test/jdk/java/lang/invoke/lookup/ReflectiveLookupTest.java

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/*
 * @test
 * @bug 8020801
 * @summary Restriction on reflective call to MethodHandles.lookup method
 * @run main java.base/java.lang.LookupTest
 * @run main ReflectiveLookupTest
 */

import java.lang.invoke.*;
import java.lang.invoke.MethodHandles.Lookup;
import java.lang.reflect.Method;

import static java.lang.invoke.MethodType.*;

/*
 * Lookup object can be obtained statically or reflectively.
 */
public class ReflectiveLookupTest {
    public static void main(String... args) throws Throwable {
        // Get a full power lookup
        Lookup lookup1 =  MethodHandles.lookup();
        MethodHandle mh1 = lookup1.findStatic(lookup1.lookupClass(),
                                              "foo",
                                              methodType(String.class));
        assertEquals((String) mh1.invokeExact(), foo());

        Method lookupMethod =  MethodHandles.class.getMethod("lookup");
        System.out.println("reflection method: " + lookupMethod);
        assertEquals(lookupMethod.getName(), "lookup");

        // Get a full power Lookup reflectively.
        Lookup lookup2 = (Lookup) lookupMethod.invoke(null);
        assertEquals(lookup1.lookupClass(), lookup2.lookupClass());
        assertEquals(lookup1.lookupModes(), lookup2.lookupModes());
        MethodHandle mh2 = lookup2.findStatic(lookup2.lookupClass(),
                                             "foo",
                                              methodType(String.class));
        assertEquals((String) mh2.invokeExact(), foo());
    }

    static String foo() {
        return "foo!";
    }

    static void assertEquals(Object o1, Object o2) {
        if (!o1.equals(o2)) {
            throw new RuntimeException(o1 + " != " + o2);
        }
    }
}