* This method is caller sensitive, which means that it may return different * values to different callers. *
* For any given caller class {@code C}, the lookup object returned by this call * has equivalent capabilities to any lookup object * supplied by the JVM to the bootstrap method of an * invokedynamic instruction * executing in the same caller class {@code C}. * @return a lookup object for the caller of this method, with private access */ @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}. * *
* Discussion: * The lookup class can be changed to any other class {@code C} using an expression of the form * {@link Lookup#in publicLookup().in(C.class)}. * Since all classes have equal access to public names, * such a change would confer no new access rights. * A public lookup object is always subject to * security manager checks. * Also, it cannot access * caller sensitive methods. * @return a lookup object which is trusted minimally */ public static Lookup publicLookup() { return Lookup.PUBLIC_LOOKUP; } /** * Performs an unchecked "crack" of a * direct method handle. * The result is as if the user had obtained a lookup object capable enough * to crack the target method handle, called * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect} * on the target to obtain its symbolic reference, and then called * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs} * to resolve the symbolic reference to a member. *
* If there is a security manager, its {@code checkPermission} method
* is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
* @param
* 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.
*
*
* 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.
*
* Discussion:
* The equivalence between looked-up method handles and underlying
* class members and bytecode behaviors
* 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, or
* because the lookup object is not trusted enough to access the member.
* 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 no more restrictive than the conditions
* under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
* Where the JVM would raise exceptions like {@code NoSuchMethodError},
* a method handle lookup will generally raise a corresponding
* checked exception, such as {@code NoSuchMethodException}.
* And the effect of invoking the method handle resulting from the lookup
* is exactly equivalent
* to executing the compiled, verified, and resolved call to {@code M}.
* The same point is true of fields and constructors.
*
* Discussion:
* 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 used
* independently of any {@code Lookup} object.
*
* 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.
*
* The JVM imposes a similar requirement on {@code invokespecial} instruction,
* that the receiver argument must match both the resolved method and
* the current class. Again, this requirement is enforced by narrowing the
* type of the leading parameter to the resulting method handle.
* (See the Java Virtual Machine Specification, section 4.10.1.9.)
*
* The JVM represents constructors and static initializer blocks as internal methods
* with special names ({@code "
* 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.
*
* The accesses permitted to a given lookup object may be limited,
* according to its set of {@link #lookupModes lookupModes},
* to a subset of members normally accessible to the lookup class.
* For example, the {@link MethodHandles#publicLookup publicLookup}
* method produces a lookup object which is only allowed to access
* public members in public classes.
* The caller sensitive method {@link MethodHandles#lookup lookup}
* produces a lookup object with full capabilities relative to
* its caller class, to emulate all supported bytecode behaviors.
* Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
* with fewer access modes than the original lookup object.
*
*
*
* Discussion of private access:
* We say that a lookup has private access
* if its {@linkplain #lookupModes lookup modes}
* include the possibility of accessing {@code private} members.
* As documented in the relevant methods elsewhere,
* only lookups with private access possess the following capabilities:
*
* Each of these permissions is a consequence of the fact that a lookup object
* with private access can be securely traced back to an originating class,
* whose bytecode behaviors and Java language access permissions
* can be reliably determined and emulated by method handles.
*
*
* If a security manager is present, member lookups are subject to
* additional checks.
* From one to three calls are made to the security manager.
* Any of these calls can refuse access by throwing a
* {@link java.lang.SecurityException SecurityException}.
* Define {@code smgr} as the security manager,
* {@code lookc} as the lookup class of the current lookup object,
* {@code refc} as the containing class in which the member
* is being sought, and {@code defc} as the class in which the
* member is actually defined.
* The value {@code lookc} is defined as not present
* if the current lookup object does not have
* private access.
* The calls are made according to the following rules:
*
* If a method handle for a caller-sensitive method is requested,
* the general rules for bytecode behaviors apply,
* but they take account of the lookup class in a special way.
* The resulting method handle behaves as if it were called
* from an instruction contained in the lookup class,
* so that the caller-sensitive method detects the lookup class.
* (By contrast, the invoker of the method handle is disregarded.)
* Thus, in the case of caller-sensitive methods,
* different lookup classes may give rise to
* differently behaving method handles.
*
* In cases where the lookup object is
* {@link MethodHandles#publicLookup() publicLookup()},
* or some other lookup object without
* private access,
* the lookup class is disregarded.
* In such cases, no caller-sensitive method handle can be created,
* access is forbidden, and the lookup fails with an
* {@code IllegalAccessException}.
*
* Discussion:
* For example, the caller-sensitive method
* {@link java.lang.Class#forName(String) Class.forName(x)}
* can return varying classes or throw varying exceptions,
* depending on the class loader of the class that calls it.
* A public lookup of {@code Class.forName} will fail, because
* there is no reasonable way to determine its bytecode behavior.
*
* If an application caches method handles for broad sharing,
* it should use {@code publicLookup()} to create them.
* If there is a lookup of {@code Class.forName}, it will fail,
* and the application must take appropriate action in that case.
* It may be that a later lookup, perhaps during the invocation of a
* bootstrap method, can incorporate the specific identity
* of the caller, making the method accessible.
*
* The function {@code MethodHandles.lookup} is caller sensitive
* so that there can be a secure foundation for lookups.
* Nearly all other methods in the JSR 292 API rely on lookup
* objects to check access requests.
*/
public static final
class Lookup {
/** The class on behalf of whom the lookup is being performed. */
private final Class lookupClass;
/** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
private final int allowedModes;
/** A single-bit mask representing {@code public} access,
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value, {@code 0x01}, happens to be the same as the value of the
* {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
*/
public static final int PUBLIC = Modifier.PUBLIC;
/** A single-bit mask representing {@code private} access,
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value, {@code 0x02}, happens to be the same as the value of the
* {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
*/
public static final int PRIVATE = Modifier.PRIVATE;
/** A single-bit mask representing {@code protected} access,
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value, {@code 0x04}, happens to be the same as the value of the
* {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
*/
public static final int PROTECTED = Modifier.PROTECTED;
/** A single-bit mask representing {@code package} access (default access),
* which may contribute to the result of {@link #lookupModes lookupModes}.
* The value is {@code 0x08}, which does not correspond meaningfully to
* any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
*/
public static final int PACKAGE = Modifier.STATIC;
private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
private static final int TRUSTED = -1;
private static int fixmods(int mods) {
mods &= (ALL_MODES - PACKAGE);
return (mods != 0) ? mods : PACKAGE;
}
/** Tells which class is performing the lookup. It is this class against
* which checks are performed for visibility and access permissions.
*
* 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.
* @return the lookup class, on behalf of which this lookup object finds members
*/
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.
* @return the lookup modes, which limit the kinds of access performed by this lookup object
*/
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, ALL_MODES);
}
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 object.
*
* 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.
*
* If the returned method handle is invoked, the method's class will
* be initialized, if it has not already been initialized.
* Example:
*
* 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.
*
* Example:
*
* 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.
*
* If the returned method handle is invoked, the constructor's class will
* be initialized, if it has not already been initialized.
* Example:
*
* Before method resolution,
* 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.
*
* (Note: JVM internal methods named {@code " Example:
*
* If the returned method handle is invoked, the field's class will
* be initialized, if it has not already been initialized.
* @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);
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.
*
* If the returned method handle is invoked, the field's class will
* be initialized, if it has not already been initialized.
* @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);
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 object.
* 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.
*
* If m is static, and
* if the returned method handle is invoked, the method's class will
* be initialized, if it has not already been initialized.
* @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 {
if (m.getDeclaringClass() == MethodHandle.class) {
MethodHandle mh = unreflectForMH(m);
if (mh != null) return mh;
}
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.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
}
private MethodHandle unreflectForMH(Method m) {
// these names require special lookups because they throw UnsupportedOperationException
if (MemberName.isMethodHandleInvokeName(m.getName()))
return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
return null;
}
/**
* Produces a method handle for a reflected method.
* It will bypass checks for overriding methods on the receiver,
* as if called from an {@code invokespecial}
* instruction from within the explicitly specified {@code specialCaller}.
* The type of the method handle will be that of the method,
* with a suitably restricted receiver type prepended.
* (The receiver type will be {@code specialCaller} or a subtype.)
* 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.
*
* Before method resolution,
* 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 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.getDirectMethodNoSecurityManager(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.
*
* If the returned method handle is invoked, the constructor's class will
* be initialized, if it has not already been initialized.
* @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
*/
public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
MemberName ctor = new MemberName(c);
assert(ctor.isConstructor());
Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
return lookup.getDirectConstructorNoSecurityManager(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.
*
* If the field is static, and
* if the returned method handle is invoked, the field's class will
* be initialized, if it has not already been initialized.
* @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.getDirectFieldNoSecurityManager(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.
*
* If the field is static, and
* if the returned method handle is invoked, the field's class will
* be initialized, if it has not already been initialized.
* @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);
}
/**
* Cracks a direct method handle
* created by this lookup object or a similar one.
* Security and access checks are performed to ensure that this lookup object
* is capable of reproducing the target method handle.
* This means that the cracking may fail if target is a direct method handle
* but was created by an unrelated lookup object.
* This can happen if the method handle is caller sensitive
* and was created by a lookup object for a different class.
* @param target a direct method handle to crack into symbolic reference components
* @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
* @exception SecurityException if a security manager is present and it
* refuses access
* @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
* @exception NullPointerException if the target is {@code null}
* @see MethodHandleInfo
* @since 1.8
*/
public MethodHandleInfo revealDirect(MethodHandle target) {
MemberName member = target.internalMemberName();
if (member == null || (!member.isResolved() && !member.isMethodHandleInvoke()))
throw newIllegalArgumentException("not a direct method handle");
Class defc = member.getDeclaringClass();
byte refKind = member.getReferenceKind();
assert(MethodHandleNatives.refKindIsValid(refKind));
if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
// Devirtualized method invocation is usually formally virtual.
// To avoid creating extra MemberName objects for this common case,
// we encode this extra degree of freedom using MH.isInvokeSpecial.
refKind = REF_invokeVirtual;
if (refKind == REF_invokeVirtual && defc.isInterface())
// Symbolic reference is through interface but resolves to Object method (toString, etc.)
refKind = REF_invokeInterface;
// Check SM permissions and member access before cracking.
try {
checkAccess(refKind, defc, member);
checkSecurityManager(defc, member);
} catch (IllegalAccessException ex) {
throw new IllegalArgumentException(ex);
}
if (allowedModes != TRUSTED && member.isCallerSensitive()) {
Class callerClass = target.internalCallerClass();
if (!hasPrivateAccess() || callerClass != lookupClass())
throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
}
// Produce the handle to the results.
return new InfoFromMemberName(this, member, refKind);
}
/// 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(); // NPE
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(); // NPE
type.getClass(); // NPE
checkMethodName(refKind, name); // NPE check on name
return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
NoSuchMethodException.class);
}
MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
member.getName().getClass(); // NPE
member.getType().getClass(); // NPE
return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
ReflectiveOperationException.class);
}
void checkSymbolicClass(Class refc) throws IllegalAccessException {
refc.getClass(); // NPE
Class caller = lookupClassOrNull();
if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
}
/** Check name for an illegal leading "<" character. */
void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
throw new NoSuchMethodException("illegal method name: "+name);
}
/**
* 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 lookups with private access are allowed to resolve caller-sensitive methods
if (hasPrivateAccess()) {
callerClass = lookupClass;
} else {
throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
}
}
return callerClass;
}
private boolean hasPrivateAccess() {
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:
boolean fullPowerLookup = hasPrivateAccess();
if (!fullPowerLookup ||
!VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
ReflectUtil.checkPackageAccess(refc);
}
// Step 2:
if (m.isPublic()) return;
if (!fullPowerLookup) {
smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
}
// Step 3:
Class defc = m.getDeclaringClass();
if (!fullPowerLookup && 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);
}
/** Check public/protected/private bits on the symbolic reference class and its member. */
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.isProtected(mods) &&
refKind == REF_invokeVirtual &&
m.getDeclaringClass() == Object.class &&
m.getName().equals("clone") &&
refc.isArray()) {
// The JVM does this hack also.
// (See ClassVerifier::verify_invoke_instructions
// and LinkResolver::check_method_accessability.)
// Because the JVM does not allow separate methods on array types,
// there is no separate method for int[].clone.
// All arrays simply inherit Object.clone.
// But for access checking logic, we make Object.clone
// (normally protected) appear to be public.
// Later on, when the DirectMethodHandle is created,
// its leading argument will be restricted to the
// requested array type.
// N.B. The return type is not adjusted, because
// that is *not* the bytecode behavior.
mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
}
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 (!hasPrivateAccess()
|| (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);
}
/** Check access and get the requested method. */
private MethodHandle getDirectMethod(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
final boolean doRestrict = true;
final boolean checkSecurity = true;
return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
}
/** Check access and get the requested method, eliding receiver narrowing rules. */
private MethodHandle getDirectMethodNoRestrict(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
final boolean doRestrict = false;
final boolean checkSecurity = true;
return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
}
/** Check access and get the requested method, eliding security manager checks. */
private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException {
final boolean doRestrict = true;
final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
}
/** Common code for all methods; do not call directly except from immediately above. */
private MethodHandle getDirectMethodCommon(byte refKind, Class refc, MemberName method,
boolean checkSecurity,
boolean doRestrict, Class callerClass) throws IllegalAccessException {
checkMethod(refKind, refc, method);
// Optionally check with the security manager; this isn't needed for unreflect* calls.
if (checkSecurity)
checkSecurityManager(refc, method);
assert(!method.isMethodHandleInvoke());
if (refKind == REF_invokeSpecial &&
refc != lookupClass() &&
!refc.isInterface() &&
refc != 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.
* If, when the invoker is called, the supplied array argument does
* not have the correct number of elements, the invoker will throw
* an {@link IllegalArgumentException} instead of invoking the target.
*
* This method is equivalent to the following code (though it may be more efficient):
*
* This method is equivalent to the following code (though it may be more efficient):
* {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
*
*
* 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
* @throws IllegalArgumentException if the resulting method handle's type would have
* too many parameters
*/
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}.
*
* This method is equivalent to the following code (though it may be more efficient):
* {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
*
* Discussion:
* A {@linkplain MethodType#genericMethodType general method type} is one which
* 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.
*
* (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 convertible to the given type
* @throws IllegalArgumentException if the resulting method handle's type would have
* too many parameters
*/
static public
MethodHandle invoker(MethodType type) {
return type.invokers().genericInvoker();
}
static /*non-public*/
MethodHandle basicInvoker(MethodType type) {
return type.invokers().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()) {
BasicType btype = I_TYPE;
Wrapper w = Wrapper.forPrimitiveType(ptype);
switch (w) {
case LONG: btype = J_TYPE; break;
case FLOAT: btype = F_TYPE; break;
case DOUBLE: btype = D_TYPE; 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_TYPE, 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 filter returns a value, the target must accept that value as
* its argument in position {@code pos}, preceded and/or followed by
* any arguments not passed to the filter.
* If the filter returns void, the target must accept all arguments
* not passed to the filter.
* No arguments are reordered, and a result returned from the filter
* replaces (in order) the whole subsequence of arguments originally
* passed to the adapter.
*
* The argument types (if any) of the filter
* replace zero or one argument types of the target, at position {@code pos},
* in the resulting adapted method handle.
* The return type of the filter (if any) must be identical to the
* argument type of the target at position {@code pos}, and that target argument
* is supplied by the return value of the filter.
*
* In all cases, {@code pos} must be greater than or equal to zero, and
* {@code pos} must also be less than or equal to the target's arity.
* Example:
* Here is pseudocode for the resulting adapter:
*
* A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
* one which first "folds" the affected arguments, and then drops them, in separate
* steps as follows:
*
* 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);
ListLookup Factory Methods
* The factory methods on a {@code Lookup} object correspond to all major
* use cases for methods, constructors, and fields.
* Each method handle created by a factory method is the functional
* equivalent of a particular bytecode behavior.
* (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
* Here is a summary of the correspondence between these factory methods and
* the behavior the resulting method handles:
*
*
*
* Access checking
* Access checks are applied in the factory methods of {@code Lookup},
* when a method handle is created.
* This is a key difference from the Core Reflection API, since
* {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
* performs access checking against every caller, on every call.
*
*
*
*
* Security manager interactions
* 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}).
*
*
* Security checks are performed after other access checks have passed.
* Therefore, the above rules presuppose a member that is public,
* or else that is being accessed from a lookup class that has
* rights to access the member.
*
* Caller sensitive methods
* A small number of Java methods have a special property called caller sensitivity.
* A caller-sensitive method can behave differently depending on the
* identity of its immediate caller.
*
*
*
* @param requestedLookupClass the desired lookup class for the new lookup object
* @return a lookup object which reports the desired lookup class
* @throws NullPointerException if the argument is null
*/
public Lookup in(Class requestedLookupClass) {
requestedLookupClass.getClass(); // null check
if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
return new Lookup(requestedLookupClass, ALL_MODES);
if (requestedLookupClass == this.lookupClass)
return this; // keep same capabilities
int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
if ((newModes & PACKAGE) != 0
&& !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
newModes &= ~(PACKAGE|PRIVATE);
}
// Allow nestmate lookups to be created without special privilege:
if ((newModes & PRIVATE) != 0
&& !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
newModes &= ~PRIVATE;
}
if ((newModes & PUBLIC) != 0
&& !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
// The requested class it not accessible from the lookup class.
// No permissions.
newModes = 0;
}
checkUnprivilegedlookupClass(requestedLookupClass, newModes);
return new Lookup(requestedLookupClass, newModes);
}
// Make sure outer class is initialized first.
static { IMPL_NAMES.getClass(); }
/** Version of lookup which is trusted minimally.
* It can only be used to create method handles to
* publicly accessible members.
*/
static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
/** Package-private version of lookup which is trusted. */
static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
private static void checkUnprivilegedlookupClass(Class lookupClass, int allowedModes) {
String name = lookupClass.getName();
if (name.startsWith("java.lang.invoke."))
throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
// For caller-sensitive MethodHandles.lookup()
// disallow lookup more restricted packages
if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
if (name.startsWith("java.") ||
(name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
}
}
}
/**
* Displays the name of the class from which lookups are to be made.
* (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
* If there are restrictions on the access permitted to this lookup,
* this is indicated by adding a suffix to the class name, consisting
* of a slash and a keyword. The keyword represents the strongest
* allowed access, and is chosen as follows:
*
*
* If none of the above cases apply, it is the case that full
* access (public, package, private, and protected) is allowed.
* In this case, no suffix is added.
* This is true only of an object obtained originally from
* {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
* Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
* always have restricted access, and will display a suffix.
*
* @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);
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 object.
* {@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
"asList", methodType(List.class, Object[].class));
assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
* }
*
* @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);
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);
if ("invokeBasic".equals(name))
return basicInvoker(type);
assert(!MemberName.isMethodHandleInvokeName(name));
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 object.
* {@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle MH_concat = publicLookup().findVirtual(String.class,
"concat", methodType(String.class, String.class));
MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
"hashCode", methodType(int.class));
MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
"hashCode", methodType(int.class));
assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
// interface method:
MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
"subSequence", methodType(CharSequence.class, int.class, int.class));
assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
// constructor "internal method" must be accessed differently:
MethodType MT_newString = methodType(void.class); //()V for new String()
try { assertEquals("impossible", lookup()
.findVirtual(String.class, "
* @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 = "{@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle MH_newArrayList = publicLookup().findConstructor(
ArrayList.class, methodType(void.class, Collection.class));
Collection orig = Arrays.asList("x", "y");
Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
assert(orig != copy);
assertEquals(orig, copy);
// a variable-arity constructor:
MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
ProcessBuilder.class, methodType(void.class, String[].class));
ProcessBuilder pb = (ProcessBuilder)
MH_newProcessBuilder.invoke("x", "y", "z");
assertEquals("[x, y, z]", pb.command().toString());
* }
*
* @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);
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);
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);
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.
* {@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
static class Listie extends ArrayList {
public String toString() { return "[wee Listie]"; }
static Lookup lookup() { return MethodHandles.lookup(); }
}
...
// no access to constructor via invokeSpecial:
MethodHandle MH_newListie = Listie.lookup()
.findConstructor(Listie.class, methodType(void.class));
Listie l = (Listie) MH_newListie.invokeExact();
try { assertEquals("impossible", Listie.lookup().findSpecial(
Listie.class, "
* 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
* @see MethodHandle#bindTo
* @see #findVirtual
*/
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);
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.
* {@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle mh0 = lookup().findVirtual(defc, name, type);
MethodHandle mh1 = mh0.bindTo(receiver);
MethodType mt1 = mh1.type();
if (mh0.isVarargsCollector())
mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
return mh1;
* }
*
*
* 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,
* or if the resulting method handle's type would have
* too many parameters
*/
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}.
* {@code
MethodHandle invoker = MethodHandles.invoker(type);
int spreadArgCount = type.parameterCount() - leadingArgCount;
invoker = invoker.asSpreader(Object[].class, spreadArgCount);
return invoker;
* }
*
* @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) {
reorder = reorder.clone();
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);
* }
* {@code
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}{@code (target, pos, valueTypes.toArray(new Class[0]))}
*
* {@code
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}{@code (target, pos, Arrays.asList(valueTypes))}
*
* {@code
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()},
* or if the resulting method handle's type would have
* too many parameters
*/
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);
}
/**
* Adapts a target method handle by pre-processing
* a sub-sequence of its arguments with a filter (another method handle).
* The pre-processed arguments are replaced by the result (if any) of the
* filter function.
* The target is then called on the modified (usually shortened) argument list.
* {@code
* 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...);
* }
* }
* {@code
import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle deepToString = publicLookup()
.findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
assertEquals("[strange]", (String) ts1.invokeExact("strange"));
MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
assertEquals("[top, [up, down], strange]",
(String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
assertEquals("[top, [up, down], [strange]]",
(String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
assertEquals("[top, [[up, down, strange], charm], bottom]",
(String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
* }
* {@code
* T target(A...,V,C...);
* V filter(B...);
* T adapter(A... a,B... b,C... c) {
* V v = filter(b...);
* return target(a...,v,c...);
* }
* // and if the filter has no arguments:
* T target2(A...,V,C...);
* V filter2();
* T adapter2(A... a,C... c) {
* V v = filter2();
* return target2(a...,v,c...);
* }
* // and if the filter has a void return:
* T target3(A...,C...);
* void filter3(B...);
* void adapter3(A... a,B... b,C... c) {
* filter3(b...);
* return target3(a...,c...);
* }
* }
* If the target method handle consumes no arguments besides than the result
* (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
* is equivalent to {@code filterReturnValue(coll, mh)}.
* If the filter method handle {@code coll} consumes one argument and produces
* a non-void result, then {@code collectArguments(mh, N, coll)}
* is equivalent to {@code filterArguments(mh, N, coll)}.
* Other equivalences are possible but would require argument permutation.
*
* @param target the method handle to invoke after filtering the subsequence of arguments
* @param pos the position of the first adapter argument to pass to the filter,
* and/or the target argument which receives the result of the filter
* @param filter method handle to call on the subsequence of arguments
* @return method handle which incorporates the specified argument subsequence filtering logic
* @throws NullPointerException if either argument is null
* @throws IllegalArgumentException if the return type of {@code filter}
* is non-void and is not the same as the {@code pos} argument of the target,
* or if {@code pos} is not between 0 and the target's arity, inclusive,
* or if the resulting method handle's type would have
* too many parameters
* @see MethodHandles#foldArguments
* @see MethodHandles#filterArguments
* @see MethodHandles#filterReturnValue
*/
public static
MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
MethodType targetType = target.type();
MethodType filterType = filter.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, filter, 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.
* {@code
* mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
* mh = MethodHandles.foldArguments(mh, coll); //step 1
* }
* {@code
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.
* {@code
* 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);
* }
* }
* {@code
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.
* {@code
* // 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{@code
* 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.
* {@code
* 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...);
* }
* }
* }