如何用Object []数组调用MethodHandle.invokeExact()?

问题描述

Java的MethodHandle.invokeExact(Object ... args)采用可变长度的参数列表.但是，当我尝试传递Object []数组而不是列表时，出现错误.见下文:

Java's MethodHandle.invokeExact(Object...args) takes a variable-length list of arguments. When I try to pass an array of Object [] instead of a list, though, I get an error. See below:

private void doIt() throws Throwable {

    Method meth = Foo.class.getDeclaredMethods()[0];

    MethodHandles.Lookup lookup = MethodHandles.lookup();
    MethodHandle mh = lookup.unreflect(meth);

    Foo foo = new Foo();
    String myStr = "aaa";
    Integer myInt = new Integer(10);
    Object [] myArray = {foo, myStr, myInt};

    mh.invokeExact(foo, myStr, myInt); // prints "Called aaa 10"
    mh.invokeExact(myArray); // throws Exception
}

class Foo {
    public void bar(String myStr, Integer myInt) {
        System.out.println("Called " + myStr + " " + myInt);
    }
}

第二次调用invokeExact()会产生此异常:

The second call to invokeExact() produces this Exception:

Exception in thread "main" java.lang.invoke.WrongMethodTypeException: (Ljava/lang/String;Ljava/lang/Integer;)V cannot be called with a different arity as ([Ljava/lang/Object;)V
    at io.rhubarb.core.TestInvoke.doIt0(TestInvoke.java:26)
    at io.rhubarb.core.TestInvoke.main(TestInvoke.java:11)

这可能与两年前修复的Eclipse中的错误有关( https://bugs .eclipse.org/bugs/show_bug.cgi?id = 385404 )，但我不这么认为，因为当我关闭Eclipse时，请删除/target目录，使用Maven重新编译所有内容，然后从命令行运行我得到相同的结果.

This might be related to a bug in Eclipse that was fixed two years ago (https://bugs.eclipse.org/bugs/show_bug.cgi?id=385404) but I don't think so, because when I close Eclipse, delete the /target directory, recompile everything using Maven, and run from the command line I get the same results.

我正在使用Eclipse Kepler SR2，所有内容都是最新的，以及JDK 1.7.0_25.

I'm using Eclipse Kepler SR2, everything fully up to date, and JDK 1.7.0_25.

推荐答案

MethodHandle.invoke()和MethodHandle.invokeExact()是特殊方法，其行为与其他可变arity方法不同:

MethodHandle.invoke() and MethodHandle.invokeExact() are special methods that don't behave like other variable arity methods:

因此，当您调用这些方法时，参数的类型确实很重要.如果要将参数作为Object[]传递，则应改用invokeWithArguments():

So, types of parameters really matter when you call these methods. If you want to pass parameters as Object[], you should use invokeWithArguments() instead:

mh.invokeWithArguments(myArray);

另请参见:

• MethodHandle javadoc

• MethodHandle javadoc

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