作为测试Gradle插件的一部分,我想要一个groovy方法:project.exec {…}.这是为了确认它正在进行正确的命令行调用.我正在尝试使用元编程:
Project proj = ProjectBuilder.builder().build() proj.MetaClass.exec = { Closure obj -> println 'MOCK EXEC' } proj.exec { executable 'echo' args 'PROJECT EXEC' } // prints 'PROJECT EXEC' instead of the 'MOCK EXEC' I expected
令人好奇的是,如果我将两个exec方法重命名为othername,那么它可以正常工作:
Project proj = ProjectBuilder.builder().build() proj.MetaClass.othername = { Closure obj -> println 'MOCK EXEC' } proj.othername { executable 'echo' args 'PROJECT EXEC' } // prints 'MOCK EXEC' as expected
我试图找出为什么现有的project.exec方法导致元编程失败以及是否有解决方法.请注意,Project是一个接口,但我正在模拟DefaultProject类型的特定实例.
用于截断单个方法的元编程方法来自这个答案:https://stackoverflow.com/a/23818476/1509221
解决方法
在Groovy中,使用MetaClass替换接口中定义的方法已被破坏.在这种情况下,exec方法在Project类中定义,它是一个接口.从
GROOVY-3493(最初在2009年报道):
"Cannot override methods via Metaclass that are part of an interface implementation"
替代方法
invokeMethod拦截所有方法并且可以工作.这有点矫枉过正,但确实有效.当方法名称与exec匹配时,它会将调用转移到mySpecialInstance对象.否则它将传递给委托,即现有方法.感谢invokeMethod delegation和Logging All Methods对此的输入.
// This intercepts all methods,stubbing out exec and passing through all other invokes this.project.MetaClass.invokeMethod = { String name,args -> if (name == 'exec') { // Call special instance to track verifications mySpecialInstance.exec((Closure) args.first()) } else { // This calls the delegate without causing infinite recursion MetaMethod MetaMethod = delegate.class.MetaClass.getMetaMethod(name,args) return MetaMethod?.invoke(delegate,args) } }
这很有效,除了你可能会看到关于“错误的参数数量”或“无法在null对象上调用方法xxxxx”的异常.问题是上面的代码不处理方法参数的强制转换.对于project.files(Object … paths),invokeMethod的args应该是[[‘path1′,’path2’]]的形式.但是,在某些情况下,调用文件(null)或文件(),因此invokeMethod的args分别为[null]和[],因为它预期[[]]失败.产生上述错误.
以下代码仅解决了文件方法的问题,但这对我的单元测试来说已经足够了.我仍然想找到一种更好的强制类型或更换单一方法的方法.
// As above but handle coercing of the files parameter types this.project.MetaClass.invokeMethod = { String name,args -> if (name == 'exec') { // Call special instance to track verifications mySpecialInstance.exec((Closure) args.first()) } else { // This calls the delegate without causing infinite recursion // https://stackoverflow.com/a/10126006/1509221 MetaMethod MetaMethod = delegate.class.MetaClass.getMetaMethod(name,args) logInvokeMethod(name,args,MetaMethod) // Special case 'files' method which can throw exceptions if (name == 'files') { // Coerce the arguments to match the signature of Project.files(Object... paths) // Todo: is there a way to do this automatically,e.g. coerceArgumentsToClasses? assert 0 == args.size() || 1 == args.size() if (args.size() == 0 || // files() args.first() == null) { // files(null) return MetaMethod?.invoke(delegate,[[] as Object[]] as Object[]) } else { // files(ArrayList) possibly,so cast ArrayList to Object[] return MetaMethod?.invoke(delegate,[(Object[]) args.first()] as Object[]) } } else { // normal pass through return MetaMethod?.invoke(delegate,args) } } }