Drools的运行时异常（org.drools.util.CompositeClassLoader.clone（）Lorg / drools / util / CompositeClassLoader）

Question

I'm running drools project with Java. The line KnowledgeBase kbase = readKnowledgeBase(); gives the exception below:

java.lang.NoSuchMethodError: org.drools.util.CompositeClassLoader.clone()Lorg/drools/util/CompositeClassLoader;
    at org.drools.compiler.PackageBuilderConfiguration.getClassLoader(PackageBuilderConfiguration.java:322)
    at org.drools.rule.builder.dialect.java.JavaDialectConfiguration.setCompiler(JavaDialectConfiguration.java:91)
    at org.drools.rule.builder.dialect.java.JavaDialectConfiguration.init(JavaDialectConfiguration.java:54)
    at org.drools.compiler.PackageBuilderConfiguration.addDialect(PackageBuilderConfiguration.java:273)
    at org.drools.compiler.PackageBuilderConfiguration.buildDialectConfigurationMap(PackageBuilderConfiguration.java:262)
    at org.drools.compiler.PackageBuilderConfiguration.init(PackageBuilderConfiguration.java:175)
    at org.drools.compiler.PackageBuilderConfiguration.<init>(PackageBuilderConfiguration.java:153)
    at org.drools.compiler.PackageBuilder.<init>(PackageBuilder.java:254)
    at org.drools.compiler.PackageBuilder.<init>(PackageBuilder.java:182)
    at org.drools.builder.impl.KnowledgeBuilderFactoryServiceImpl.newKnowledgeBuilder(KnowledgeBuilderFactoryServiceImpl.java:34)
    at org.drools.builder.KnowledgeBuilderFactory.newKnowledgeBuilder(KnowledgeBuilderFactory.java:47)
    at com.sample.TestExample.readKnowledgeBase(TestExample.java:36)
    at com.sample.TestExample.ProductClassHolder(TestExample.java:56)
    at com.sample.TestExample.main(TestExample.java:30)

Answer 1

I had the same issue and struggled with it for a while. In my case the issue was due to the conflict of libraries drools-api.jar v5.1.1 and knowledge-api-5.4.0.Final.jar at runtime. Both of these libraries have class org.drools.util.CompositeClassLoader but the one in drools-api.jar doesn't have the clone() method and this was getting loaded at runtime. I removed drools-api.jar and now it is working fine and rules are also getting executed.