Question

我在运行Java程序时遇到空指针异常 addPackageFromDrl无法正常工作，因此从builder.getPackage()返回的pkg为空。

我正在使用Drools 6

private static RuleBase readRules() throws DroolsParserException, IOException {
    Reader source = new InputStreamReader(   
    MessageDroolsTest1.class.getClassLoader().getResourceAsStream( "rule.drl" ) );

    System.out.println("Source:" + source);

    PackageBuilder builder = new PackageBuilder();
    builder.addPackageFromDrl( source );
    System.out.println("Builder:" + builder);

    Package pkg = builder.getPackage();
    System.out.println("Package:" + pkg);

    RuleBase ruleBase = RuleBaseFactory.newRuleBase();
    ruleBase.addPackage( pkg );
    return ruleBase;            
}

我尝试了另一种方法，但仍然遇到运行时异常。

private static KnowledgeBase createKnowledgeBase() {  
    KnowledgeBuilder builder = KnowledgeBuilderFactory.newKnowledgeBuilder();  
            //Add drl file into builder  
    File drl = new File("rules.drl");  
    builder.add(ResourceFactory.newFileResource(drl), ResourceType.DRL);  
    if (builder.hasErrors()) {  
        throw new RuntimeException(builder.getErrors().toString());  
    }  

    KnowledgeBase knowledgeBase = KnowledgeBaseFactory.newKnowledgeBase();  
            //Add to Knowledge Base packages from the builder which are actually the rules from the drl file.  
    knowledgeBase.addKnowledgePackages(builder.getKnowledgePackages());  
    return knowledgeBase;  
}

错误

Exception in thread "main" org.drools.RuntimeDroolsException:  
Unable to load dialect 'org.drools.rule.builder.dialect.java.JavaDialectConfiguration:  
java:org.drools.rule.builder.dialect.java.JavaDialectConfiguration'

Answer 1

这对我有用，至少对于正确的DRL文件。

我建议您添加

    System.out.println("Builder:" + builder);
    if( builder.hasErrors() ){
    System.out.println("Builder has errors!");
}

如果这表明存在错误，请使用其他方法检索消息。

Drools 6引入了一整套新类（Knowledge *），您应该使用它。建议不要使用内部API（或Drools 5中使用的内容），并且您的代码可能会因任何版本更改而中断。

**后来**

6.x的简单构建过程：

public void build() throws Exception {
    KieServices kieServices = KieServices.Factory.get();
    KieFileSystem kfs = kieServices.newKieFileSystem();
    FileInputStream fis = new FileInputStream( "simple.drl" );
    kfs.write( "src/main/resources/simple.drl",
                kieServices.getResources().newInputStreamResource( fis ) );
    KieBuilder kieBuilder = kieServices.newKieBuilder( kfs ).buildAll();
    Results results = kieBuilder.getResults();
    if( results.hasMessages( Message.Level.ERROR ) ){
        System.out.println( results.getMessages() );
        throw new IllegalStateException( "### errors ###" );
    }
    KieContainer kieContainer =
       kieServices.newKieContainer( kieServices.getRepository().getDefaultReleaseId() );
    KieBase kieBase = kieContainer.getKieBase();
    kieSession = kieContainer.newKieSession();
}

Drools API中的NullPointerException

1 个答案: