gistfile1.txt

import static org.objectweb.asm.Opcodes.ACC_BRIDGE;
import static org.objectweb.asm.Opcodes.ACC_FINAL;
import static org.objectweb.asm.Opcodes.ACC_PUBLIC;
import static org.objectweb.asm.Opcodes.ACC_STATIC;
import static org.objectweb.asm.Opcodes.ACC_SUPER;
import static org.objectweb.asm.Opcodes.ACC_SYNTHETIC;
import static org.objectweb.asm.Opcodes.ALOAD;
import static org.objectweb.asm.Opcodes.ARETURN;
import static org.objectweb.asm.Opcodes.INVOKESPECIAL;
import static org.objectweb.asm.Opcodes.INVOKESTATIC;
import static org.objectweb.asm.Opcodes.INVOKEVIRTUAL;
import static org.objectweb.asm.Opcodes.RETURN;
import static org.objectweb.asm.Opcodes.V17;

import java.io.File;
import java.io.IOException;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodHandles.Lookup;
import java.lang.module.ModuleDescriptor.Opens;
import java.net.URL;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Enumeration;
import java.util.function.Supplier;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;

/**
 *
 */
public class PrivateLookup {

    public static Lookup privateLookup(Lookup base, Class<?> clazz) throws IllegalAccessException {
        base.lookupClass().getModule().addReads(clazz.getModule());
        try {
            return MethodHandles.privateLookupIn(clazz, base);
        } catch (IllegalAccessException e) {
            try {
                return privateLookup0(base, clazz, e);
            } catch (IOException | InstantiationException ioe) {
                throw e;
            }
        }
    }

    private static Lookup privateLookup0(Lookup base, Class<?> clazz, IllegalAccessException e)
            throws IllegalAccessException, IOException, InstantiationException {
        for (Opens o : clazz.getModule().getDescriptor().opens()) {
            if (o.targets().contains(base.lookupClass().getModule().getName())) {
                String path = o.source().replace('.', '/');
                Enumeration<URL> resources = clazz.getClassLoader().getResources(path);
                while (resources.hasMoreElements()) {
                    File f = new File(resources.nextElement().getFile());
                    for (Path p : Files.newDirectoryStream(f.toPath(), "*.class")) {
                        String fname = p.getFileName().toString();
                        String className = o.source() + "." + fname.substring(0, fname.length() - 6);
                        try {
                            Class<?> cl = clazz.getClassLoader().loadClass(className);
                            Lookup lookup = MethodHandles.privateLookupIn(cl, base);
                            String newClass = cl.getPackageName().replace(".", "/") + "/" + System.nanoTime();
                            Class<?> c = lookup.defineClass(generate(newClass));
                            Supplier<Lookup> s = (Supplier<Lookup>) c.newInstance();
                            Lookup l = s.get();
                            return MethodHandles.privateLookupIn(clazz, l);
                        } catch (ClassNotFoundException ignore) {}
                    }
                }
            }
        }

        throw e;
    }

    public static byte[] generate(String cName) {

        ClassWriter classWriter = new ClassWriter(0);
        MethodVisitor methodVisitor;
        classWriter.visit(V17, ACC_PUBLIC | ACC_SUPER, cName, "Ljava/lang/Object;Ljava/util/function/Supplier<Ljava/lang/invoke/MethodHandles$Lookup;>;",
                "java/lang/Object", new String[] { "java/util/function/Supplier" });
        classWriter.visitInnerClass("java/lang/invoke/MethodHandles$Lookup", "java/lang/invoke/MethodHandles", "Lookup", ACC_PUBLIC | ACC_FINAL | ACC_STATIC);
        {
            methodVisitor = classWriter.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
            methodVisitor.visitCode();
            methodVisitor.visitVarInsn(ALOAD, 0);
            methodVisitor.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
            methodVisitor.visitInsn(RETURN);
            methodVisitor.visitMaxs(1, 1);
            methodVisitor.visitEnd();
        }
        {
            methodVisitor = classWriter.visitMethod(ACC_PUBLIC, "get", "()Ljava/lang/invoke/MethodHandles$Lookup;", null, null);
            methodVisitor.visitCode();
            methodVisitor.visitMethodInsn(INVOKESTATIC, "java/lang/invoke/MethodHandles", "lookup", "()Ljava/lang/invoke/MethodHandles$Lookup;", false);
            methodVisitor.visitInsn(ARETURN);
            methodVisitor.visitMaxs(1, 1);
            methodVisitor.visitEnd();
        }
        {
            methodVisitor = classWriter.visitMethod(ACC_PUBLIC | ACC_BRIDGE | ACC_SYNTHETIC, "get", "()Ljava/lang/Object;", null, null);
            methodVisitor.visitCode();
            methodVisitor.visitVarInsn(ALOAD, 0);
            methodVisitor.visitMethodInsn(INVOKEVIRTUAL, cName, "get", "()Ljava/lang/invoke/MethodHandles$Lookup;", false);
            methodVisitor.visitInsn(ARETURN);
            methodVisitor.visitMaxs(1, 1);
            methodVisitor.visitEnd();
        }
        classWriter.visitEnd();
        return classWriter.toByteArray();
    }
}