* @author John Rose, JSR 292 EG */ public class MethodHandles { private MethodHandles() { } // do not instantiate private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); static { MethodHandleImpl.initStatics(); } // See IMPL_LOOKUP below. //// Method handle creation from ordinary methods. /** * Returns a {@link Lookup lookup object} on the caller, * which has the capability to access any method handle that the caller has access to, * including direct method handles to private fields and methods. * This lookup object is a capability which may be delegated to trusted agents. * Do not store it in place where untrusted code can access it. */ @CallerSensitive public static Lookup lookup() { return new Lookup(Reflection.getCallerClass()); } /** * Returns a {@link Lookup lookup object} which is trusted minimally. * It can only be used to create method handles to * publicly accessible fields and methods. *
* As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class} * of this lookup object will be {@link java.lang.Object}. *
* The lookup class can be changed to any other class {@code C} using an expression of the form
* {@linkplain Lookup#in publicLookup().in(C.class)}.
* Since all classes have equal access to public names,
* such a change would confer no new access rights.
*/
public static Lookup publicLookup() {
return Lookup.PUBLIC_LOOKUP;
}
/**
* A lookup object is a factory for creating method handles,
* when the creation requires access checking.
* Method handles do not perform
* access checks when they are called, but rather when they are created.
* Therefore, method handle access
* restrictions must be enforced when a method handle is created.
* The caller class against which those restrictions are enforced
* is known as the {@linkplain #lookupClass lookup class}.
*
* A lookup class which needs to create method handles will call * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself. * When the {@code Lookup} factory object is created, the identity of the lookup class is * determined, and securely stored in the {@code Lookup} object. * The lookup class (or its delegates) may then use factory methods * on the {@code Lookup} object to create method handles for access-checked members. * This includes all methods, constructors, and fields which are allowed to the lookup class, * even private ones. *
* The factory methods on a {@code Lookup} object correspond to all major
* use cases for methods, constructors, and fields.
* Here is a summary of the correspondence between these factory methods and
* the behavior the resulting method handles:
*
*
* Here, the type {@code C} is the class or interface being searched for a member,
* documented as a parameter named {@code refc} in the lookup methods.
* The method or constructor type {@code MT} is composed from the return type {@code T}
* and the sequence of argument types {@code A*}.
* Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
* The formal parameter {@code this} stands for the self-reference of type {@code C};
* if it is present, it is always the leading argument to the method handle invocation.
* (In the case of some {@code protected} members, {@code this} may be
* restricted in type to the lookup class; see below.)
* The name {@code arg} stands for all the other method handle arguments.
* In the code examples for the Core Reflection API, the name {@code thisOrNull}
* stands for a null reference if the accessed method or field is static,
* and {@code this} otherwise.
* The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
* for reflective objects corresponding to the given members.
*
*
* lookup expression member behavior
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}
* FT f; (T) this.f;
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}
* static
FT f;(T) C.f;
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}
* FT f; this.f = x;
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}
* static
FT f;C.f = arg;
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}
* T m(A*); (T) this.m(arg*);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}
* static
T m(A*);(T) C.m(arg*);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}
* T m(A*); (T) super.m(arg*);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}
* C(A*); (T) new C(arg*);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}
* (static)?
FT f;(FT) aField.get(thisOrNull);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}
* (static)?
FT f;aField.set(thisOrNull, arg);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}
* (static)?
T m(A*);(T) aMethod.invoke(thisOrNull, arg*);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}
* C(A*); (C) aConstructor.newInstance(arg*);
*
*
* {@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}
* (static)?
T m(A*);(T) aMethod.invoke(thisOrNull, arg*);
*
* In cases where the given member is of variable arity (i.e., a method or constructor) * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. * In all other cases, the returned method handle will be of fixed arity. *
* The equivalence between looked-up method handles and underlying * class members can break down in a few ways: *
* All access checks start from a {@code Lookup} object, which * compares its recorded lookup class against all requests to * create method handles. * A single {@code Lookup} object can be used to create any number * of access-checked method handles, all checked against a single * lookup class. *
* A {@code Lookup} object can be shared with other trusted code, * such as a metaobject protocol. * A shared {@code Lookup} object delegates the capability * to create method handles on private members of the lookup class. * Even if privileged code uses the {@code Lookup} object, * the access checking is confined to the privileges of the * original lookup class. *
* A lookup can fail, because * the containing class is not accessible to the lookup class, or * because the desired class member is missing, or because the * desired class member is not accessible to the lookup class. * In any of these cases, a {@code ReflectiveOperationException} will be * thrown from the attempted lookup. The exact class will be one of * the following: *
* In general, the conditions under which a method handle may be * looked up for a method {@code M} are exactly equivalent to the conditions * under which the lookup class could have compiled and resolved a call to {@code M}. * And the effect of invoking the method handle resulting from the lookup * is exactly equivalent to executing the compiled and resolved call to {@code M}. * The same point is true of fields and constructors. *
* If the desired member is {@code protected}, the usual JVM rules apply, * including the requirement that the lookup class must be either be in the * same package as the desired member, or must inherit that member. * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.) * In addition, if the desired member is a non-static field or method * in a different package, the resulting method handle may only be applied * to objects of the lookup class or one of its subclasses. * This requirement is enforced by narrowing the type of the leading * {@code this} parameter from {@code C} * (which will necessarily be a superclass of the lookup class) * to the lookup class itself. *
* In some cases, access between nested classes is obtained by the Java compiler by creating * an wrapper method to access a private method of another class * in the same top-level declaration. * For example, a nested class {@code C.D} * can access private members within other related classes such as * {@code C}, {@code C.D.E}, or {@code C.B}, * but the Java compiler may need to generate wrapper methods in * those related classes. In such cases, a {@code Lookup} object on * {@code C.E} would be unable to those private members. * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, * which can transform a lookup on {@code C.E} into one on any of those other * classes, without special elevation of privilege. *
* Although bytecode instructions can only refer to classes in * a related class loader, this API can search for methods in any * class, as long as a reference to its {@code Class} object is * available. Such cross-loader references are also possible with the * Core Reflection API, and are impossible to bytecode instructions * such as {@code invokestatic} or {@code getfield}. * There is a {@linkplain java.lang.SecurityManager security manager API} * to allow applications to check such cross-loader references. * These checks apply to both the {@code MethodHandles.Lookup} API * and the Core Reflection API * (as found on {@link java.lang.Class Class}). *
* Access checks only apply to named and reflected methods, * constructors, and fields. * Other method handle creation methods, such as * {@link MethodHandle#asType MethodHandle.asType}, * do not require any access checks, and are done * with static methods of {@link MethodHandles}, * independently of any {@code Lookup} object. * *
* The class implies a maximum level of access permission, * but the permissions may be additionally limited by the bitmask * {@link #lookupModes lookupModes}, which controls whether non-public members * can be accessed. */ public Class lookupClass() { return lookupClass; } // This is just for calling out to MethodHandleImpl. private Class lookupClassOrNull() { return (allowedModes == TRUSTED) ? null : lookupClass; } /** Tells which access-protection classes of members this lookup object can produce. * The result is a bit-mask of the bits * {@linkplain #PUBLIC PUBLIC (0x01)}, * {@linkplain #PRIVATE PRIVATE (0x02)}, * {@linkplain #PROTECTED PROTECTED (0x04)}, * and {@linkplain #PACKAGE PACKAGE (0x08)}. *
* A freshly-created lookup object * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} * has all possible bits set, since the caller class can access all its own members. * A lookup object on a new lookup class * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} * may have some mode bits set to zero. * The purpose of this is to restrict access via the new lookup object, * so that it can access only names which can be reached by the original * lookup object, and also by the new lookup class. */ public int lookupModes() { return allowedModes & ALL_MODES; } /** Embody the current class (the lookupClass) as a lookup class * for method handle creation. * Must be called by from a method in this package, * which in turn is called by a method not in this package. */ Lookup(Class lookupClass) { this(lookupClass, ALL_MODES); // make sure we haven't accidentally picked up a privileged class: checkUnprivilegedlookupClass(lookupClass); } private Lookup(Class lookupClass, int allowedModes) { this.lookupClass = lookupClass; this.allowedModes = allowedModes; } /** * Creates a lookup on the specified new lookup class. * The resulting object will report the specified * class as its own {@link #lookupClass lookupClass}. *
* However, the resulting {@code Lookup} object is guaranteed * to have no more access capabilities than the original. * In particular, access capabilities can be lost as follows:
* (It may seem strange that protected access should be * stronger than private access. Viewed independently from * package access, protected access is the first to be lost, * because it requires a direct subclass relationship between * caller and callee.) * @see #in */ @Override public String toString() { String cname = lookupClass.getName(); switch (allowedModes) { case 0: // no privileges return cname + "/noaccess"; case PUBLIC: return cname + "/public"; case PUBLIC|PACKAGE: return cname + "/package"; case ALL_MODES & ~PROTECTED: return cname + "/private"; case ALL_MODES: return cname; case TRUSTED: return "/trusted"; // internal only; not exported default: // Should not happen, but it's a bitfield... cname = cname + "/" + Integer.toHexString(allowedModes); assert(false) : cname; return cname; } } /** * Produces a method handle for a static method. * The type of the method handle will be that of the method. * (Since static methods do not take receivers, there is no * additional receiver argument inserted into the method handle type, * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) * The method and all its argument types must be accessible to the lookup class. * If the method's class has not yet been initialized, that is done * immediately, before the method handle is returned. *
* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set. * @param refc the class from which the method is accessed * @param name the name of the method * @param type the type of the method * @return the desired method handle * @throws NoSuchMethodException if the method does not exist * @throws IllegalAccessException if access checking fails, * or if the method is not {@code static}, * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findStatic(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type); checkSecurityManager(refc, method); return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method)); } /** * Produces a method handle for a virtual method. * The type of the method handle will be that of the method, * with the receiver type (usually {@code refc}) prepended. * The method and all its argument types must be accessible to the lookup class. *
* When called, the handle will treat the first argument as a receiver * and dispatch on the receiver's type to determine which method * implementation to enter. * (The dispatching action is identical with that performed by an * {@code invokevirtual} or {@code invokeinterface} instruction.) *
* The first argument will be of type {@code refc} if the lookup * class has full privileges to access the member. Otherwise * the member must be {@code protected} and the first argument * will be restricted in type to the lookup class. *
* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set. *
* Because of the general equivalence between {@code invokevirtual} * instructions and method handles produced by {@code findVirtual}, * if the class is {@code MethodHandle} and the name string is * {@code invokeExact} or {@code invoke}, the resulting * method handle is equivalent to one produced by * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} * with the same {@code type} argument. * * @param refc the class or interface from which the method is accessed * @param name the name of the method * @param type the type of the method, with the receiver argument omitted * @return the desired method handle * @throws NoSuchMethodException if the method does not exist * @throws IllegalAccessException if access checking fails, * or if the method is {@code static} * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findVirtual(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { if (refc == MethodHandle.class) { MethodHandle mh = findVirtualForMH(name, type); if (mh != null) return mh; } byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual); MemberName method = resolveOrFail(refKind, refc, name, type); checkSecurityManager(refc, method); return getDirectMethod(refKind, refc, method, findBoundCallerClass(method)); } private MethodHandle findVirtualForMH(String name, MethodType type) { // these names require special lookups because of the implicit MethodType argument if ("invoke".equals(name)) return invoker(type); if ("invokeExact".equals(name)) return exactInvoker(type); return null; } /** * Produces a method handle which creates an object and initializes it, using * the constructor of the specified type. * The parameter types of the method handle will be those of the constructor, * while the return type will be a reference to the constructor's class. * The constructor and all its argument types must be accessible to the lookup class. * If the constructor's class has not yet been initialized, that is done * immediately, before the method handle is returned. *
* Note: The requested type must have a return type of {@code void}. * This is consistent with the JVM's treatment of constructor type descriptors. *
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the constructor's variable arity modifier bit ({@code 0x0080}) is set.
* @param refc the class or interface from which the method is accessed
* @param type the type of the method, with the receiver argument omitted, and a void return type
* @return the desired method handle
* @throws NoSuchMethodException if the constructor does not exist
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws NullPointerException if any argument is null
*/
public MethodHandle findConstructor(Class refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
String name = "
* When called, the handle will treat the first argument as a receiver,
* but will not dispatch on the receiver's type.
* (This direct invocation action is identical with that performed by an
* {@code invokespecial} instruction.)
*
* If the explicitly specified caller class is not identical with the
* lookup class, or if this lookup object does not have private access
* privileges, the access fails.
*
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* @param refc the class or interface from which the method is accessed
* @param name the name of the method (which must not be "<init>")
* @param type the type of the method, with the receiver argument omitted
* @param specialCaller the proposed calling class to perform the {@code invokespecial}
* @return the desired method handle
* @throws NoSuchMethodException if the method does not exist
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws NullPointerException if any argument is null
*/
public MethodHandle findSpecial(Class refc, String name, MethodType type,
Class specialCaller) throws NoSuchMethodException, IllegalAccessException {
checkSpecialCaller(specialCaller);
Lookup specialLookup = this.in(specialCaller);
MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
checkSecurityManager(refc, method);
return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
}
/**
* Produces a method handle giving read access to a non-static field.
* The type of the method handle will have a return type of the field's
* value type.
* The method handle's single argument will be the instance containing
* the field.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can load values from the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is {@code static}
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws NullPointerException if any argument is null
*/
public MethodHandle findGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(REF_getField, refc, name, type);
checkSecurityManager(refc, field);
return getDirectField(REF_getField, refc, field);
}
/**
* Produces a method handle giving write access to a non-static field.
* The type of the method handle will have a void return type.
* The method handle will take two arguments, the instance containing
* the field, and the value to be stored.
* The second argument will be of the field's value type.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can store values into the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is {@code static}
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws NullPointerException if any argument is null
*/
public MethodHandle findSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(REF_putField, refc, name, type);
checkSecurityManager(refc, field);
return getDirectField(REF_putField, refc, field);
}
/**
* Produces a method handle giving read access to a static field.
* The type of the method handle will have a return type of the field's
* value type.
* The method handle will take no arguments.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can load values from the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws NullPointerException if any argument is null
*/
public MethodHandle findStaticGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
checkSecurityManager(refc, field);
return getDirectField(REF_getStatic, refc, field);
}
/**
* Produces a method handle giving write access to a static field.
* The type of the method handle will have a void return type.
* The method handle will take a single
* argument, of the field's value type, the value to be stored.
* Access checking is performed immediately on behalf of the lookup class.
* @param refc the class or interface from which the method is accessed
* @param name the field's name
* @param type the field's type
* @return a method handle which can store values into the field
* @throws NoSuchFieldException if the field does not exist
* @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws NullPointerException if any argument is null
*/
public MethodHandle findStaticSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
checkSecurityManager(refc, field);
return getDirectField(REF_putStatic, refc, field);
}
/**
* Produces an early-bound method handle for a non-static method.
* The receiver must have a supertype {@code defc} in which a method
* of the given name and type is accessible to the lookup class.
* The method and all its argument types must be accessible to the lookup class.
* The type of the method handle will be that of the method,
* without any insertion of an additional receiver parameter.
* The given receiver will be bound into the method handle,
* so that every call to the method handle will invoke the
* requested method on the given receiver.
*
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set
* and the trailing array argument is not the only argument.
* (If the trailing array argument is the only argument,
* the given receiver value will be bound to it.)
*
* This is equivalent to the following code:
*
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* @param m the reflected method
* @return a method handle which can invoke the reflected method
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @throws NullPointerException if the argument is null
*/
public MethodHandle unreflect(Method m) throws IllegalAccessException {
MemberName method = new MemberName(m);
byte refKind = method.getReferenceKind();
if (refKind == REF_invokeSpecial)
refKind = REF_invokeVirtual;
assert(method.isMethod());
Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
return lookup.getDirectMethod(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
}
/**
* Produces a method handle for a reflected method.
* It will bypass checks for overriding methods on the receiver,
* as if by a {@code invokespecial} instruction from within the {@code specialCaller}.
* The type of the method handle will be that of the method,
* with the special caller type prepended (and not the receiver of the method).
* If the method's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class,
* as if {@code invokespecial} instruction were being linked.
*
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the method's variable arity modifier bit ({@code 0x0080}) is set.
* @param m the reflected method
* @param specialCaller the class nominally calling the method
* @return a method handle which can invoke the reflected method
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @throws NullPointerException if any argument is null
*/
public MethodHandle unreflectSpecial(Method m, Class specialCaller) throws IllegalAccessException {
checkSpecialCaller(specialCaller);
Lookup specialLookup = this.in(specialCaller);
MemberName method = new MemberName(m, true);
assert(method.isMethod());
// ignore m.isAccessible: this is a new kind of access
return specialLookup.getDirectMethod(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
}
/**
* Produces a method handle for a reflected constructor.
* The type of the method handle will be that of the constructor,
* with the return type changed to the declaring class.
* The method handle will perform a {@code newInstance} operation,
* creating a new instance of the constructor's class on the
* arguments passed to the method handle.
*
* If the constructor's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
*
* The returned method handle will have
* {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
* the constructor's variable arity modifier bit ({@code 0x0080}) is set.
* @param c the reflected constructor
* @return a method handle which can invoke the reflected constructor
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @throws NullPointerException if the argument is null
*/
@SuppressWarnings("rawtypes") // Will be Constructor after JSR 292 MR
public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
MemberName ctor = new MemberName(c);
assert(ctor.isConstructor());
Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
return lookup.getDirectConstructor(ctor.getDeclaringClass(), ctor);
}
/**
* Produces a method handle giving read access to a reflected field.
* The type of the method handle will have a return type of the field's
* value type.
* If the field is static, the method handle will take no arguments.
* Otherwise, its single argument will be the instance containing
* the field.
* If the field's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
* @param f the reflected field
* @return a method handle which can load values from the reflected field
* @throws IllegalAccessException if access checking fails
* @throws NullPointerException if the argument is null
*/
public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
return unreflectField(f, false);
}
private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
MemberName field = new MemberName(f, isSetter);
assert(isSetter
? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
: MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
return lookup.getDirectField(field.getReferenceKind(), f.getDeclaringClass(), field);
}
/**
* Produces a method handle giving write access to a reflected field.
* The type of the method handle will have a void return type.
* If the field is static, the method handle will take a single
* argument, of the field's value type, the value to be stored.
* Otherwise, the two arguments will be the instance containing
* the field, and the value to be stored.
* If the field's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
* @param f the reflected field
* @return a method handle which can store values into the reflected field
* @throws IllegalAccessException if access checking fails
* @throws NullPointerException if the argument is null
*/
public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
return unreflectField(f, true);
}
/// Helper methods, all package-private.
MemberName resolveOrFail(byte refKind, Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException {
checkSymbolicClass(refc); // do this before attempting to resolve
name.getClass(); type.getClass(); // NPE
return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
NoSuchFieldException.class);
}
MemberName resolveOrFail(byte refKind, Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
checkSymbolicClass(refc); // do this before attempting to resolve
name.getClass(); type.getClass(); // NPE
return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
NoSuchMethodException.class);
}
void checkSymbolicClass(Class refc) throws IllegalAccessException {
Class caller = lookupClassOrNull();
if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
}
/**
* Find my trustable caller class if m is a caller sensitive method.
* If this lookup object has private access, then the caller class is the lookupClass.
* Otherwise, if m is caller-sensitive, throw IllegalAccessException.
*/
Class findBoundCallerClass(MemberName m) throws IllegalAccessException {
Class callerClass = null;
if (MethodHandleNatives.isCallerSensitive(m)) {
// Only full-power lookup is allowed to resolve caller-sensitive methods
if (isFullPowerLookup()) {
callerClass = lookupClass;
} else {
throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
}
}
return callerClass;
}
private boolean isFullPowerLookup() {
return (allowedModes & PRIVATE) != 0;
}
/**
* Perform necessary access checks.
* Determines a trustable caller class to compare with refc, the symbolic reference class.
* If this lookup object has private access, then the caller class is the lookupClass.
*/
void checkSecurityManager(Class refc, MemberName m) {
SecurityManager smgr = System.getSecurityManager();
if (smgr == null) return;
if (allowedModes == TRUSTED) return;
// Step 1:
if (!isFullPowerLookup() ||
!VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
ReflectUtil.checkPackageAccess(refc);
}
// Step 2:
if (m.isPublic()) return;
Class defc = m.getDeclaringClass();
{
if (!isFullPowerLookup()) {
smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
}
}
// Step 3:
if (defc != refc) {
ReflectUtil.checkPackageAccess(defc);
}
}
void checkMethod(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
boolean wantStatic = (refKind == REF_invokeStatic);
String message;
if (m.isConstructor())
message = "expected a method, not a constructor";
else if (!m.isMethod())
message = "expected a method";
else if (wantStatic != m.isStatic())
message = wantStatic ? "expected a static method" : "expected a non-static method";
else
{ checkAccess(refKind, refc, m); return; }
throw m.makeAccessException(message, this);
}
void checkField(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
String message;
if (wantStatic != m.isStatic())
message = wantStatic ? "expected a static field" : "expected a non-static field";
else
{ checkAccess(refKind, refc, m); return; }
throw m.makeAccessException(message, this);
}
void checkAccess(byte refKind, Class refc, MemberName m) throws IllegalAccessException {
assert(m.referenceKindIsConsistentWith(refKind) &&
MethodHandleNatives.refKindIsValid(refKind) &&
(MethodHandleNatives.refKindIsField(refKind) == m.isField()));
int allowedModes = this.allowedModes;
if (allowedModes == TRUSTED) return;
int mods = m.getModifiers();
if (Modifier.isFinal(mods) &&
MethodHandleNatives.refKindIsSetter(refKind))
throw m.makeAccessException("unexpected set of a final field", this);
if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
return; // common case
int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
if ((requestedModes & allowedModes) != 0) {
if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
mods, lookupClass(), allowedModes))
return;
} else {
// Protected members can also be checked as if they were package-private.
if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
&& VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
return;
}
throw m.makeAccessException(accessFailedMessage(refc, m), this);
}
String accessFailedMessage(Class refc, MemberName m) {
Class defc = m.getDeclaringClass();
int mods = m.getModifiers();
// check the class first:
boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
(defc == refc ||
Modifier.isPublic(refc.getModifiers())));
if (!classOK && (allowedModes & PACKAGE) != 0) {
classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
(defc == refc ||
VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
}
if (!classOK)
return "class is not public";
if (Modifier.isPublic(mods))
return "access to public member failed"; // (how?)
if (Modifier.isPrivate(mods))
return "member is private";
if (Modifier.isProtected(mods))
return "member is protected";
return "member is private to package";
}
private static final boolean ALLOW_NESTMATE_ACCESS = false;
private void checkSpecialCaller(Class specialCaller) throws IllegalAccessException {
int allowedModes = this.allowedModes;
if (allowedModes == TRUSTED) return;
if ((allowedModes & PRIVATE) == 0
|| (specialCaller != lookupClass()
&& !(ALLOW_NESTMATE_ACCESS &&
VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
throw new MemberName(specialCaller).
makeAccessException("no private access for invokespecial", this);
}
private boolean restrictProtectedReceiver(MemberName method) {
// The accessing class only has the right to use a protected member
// on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
if (!method.isProtected() || method.isStatic()
|| allowedModes == TRUSTED
|| method.getDeclaringClass() == lookupClass()
|| VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
|| (ALLOW_NESTMATE_ACCESS &&
VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
return false;
return true;
}
private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class caller) throws IllegalAccessException {
assert(!method.isStatic());
// receiver type of mh is too wide; narrow to caller
if (!method.getDeclaringClass().isAssignableFrom(caller)) {
throw method.makeAccessException("caller class must be a subclass below the method", caller);
}
MethodType rawType = mh.type();
if (rawType.parameterType(0) == caller) return mh;
MethodType narrowType = rawType.changeParameterType(0, caller);
return mh.viewAsType(narrowType);
}
private MethodHandle getDirectMethod(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
return getDirectMethodCommon(refKind, refc, method,
(refKind == REF_invokeSpecial ||
(MethodHandleNatives.refKindHasReceiver(refKind) &&
restrictProtectedReceiver(method))), callerClass);
}
private MethodHandle getDirectMethodNoRestrict(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
return getDirectMethodCommon(refKind, refc, method, false, callerClass);
}
private MethodHandle getDirectMethodCommon(byte refKind, Class refc, MemberName method,
boolean doRestrict, Class callerClass) throws IllegalAccessException {
checkMethod(refKind, refc, method);
if (method.isMethodHandleInvoke())
return fakeMethodHandleInvoke(method);
Class refcAsSuper;
if (refKind == REF_invokeSpecial &&
refc != lookupClass() &&
refc != (refcAsSuper = lookupClass().getSuperclass()) &&
refc.isAssignableFrom(lookupClass())) {
assert(!method.getName().equals("
* The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
* the indicated {@code type}.
* That is, if the target is exactly of the given {@code type}, it will behave
* like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
* is used to convert the target to the required {@code type}.
*
* The type of the returned invoker will not be the given {@code type}, but rather
* will have all parameters except the first {@code leadingArgCount}
* replaced by a single array of type {@code Object[]}, which will be
* the final parameter.
*
* Before invoking its target, the invoker will spread the final array, apply
* reference casts as necessary, and unbox and widen primitive arguments.
*
* This method is equivalent to the following code (though it may be more efficient):
*
* This method throws no reflective or security exceptions.
* @param type the desired target type
* @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
* @return a method handle suitable for invoking any method handle of the given type
* @throws NullPointerException if {@code type} is null
* @throws IllegalArgumentException if {@code leadingArgCount} is not in
* the range from 0 to {@code type.parameterCount()} inclusive
*/
static public
MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
throw new IllegalArgumentException("bad argument count "+leadingArgCount);
return type.invokers().spreadInvoker(leadingArgCount);
}
/**
* Produces a special invoker method handle which can be used to
* invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
* The resulting invoker will have a type which is
* exactly equal to the desired type, except that it will accept
* an additional leading argument of type {@code MethodHandle}.
*
* This method is equivalent to the following code (though it may be more efficient):
*
* Discussion:
* Invoker method handles can be useful when working with variable method handles
* of unknown types.
* For example, to emulate an {@code invokeExact} call to a variable method
* handle {@code M}, extract its type {@code T},
* look up the invoker method {@code X} for {@code T},
* and call the invoker method, as {@code X.invoke(T, A...)}.
* (It would not work to call {@code X.invokeExact}, since the type {@code T}
* is unknown.)
* If spreading, collecting, or other argument transformations are required,
* they can be applied once to the invoker {@code X} and reused on many {@code M}
* method handle values, as long as they are compatible with the type of {@code X}.
*
* (Note: The invoker method is not available via the Core Reflection API.
* An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
* on the declared {@code invokeExact} or {@code invoke} method will raise an
* {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)
*
* This method throws no reflective or security exceptions.
* @param type the desired target type
* @return a method handle suitable for invoking any method handle of the given type
*/
static public
MethodHandle exactInvoker(MethodType type) {
return type.invokers().exactInvoker();
}
/**
* Produces a special invoker method handle which can be used to
* invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
* The resulting invoker will have a type which is
* exactly equal to the desired type, except that it will accept
* an additional leading argument of type {@code MethodHandle}.
*
* Before invoking its target, if the target differs from the expected type,
* the invoker will apply reference casts as
* necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
* Similarly, the return value will be converted as necessary.
* If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
* the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
*
* A {@linkplain MethodType#genericMethodType general method type},
* mentions only {@code Object} arguments and return values.
* An invoker for such a type is capable of calling any method handle
* of the same arity as the general type.
*
* This method is equivalent to the following code (though it may be more efficient):
*
* This method throws no reflective or security exceptions.
* @param type the desired target type
* @return a method handle suitable for invoking any method handle convertible to the given type
*/
static public
MethodHandle invoker(MethodType type) {
return type.invokers().generalInvoker();
}
static /*non-public*/
MethodHandle basicInvoker(MethodType type) {
return type.form().basicInvoker();
}
/// method handle modification (creation from other method handles)
/**
* Produces a method handle which adapts the type of the
* given method handle to a new type by pairwise argument and return type conversion.
* The original type and new type must have the same number of arguments.
* The resulting method handle is guaranteed to report a type
* which is equal to the desired new type.
*
* If the original type and new type are equal, returns target.
*
* The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
* and some additional conversions are also applied if those conversions fail.
* Given types T0, T1, one of the following conversions is applied
* if possible, before or instead of any conversions done by {@code asType}:
*
* The given array controls the reordering.
* Call {@code #I} the number of incoming parameters (the value
* {@code newType.parameterCount()}, and call {@code #O} the number
* of outgoing parameters (the value {@code target.type().parameterCount()}).
* Then the length of the reordering array must be {@code #O},
* and each element must be a non-negative number less than {@code #I}.
* For every {@code N} less than {@code #O}, the {@code N}-th
* outgoing argument will be taken from the {@code I}-th incoming
* argument, where {@code I} is {@code reorder[N]}.
*
* No argument or return value conversions are applied.
* The type of each incoming argument, as determined by {@code newType},
* must be identical to the type of the corresponding outgoing parameter
* or parameters in the target method handle.
* The return type of {@code newType} must be identical to the return
* type of the original target.
*
* The reordering array need not specify an actual permutation.
* An incoming argument will be duplicated if its index appears
* more than once in the array, and an incoming argument will be dropped
* if its index does not appear in the array.
* As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
* incoming arguments which are not mentioned in the reordering array
* are may be any type, as determined only by {@code newType}.
*
* Before the method handle is returned, the passed-in value is converted to the requested type.
* If the requested type is primitive, widening primitive conversions are attempted,
* else reference conversions are attempted.
* The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
* @param type the return type of the desired method handle
* @param value the value to return
* @return a method handle of the given return type and no arguments, which always returns the given value
* @throws NullPointerException if the {@code type} argument is null
* @throws ClassCastException if the value cannot be converted to the required return type
* @throws IllegalArgumentException if the given type is {@code void.class}
*/
public static
MethodHandle constant(Class type, Object value) {
if (type.isPrimitive()) {
if (type == void.class)
throw newIllegalArgumentException("void type");
Wrapper w = Wrapper.forPrimitiveType(type);
return insertArguments(identity(type), 0, w.convert(value, type));
} else {
return identity(type).bindTo(type.cast(value));
}
}
/**
* Produces a method handle which returns its sole argument when invoked.
* @param type the type of the sole parameter and return value of the desired method handle
* @return a unary method handle which accepts and returns the given type
* @throws NullPointerException if the argument is null
* @throws IllegalArgumentException if the given type is {@code void.class}
*/
public static
MethodHandle identity(Class type) {
if (type == void.class)
throw newIllegalArgumentException("void type");
else if (type == Object.class)
return ValueConversions.identity();
else if (type.isPrimitive())
return ValueConversions.identity(Wrapper.forPrimitiveType(type));
else
return MethodHandleImpl.makeReferenceIdentity(type);
}
/**
* Provides a target method handle with one or more bound arguments
* in advance of the method handle's invocation.
* The formal parameters to the target corresponding to the bound
* arguments are called bound parameters.
* Returns a new method handle which saves away the bound arguments.
* When it is invoked, it receives arguments for any non-bound parameters,
* binds the saved arguments to their corresponding parameters,
* and calls the original target.
*
* The type of the new method handle will drop the types for the bound
* parameters from the original target type, since the new method handle
* will no longer require those arguments to be supplied by its callers.
*
* Each given argument object must match the corresponding bound parameter type.
* If a bound parameter type is a primitive, the argument object
* must be a wrapper, and will be unboxed to produce the primitive value.
*
* The {@code pos} argument selects which parameters are to be bound.
* It may range between zero and N-L (inclusively),
* where N is the arity of the target method handle
* and L is the length of the values array.
* @param target the method handle to invoke after the argument is inserted
* @param pos where to insert the argument (zero for the first)
* @param values the series of arguments to insert
* @return a method handle which inserts an additional argument,
* before calling the original method handle
* @throws NullPointerException if the target or the {@code values} array is null
* @see MethodHandle#bindTo
*/
public static
MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
int insCount = values.length;
MethodType oldType = target.type();
int outargs = oldType.parameterCount();
int inargs = outargs - insCount;
if (inargs < 0)
throw newIllegalArgumentException("too many values to insert");
if (pos < 0 || pos > inargs)
throw newIllegalArgumentException("no argument type to append");
MethodHandle result = target;
for (int i = 0; i < insCount; i++) {
Object value = values[i];
Class ptype = oldType.parameterType(pos+i);
if (ptype.isPrimitive()) {
char btype = 'I';
Wrapper w = Wrapper.forPrimitiveType(ptype);
switch (w) {
case LONG: btype = 'J'; break;
case FLOAT: btype = 'F'; break;
case DOUBLE: btype = 'D'; break;
}
// perform unboxing and/or primitive conversion
value = w.convert(value, ptype);
result = result.bindArgument(pos, btype, value);
continue;
}
value = ptype.cast(value); // throw CCE if needed
if (pos == 0) {
result = result.bindReceiver(value);
} else {
result = result.bindArgument(pos, 'L', value);
}
}
return result;
}
/**
* Produces a method handle which will discard some dummy arguments
* before calling some other specified target method handle.
* The type of the new method handle will be the same as the target's type,
* except it will also include the dummy argument types,
* at some given position.
*
* The {@code pos} argument may range between zero and N,
* where N is the arity of the target.
* If {@code pos} is zero, the dummy arguments will precede
* the target's real arguments; if {@code pos} is N
* they will come after.
*
* Example:
*
* This method is also equivalent to the following code:
*
* The {@code pos} argument may range between zero and N,
* where N is the arity of the target.
* If {@code pos} is zero, the dummy arguments will precede
* the target's real arguments; if {@code pos} is N
* they will come after.
*
* Example:
*
* This method is also equivalent to the following code:
*
* The pre-processing is performed by one or more method handles,
* specified in the elements of the {@code filters} array.
* The first element of the filter array corresponds to the {@code pos}
* argument of the target, and so on in sequence.
*
* Null arguments in the array are treated as identity functions,
* and the corresponding arguments left unchanged.
* (If there are no non-null elements in the array, the original target is returned.)
* Each filter is applied to the corresponding argument of the adapter.
*
* If a filter {@code F} applies to the {@code N}th argument of
* the target, then {@code F} must be a method handle which
* takes exactly one argument. The type of {@code F}'s sole argument
* replaces the corresponding argument type of the target
* in the resulting adapted method handle.
* The return type of {@code F} must be identical to the corresponding
* parameter type of the target.
*
* It is an error if there are elements of {@code filters}
* (null or not)
* which do not correspond to argument positions in the target.
* Example:
* Here is pseudocode for the resulting adapter:
*
* If the target returns a value, the filter must accept that value as
* its only argument.
* If the target returns void, the filter must accept no arguments.
*
* The return type of the filter
* replaces the return type of the target
* in the resulting adapted method handle.
* The argument type of the filter (if any) must be identical to the
* return type of the target.
* Example:
* Here is pseudocode for the resulting adapter:
*
* The pre-processing is performed by {@code combiner}, a second method handle.
* Of the arguments passed to the adapter, the first {@code N} arguments
* are copied to the combiner, which is then called.
* (Here, {@code N} is defined as the parameter count of the combiner.)
* After this, control passes to the target, with any result
* from the combiner inserted before the original {@code N} incoming
* arguments.
*
* If the combiner returns a value, the first parameter type of the target
* must be identical with the return type of the combiner, and the next
* {@code N} parameter types of the target must exactly match the parameters
* of the combiner.
*
* If the combiner has a void return, no result will be inserted,
* and the first {@code N} parameter types of the target
* must exactly match the parameters of the combiner.
*
* The resulting adapter is the same type as the target, except that the
* first parameter type is dropped,
* if it corresponds to the result of the combiner.
*
* (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
* that either the combiner or the target does not wish to receive.
* If some of the incoming arguments are destined only for the combiner,
* consider using {@link MethodHandle#asCollector asCollector} instead, since those
* arguments will not need to be live on the stack on entry to the
* target.)
* Example:
* Here is pseudocode for the resulting adapter:
* Here is pseudocode for the resulting adapter:
*
* The target and handler must have the same corresponding
* argument and return types, except that handler may omit trailing arguments
* (similarly to the predicate in {@link #guardWithTest guardWithTest}).
* Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
* Here is pseudocode for the resulting adapter:
*
* The target and handler must return the same type, even if the handler
* always throws. (This might happen, for instance, because the handler
* is simulating a {@code finally} clause).
* To create such a throwing handler, compose the handler creation logic
* with {@link #throwException throwException},
* in order to create a method handle of the correct return type.
* @param target method handle to call
* @param exType the type of exception which the handler will catch
* @param handler method handle to call if a matching exception is thrown
* @return method handle which incorporates the specified try/catch logic
* @throws NullPointerException if any argument is null
* @throws IllegalArgumentException if {@code handler} does not accept
* the given exception type, or if the method handle types do
* not match in their return types and their
* corresponding parameters
*/
public static
MethodHandle catchException(MethodHandle target,
Class exType,
MethodHandle handler) {
MethodType ttype = target.type();
MethodType htype = handler.type();
if (htype.parameterCount() < 1 ||
!htype.parameterType(0).isAssignableFrom(exType))
throw newIllegalArgumentException("handler does not accept exception type "+exType);
if (htype.returnType() != ttype.returnType())
throw misMatchedTypes("target and handler return types", ttype, htype);
List
* where {@code defc} is either {@code receiver.getClass()} or a super
* type of that class, in which the requested method is accessible
* to the lookup class.
* (Note that {@code bindTo} does not preserve variable arity.)
* @param receiver the object from which the method is accessed
* @param name the name of the method
* @param type the type of the method, with the receiver argument omitted
* @return the desired method handle
* @throws NoSuchMethodException if the method does not exist
* @throws IllegalAccessException if access checking fails
* or if the method's variable arity modifier bit
* is set and {@code asVarargsCollector} fails
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws NullPointerException if any argument is null
*/
public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
Class refc = receiver.getClass(); // may get NPE
MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
checkSecurityManager(refc, method);
MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
return mh.bindReceiver(receiver).setVarargs(method);
}
/**
* Makes a direct method handle to m, if the lookup class has permission.
* If m is non-static, the receiver argument is treated as an initial argument.
* If m is virtual, overriding is respected on every call.
* Unlike the Core Reflection API, exceptions are not wrapped.
* The type of the method handle will be that of the method,
* with the receiver type prepended (but only if it is non-static).
* If the method's {@code accessible} flag is not set,
* access checking is performed immediately on behalf of the lookup class.
* If m is not public, do not share the resulting handle with untrusted parties.
*
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle mh0 = lookup().{@link #findVirtual findVirtual}(defc, name, type);
MethodHandle mh1 = mh0.{@link MethodHandle#bindTo bindTo}(receiver);
MethodType mt1 = mh1.type();
if (mh0.isVarargsCollector())
mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
return mh1;
*
*
*
*
MethodHandle invoker = MethodHandles.invoker(type);
int spreadArgCount = type.parameterCount() - leadingArgCount;
invoker = invoker.asSpreader(Object[].class, spreadArgCount);
return invoker;
*
*
*
publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)
*
*
publicLookup().findVirtual(MethodHandle.class, "invoke", type)
*
*
* @param target the method handle to invoke after arguments are retyped
* @param newType the expected type of the new method handle
* @return a method handle which delegates to the target after performing
* any necessary argument conversions, and arranges for any
* necessary return value conversions
* @throws NullPointerException if either argument is null
* @throws WrongMethodTypeException if the conversion cannot be made
* @see MethodHandle#asType
*/
public static
MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
if (!target.type().isCastableTo(newType)) {
throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType);
}
return MethodHandleImpl.makePairwiseConvert(target, newType, 2);
}
/**
* Produces a method handle which adapts the calling sequence of the
* given method handle to a new type, by reordering the arguments.
* The resulting method handle is guaranteed to report a type
* which is equal to the desired new type.
*
* @param target the method handle to invoke after arguments are reordered
* @param newType the expected type of the new method handle
* @param reorder an index array which controls the reordering
* @return a method handle which delegates to the target after it
* drops unused arguments and moves and/or duplicates the other arguments
* @throws NullPointerException if any argument is null
* @throws IllegalArgumentException if the index array length is not equal to
* the arity of the target, or if any index array element
* not a valid index for a parameter of {@code newType},
* or if two corresponding parameter types in
* {@code target.type()} and {@code newType} are not identical,
*/
public static
MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
checkReorder(reorder, newType, target.type());
return target.permuteArguments(newType, reorder);
}
private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
if (newType.returnType() != oldType.returnType())
throw newIllegalArgumentException("return types do not match",
oldType, newType);
if (reorder.length == oldType.parameterCount()) {
int limit = newType.parameterCount();
boolean bad = false;
for (int j = 0; j < reorder.length; j++) {
int i = reorder[j];
if (i < 0 || i >= limit) {
bad = true; break;
}
Class src = newType.parameterType(i);
Class dst = oldType.parameterType(j);
if (src != dst)
throw newIllegalArgumentException("parameter types do not match after reorder",
oldType, newType);
}
if (!bad) return;
}
throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
}
/**
* Produces a method handle of the requested return type which returns the given
* constant value every time it is invoked.
* {@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodType intfn1 = methodType(int.class, int.class);
MethodType intfn2 = methodType(int.class, int.class, int.class);
MethodHandle sub = ... {int x, int y => x-y} ...;
assert(sub.type().equals(intfn2));
MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
assert((int)rsub.invokeExact(1, 100) == 99);
MethodHandle add = ... {int x, int y => x+y} ...;
assert(add.type().equals(intfn2));
MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
assert(twice.type().equals(intfn1));
assert((int)twice.invokeExact(21) == 42);
* }
*
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
assertEquals(bigType, d0.type());
assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
*
* @param target the method handle to invoke after the arguments are dropped
* @param valueTypes the type(s) of the argument(s) to drop
* @param pos position of first argument to drop (zero for the leftmost)
* @return a method handle which drops arguments of the given types,
* before calling the original method handle
* @throws NullPointerException if the target is null,
* or if the {@code valueTypes} list or any of its elements is null
* @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
* or if {@code pos} is negative or greater than the arity of the target,
* or if the new method handle's type would have too many parameters
*/
public static
MethodHandle dropArguments(MethodHandle target, int pos, List
* {@link #dropArguments(MethodHandle,int,Class...) dropArguments}(target, pos, valueTypes.toArray(new Class[0]))
*
*
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle d0 = dropArguments(cat, 0, String.class);
assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
MethodHandle d1 = dropArguments(cat, 1, String.class);
assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
MethodHandle d2 = dropArguments(cat, 2, String.class);
assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
*
* @param target the method handle to invoke after the arguments are dropped
* @param valueTypes the type(s) of the argument(s) to drop
* @param pos position of first argument to drop (zero for the leftmost)
* @return a method handle which drops arguments of the given types,
* before calling the original method handle
* @throws NullPointerException if the target is null,
* or if the {@code valueTypes} array or any of its elements is null
* @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
* or if {@code pos} is negative or greater than the arity of the target,
* or if the new method handle's type would have too many parameters
*/
public static
MethodHandle dropArguments(MethodHandle target, int pos, Class... valueTypes) {
return dropArguments(target, pos, Arrays.asList(valueTypes));
}
/**
* Adapts a target method handle by pre-processing
* one or more of its arguments, each with its own unary filter function,
* and then calling the target with each pre-processed argument
* replaced by the result of its corresponding filter function.
*
* {@link #dropArguments(MethodHandle,int,List) dropArguments}(target, pos, Arrays.asList(valueTypes))
*
*
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
MethodHandle upcase = lookup().findVirtual(String.class,
"toUpperCase", methodType(String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle f0 = filterArguments(cat, 0, upcase);
assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
MethodHandle f1 = filterArguments(cat, 1, upcase);
assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
*
*
* @param target the method handle to invoke after arguments are filtered
* @param pos the position of the first argument to filter
* @param filters method handles to call initially on filtered arguments
* @return method handle which incorporates the specified argument filtering logic
* @throws NullPointerException if the target is null
* or if the {@code filters} array is null
* @throws IllegalArgumentException if a non-null element of {@code filters}
* does not match a corresponding argument type of target as described above,
* or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}
*/
public static
MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
MethodType targetType = target.type();
MethodHandle adapter = target;
MethodType adapterType = null;
assert((adapterType = targetType) != null);
int maxPos = targetType.parameterCount();
if (pos + filters.length > maxPos)
throw newIllegalArgumentException("too many filters");
int curPos = pos-1; // pre-incremented
for (MethodHandle filter : filters) {
curPos += 1;
if (filter == null) continue; // ignore null elements of filters
adapter = filterArgument(adapter, curPos, filter);
assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null);
}
assert(adapterType.equals(adapter.type()));
return adapter;
}
/*non-public*/ static
MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
MethodType targetType = target.type();
MethodType filterType = filter.type();
if (filterType.parameterCount() != 1
|| filterType.returnType() != targetType.parameterType(pos))
throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
return MethodHandleImpl.makeCollectArguments(target, filter, pos, false);
}
// FIXME: Make this public in M1.
/*non-public*/ static
MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle collector) {
MethodType targetType = target.type();
MethodType filterType = collector.type();
if (filterType.returnType() != void.class &&
filterType.returnType() != targetType.parameterType(pos))
throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
return MethodHandleImpl.makeCollectArguments(target, collector, pos, false);
}
/**
* Adapts a target method handle by post-processing
* its return value (if any) with a filter (another method handle).
* The result of the filter is returned from the adapter.
*
* V target(P... p, A[i]... a[i], B... b);
* A[i] filter[i](V[i]);
* T adapter(P... p, V[i]... v[i], B... b) {
* return target(p..., f[i](v[i])..., b...);
* }
*
*
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
MethodHandle length = lookup().findVirtual(String.class,
"length", methodType(int.class));
System.out.println((String) cat.invokeExact("x", "y")); // xy
MethodHandle f0 = filterReturnValue(cat, length);
System.out.println((int) f0.invokeExact("x", "y")); // 2
*
* @param target the method handle to invoke before filtering the return value
* @param filter method handle to call on the return value
* @return method handle which incorporates the specified return value filtering logic
* @throws NullPointerException if either argument is null
* @throws IllegalArgumentException if the argument list of {@code filter}
* does not match the return type of target as described above
*/
public static
MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
MethodType targetType = target.type();
MethodType filterType = filter.type();
Class rtype = targetType.returnType();
int filterValues = filterType.parameterCount();
if (filterValues == 0
? (rtype != void.class)
: (rtype != filterType.parameterType(0)))
throw newIllegalArgumentException("target and filter types do not match", target, filter);
// result = fold( lambda(retval, arg...) { filter(retval) },
// lambda( arg...) { target(arg...) } )
return MethodHandleImpl.makeCollectArguments(filter, target, 0, false);
}
/**
* Adapts a target method handle by pre-processing
* some of its arguments, and then calling the target with
* the result of the pre-processing, inserted into the original
* sequence of arguments.
*
* V target(A...);
* T filter(V);
* T adapter(A... a) {
* V v = target(a...);
* return filter(v);
* }
* // and if the target has a void return:
* void target2(A...);
* T filter2();
* T adapter2(A... a) {
* target2(a...);
* return filter2();
* }
* // and if the filter has a void return:
* V target3(A...);
* void filter3(V);
* void adapter3(A... a) {
* V v = target3(a...);
* filter3(v);
* }
*
*
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
"println", methodType(void.class, String.class))
.bindTo(System.out);
MethodHandle cat = lookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
MethodHandle catTrace = foldArguments(cat, trace);
// also prints "boo":
assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
*
* @param target the method handle to invoke after arguments are combined
* @param combiner method handle to call initially on the incoming arguments
* @return method handle which incorporates the specified argument folding logic
* @throws NullPointerException if either argument is null
* @throws IllegalArgumentException if {@code combiner}'s return type
* is non-void and not the same as the first argument type of
* the target, or if the initial {@code N} argument types
* of the target
* (skipping one matching the {@code combiner}'s return type)
* are not identical with the argument types of {@code combiner}
*/
public static
MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
int pos = 0;
MethodType targetType = target.type();
MethodType combinerType = combiner.type();
int foldPos = pos;
int foldArgs = combinerType.parameterCount();
int foldVals = combinerType.returnType() == void.class ? 0 : 1;
int afterInsertPos = foldPos + foldVals;
boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
if (ok && !(combinerType.parameterList()
.equals(targetType.parameterList().subList(afterInsertPos,
afterInsertPos + foldArgs))))
ok = false;
if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0)))
ok = false;
if (!ok)
throw misMatchedTypes("target and combiner types", targetType, combinerType);
MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos);
return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true);
}
/**
* Makes a method handle which adapts a target method handle,
* by guarding it with a test, a boolean-valued method handle.
* If the guard fails, a fallback handle is called instead.
* All three method handles must have the same corresponding
* argument and return types, except that the return type
* of the test must be boolean, and the test is allowed
* to have fewer arguments than the other two method handles.
*
* // there are N arguments in A...
* T target(V, A[N]..., B...);
* V combiner(A...);
* T adapter(A... a, B... b) {
* V v = combiner(a...);
* return target(v, a..., b...);
* }
* // and if the combiner has a void return:
* T target2(A[N]..., B...);
* void combiner2(A...);
* T adapter2(A... a, B... b) {
* combiner2(a...);
* return target2(a..., b...);
* }
*
* Note that the test arguments ({@code a...} in the pseudocode) cannot
* be modified by execution of the test, and so are passed unchanged
* from the caller to the target or fallback as appropriate.
* @param test method handle used for test, must return boolean
* @param target method handle to call if test passes
* @param fallback method handle to call if test fails
* @return method handle which incorporates the specified if/then/else logic
* @throws NullPointerException if any argument is null
* @throws IllegalArgumentException if {@code test} does not return boolean,
* or if all three method types do not match (with the return
* type of {@code test} changed to match that of the target).
*/
public static
MethodHandle guardWithTest(MethodHandle test,
MethodHandle target,
MethodHandle fallback) {
MethodType gtype = test.type();
MethodType ttype = target.type();
MethodType ftype = fallback.type();
if (!ttype.equals(ftype))
throw misMatchedTypes("target and fallback types", ttype, ftype);
if (gtype.returnType() != boolean.class)
throw newIllegalArgumentException("guard type is not a predicate "+gtype);
List
* boolean test(A...);
* T target(A...,B...);
* T fallback(A...,B...);
* T adapter(A... a,B... b) {
* if (test(a...))
* return target(a..., b...);
* else
* return fallback(a..., b...);
* }
*
* Note that the saved arguments ({@code a...} in the pseudocode) cannot
* be modified by execution of the target, and so are passed unchanged
* from the caller to the handler, if the handler is invoked.
*
* T target(A..., B...);
* T handler(ExType, A...);
* T adapter(A... a, B... b) {
* try {
* return target(a..., b...);
* } catch (ExType ex) {
* return handler(ex, a...);
* }
* }
*