Java中动态规则的实现方式示例详解

Foo foo = new Foo();
foo.setName("test");
Map<String, Object> context = new HashMap<String, Object>();
context.put("foo",foo);
String expression = "foo.name == 'test'";
try {
 Boolean result = (Boolean) Ognl.getValue(expression,context);
 System.out.println(result);
} catch (OgnlException e) {
 e.printStackTrace();
}

//解释模式
Foo foo = new Foo();
foo.setName("test");
Map context = new HashMap();
String expression = "foo.name == 'test'";
VariableResolverFactory functionFactory = new MapVariableResolverFactory(context);
context.put("foo",foo);
Boolean result = (Boolean) MVEL.eval(expression,functionFactory);
System.out.println(result);

//编译模式
Foo foo = new Foo();foo.setName("test");
Map context = new HashMap();
String expression = "foo.name == 'test'";
VariableResolverFactory functionFactory = new MapVariableResolverFactory(context);context.put("foo",foo);
Serializable compileExpression = MVEL.compileExpression(expression);

//解释器模式
Foo foo = new Foo();
foo.setName("test");
// Turn on:
// - auto null reference initialization
// - auto collection growing
SpelParserConfiguration config = new SpelParserConfiguration(true,true);
ExpressionParser parser = new SpelExpressionParser(config);
String expressionStr = "#foo.name == 'test'";
StandardEvaluationContext context = new StandardEvaluationContext();
context.setVariable("foo",foo);
Expression expression = parser.parseExpression(expressionStr);
Boolean result = expression.getValue(context,Boolean.class);

//编译模式
config = new SpelParserConfiguration(SpelCompilerMode.IMMEDIATE, RunSpel.class.getClassLoader());
parser = new SpelExpressionParser(config);
context = new StandardEvaluationContext();
context.setVariable("foo",foo);
expression = parser.parseExpression(expressionStr);
result = expression.getValue(context,Boolean.class);

public class Test {
 public static void main(String[] args) {
  String expression = "a+(b-c)>100";
  // 编译表达式
  Expression compiledExp = AviatorEvaluator.compile(expression);

  Map<String, Object> env = new HashMap<>();
  env.put("a", 100.3);
  env.put("b", 45);
  env.put("c", -199.100);

  // 执行表达式
  Boolean result = (Boolean) compiledExp.execute(env);
  System.out.println(result);
 }
}

@Rule(name = "weather rule", description = "if it rains then take an umbrella")
public class WeatherRule {

 @Condition
 public boolean itRains(@Fact("rain") boolean rain) {
  return rain;
 }
 
 @Action
 public void takeAnUmbrella() {
  System.out.println("It rains, take an umbrella!");
 }
}

Rule weatherRule = new RuleBuilder()
  .name("weather rule")
  .description("if it rains then take an umbrella")
  .when(facts -> facts.get("rain").equals(true))
  .then(facts -> System.out.println("It rains, take an umbrella!"))
  .build();

name: "weather rule"
description: "if it rains then take an umbrella"
condition: "rain == true"
actions:
 - "System.out.println(\"It rains, take an umbrella!\");"
MVELRuleFactory ruleFactory = new MVELRuleFactory(new YamlRuleDefinitionReader());
Rule weatherRule = ruleFactory.createRule(new FileReader("weather-rule.yml"));

public class Test {
 public static void main(String[] args) {
  // define facts
  Facts facts = new Facts();
  facts.put("rain", true);

  // define rules
  Rule weatherRule = ...
  Rules rules = new Rules();
  rules.register(weatherRule);

  // fire rules on known facts
  RulesEngine rulesEngine = new DefaultRulesEngine();
  rulesEngine.fire(rules, facts);
 }
}

import com.lrq.wechatDemo.domain.User // 导入类
dialect "mvel"
rule "age" // 规则名，唯一
 when
  $user : User(age<15 || age>60) //规则的条件部分
 then
  System.out.println("年龄不符合要求！");
end

public class TestUser {
 private static KieContainer container = null;
 private KieSession statefulKieSession = null;

 @Test
 public void test(){
  KieServices kieServices = KieServices.Factory.get();
  container = kieServices.getKieClasspathContainer();
  statefulKieSession = container.newKieSession("myAgeSession");
  User user = new User("duval yang",12);
  statefulKieSession.insert(user);
  statefulKieSession.fireAllRules();
  statefulKieSession.dispose();
 }
}

public class Test {
 public static void main(String[] args) throws InterruptedException {
  EPServiceProvider epService = EPServiceProviderManager.getDefaultProvider();
 
  EPAdministrator admin = epService.getEPAdministrator();
 
  String product = Apple.class.getName();
  String epl = "select avg(price) from " + product + ".win:length_batch(3)";
 
  EPStatement state = admin.createEPL(epl);
  state.addListener(new AppleListener());
 
  EPRuntime runtime = epService.getEPRuntime();
 
  Apple apple1 = new Apple();
  apple1.setId(1);
  apple1.setPrice(5);
  runtime.sendEvent(apple1);
 
  Apple apple2 = new Apple();
  apple2.setId(2);
  apple2.setPrice(2);
  runtime.sendEvent(apple2);
 
  Apple apple3 = new Apple();
  apple3.setId(3);
  apple3.setPrice(5);
  runtime.sendEvent(apple3);
 }
}

public class GroovyFilter implements Filter {
 private static String template = "" +
   "package com.alarm.eagle.filter;" +
   "import com.fasterxml.jackson.databind.node.ObjectNode;" +
   "def match(ObjectNode o){[exp]}";

 private static String method = "match";

 private String filterExp;

 private transient GroovyObject filterObj;

 public GroovyFilter(String filterExp) throws Exception {
  ClassLoader parent = Thread.currentThread().getContextClassLoader();
  GroovyClassLoader classLoader = new GroovyClassLoader(parent);
  Class clazz = classLoader.parseClass(template.replace("[exp]", filterExp));
  filterObj = (GroovyObject)clazz.newInstance();
 }

 public boolean filter(ObjectNode objectNode) {
  return (boolean)filterObj.invokeMethod(method, objectNode);
 }
}