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⏎ java/lang/invoke/MethodHandleProxies.java
/*
* Copyright (c) 2008, 2016, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.lang.invoke;
import java.lang.reflect.*;
import java.security.AccessController;
import java.security.PrivilegedAction;
import sun.invoke.WrapperInstance;
import java.util.ArrayList;
import jdk.internal.reflect.CallerSensitive;
import jdk.internal.reflect.Reflection;
import sun.reflect.misc.ReflectUtil;
import static java.lang.invoke.MethodHandleStatics.*;
/**
* This class consists exclusively of static methods that help adapt
* method handles to other JVM types, such as interfaces.
*
* @since 1.7
*/
public class MethodHandleProxies {
private MethodHandleProxies() { } // do not instantiate
/**
* Produces an instance of the given single-method interface which redirects
* its calls to the given method handle.
* <p>
* A single-method interface is an interface which declares a uniquely named method.
* When determining the uniquely named method of a single-method interface,
* the public {@code Object} methods ({@code toString}, {@code equals}, {@code hashCode})
* are disregarded. For example, {@link java.util.Comparator} is a single-method interface,
* even though it re-declares the {@code Object.equals} method.
* <p>
* The interface must be public. No additional access checks are performed.
* <p>
* The resulting instance of the required type will respond to
* invocation of the type's uniquely named method by calling
* the given target on the incoming arguments,
* and returning or throwing whatever the target
* returns or throws. The invocation will be as if by
* {@code target.invoke}.
* The target's type will be checked before the
* instance is created, as if by a call to {@code asType},
* which may result in a {@code WrongMethodTypeException}.
* <p>
* The uniquely named method is allowed to be multiply declared,
* with distinct type descriptors. (E.g., it can be overloaded,
* or can possess bridge methods.) All such declarations are
* connected directly to the target method handle.
* Argument and return types are adjusted by {@code asType}
* for each individual declaration.
* <p>
* The wrapper instance will implement the requested interface
* and its super-types, but no other single-method interfaces.
* This means that the instance will not unexpectedly
* pass an {@code instanceof} test for any unrequested type.
* <p style="font-size:smaller;">
* <em>Implementation Note:</em>
* Therefore, each instance must implement a unique single-method interface.
* Implementations may not bundle together
* multiple single-method interfaces onto single implementation classes
* in the style of {@link java.awt.AWTEventMulticaster}.
* <p>
* The method handle may throw an <em>undeclared exception</em>,
* which means any checked exception (or other checked throwable)
* not declared by the requested type's single abstract method.
* If this happens, the throwable will be wrapped in an instance of
* {@link java.lang.reflect.UndeclaredThrowableException UndeclaredThrowableException}
* and thrown in that wrapped form.
* <p>
* Like {@link java.lang.Integer#valueOf Integer.valueOf},
* {@code asInterfaceInstance} is a factory method whose results are defined
* by their behavior.
* It is not guaranteed to return a new instance for every call.
* <p>
* Because of the possibility of {@linkplain java.lang.reflect.Method#isBridge bridge methods}
* and other corner cases, the interface may also have several abstract methods
* with the same name but having distinct descriptors (types of returns and parameters).
* In this case, all the methods are bound in common to the one given target.
* The type check and effective {@code asType} conversion is applied to each
* method type descriptor, and all abstract methods are bound to the target in common.
* Beyond this type check, no further checks are made to determine that the
* abstract methods are related in any way.
* <p>
* Future versions of this API may accept additional types,
* such as abstract classes with single abstract methods.
* Future versions of this API may also equip wrapper instances
* with one or more additional public "marker" interfaces.
* <p>
* If a security manager is installed, this method is caller sensitive.
* During any invocation of the target method handle via the returned wrapper,
* the original creator of the wrapper (the caller) will be visible
* to context checks requested by the security manager.
*
* @param <T> the desired type of the wrapper, a single-method interface
* @param intfc a class object representing {@code T}
* @param target the method handle to invoke from the wrapper
* @return a correctly-typed wrapper for the given target
* @throws NullPointerException if either argument is null
* @throws IllegalArgumentException if the {@code intfc} is not a
* valid argument to this method
* @throws WrongMethodTypeException if the target cannot
* be converted to the type required by the requested interface
*/
// Other notes to implementors:
// <p>
// No stable mapping is promised between the single-method interface and
// the implementation class C. Over time, several implementation
// classes might be used for the same type.
// <p>
// If the implementation is able
// to prove that a wrapper of the required type
// has already been created for a given
// method handle, or for another method handle with the
// same behavior, the implementation may return that wrapper in place of
// a new wrapper.
// <p>
// This method is designed to apply to common use cases
// where a single method handle must interoperate with
// an interface that implements a function-like
// API. Additional variations, such as single-abstract-method classes with
// private constructors, or interfaces with multiple but related
// entry points, must be covered by hand-written or automatically
// generated adapter classes.
//
@CallerSensitive
public static
<T> T asInterfaceInstance(final Class<T> intfc, final MethodHandle target) {
if (!intfc.isInterface() || !Modifier.isPublic(intfc.getModifiers()))
throw newIllegalArgumentException("not a public interface", intfc.getName());
final MethodHandle mh;
if (System.getSecurityManager() != null) {
final Class<?> caller = Reflection.getCallerClass();
final ClassLoader ccl = caller != null ? caller.getClassLoader() : null;
ReflectUtil.checkProxyPackageAccess(ccl, intfc);
mh = ccl != null ? bindCaller(target, caller) : target;
} else {
mh = target;
}
ClassLoader proxyLoader = intfc.getClassLoader();
if (proxyLoader == null) {
ClassLoader cl = Thread.currentThread().getContextClassLoader(); // avoid use of BCP
proxyLoader = cl != null ? cl : ClassLoader.getSystemClassLoader();
}
final Method[] methods = getSingleNameMethods(intfc);
if (methods == null)
throw newIllegalArgumentException("not a single-method interface", intfc.getName());
final MethodHandle[] vaTargets = new MethodHandle[methods.length];
for (int i = 0; i < methods.length; i++) {
Method sm = methods[i];
MethodType smMT = MethodType.methodType(sm.getReturnType(), sm.getParameterTypes());
MethodHandle checkTarget = mh.asType(smMT); // make throw WMT
checkTarget = checkTarget.asType(checkTarget.type().changeReturnType(Object.class));
vaTargets[i] = checkTarget.asSpreader(Object[].class, smMT.parameterCount());
}
final InvocationHandler ih = new InvocationHandler() {
private Object getArg(String name) {
if ((Object)name == "getWrapperInstanceTarget") return target;
if ((Object)name == "getWrapperInstanceType") return intfc;
throw new AssertionError();
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
for (int i = 0; i < methods.length; i++) {
if (method.equals(methods[i]))
return vaTargets[i].invokeExact(args);
}
if (method.getDeclaringClass() == WrapperInstance.class)
return getArg(method.getName());
if (isObjectMethod(method))
return callObjectMethod(proxy, method, args);
throw newInternalError("bad proxy method: "+method);
}
};
final Object proxy;
if (System.getSecurityManager() != null) {
// sun.invoke.WrapperInstance is a restricted interface not accessible
// by any non-null class loader.
final ClassLoader loader = proxyLoader;
proxy = AccessController.doPrivileged(new PrivilegedAction<>() {
public Object run() {
return Proxy.newProxyInstance(
loader,
new Class<?>[]{ intfc, WrapperInstance.class },
ih);
}
});
} else {
proxy = Proxy.newProxyInstance(proxyLoader,
new Class<?>[]{ intfc, WrapperInstance.class },
ih);
}
return intfc.cast(proxy);
}
private static MethodHandle bindCaller(MethodHandle target, Class<?> hostClass) {
return MethodHandleImpl.bindCaller(target, hostClass).withVarargs(target.isVarargsCollector());
}
/**
* Determines if the given object was produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.
* @param x any reference
* @return true if the reference is not null and points to an object produced by {@code asInterfaceInstance}
*/
public static
boolean isWrapperInstance(Object x) {
return x instanceof WrapperInstance;
}
private static WrapperInstance asWrapperInstance(Object x) {
try {
if (x != null)
return (WrapperInstance) x;
} catch (ClassCastException ex) {
}
throw newIllegalArgumentException("not a wrapper instance");
}
/**
* Produces or recovers a target method handle which is behaviorally
* equivalent to the unique method of this wrapper instance.
* The object {@code x} must have been produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.
* This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.
* @param x any reference
* @return a method handle implementing the unique method
* @throws IllegalArgumentException if the reference x is not to a wrapper instance
*/
public static
MethodHandle wrapperInstanceTarget(Object x) {
return asWrapperInstance(x).getWrapperInstanceTarget();
}
/**
* Recovers the unique single-method interface type for which this wrapper instance was created.
* The object {@code x} must have been produced by a call to {@link #asInterfaceInstance asInterfaceInstance}.
* This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.
* @param x any reference
* @return the single-method interface type for which the wrapper was created
* @throws IllegalArgumentException if the reference x is not to a wrapper instance
*/
public static
Class<?> wrapperInstanceType(Object x) {
return asWrapperInstance(x).getWrapperInstanceType();
}
private static
boolean isObjectMethod(Method m) {
switch (m.getName()) {
case "toString":
return (m.getReturnType() == String.class
&& m.getParameterTypes().length == 0);
case "hashCode":
return (m.getReturnType() == int.class
&& m.getParameterTypes().length == 0);
case "equals":
return (m.getReturnType() == boolean.class
&& m.getParameterTypes().length == 1
&& m.getParameterTypes()[0] == Object.class);
}
return false;
}
private static
Object callObjectMethod(Object self, Method m, Object[] args) {
assert(isObjectMethod(m)) : m;
switch (m.getName()) {
case "toString":
return self.getClass().getName() + "@" + Integer.toHexString(self.hashCode());
case "hashCode":
return System.identityHashCode(self);
case "equals":
return (self == args[0]);
}
return null;
}
private static
Method[] getSingleNameMethods(Class<?> intfc) {
ArrayList<Method> methods = new ArrayList<>();
String uniqueName = null;
for (Method m : intfc.getMethods()) {
if (isObjectMethod(m)) continue;
if (!Modifier.isAbstract(m.getModifiers())) continue;
String mname = m.getName();
if (uniqueName == null)
uniqueName = mname;
else if (!uniqueName.equals(mname))
return null; // too many abstract methods
methods.add(m);
}
if (uniqueName == null) return null;
return methods.toArray(new Method[methods.size()]);
}
}
⏎ java/lang/invoke/MethodHandleProxies.java
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File name: java.base-11.0.1-src.zip File size: 8740354 bytes Release date: 2018-11-04 Download
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