为什么Clojure用未经检查的异常包装检查异常？

Question

下面的代码演示了ExecutionException一个操作引发检查异常的情况,Clojure将其包装起来RuntimeException.

为什么Clojure这样做？这是正常的吗？在这种情况下,Clojure似乎做了与Java不同的事情.在这种情况下Exception,处理失败的实际异常的惯用方法是什么？

user=> (def f (future (Thread/sleep 10000) (throw (Exception. "hello world"))))
#'user/f

user=> (.get f)
Exception hello world  user/fn--318 (NO_SOURCE_FILE:81)

user=> (.printStackTrace *e)
java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.Exception: hello world
    at clojure.lang.Util.runtimeException(Util.java:165)
    at clojure.lang.Reflector.invokeMatchingMethod(Reflector.java:97)
    at clojure.lang.Reflector.invokeNoArgInstanceMember(Reflector.java:316)
    at user$eval320.invoke(NO_SOURCE_FILE:82)
    at clojure.lang.Compiler.eval(Compiler.java:6465)
    at clojure.lang.Compiler.eval(Compiler.java:6431)
    at clojure.core$eval.invoke(core.clj:2795)
    at clojure.main$repl$read_eval_print__5967.invoke(main.clj:244)
    at clojure.main$repl$fn__5972.invoke(main.clj:265)
    at clojure.main$repl.doInvoke(main.clj:265)
    at clojure.lang.RestFn.invoke(RestFn.java:421)
    at clojure.main$repl_opt.invoke(main.clj:331)
    at clojure.main$main.doInvoke(main.clj:427)
    at clojure.lang.RestFn.invoke(RestFn.java:397)
    at clojure.lang.Var.invoke(Var.java:397)
    at clojure.lang.AFn.applyToHelper(AFn.java:159)
    at clojure.lang.Var.applyTo(Var.java:518)
    at clojure.main.main(main.java:37)
Caused by: java.util.concurrent.ExecutionException: java.lang.Exception: hello world
    at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
    at java.util.concurrent.FutureTask.get(FutureTask.java:83)
    at clojure.core$future_call$reify__5684.get(core.clj:6064)
    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 clojure.lang.Reflector.invokeMatchingMethod(Reflector.java:92)
    ... 16 more
Caused by: java.lang.Exception: hello world
    at user$fn__318.invoke(NO_SOURCE_FILE:81)
nil
    at clojure.core$binding_conveyor_fn$fn__3713.invoke(core.clj:1817)
    at clojure.lang.AFn.call(AFn.java:18)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:680)

Answer 1

请注意,确实抛出了ExcecutionException - 只是异常被Clojure捕获并处理.

Clojure在处理它们时会在RuntimeException中包装某些异常 - 我相信这样做是为了避免在Clojure源代码中处理已检查的异常.

如果你想访问底层的异常,那么(.getCause e)应该工作.