在Drools中使用MVEL

dialect设置规则当中要使用的语言类型 ，默认除了java还有mevl。本文简单介绍mvel。?
mvel是一种嵌入式脚本语言,在规则文件上可以用这种语言建立他们的断言、返回值、Eval和推论。mvel分解析模式(Interpreted Mode)和编译模式(Compiled Mode)?


mvel语法:?
表示对象的属性?

user.name?? 相当于java代码 user.getName()?
user.manager.name? 相当于java代码 user.getManager().getName()?
比较?
user.name == 'John Doe'?
(user.name == 'John Doe') && ((x * 2) - 1) > 20?


返回值?
a = 10;?
b = (a = a * 2) + 10; 相当于java代码? a=10; a= a*2; b=? a + 10;?
return a;?


数组和list访问:user[5]?? 相当于java代码 user.get(5);?
Map访问:user["foobar"]?? 相当于java代码 user.get("foobar")?


创建对象:?
new String("foo")?


对一个对象，多个属性赋值?
with (user = new User()) {?
?????? name = "John Doe",?
?????? age = 28,?
?????? sex = Sex.MALE,?
?????? admin = true?
??? }?




脚本:?
note：?
语法跟一些函数语言或脚本语言差不多，如scala?


调用某些方法?
String test = "Hello";?
Object result = MVEL.eval("toUpperCase()", test);?


获取pojo的属性值?
User user = new User();?
user.setName("Bob");?
user.setPassword("Despot");?
user.setAge(30);?


String name = (String) MVEL.eval("name", user);?


比较?
public class Person {?
??? private String name;?
??? public void setName(String name) { this.name = name; }?
??? public String getName() { return this.name; }?
}?


Person?
personInst = new Person();?
personInst.setName("Mr. Foo");?


Object result = MVEL.eval("name == 'Mr. Foo' ", personInst);?


赋值?
Map vars = new HashMap();?
vars.put("x", new Integer(5));?
vars.put("y", new Integer(10));?


Integer result = (Integer) MVEL.eval("x * y", vars);?
相当于java代码 Integer? result =? (Integer)vars.get("x") *? (Integer)vars.get(" y ")?
assert result.intValue() == 50;? // Mind the JDK 1.4 compatible code?


规则文件使用mvel示例?



示例1：?

package com.demo.mvel import com.demo.* rule "rule1" dialect "mvel" when #设是规则引擎语法 $a : Applicant( age < 18 ) then   #mvel 语法 $a.valid = false; end 

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示例2：?

package com.demo.mvel import com.demo.* import java.util.List; rule "rule1"     salience 2      dialect "java"      when   eval(true);      then   Applicant app = new Applicant("依晨",20);   insert(app); end rule "rule2"     salience 1     dialect "mvel"     #no-loop true 不会循环     when        $app:Applicant(name == "依晨",age<30)     then        #update方法2       #$app.age + 1是mvel语法        Applicant app = new Applicant("依晨",$app.age + 1);        update(drools.getWorkingMemory().getFactHandleByIdentity($app),app);            #update方法1        #$app.setAge($app.getAge() + 1);        #update($app);        System.out.println("------" + $app.name+"("+ $app.age + ")"); end

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