java - 在 Groovy 中使用 Google-Reflection 会导致异常，而等效的 Java 代码可以工作

Question

我正在尝试使用 another answer on SO 中的一些代码，并且当代码在 Java 中运行时，从 Groovy 会导致异常。

有问题的代码是:

Reflections reflections = new Reflections(new ConfigurationBuilder()
        .setScanners( new SubTypesScanner(false /* don't exclude Object.class */), new ResourcesScanner() )
        .setUrls(ClasspathHelper.forClassLoader(classLoadersList.toArray(new ClassLoader[0])))
        .filterInputsBy(
        new FilterBuilder()
                .include( prefix( "net.initech" ) )
                .exclude( prefix( "net.initech.util" )
        )));

有问题的抛出异常似乎是: ClasspathHelper.forClassLoader(...)
无论我是否使用 @CompileStatic，都会发生这种情况或不。另外，尝试使用 this.getClassLoader()并发生同样的问题。

异常(exception)是:

Exception in thread "main" java.lang.NoClassDefFoundError: javax/servlet/ServletContext
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2688)
at java.lang.Class.getDeclaredMethods(Class.java:1962)
at org.codehaus.groovy.reflection.stdclasses.CachedSAMClass.getAbstractMethods(CachedSAMClass.java:91)
at org.codehaus.groovy.reflection.stdclasses.CachedSAMClass.getSAMMethod(CachedSAMClass.java:155)
at org.codehaus.groovy.reflection.ClassInfo.isSAM(ClassInfo.java:280)
at org.codehaus.groovy.reflection.ClassInfo.createCachedClass(ClassInfo.java:270)
at org.codehaus.groovy.reflection.ClassInfo.access$400(ClassInfo.java:36)
at org.codehaus.groovy.reflection.ClassInfo$LazyCachedClassRef.initValue(ClassInfo.java:441)
at org.codehaus.groovy.reflection.ClassInfo$LazyCachedClassRef.initValue(ClassInfo.java:432)
at org.codehaus.groovy.util.LazyReference.getLocked(LazyReference.java:46)
at org.codehaus.groovy.util.LazyReference.get(LazyReference.java:33)
at org.codehaus.groovy.reflection.ClassInfo.getCachedClass(ClassInfo.java:89)
at org.codehaus.groovy.reflection.ReflectionCache.getCachedClass(ReflectionCache.java:107)
at groovy.lang.MetaClassImpl.(MetaClassImpl.java:163)
at groovy.lang.MetaClassImpl.(MetaClassImpl.java:187)
at groovy.lang.MetaClassImpl.(MetaClassImpl.java:193)
at groovy.lang.MetaClassRegistry$MetaClassCreationHandle.createNormalMetaClass(MetaClassRegistry.java:158)
at groovy.lang.MetaClassRegistry$MetaClassCreationHandle.createWithCustomLookup(MetaClassRegistry.java:148)
at groovy.lang.MetaClassRegistry$MetaClassCreationHandle.create(MetaClassRegistry.java:131)
at org.codehaus.groovy.reflection.ClassInfo.getMetaClassUnderLock(ClassInfo.java:175)
at org.codehaus.groovy.reflection.ClassInfo.getMetaClass(ClassInfo.java:192)
at org.codehaus.groovy.runtime.metaclass.MetaClassRegistryImpl.getMetaClass(MetaClassRegistryImpl.java:255)
at org.codehaus.groovy.runtime.InvokerHelper.getMetaClass(InvokerHelper.java:859)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.createCallStaticSite(CallSiteArray.java:72)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.createCallSite(CallSiteArray.java:159)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
at net.initech.DeltaCodeGen.main(DeltaCodeGen.groovy:27)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.lang.ClassNotFoundException: javax.servlet.ServletContext
at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 35 more

我可以通过添加到我的 POM.xml 来解决这个问题

    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>servlet-api</artifactId>
        <version>6.0.37</version>
    </dependency>

但我不应该有，也没有在 Java 版本中。

Answer 1

您可能会遇到一个众所周知的问题，即 Groovy 编译器有时需要将运行时依赖项放在其编译类路径中。这是因为编译器使用 Java 反射来访问其编译类路径。有具体计划在即将发布的版本中解决此问题(不记得是 2.x 还是 3.0)。