Drools动态结构规则内容

Drools动态构造规则内容

package com.sample;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

import org.drools.RuleBase;
import org.drools.RuleBaseFactory;
import org.drools.WorkingMemory;
import org.drools.compiler.DroolsParserException;
import org.drools.compiler.PackageBuilder;
import org.drools.definition.type.FactType;
import org.drools.event.DebugWorkingMemoryEventListener;
import org.drools.rule.Package;

public class DynamicRules {

	public static String buildRuleSource(){
		//完整的规则内容如下：
		/*
	    package com.sample
		declare People
			id:String
			name:String
			returnContent:String
		end
		 
		rule "rule2"
			when
				$people : People( id == "001")
			then
				System.out.println( $people.getName()); 
		end
		 */
		
		StringBuffer sb = new StringBuffer();
		sb.append("package com.sample");
		sb.append("\r\n");
		sb.append("declare People");
		sb.append("\r\n");
		sb.append("id:String");
		sb.append("\r\n");
		sb.append("name:String");
		sb.append("\r\n");
		sb.append("end");
		sb.append("\r\n");
		sb.append("rule \"rule2\"");
		sb.append("\r\n");
		sb.append("when");
		sb.append("\r\n");
		sb.append("$People : People( id == \"001\")");
		sb.append("\r\n");
		sb.append("then");
		sb.append("\r\n");
		sb.append("System.out.println( $People.getName());");
		sb.append("\r\n");
		sb.append("end");

		//System.out.println(sb.toString());
		return sb.toString();
	}
	
	public static void executeRules(Reader source) throws DroolsParserException, IOException{
		try {

			//创建PackageBuilder
			PackageBuilder packgebuilder = new PackageBuilder();
	
			//解析编译规则包，可加入多个source
			packgebuilder.addPackageFromDrl(source);
	
			//获得已经编译的规则包
			Package pkg = packgebuilder.getPackage();
			
			//创建一个规则集
			RuleBase ruleBase  = RuleBaseFactory.newRuleBase();
			
			//加载已规则包
			ruleBase.addPackage(pkg);
			
			//获得规则中需要使用的事实对象,方式:包名.事实名
			FactType factType = ruleBase.getFactType("com.sample.People");
			
			//创建一个事实实例
			Object factPeople1 = factType.newInstance();
			
			//给事实属性赋值
			factType.set(factPeople1, "id", "001");   
			factType.set(factPeople1, "name", "tom");   
			
			//执行规则。方法1，使用StatefulSession，一次只能插入一个事实
			//WorkingMemory workingMemory = ruleBase.newStatefulSession();
			//workingMemory.addEventListener(new DebugWorkingMemoryEventListener());
			//workingMemory.insert(factPeople1);
			//workingMemory.fireAllRules();
			
			//执行规则。方法2,使用StatelessSession执行规则
			//可传入Collect/Object[]/Object
			ruleBase.newStatelessSession().execute(new Object[] {factPeople1});
			
		} catch (Throwable t) {
			t.printStackTrace();
		}
	}
	
	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//构造规则内容字符串，此处可换成从数据库读取规则的各个部分，包括事实、包名称、函数、import内容构造一个完整的规则文件
		String s = buildRuleSource();
		//转换成Reader
		StringReader source = new StringReader(s); 
		try{
			executeRules(source);
		}
		catch(Throwable t){
			t.printStackTrace();
		}
	}
}