获取Java lambda表达式的封闭类

我有一个采用功能参数的方法,例如a Runnable.由于它是一个库方法,我希望它使用从函数参数派生的记录器.调用getClass函数参数适用于普通类,我可以getEnclosingClass用于嵌套或匿名类; 但如果它是一个lambda表达式,它会返回一个含有的模糊名称$$Lambda$,我可以像这样手动剥离:

Class type = runnable.getClass();
String canonical = type.getCanonicalName();
int lambdaOffset = canonical.indexOf("$$Lambda$");
if (lambdaOffset > 0) {
    try {
        type = Class.forName(canonical.substring(0, lambdaOffset));
    } catch (ClassNotFoundException e) {
        // strange, but we can stick to the type we already have
    }
}

正如你所看到的那样,这不是很优雅,也可能不便携.我试过getEnclosingClass,getEnclosingMethod和getEnclosingConstructor,但他们都返回null.

有任何想法吗？

正如Tassos Bassoukos已经提到的,它是设计的.

Lambda(类)的字节码是在运行时生成的.所以你得到的是班级的实际名称.并且名称生成为target class name + "$$Lambda$" + a counter.

找一个小片段进行演示.

package sub.optimal;
import static java.lang.System.out;

public class EnclosingClass {

    static class InnerRunnable implements Runnable {

        @Override
        public void run() {
            out.println("--- inner class");
        }
    }

    public static void main(String... args) {
        showIdentity(() -> System.out.println("--- lambda 1"));
        showIdentity(() -> System.out.println("--- lambda 2"));
        showIdentity(new InnerRunnable());
        showIdentity(new Runnable() {
            @Override
            public void run() {
                out.println("--- anonymous class");
            }
        });
    }

    private static void showIdentity(Runnable runnable) {
        runnable.run();
        Class clazz = runnable.getClass();
        out.printf("class name     : %s%n", clazz.getName());
        out.printf("class hashcode : %s%n", clazz.hashCode());
        out.printf("canonical name : %s%n", clazz.getCanonicalName());
        out.printf("enclosing class: %s%n", clazz.getEnclosingClass());
        out.println();
    }
}

产量

--- lambda 1
class name     : sub.optimal.EnclosingClass$$Lambda$1/2147972
class hashcode : 2147972
canonical name : sub.optimal.EnclosingClass$$Lambda$1/2147972
enclosing class: null

--- lambda 2
class name     : sub.optimal.EnclosingClass$$Lambda$2/10376386
class hashcode : 10376386
canonical name : sub.optimal.EnclosingClass$$Lambda$2/10376386
enclosing class: null

--- inner class
class name     : sub.optimal.EnclosingClass$InnerRunnable
class hashcode : 28014437
canonical name : sub.optimal.EnclosingClass.InnerRunnable
enclosing class: class sub.optimal.EnclosingClass

--- anonymous class
class name     : sub.optimal.EnclosingClass$1
class hashcode : 19451386
canonical name : null
enclosing class: class sub.optimal.EnclosingClass