Java Code Examples for java.lang.invoke.MethodHandles#lookup()

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findVirtual(LambdaReceiver_A.class, "f", mt(int.class));
    MethodType X = mt(int.class, LambdaReceiver.class);
    MethodType A = mt(int.class, LambdaReceiver_A.class);
    MethodType mti = mt(IA.class);
    CallSite cs = LambdaMetafactory.metafactory(l, "m", mti,A,h,X);
    IA p = (IA)cs.dynamicInvoker().invoke();
    LambdaReceiver_A lra = new LambdaReceiver_A();
    try {
        p.m(lra);
    } catch (ClassCastException cce) {
        return;
    }
    throw new AssertionError("CCE expected");
}
 

/**
 * Hop from unnamed to named module.
 *
 * [A0] retains PUBLIC access
 */
public void testFromUnnamedToNamedModule() throws Exception {
    Lookup lookup = MethodHandles.lookup();
    lookup = MethodHandles.privateLookupIn(unnamedClass, lookup).in(p1_Type1);
    assertTrue(lookup.lookupModes() == PUBLIC); // A0

    // m1
    findConstructor(lookup, p1_Type1, void.class);
    findConstructorExpectingIAE(lookup, p2_Type2, void.class);

    // m2
    findConstructor(lookup, q1_Type1, void.class);
    findConstructorExpectingIAE(lookup, q2_Type2, void.class);

    // java.base
    findConstructor(lookup, Object.class, void.class);
    findConstructorExpectingIAE(lookup, x500NameClass, void.class, String.class);

    // unnamed
    findConstructor(lookup, unnamedClass, void.class);
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findVirtual(LambdaReceiver_A.class, "f", mt(int.class));
    MethodType X = mt(int.class, LambdaReceiver.class);
    MethodType A = mt(int.class, LambdaReceiver_A.class);
    MethodType mti = mt(IA.class);
    CallSite cs = LambdaMetafactory.metafactory(l, "m", mti,A,h,X);
    IA p = (IA)cs.dynamicInvoker().invoke();
    LambdaReceiver_A lra = new LambdaReceiver_A();
    try {
        p.m(lra);
    } catch (ClassCastException cce) {
        return;
    }
    throw new AssertionError("CCE expected");
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findVirtual(LambdaReceiver_A.class, "f", mt(int.class));
    MethodType X = mt(int.class, LambdaReceiver.class);
    MethodType A = mt(int.class, LambdaReceiver_A.class);
    MethodType mti = mt(IA.class);
    CallSite cs = LambdaMetafactory.metafactory(l, "m", mti,A,h,X);
    IA p = (IA)cs.dynamicInvoker().invoke();
    LambdaReceiver_A lra = new LambdaReceiver_A();
    try {
        p.m(lra);
    } catch (ClassCastException cce) {
        return;
    }
    throw new AssertionError("CCE expected");
}
 

@Test
public void testReturnOnStack() throws Throwable {
    MethodHandles.Lookup l = MethodHandles.lookup();

    MethodHandle consumeIdentity = l.findStatic(
            PermuteArgsReturnVoidTest.class, "consumeIdentity",
            MethodType.methodType(String.class, String.class, int.class, int.class));
    MethodHandle consumeVoid = l.findStatic(
            PermuteArgsReturnVoidTest.class, "consumeVoid",
            MethodType.methodType(void.class, String.class, int.class, int.class));

    MethodHandle f = MethodHandles.foldArguments(consumeIdentity, consumeVoid);

    MethodHandle p = MethodHandles.permuteArguments(f, MethodType.methodType(String.class, String.class, int.class, int.class), 0, 2, 1);

    String s = (String) p.invoke("IN", 0, 0);
    Assert.assertEquals(s.getClass(), String.class);
    Assert.assertEquals(s, "IN");
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findVirtual(LambdaReceiver_A.class, "f", mt(int.class));
    MethodType X = mt(int.class, LambdaReceiver.class);
    MethodType A = mt(int.class, LambdaReceiver_A.class);
    MethodType mti = mt(IA.class);
    CallSite cs = LambdaMetafactory.metafactory(l, "m", mti,A,h,X);
    IA p = (IA)cs.dynamicInvoker().invoke();
    LambdaReceiver_A lra = new LambdaReceiver_A();
    try {
        p.m(lra);
    } catch (ClassCastException cce) {
        return;
    }
    throw new AssertionError("CCE expected");
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findVirtual(LambdaReceiver_A.class, "f", mt(int.class));
    MethodType X = mt(int.class, LambdaReceiverBridge.class);
    MethodType A = mt(int.class, LambdaReceiver_A.class);
    MethodType mti = mt(IA.class);
    CallSite cs = LambdaMetafactory.altMetafactory(l, "m", mti,X,h,X,
                                      LambdaMetafactory.FLAG_BRIDGES, 1, A);
    IA p = (IA)cs.dynamicInvoker().invoke();
    LambdaReceiver_A lra = new LambdaReceiver_A();
    try {
        p.m(lra);
    } catch (ClassCastException cce) {
        return;
    }
    throw new AssertionError("CCE expected");
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    MethodHandle hV = l.findStatic(LambdaReturn.class, "hereV", mt(void.class));
    MethodHandle hS = l.findStatic(LambdaReturn.class, "hereS", mt(String.class));
    List<String> errs = new ArrayList<>();
    MethodType V = mt(void.class);
    MethodType S = mt(String.class);
    MethodType O = mt(Object.class);
    MethodType I = mt(int.class);
    amf(errs, hS, S, S, O, true);
    amf(errs, hS, S, S, V, false);
    amf(errs, hS, S, S, I, false);
    amf(errs, hS, O, S, S, true);
    amf(errs, hS, V, S, S, false);
    amf(errs, hS, I, S, S, false);
    amf(errs, hS, O, O, S, false);
    amf(errs, hS, S, O, O, false);
    amf(errs, hV, V, V, O, false);
    amf(errs, hV, V, V, I, false);
    amf(errs, hV, V, V, S, false);
    amf(errs, hV, O, V, V, false);
    amf(errs, hV, I, V, V, false);
    amf(errs, hV, S, V, V, false);

    if (errs.size() > 0) {
        for (String err : errs) {
            System.err.println(err);
        }
        throw new AssertionError("Errors: " + errs.size());
    }
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findVirtual(T8032697_A.class, "f", mt(int.class));
    if (mf(mt(I.class, T8032697.class), mt(int.class))) throw new AssertionError("Error: Should work");
    if (mf(mt(IA.class), mt(int.class, T8032697.class))) throw new AssertionError("Error: Should work");
    if (!mf(mt(I.class, T8032697_A.class), mt(int.class))) throw new AssertionError("Error: Should fail");
    if (!mf(mt(IA.class), mt(int.class, T8032697_A.class))) throw new AssertionError("Error: Should fail");
}
 

/**
 * Starting with a full power Lookup, use dropLookupMode to create new Lookups
 * with reduced access.
 */
public void testReducingAccess() {
    Lookup lookup = MethodHandles.lookup();
    final Class<?> lc = lookup.lookupClass();
    assertTrue(lookup.lookupModes() == (PUBLIC|MODULE|PACKAGE|PROTECTED|PRIVATE));

    lookup = lookup.dropLookupMode(PROTECTED);
    assertTrue(lookup.lookupClass() == lc);
    assertTrue(lookup.lookupModes() == (PUBLIC|MODULE|PACKAGE|PRIVATE));

    lookup = lookup.dropLookupMode(PRIVATE);
    assertTrue(lookup.lookupClass() == lc);
    assertTrue(lookup.lookupModes() == (PUBLIC|MODULE|PACKAGE));

    lookup = lookup.dropLookupMode(PACKAGE);
    assertTrue(lookup.lookupClass() == lc);
    assertTrue(lookup.lookupModes() == (PUBLIC|MODULE));

    lookup = lookup.dropLookupMode(MODULE);
    assertTrue(lookup.lookupClass() == lc);
    assertTrue(lookup.lookupModes() == PUBLIC);

    lookup = lookup.dropLookupMode(PUBLIC);
    assertTrue(lookup.lookupClass() == lc);
    assertTrue(lookup.lookupModes() == 0);

    // repeat with lookup has no access
    lookup = lookup.dropLookupMode(PUBLIC);
    assertTrue(lookup.lookupClass() == lc);
    assertTrue(lookup.lookupModes() == 0);
}
 

private static MethodHandle initRegisterShutdownHookMethodHandle() {
    final MethodHandles.Lookup lookup = MethodHandles.lookup();

    try {
        final Class<?> javaLangAccessClazz = findJavaLangAccessClass(lookup);
        return findRegisterShutdownHookMethodHandle(lookup, javaLangAccessClazz);
    } catch (Throwable t) {
        logger.warn("Failed to initialized registerShutdownHook MethodHandle", t);
        dumpJdkInfo();
    }
    return null;
}
 

public static void main(String[] args) throws Throwable {
    MethodHandles.Lookup ll = MethodHandles.lookup();
    h = ll.findStatic(T8032704.class, "here", mt(void.class));
    if (mf(ll)) throw new AssertionError("Error: Should work");
    if (!mf(MethodHandles.publicLookup())) throw new AssertionError("Error: Should fail - public");
    if (!mf(ll.in(T8032704other.class))) throw new AssertionError("Error: Should fail - other");
    if (!mf(ll.in(Thread.class))) throw new AssertionError("Error: Should fail - Thread");
}
 

public void test() throws Throwable {
    MethodHandles.Lookup lookup = MethodHandles.lookup();
    MethodType mt = MethodType.methodType(void.class);
    try {
        Class<?> checkInittedHolder = TestPrivateMemberPackageSibling.class;
        // Original model:  checkInittedHolder = Class.class;
        // Not using Class.checkInitted because it could change without notice.
        MethodHandle mh = lookup.findStatic(checkInittedHolder, "checkInitted", mt);
        throw new RuntimeException("IllegalAccessException not thrown");
    } catch (IllegalAccessException e) {
        // okay
        System.out.println("Expected exception: " + e.getMessage());
    }
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    MethodHandle hV = l.findStatic(LambdaReturn.class, "hereV", mt(void.class));
    MethodHandle hS = l.findStatic(LambdaReturn.class, "hereS", mt(String.class));
    List<String> errs = new ArrayList<>();
    MethodType V = mt(void.class);
    MethodType S = mt(String.class);
    MethodType O = mt(Object.class);
    MethodType I = mt(int.class);
    amf(errs, hS, S, S, O, true);
    amf(errs, hS, S, S, V, false);
    amf(errs, hS, S, S, I, false);
    amf(errs, hS, O, S, S, true);
    amf(errs, hS, V, S, S, false);
    amf(errs, hS, I, S, S, false);
    amf(errs, hS, O, O, S, false);
    amf(errs, hS, S, O, O, false);
    amf(errs, hV, V, V, O, false);
    amf(errs, hV, V, V, I, false);
    amf(errs, hV, V, V, S, false);
    amf(errs, hV, O, V, V, false);
    amf(errs, hV, I, V, V, false);
    amf(errs, hV, S, V, V, false);

    if (errs.size() > 0) {
        for (String err : errs) {
            System.err.println(err);
        }
        throw new AssertionError("Errors: " + errs.size());
    }
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findStatic(T8032711.class, "here", mt(void.class));
    if (mf(void.class)) throw new AssertionError("Error: Should work");
    if (!mf(String.class)) throw new AssertionError("Error: Should fail");
}
 

@Test
@Tag("PASSING")
@Order(2)
public void methodHandlePrivateMethod() {

    String expectedOutput = "[DemoClass] - Private method via Method Handles";

    /*
     * DONE:
     *  Get a non-public lookup from java.lang.invoke.MethodHandles
     *  Non-public methods are looked up via "lookup"
     *  Find the differences between lookup() and publicLookup() on MethodHandles.
     *  Check API: java.lang.invoke.MethodHandles.lookup()
     */
    MethodHandles.Lookup privateMethodHandlesLookup = MethodHandles.lookup();

    try {

        /*
         * DONE:
         *  Replace the "null"s with valid values to produce a privateMethod instance.
         *  Create a method instance that matches the name "privateMethod()"
         *  See java.lang.class for a getDeclaredMethod()
         *  Look for the declared method on the DemoClass.class
         *  The privateMethod() needs a String input parameter.
         *  Same call as is used in vanilla reflection.
         *  Check API: java.lang.Class.getDeclaredMethod(?, ?)
         */
        Method privateMethod =
                DemoClass.class.getDeclaredMethod("privateMethod",
                        String.class); // Method name, Class ... = Parameter types

        /*
         * Method has to be made accessible.
         * Not setting this will cause IllegalAccessException
         * Setting accessible to true causes the JVM to skip access control checks
         *
         * This is needed to access non-public content
         */
        privateMethod.setAccessible(true);

        /*
         * DONE:
         *  Replace the "null" with a valid value to get an unreflected private method handle.
         *  Unreflect to create a method handle from a method instance
         *  Generate a MethodHandle from the method instance created earlier.
         *  See unreflect method in the innerclass Lookup of MethodHandles.
         *  java.lang.invoke.MethodHandles.Lookup.unreflect()
         *  We can unreflect the method since we bypassed the access control checks above.
         *  Check API: java.lang.invoke.MethodHandles.Lookup.unreflect(?)
         */
        MethodHandle privateMethodHandle =
                privateMethodHandlesLookup.unreflect(privateMethod);

        DemoClass demoClass = new DemoClass();

        assertEquals(expectedOutput,
                privateMethodHandle.invoke(demoClass,
                        "via Method Handles"),
                "Method handles invocation failed");

    } catch (NoSuchMethodException | IllegalAccessException e) {

        fail("Failed to execute a private method invocation via Method Handles: "
                + e.getMessage());
    } catch (Throwable t) {

        // invoke throws a Throwable (hence catching Throwable separately).
        fail(TEST_FAILURE.getValue() + t.getMessage());
    }
}
 

public static void main(String[] args) throws Throwable {
    l = MethodHandles.lookup();
    h = l.findStatic(T8032711.class, "here", mt(void.class));
    if (mf(void.class)) throw new AssertionError("Error: Should work");
    if (!mf(String.class)) throw new AssertionError("Error: Should fail");
}
 

public static Lookup lookup() { return MethodHandles.lookup(); } 

public static MethodHandles.Lookup lookup() { return MethodHandles.lookup(); } 

public static MethodHandles.Lookup lookup() { return MethodHandles.lookup(); }