Class.forName（...）Vs. Thread.currentThread.getContextClassLoader.loadClass（...）行爲

Question

我想動態加載由Scala REPL的Guava庫定義的對象Class。然而，我發現這取決於我檢索Class定義的方式不同的行爲：

scala> :cp guava-10.0.1.jar 
Added '/Users/xxx/guava-10.0.1.jar'. Your new classpath is: 
"/Users/rouvoy/Development/tools/axis/default/lib:/Users/xxx/guava-10.0.1.jar" 

scala> Class.forName("com.google.common.base.Ascii") 
res0: java.lang.Class[_] = class com.google.common.base.Ascii 

的Class.forName(...)方法工作正常，並設法獲取Class對象，但我想了解使用ContextClassLoader時候爲什麼，我我無法找到類定義 - 儘管它在Java中完美工作？

scala> Thread.currentThread.getContextClassLoader.loadClass("com.google.common.base.Ascii") 
java.lang.ClassNotFoundException: com.google.common.base.Ascii 
at java.net.URLClassLoader$1.run(URLClassLoader.java:202) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.net.URLClassLoader.findClass(URLClassLoader.java:190) 
at java.lang.ClassLoader.loadClass(ClassLoader.java:306) 
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) 
at java.lang.ClassLoader.loadClass(ClassLoader.java:247) 
at .<init>(<console>:8) 
at .<clinit>(<console>) 
at .<init>(<console>:11) 
at .<clinit>(<console>) 
at $print(<console>) 
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 
at java.lang.reflect.Method.invoke(Method.java:597) 
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704) 
at scala.tools.nsc.interpreter.IMain$Request$$anonfun$14.apply(IMain.scala:920) 
at scala.tools.nsc.interpreter.Line$$anonfun$1.apply$mcV$sp(Line.scala:43) 
at scala.tools.nsc.io.package$$anon$2.run(package.scala:25) 
at java.lang.Thread.run(Thread.java:680) 

scala> Class.forName("com.google.common.base.Ascii",true,Thread.currentThread.getContextClassLoader) 
java.lang.ClassNotFoundException: com.google.common.base.Ascii 
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.net.URLClassLoader.findClass(URLClassLoader.java:190) 
at java.lang.ClassLoader.loadClass(ClassLoader.java:306) 
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) 
at java.lang.ClassLoader.loadClass(ClassLoader.java:247) 
at java.lang.Class.forName0(Native Method) 
at java.lang.Class.forName(Class.java:247) 
at .<init>(<console>:8) 
at .<clinit>(<console>) 
at .<init>(<console>:11) 
at .<clinit>(<console>) 
at $print(<console>) 
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) 
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) 
at java.lang.reflect.Method.invoke(Method.java:597) 
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704) 
at scala.tools.nsc.interpreter.IMain$Request$$anonfun$14.apply(IMain.scala:920) 
at scala.tools.nsc.interpreter.Line$$anonfun$1.apply$mcV$sp(Line.scala:43) 
at scala.tools.nsc.io.package$$anon$2.run(package.scala:25) 
at java.lang.Thread.run(Thread.java:680) 

Answer 1

Scala和Java之間的類加載有細微的差別。當你爲scala可執行文件（script或.bat）指定-cp時，它不會被添加到基類路徑中，它只會被添加到Scala Class Loader中。我懷疑當您指定時，REPL也是如此：cp。

要真正地將某些東西添加到java類路徑中，請使用-toolcp選項將scala或scalac。

查看我的回答：scala classloaders confusion。