Drools从字符串中加载规则

最新推荐文章于 2022-05-26 14:35:47 发布

转载最新推荐文章于 2022-05-26 14:35:47 发布 · 712 阅读

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原文链接：https://my.oschina.net/xishuixixia/blog/126166

文章标签：

#java #python #runtime

本文介绍如何使用Drools规则引擎动态地从字符串加载规则，并提供了一个完整的示例代码，展示了如何定义规则、初始化Drools环境、插入事实对象及触发规则执行。

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看了Drools官方的例子后发现，他的规则基本都是从Drl文件中读取的，而在我们的项目中(其实我们的项目代表很多的使用场景)，规则是根据配置条件动态组装的，最后会组装成一个String字符串然后交给Drools处理。查了API后，找到了如下的使用方法：

// read rule from String
String myRule = "import hellodrools.Message rule \"Hello World 2\" when message:Message (type==\"Test\") then System.out.println(\"Test, Drools!\"); end";
Resource myResource = ResourceFactory.newReaderResource((Reader) new StringReader(myRule));
kbuilder.add(myResource, ResourceType.DRL);

完整的测试代码如下，供大家参考：

package hellodrools;
 
import java.io.Reader;
import java.io.StringReader;
import java.util.Collection;
import org.drools.KnowledgeBase;
import org.drools.KnowledgeBaseFactory;
import org.drools.builder.KnowledgeBuilder;
import org.drools.builder.KnowledgeBuilderFactory;
import org.drools.builder.ResourceType;
import org.drools.definition.KnowledgePackage;
import org.drools.io.Resource;
import org.drools.io.ResourceFactory;
import org.drools.runtime.StatefulKnowledgeSession;
 
public class HelloDroolsNew {
 
    private static KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
    private static Collection<KnowledgePackage> pkgs;
    private static KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
    private static StatefulKnowledgeSession ksession;
 
    public static void main(final String[] args) {
 
        initDrools();
        initMessageObject();
        fireRules();
 
    }
 
    private static void initDrools(){
 
        // this will parse and compile in one step
        // read from file
        kbuilder.add( ResourceFactory.newClassPathResource( "/hellodrools/testrules.drl",HelloDroolsNew.class),ResourceType.DRL );
 
        // read second rule from String
        String myRule = "import hellodrools.Message rule \"Hello World 2\" when message:Message (type==\"Test\") then System.out.println(\"Test, Drools!\"); end";
        Resource myResource = ResourceFactory.newReaderResource((Reader) new StringReader(myRule));
        kbuilder.add(myResource, ResourceType.DRL);
 
        // Check the builder for errors
        if ( kbuilder.hasErrors() ) {
            System.out.println( kbuilder.getErrors().toString() );
            throw new RuntimeException( "Unable to compile drl\"." );
        }
 
        // get the compiled packages (which are serializable)
        pkgs = kbuilder.getKnowledgePackages();
 
        // add the packages to a knowledgebase (deploy the knowledge packages).
        kbase.addKnowledgePackages( pkgs );
 
        ksession = kbase.newStatefulKnowledgeSession(); }
 
    private static void fireRules(){
        ksession.fireAllRules();
        ksession.dispose();
    }
 
    private static void initMessageObject() {
        Message msg = new Message();
        msg.setType("Test");
        ksession.insert(msg);
    }
}

转载于:https://my.oschina.net/xishuixixia/blog/126166