version>    </dependency>        <dependency>        <groupId>org.drools</groupId>        <artifactId>drools-bpmn2</artifactId>        <version>5.1.1</version>    </dependency>        <dependency>        <groupId>com.thoughtworks.xstream</groupId>        <artifactId>xstream</artifactId>        <version>1.3.1</version></dependency>      </dependencies>  </project>