4. Drl规则内容几种写法测试代码

 public Object checkRule(Object msg) {
        List<String> drlContentList=new ArrayList<>();

         //当一个Fact对象为集合对象时的判断
        //这个是当把某个集合（List）当成一个fact传入工作内存中后，规则有效
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
                "import cn.zuowenjun.model.Message;\n" +
                "import java.util.List;\n" +
                "rule \"test rule 0\"\n" +
                "when \n" +
                "$list:List(size>0) \n" +
                "$msg:Message(createBy==\"zuowj\") from $list \n " +
                "then\n" +
                "System.out.println(\"hello zuowj! ---rule 0\");\n" +
                "$msg.setReplyBy(\"rule 0\");\n" +
                "end");

         //普通Pattern 模式+字段约束
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
                "import cn.zuowenjun.model.Message;\n" +
                "rule \"test rule 1\"\n" +
                "when \n" +
                "$msg:Message(createBy==\"zuowj\")\n " +
                "then\n" +
                "System.out.println(\"hello zuowj! ---rule 1\");\n" +
                "$msg.setReplyBy(\"rule 1\");\n" +
                "end");

         //accumulate 内联方式（类似for循环处理）
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
                "import cn.zuowenjun.model.Message;\n" +
                "rule \"test rule 2\"\n" +
                "when \n" +
                "exists(Message(createBy==\"zuowj\"))\n"+
                "$res:String() from accumulate(Message(createBy==\"zuowj\",$cont:content),init(String allContent=\"\";),action(allContent +=$cont;),result(allContent))"+
                "then\n" +
                "System.out.println($res +\"---rule 2\");\n" +
                "end");

         //accumulate 普通函数方式
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
                "import cn.zuowenjun.model.Message;\n" +
                "rule \"test rule 2-2\"\n" +
                "when \n" + "accumulate(Message(createBy==\"zuowj\",$id:id);$countNum:count($id);$countNum>1) \n"+
                "then\n" +
                "System.out.println(\"count number:\"+ $countNum +\"---rule 2-2\");\n" +
                "end");

         //not，不满足时
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
               "import cn.zuowenjun.model.Message;\n" +
                "rule \"test rule 3\"\n" +
                "when not Message()\n" +
                "then\n" +
                "System.out.println(\"no message don't say hello! ---rule 3\");\n" +
                "end");

         //exists，匹配执行一次
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
                "import cn.zuowenjun.model.Message;\n" +
                "rule \"test rule 4\"\n" +
                "when exists(Message(createBy==\"zuowj\"))\n" +
                "then\n" +
                "System.out.println(\"exists Message(createBy==zuowj) fact! ---rule 4\");\n" +
                "end");

         //forall，工作内存中所有fact对象必需都满足时才匹配规则
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
                "import cn.zuowenjun.model.Message;\n" +
                "rule \"test rule 5\"\n" +
                "when forall(Message(createBy==\"zuowj\"))\n" +
                "then\n" +
                "System.out.println(\"for all Message(createBy==zuowj) fact! ---rule 5\");\n" +
                "end");

         //collect,将工作内存中所有fact对象添加到同一个集合中
        drlContentList.add("package zuowenjun.drools.rule.demo\n" +
                "import cn.zuowenjun.model.Message;\n" +
                "rule \"test rule 6\"\n" +
                "when Message() && $msgs:List(size>=9) from collect(Message(createBy==\"zuowj\"))\n" +
                "then\n" +
                "System.out.println(\"collect all Message fact(size=\" + $msgs.size() +\")! ---rule 6\");\n" +
                "end");

        KieHelper kieHelper=new KieHelper();
        for(String drl:drlContentList){
            kieHelper.addContent(drl,ResourceType.DRL);
        }

        KieBase kieBase = kieHelper.build();
        StatelessKieSession kieSession = kieBase.newStatelessKieSession();
        if (msg instanceof List){
            kieSession.execute((List<?>)msg);
        } else{
            kieSession.execute(msg);
        }

        return msg;
    }

//单元测试
/**
 * @author zuowenjun
 */
@RunWith(SpringRunner.class)
@SpringBootTest(classes = {FmsHelperApplication.class}, webEnvironment = SpringBootTest.WebEnvironment.NONE)
public class RuleTests {

    @Autowired
    private RuleDemo ruleDemo;

    @Test
    public void testRule() {
        List<Message> msgList=new ArrayList<>();
        for(int i=1;i<=10;i++) {
            int n=i;
            Message msg = new Message() {
                {
                    setCreateBy("zuowj");
                    setContent("hello drools" + String.valueOf(n));
                }
            };
            if (n==1){
                msg.setCreateBy("zuowenjun.cn");
            }
            msgList.add(msg);
        }

        Object obj = ruleDemo.checkRule(msgList);
        System.out.println(JsonUtils.deserializer(obj));
    }
 ｝

5. 规则引擎引发的举一反三，自己实现一个规则引擎

思路：1.定义规则内容（即：规则执行单元），2.定义贯穿整个规则执行链条的上下文，内部就放fact、global等，具体实现参照如下示例代码【注意：如果仅是示例测试代码，并不规范，仅为演示提供思路】，整个规则执行采取：责任链的设计模式，即：每个规则只负责满足自己条件的执行逻辑，最后更新上下文中相关的内容。

//规则链上下文，里面就包含fact集合，全局对象及执行过的rule
    public class RuleChainContext {
        public List<Object> factList;
        public static Map<String, Object> global;
        public RuleUnit execedRule;
    }

 //规则执行单元抽象类（这里用抽象类而没有用接口，是因为我要限定组织逻辑，可以理解为模板用法）
    public abstract class RuleUnit {
        public RuleUnit nextExecedRule;

        protected String name;

        public abstract String getName();

        public abstract boolean matchWhen(RuleChainContext context);

        public abstract void doThen(RuleChainContext context);

        public final void execute(RuleChainContext context) {
            if (matchWhen(context)) {
                doThen(context);
            }
            if (context.execedRule == null) {
                context.execedRule = this;
            }
            context.execedRule.nextExecedRule = this;
        }

    }

通过单元测试模拟调用：

 @Test
    public void testDefRules() {
        List<RuleUnit> ruleUnitList = new ArrayList<>();
        ruleUnitList.add(new RuleUnit() {
            @Override
            public String getName() {
                name= "rule-1";
                return name;
            }

            @Override
            public boolean matchWhen(RuleChainContext context) {
                return context.factList.stream().anyMatch(f->f instanceof Integer && 1==(Integer)f);
            }

            @Override
            public void doThen(RuleChainContext context) {
                System.out.println("rule[include 1] do");
                //TODO:context
            }
        });

        ruleUnitList.add(new RuleUnit() {
            @Override
            public String getName() {
                name= "rule-2";
                return name;
            }

            @Override
            public boolean matchWhen(RuleChainContext context) {
                return context.factList.stream().anyMatch(f->f instanceof Integer && 2==(Integer)f);
            }

            @Override
            public void doThen(RuleChainContext context) {
                System.out.println("rule[exclude 2] do");
                //TODO:context
            }
        });

        RuleChainContext context=new RuleChainContext();
        context.factList=new ArrayList<>();
        context.factList.add(1);//加入1则触发规则1
        context.factList.add(2);//加入2则触发规则2，若减少规则相应减少

        for(RuleUnit ruleUnit:ruleUnitList){
            ruleUnit.execute(context);
        }

        System.out.println("result context:\n" + JsonUtils.deserializer(context));

    }

最终结果：

rule[include 1] do
rule[exclude 2] do
result context:
{"factList":[1,2],"execedRule":{"nextExecedRule":{"nextExecedRule":null,"name":"rule-2"},"name":"rule-1"}}

从输出的结果可以看出，还是可以达到规则引擎的简单效果的，当然如果想在生产环境实际应用自己实现的“类规则引擎”代码，实现规则与执行分开，也可将规则执行单元（RuleUnit）实现类单独放到一个JAR包，然后再借助于URLClassLoader实现动态加载并添加自定义的实现规则执行单元（RuleUnit）的类，最后执行即可。【.NET方面的同学实现亦同理】

注：文中相关名词解释来源于网上，并非原创，我这里仅为知识点总结！

可参考相关drools系列文章：

Drools_miemieY89-CSDN博客

邵飞翔的图书馆 (360doc.com)