Drools最基本最常用的有以下四種

布林運算與數值運算規則

rule "Add 5% discount for minors or seniors"
    when $o: Order(customer.age < 18 || customer.age > 60)
    then $o.increaseDiscount(0.05);
end

基於集合的規則

(contains and memberOf)　他們主要用來檢測集合是否包含不包含某元素

rule "print orders with pencils in them"
    when
        $i: Item(name == "pencil")
        $ol: OrderLine(item == $i)
        $o: Order($ol memberOf orderLines,
        orderLines contains $ol)
    then
        System.out.println("order with pencils: " + $o);
end
 

from: 找到集合裡面對應條件的資料

rule "match all famale by from"
    when
      Company($persons: persons)
      $p:Person(gender == Person.GENDER_FEMALE) from $persons
    then
      System.out.println("girl'name is " + $p.getName());
end

　　　　　Person p = new Person();
        p.setName("Wang");
        p.setGender(Person.GENDER_FEMALE);

        Person p2 = new Person();
        p2.setName("Depu");
        p2.setGender(Person.GENDER_MALE);

        List<Person> persons = new ArrayList<>();
        persons.add(p);
        persons.add(p2);
        Company c = new Company();
        c.setPersons(persons);

        ks.insert(c);
 

collect(以下的程式碼的意思是把是Person物件的都集中起來放在一個List裡面)

rule "match all famale by collect"
    when
      $grils:List(size>0) from collect(Person(name=="Depu"))
    then
      System.out.println("gril's size " + $grils.size());
end

    @Test
    public void testCollect() {
        Person p = new Person();
        p.setName("Wang");
        p.setGender(Person.GENDER_FEMALE);

        Person p2 = new Person();
        p.setName("Depu");
        p.setGender(Person.GENDER_MALE);
    
        ks.insert(p);
        ks.insert(p2);

        int count = ks.fireAllRules();
        System.out.println("total run " +count+ " rules");
    }
 

正則匹配規則

rule "validate customer emails"
    when 
        $c: Customer(email not matches "[A-Za-z0-9-.][email protected][A-Za-z0-9-.]+$")
    then 
        $c.setEmail(null); //invalidate email
end

Accumulate 關鍵字  這是一個很強大的功能，它提供了強大的過濾功能，比如使用者A有一批訂單，使用者實體類裡面有一個集合是儲存的訂單，通過這個關鍵字可以根據訂單的欄位過濾出符合條件的訂單

以下的程式碼表達的意思是，對Account類的balance求平均值，將最終的計算結果放在$averageBalancez中

query averageBalanceQuery
  Number( $averageBalance : doubleValue ) from accumulate(
    $account : Account($balance : balance), average($balance))
end

    @Test
    @Parameters("17.00,50.0,22.0,5.0")
    public void testAverage(double val1, double val2, double val3, double val4){
        ks.fireAllRules();
        System.out.println(getAverageBalance());// 0.0
        ks.insert(new Account(val1));
        ks.insert(new Account(val2));
        ks.insert(new Account(val3));
        ks.insert(new Account(val4));
        System.out.println(getAverageBalance());// 23.5

    }

    BigDecimal getAverageBalance() {
        QueryResults queryResults = ks.getQueryResults("averageBalanceQuery");
        return BigDecimal.valueOf((Double) queryResults
                .iterator().next().get("$averageBalance"));
    }