如何使用MethodHandle来调用私有实例方法？ [英] How to use a MethodHandle to invoke a private instance method?

问题描述

我有这个课程：

I have this class:

package com.gmail.inverseconduit.jchatexchange.assets;

import jchatexchange.util.User;

public class UserFactory implements jchatexchange.factory.Factory {

    private boolean cnu(User user) {
        [implementation dependant on #cnuz(User)]
    }

    private int cnuz(User user) {
        [my implementation]
    }

    @Override
    public User createNewUser(int id) {
        [my implementation]
    }

    // Other methods

}

我想获得另一个类中三种方法中每种方法的 MethodHandle ，所以我使用了：

I want to obtain a MethodHandle of each of the three methods in another class, so I used:

class Baz {

    public static void main(String..$) {
        Lookup myLookup = MethodHandles.lookup();
        UserFactory foo = new UserFactory(); // test
    
        try {
            MethodType signature = MethodType.methodType(boolean.class, User.class);
            MethodHandle pmh = lookup.findVirtual(UserFactory.class, "cnu", signature);
            // ??? what now? I can't find any method in Java API that does what I need -
            // to actually invoke a private method with this.
    
            // I would have expected this to work:
            boolean cnuResult = pmh.bindTo(foo).invoke();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

我需要 Lookup.IMPL_LOOKUP ，但没有允许它的公共方式。我应该使用什么来使其工作？



附加说明： MethodHandle s在Java 6中添加，但我使用的是Java 8，因此任何与Java 8相关的技巧都将受到赞赏。

I need Lookup.IMPL_LOOKUP, but there is no public way that allows it. What should I use in order for this to work?

Additional note: MethodHandles are added in Java 6, but I'm using Java 8, so any tricks related to Java 8 will be appreciated as well.

推荐答案

）{
Lookup myLookup = MethodHandles.lookup（）;
UserFactory foo = new UserFactory（）; // test

尝试 {
MethodType signature = MethodType.methodType（ boolean 。 class ，User。 class ）;
MethodHandle pmh = lookup.findVirtual（UserFactory。 class ， cnu，签名）;
// ???现在怎么办？我在Java API中找不到我需要的任何方法 -
// 用它来实际调用私有方法。

// 我会有期望这个工作：
boolean cnuResult = pmh.bindTo（foo）.invoke（）;
} catch （例外e）{
e.printStackTrace（）;
}
}

}

) { Lookup myLookup = MethodHandles.lookup(); UserFactory foo = new UserFactory(); // test try { MethodType signature = MethodType.methodType(boolean.class, User.class); MethodHandle pmh = lookup.findVirtual(UserFactory.class, "cnu", signature); // ??? what now? I can't find any method in Java API that does what I need - // to actually invoke a private method with this. // I would have expected this to work: boolean cnuResult = pmh.bindTo(foo).invoke(); } catch (Exception e) { e.printStackTrace(); } } }

我需要 Lookup.IMPL_LOOKUP ，但没有允许它的公共方式。我应该使用什么来使其工作？



附加说明： MethodHandle s在Java 6中添加，但我使用的是Java 8，因此任何与Java 8相关的技巧都将受到赞赏。

I need Lookup.IMPL_LOOKUP, but there is no public way that allows it. What should I use in order for this to work?

Additional note: MethodHandles are added in Java 6, but I'm using Java 8, so any tricks related to Java 8 will be appreciated as well.

您可以使用Lookup.unreflect [<一个href =http://docs.oracle.com/javase/8/docs/api/java/lang/invoke/MethodHandles.Lookup.html#unreflect-java.lang.reflect.Method-\"target =_ blanktitle =新窗口> ^ ]：

You can use Lookup.unreflect[^]:

public static void main(String..

）{
Lookup myLookup = MethodHandles.lookup（）;
UserFactory foo = new UserFactory（）; // test
用户baz = new User（）;

尝试 {
方法m = UserFactory。 class .getDeclaredMethod （ cnu，User。 class ）;
m.setAccessible（true）;
MethodHandle pmh = myLookup.unreflect（m）;
boolean b =（ boolean ）pmh.invoke（foo，baz）;

} catch （例外e）{
e.printStackTrace（）;
} catch （Throwable e）{
e.printStackTrace（）;
}
}

) { Lookup myLookup = MethodHandles.lookup(); UserFactory foo = new UserFactory(); // test User baz = new User(); try { Method m = UserFactory.class.getDeclaredMethod("cnu", User.class); m.setAccessible(true); MethodHandle pmh = myLookup.unreflect(m); boolean b = (boolean)pmh.invoke(foo, baz); } catch (Exception e) { e.printStackTrace(); } catch (Throwable e) { e.printStackTrace(); } }

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