java.lang.invoke.MethodHandles Java Examples

private static MethodHandle forSpreadCall(MethodHandle mh, MethodType type) {
    int expectedParameters = mh.type().parameterCount();
    int actualParameters = type.parameterCount();
    if (!mh.isVarargsCollector() || !mh.type().parameterType(expectedParameters - 1).equals(Object[].class)) {
        throw new WrongMethodTypeException("Not Object[] var-args collector");
    }
    if (expectedParameters > actualParameters) {
        throw new WrongMethodTypeException("Too few arguments");
    }
    if (expectedParameters < actualParameters) {
        int fixedCount = actualParameters - expectedParameters;
        int firstFixed = expectedParameters - 1;
        List<Class<?>> fixed = type.parameterList().subList(firstFixed, firstFixed + fixedCount);
        mh = MethodHandles.collectArguments(mh, firstFixed, combineArraysMH);
        mh = MethodHandles.collectArguments(mh, firstFixed, toObjectArray(fixed));
    }
    return mh.asType(type);
}
 

private long uniqueInstanceMethodHandleInstanceFieldWriteAccessInvokeOnly(int spins) throws Throwable {
    ReflectionTarget[] targets = new ReflectionTarget[spins];
    MethodHandle[] fields = new MethodHandle[spins];

    for (int i = 0; i < spins; i++) {
        ClassLoader loader = new URLClassLoader(new URL[]{ classpathDirectory.toURI().toURL() });
        Class<?> clazz = loader.loadClass(targetClassName);
        targets[i] = (ReflectionTarget) MethodHandles.lookup().findConstructor(clazz, MethodType.methodType(void.class)).invoke();
        fields[i] = MethodHandles.lookup().findSetter(clazz, instanceField, Object.class);
    }

    Object object = new Object();

    long start = System.nanoTime();
    for (int i = 0; i < spins; i++) {
        fields[i].invoke(targets[i], object);
    }
    long end = System.nanoTime();
    return end - start;
}
 

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");
}
 

static MethodHandle linkMissingBeanMember(final LinkRequest linkRequest, final LinkerServices linkerServices) throws Exception {
    final CallSiteDescriptor desc = linkRequest.getCallSiteDescriptor();
    final String operand = NashornCallSiteDescriptor.getOperand(desc);
    switch (NashornCallSiteDescriptor.getStandardOperation(desc)) {
    case GET:
        if (NashornCallSiteDescriptor.isOptimistic(desc)) {
            return adaptThrower(MethodHandles.insertArguments(THROW_OPTIMISTIC_UNDEFINED, 0, NashornCallSiteDescriptor.getProgramPoint(desc)), desc);
        } else if (operand != null) {
            return getInvocation(EMPTY_PROP_GETTER, linkerServices, desc);
        }
        return getInvocation(EMPTY_ELEM_GETTER, linkerServices, desc);
    case SET:
        final boolean strict = NashornCallSiteDescriptor.isStrict(desc);
        if (strict) {
            return adaptThrower(bindOperand(THROW_STRICT_PROPERTY_SETTER, operand), desc);
        } else if (operand != null) {
            return getInvocation(EMPTY_PROP_SETTER, linkerServices, desc);
        }
        return getInvocation(EMPTY_ELEM_SETTER, linkerServices, desc);
    default:
        throw new AssertionError("unknown call type " + desc);
    }
}
 

public static void main(String[] args) {
	String str = "*****\n  Hi\n  \tHello Pankaj\rHow are you?\n*****";

	// 1. public String indent​(int n)
	System.out.println(str.indent(0));
	System.out.println(str.indent(3));
	System.out.println(str.indent(-3));

	// 2. public <R> R transform​(Function<? super String,​? extends R> f)
	String s = "Hi,Hello,Howdy";
	List<String> strList = s.transform(s1 -> {return Arrays.asList(s1.split(","));});
	System.out.println(strList);

	//Java 12 String implements Constable, ConstantDesc - hence two new methods
	// 3. public Optional<String> describeConstable()
	String so = "Hello";
	Optional<String> os = so.describeConstable();
	System.out.println(os);
	System.out.println(os.get());
	
	// 4. public String resolveConstantDesc​(MethodHandles.Lookup lookup)
	String so1 = "Hello";
	System.out.println(so1.resolveConstantDesc(MethodHandles.lookup()));
	
	
}
 

private Handle generateBootstrapMethod(Handle h) {
    String bootstrapName = "bootstrapMethod";
    MethodType bootstrapType = MethodType.methodType(CallSite.class, MethodHandles.Lookup.class, String.class, MethodType.class);

    MethodVisitor bmv = cv.visitMethod(ACC_PUBLIC | ACC_STATIC, bootstrapName, bootstrapType.toMethodDescriptorString(), null, null);
    bmv.visitCode();

    String constCallSite = "java/lang/invoke/ConstantCallSite";
    bmv.visitTypeInsn(NEW, constCallSite);
    bmv.visitInsn(DUP);

    bmv.visitLdcInsn(h);

    bmv.visitMethodInsn(INVOKESPECIAL, constCallSite, "<init>", "(Ljava/lang/invoke/MethodHandle;)V", false);
    bmv.visitInsn(ARETURN);

    bmv.visitMaxs(0,0);
    bmv.visitEnd();

    return new Handle(H_INVOKESTATIC, ownerClassName, bootstrapName, bootstrapType.toMethodDescriptorString());
}
 

@Test
void dumpOpenSslInfoDoNotThrowStackOverFlowError() throws Throwable {
    assumeThat(OpenSsl.isAvailable()).isTrue();
    System.setProperty("com.linecorp.armeria.dumpOpenSslInfo", "true");

    // There's a chance that Flags.useOpenSsl() is already called by other test cases, which means that
    // we cannot set dumpOpenSslInfo. So we use our own class loader to load the Flags class.
    final FlagsClassLoader classLoader = new FlagsClassLoader();
    final Class<?> flags = classLoader.loadClass("com.linecorp.armeria.common.Flags");
    final Lookup lookup = MethodHandles.publicLookup();
    final MethodHandle useOpenSslMethodHandle = lookup.findStatic(flags, "useOpenSsl",
                                                                  MethodType.methodType(boolean.class));
    useOpenSslMethodHandle.invoke(); // Call Flags.useOpenSsl();

    final MethodHandle dumpOpenSslInfoMethodHandle =
            lookup.findStatic(flags, "dumpOpenSslInfo", MethodType.methodType(boolean.class));
    // // Call Flags.dumpOpenSslInfo();
    assertThat(dumpOpenSslInfoMethodHandle.invoke()).isSameAs(Boolean.TRUE);
}
 

@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");
}
 

@BeforeClass
public void setup() throws Exception {
    vhFinalField = MethodHandles.lookup().findVarHandle(
            VarHandleTestAccessBoolean.class, "final_v", boolean.class);

    vhField = MethodHandles.lookup().findVarHandle(
            VarHandleTestAccessBoolean.class, "v", boolean.class);

    vhStaticFinalField = MethodHandles.lookup().findStaticVarHandle(
        VarHandleTestAccessBoolean.class, "static_final_v", boolean.class);

    vhStaticField = MethodHandles.lookup().findStaticVarHandle(
        VarHandleTestAccessBoolean.class, "static_v", boolean.class);

    vhArray = MethodHandles.arrayElementVarHandle(boolean[].class);
}
 

private MethodHandle introspectConstructor()
{
  try {
    Method m = _type.getMethod("valueOf", String.class);
    
    Objects.requireNonNull(m);
    
    m.setAccessible(true);
      
    MethodHandle mh = MethodHandles.lookup().unreflect(m);
        
    mh = mh.asType(MethodType.methodType(Object.class, String.class));
      
    return mh;
  } catch (Exception e) {
    throw new H3ExceptionIn(_type.getName() + ": " + e.getMessage(), e);
  }
}
 

private final MethodHandle findReadWriteObjectForSerialization(Class<?> cl,
                                                               String methodName,
                                                               Class<?> streamClass) {
    if (!Serializable.class.isAssignableFrom(cl)) {
        return null;
    }

    try {
        Method meth = cl.getDeclaredMethod(methodName, streamClass);
        int mods = meth.getModifiers();
        if (meth.getReturnType() != Void.TYPE ||
                Modifier.isStatic(mods) ||
                !Modifier.isPrivate(mods)) {
            return null;
        }
        meth.setAccessible(true);
        return MethodHandles.lookup().unreflect(meth);
    } catch (NoSuchMethodException ex) {
        return null;
    } catch (IllegalAccessException ex1) {
        throw new InternalError("Error", ex1);
    }
}
 

private MethodHandle getTestMH(Class clazz, String methodName,
        Object param, boolean isNegativeTest)
        throws Exception {
    MethodType mType = (param != null)
            ? MethodType.genericMethodType(1)
            : MethodType.methodType(String.class);
    MethodHandles.Lookup lookup = MethodHandles.lookup();
    if (!isNegativeTest) {
        return methodName.equals("staticMethod")
                ? lookup.findStatic(clazz, methodName, mType)
                : lookup.findVirtual(clazz, methodName, mType);
    } else {
        return methodName.equals("staticMethod")
                ? lookup.findVirtual(clazz, methodName, mType)
                : lookup.findStatic(clazz, methodName, mType);
    }
}
 

@Test
public void testFindSpecial() throws Throwable {
    MethodHandles.Lookup lookup = (MethodHandles.Lookup)t3.getDeclaredMethod("getLookup").invoke(null);
    MethodHandle mh = lookup.findSpecial(t1, "m", MethodType.methodType(int.class), t3);
    int result = (int)mh.invoke(t3.newInstance());
    assertEquals(result, 1); // T1.m should be invoked.
}
 

private static void checkForWrongMethodTypeException(MethodHandle mh, MethodType mt) {
    try {
        MethodHandles.explicitCastArguments(mh, mt);
        throw new AssertionError("Expected WrongMethodTypeException is not thrown");
    } catch (WrongMethodTypeException wmte) {
        if (VERBOSE) {
            System.out.printf("Expected exception %s: %s\n",
                    wmte.getClass(), wmte.getMessage());
        }
    }
}
 

private static MethodHandle applyConverters(final MethodHandle handle, final int pos, final List<MethodHandle> converters) {
    if(converters.isEmpty()) {
        return handle;
    }
    final MethodHandle newHandle =
            MethodHandles.filterArguments(handle, pos, converters.toArray(new MethodHandle[converters.size()]));
    converters.clear();
    return newHandle;
}
 

private void introspectFields(ArrayList<MarshalField> fieldList,
                              PodImport moduleImport,
                              Class<?> sourceClass)
{
  if (sourceClass == null || Object.class.equals(sourceClass)) {
    return;
  }
  
  introspectFields(fieldList, 
                   moduleImport,
                   sourceClass.getSuperclass());
  
  Lookup lookup = MethodHandles.lookup();
  
  for (Field sourceField : sourceClass.getDeclaredFields()) {
    if (Modifier.isStatic(sourceField.getModifiers())) {
      continue;
    }
    
    try {
      sourceField.setAccessible(true);
      
      ModuleMarshal marshal;
      marshal = moduleImport.marshalArg(sourceField.getType(),
                                        Object.class);
      
      MethodHandle sourceHandle = lookup.unreflectGetter(sourceField);
      sourceHandle = sourceHandle.asType(MethodType.methodType(Object.class, Object.class));
    
      MarshalField fieldMarshal = new MarshalFieldObject(sourceField.getName(),
                                                         marshal, 
                                                         sourceHandle);
      
      fieldList.add(fieldMarshal);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}
 

private void handleNullWithoutBoolean() {
    if (handle != null || args[0] != null) return;

    if (staticTargetType.isPrimitive()) {
        handle = MethodHandles.insertArguments(GROOVY_CAST_EXCEPTION, 1, staticTargetType);
        // need to call here here because we used the static target type
        // it won't be done otherwise because handle.type() == callSite.type()
        castAndSetGuards();
    } else {
        handle = MethodHandles.identity(staticSourceType);
    }
}
 

private NashornCallSiteDescriptor(final MethodHandles.Lookup lookup, final String operator, final String operand,
        final MethodType methodType, final int flags) {
    this.lookup = lookup;
    this.operator = operator;
    this.operand = operand;
    this.methodType = methodType;
    this.flags = flags;
}
 

public static void main(String[] args) throws Exception {
    MethodHandles.lookup()
            .findStaticGetter(Intf.class, "i", int.class)
            .getClass(); // null check

    System.out.println("TEST PASSED");
}
 

@Override
public MethodHandle setter(final MethodHandles.Lookup explicitLookup, final Class<?> clazz, final String name, final Class<?> type) {
    try {
        final MethodHandle mh = explicitLookup.findSetter(clazz, name, type);
        return debug(mh, "setter", explicitLookup, clazz, name, type);
    } catch (final NoSuchFieldException | IllegalAccessException e) {
        throw new LookupException(e);
    }
}
 

@Test
public void whenVariableHandleForPublicVariableIsCreated_ThenItIsInitializedProperly() throws NoSuchFieldException, IllegalAccessException {
    VarHandle PUBLIC_TEST_VARIABLE = MethodHandles
      .lookup()
      .in(VariableHandlesUnitTest.class)
      .findVarHandle(VariableHandlesUnitTest.class, "publicTestVariable", int.class);

    assertEquals(1, PUBLIC_TEST_VARIABLE.coordinateTypes().size());
    assertEquals(VariableHandlesUnitTest.class, PUBLIC_TEST_VARIABLE.coordinateTypes().get(0));
}
 

private static MethodHandle unbox(Wrapper wrap, int kind) {
    // kind 0 -> strongly typed with NPE
    // kind 1 -> strongly typed but zero for null,
    // kind 2 -> asType rules: accept multiple box types but only widening conversions with NPE
    // kind 3 -> explicitCastArguments rules: allow narrowing conversions, zero for null
    WrapperCache cache = UNBOX_CONVERSIONS[kind];
    MethodHandle mh = cache.get(wrap);
    if (mh != null) {
        return mh;
    }
    // slow path
    switch (wrap) {
        case OBJECT:
        case VOID:
            throw new IllegalArgumentException("unbox "+wrap);
    }
    // look up the method
    String name = "unbox" + wrap.wrapperSimpleName();
    MethodType type = unboxType(wrap, kind);
    try {
        mh = IMPL_LOOKUP.findStatic(THIS_CLASS, name, type);
    } catch (ReflectiveOperationException ex) {
        mh = null;
    }
    if (mh != null) {
        if (kind > 0) {
            boolean cast = (kind != 2);
            mh = MethodHandles.insertArguments(mh, 1, cast);
        }
        if (kind == 1) {  // casting but exact (null -> zero)
            mh = mh.asType(unboxType(wrap, 0));
        }
        return cache.put(wrap, mh);
    }
    throw new IllegalArgumentException("cannot find unbox adapter for " + wrap
            + (kind <= 1 ? " (exact)" : kind == 3 ? " (cast)" : ""));
}
 

private static NashornCallSiteDescriptor get(final MethodHandles.Lookup lookup, final String operator, final String operand, final MethodType methodType, final int flags) {
    final NashornCallSiteDescriptor csd = new NashornCallSiteDescriptor(lookup, operator, operand, methodType, flags);
    // Many of these call site descriptors are identical (e.g. every getter for a property color will be
    // "dyn:getProp:color(Object)Object", so it makes sense canonicalizing them.
    final ConcurrentMap<NashornCallSiteDescriptor, NashornCallSiteDescriptor> classCanonicals = canonicals.get(lookup.lookupClass());
    final NashornCallSiteDescriptor canonical = classCanonicals.putIfAbsent(csd, csd);
    return canonical != null ? canonical : csd;
}
 

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");
}
 

@Override
public MethodHandle findSpecial(final MethodHandles.Lookup explicitLookup, final Class<?> clazz, final String name, final MethodType type, final Class<?> thisClass) {
    try {
        final MethodHandle mh = explicitLookup.findSpecial(clazz, name, type, thisClass);
        return debug(mh, "findSpecial", explicitLookup, clazz, name, type);
    } catch (final NoSuchMethodException | IllegalAccessException e) {
        throw new LookupException(e);
    }
}
 

/**
 * Composes the invocation, switchpoint, and the guard into a composite method handle that knows how to fall back.
 * @param switchpointFallback the fallback method handle in case switchpoint is invalidated.
 * @param guardFallback the fallback method handle in case guard returns false.
 * @param catchFallback the fallback method in case the exception handler triggers
 * @return a composite method handle.
 */
public MethodHandle compose(final MethodHandle guardFallback, final MethodHandle switchpointFallback, final MethodHandle catchFallback) {
    final MethodHandle guarded =
            guard == null ?
                    invocation :
                    MethodHandles.guardWithTest(
                            guard,
                            invocation,
                            guardFallback);

    final MethodHandle catchGuarded =
            exception == null ?
                    guarded :
                    MH.catchException(
                            guarded,
                            exception,
                            MethodHandles.dropArguments(
                                catchFallback,
                                0,
                                exception));

    if (switchPoints == null) {
        return catchGuarded;
    }

    MethodHandle spGuarded = catchGuarded;
    for (final SwitchPoint sp : switchPoints) {
        spGuarded = sp.guardWithTest(spGuarded, switchpointFallback);
    }

    return spGuarded;
}
 

private RpcMethod(INSTANCE instance, Method method, String[] parameterNames,String methodName,
                  boolean returnTypeJdk9PublisherFlag, boolean returnTypeReactivePublisherFlag,
                  boolean returnRxjava3ObservableFlag, boolean returnRxjava3FlowableFlag) {
    this.instance = instance;
    this.method = method;
    this.methodName = methodName;
    this.parameterNames = parameterNames;
    this.returnTypeJdk9PublisherFlag = returnTypeJdk9PublisherFlag;
    this.returnTypeReactivePublisherFlag = returnTypeReactivePublisherFlag;
    this.returnRxjava3ObservableFlag = returnRxjava3ObservableFlag;
    this.returnRxjava3FlowableFlag = returnRxjava3FlowableFlag;
    this.returnCompletableFutureFlag = CompletableFuture.class.isAssignableFrom(method.getReturnType());
    this.returnCompletionStageFlag = CompletionStage.class.isAssignableFrom(method.getReturnType());
    this.returnFutureFlag = Future.class.isAssignableFrom(method.getReturnType());
    this.parameterTypes = method.getParameterTypes();
    if(returnTypeJdk9PublisherFlag || returnTypeReactivePublisherFlag
            || returnRxjava3ObservableFlag || returnRxjava3FlowableFlag
            || returnCompletableFutureFlag || returnCompletionStageFlag || returnFutureFlag){
        this.genericReturnType = getParameterizedType(method);
    }else {
        this.genericReturnType = method.getGenericReturnType();
    }
    this.innerMethodFlag = RpcServerInstance.isRpcInnerClass(method.getDeclaringClass());
    this.parameterTypeDescriptorName = Stream.of(parameterTypes)
            .map(Class::getSimpleName)
            .collect(Collectors.joining(","));
    this.methodDescriptorName = getMethodDescriptorName(method);
    this.parameterCount = method.getParameterCount();
    MethodHandle methodHandle;
    try {
        MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
        MethodType methodType = MethodType.methodType(method.getReturnType(), method.getParameterTypes());
        methodHandle = publicLookup.findVirtual(method.getDeclaringClass(), method.getName(), methodType);
    } catch (NoSuchMethodException | IllegalAccessException e) {
        methodHandle = null;
    }
    this.methodHandle = methodHandle;
}
 

private void runTest() {
    Helper.clear();

    Object[] args = Helper.randomArgs(
            argsCount, thrower.type().parameterArray());
    Object arg0 = Helper.MISSING_ARG;
    Object arg1 = testCase.thrown;
    if (argsCount > 0) {
        arg0 = args[0];
    }
    if (argsCount > 1) {
        args[1] = arg1;
    }
    Asserts.assertEQ(nargs, thrower.type().parameterCount());
    if (argsCount < nargs) {
        Object[] appendArgs = {arg0, arg1};
        appendArgs = Arrays.copyOfRange(appendArgs, argsCount, nargs);
        thrower = MethodHandles.insertArguments(
                thrower, argsCount, appendArgs);
    }
    Asserts.assertEQ(argsCount, thrower.type().parameterCount());

    MethodHandle target = MethodHandles.catchException(
            testCase.filter(thrower), testCase.throwableClass,
            testCase.filter(catcher));

    Asserts.assertEQ(thrower.type(), target.type());
    Asserts.assertEQ(argsCount, target.type().parameterCount());

    Object returned;
    try {
        returned = target.invokeWithArguments(args);
    } catch (Throwable ex) {
        testCase.assertCatch(ex);
        returned = ex;
    }

    testCase.assertReturn(returned, arg0, arg1, dropped, args);
}
 

/**
 * Set MOP based constructor invocation path.
 */
@Override
public void setMetaClassCallHandleIfNeeded(boolean standardMetaClass) {
    if (handle != null) return;
    useMetaClass = true;
    if (LOG_ENABLED) LOG.info("set meta class invocation path");
    handle = MOP_INVOKE_CONSTRUCTOR.bindTo(mc);
    handle = handle.asCollector(Object[].class, targetType.parameterCount() - 1);
    handle = MethodHandles.dropArguments(handle, 0, Class.class);
    if (LOG_ENABLED) LOG.info("create collector for arguments");
}
 

@Override
public MethodHandle findStatic(final MethodHandles.Lookup explicitLookup, final Class<?> clazz, final String name, final MethodType type) {
    try {
        return explicitLookup.findStatic(clazz, name, type);
    } catch (final NoSuchMethodException | IllegalAccessException e) {
        throw new LookupException(e);
    }
}