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This file contains all the changes in documentation in the packagejava.lang.reflect
as colored differences. Deletions are shownlike this, and additions are shown like this.
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Class Proxy, Class getProxyClass(ClassLoader, Class[])Proxy
provides static methods for creating dynamic proxy classes and instances and it is also the superclass of all dynamic proxy classes created by those methods.To create a proxy for some interface
Foo
:InvocationHandler handler = new MyInvocationHandler(...); Class proxyClass = Proxy.getProxyClass( Foo.class.getClassLoader() new Class[] { Foo.class }); Foo f = (Foo) proxyClass. getConstructor(new Class[] { InvocationHandler.class }). newInstance(new Object[] { handler });or more simply:Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader() new Class[] { Foo.class } handler);A dynamic proxy class (simply referred to as a proxy class below) is a class that implements a list of interfaces specified at runtime when the class is created with behavior as described below. A proxy interface is such an interface that is implemented by a proxy class. A proxy instance is an instance of a proxy class. Each proxy instance has an associated invocation handler object which implements the interface InvocationHandler A method invocation on a proxy instance through one of its proxy interfaces will be dispatched to the invoke method of the instance's invocation handler passing the proxy instance a
java.lang.reflect.Method
object identifying the method that was invoked and an array of typeObject
containing the arguments. The invocation handler processes the encoded method invocation as appropriate and the result that it returns will be returned as the result of the method invocation on the proxy instance.A proxy class has the following properties:
- Proxy classes are public final and not abstract.
- The unqualified name of a proxy class is unspecified. The space of class names that begin with the string
"$Proxy"
should be however reserved for proxy classes.- A proxy class extends
java.lang.reflect.Proxy
.- A proxy class implements exactly the interfaces specified at its creation in the same order.
- If a proxy class implements a non-public interface then it will be defined in the same package as that interface. Otherwise the package of a proxy class is also unspecified. Note that package sealing will not prevent a proxy class from being successfully defined in a particular package at runtime and neither will classes already defined
inby the same class loader and the same package with particular signers.- Since a proxy class implements all of the interfaces specified at its creation invoking
getInterfaces
on itsClass
object will return an array containing the same list of interfaces (in the order specified at its creation) invokinggetMethods
on itsClass
object will return an array ofMethod
objects that include all of the methods in those interfaces and invokinggetMethod
will find methods in the proxy interfaces as would be expected.- The Proxy.isProxyClass method will return true if it is passed a proxy class-- a class returned by
Proxy.getProxyClass
or the class of an object returned byProxy.newProxyInstance
-- and false otherwise.- The
java.security.ProtectionDomain
of a proxy class is the same as that of system classes loaded by the bootstrap class loader such asjava.lang.Object
because the code for a proxy class is generated by trusted system code. This protection domain will typically be grantedjava.security.AllPermission
.- Each proxy class has one public constructor that takes one argument an implementation of the interface InvocationHandler to set the invocation handler for a proxy instance. Rather than having to use the reflection API to access the public constructor a proxy instance can be also be created by calling the Proxy.newInstance method which combines the actions of calling Proxy.getProxyClass with invoking the constructor with an invocation handler.
A proxy instance has the following properties:
- Given a proxy instance
proxy
and one of the interfaces implemented by its proxy classFoo
the following expression will return true:and the following cast operation will succeed (rather than throwing aproxy instanceof Foo
ClassCastException
):(Foo) proxy
- Each proxy instance has an associated invocation handler the one that was passed to its constructor. The static Proxy.getInvocationHandler method will return the invocation handler associated with the proxy instance passed as its argument.
- An interface method invocation on a proxy instance will be encoded and dispatched to the invocation handler's invoke method as described in the documentation for that method.
- An invocation of the
hashCode
equals
ortoString
methods declared injava.lang.Object
on a proxy instance will be encoded and dispatched to the invocation handler'sinvoke
method in the same manner as interface method invocations are encoded and dispatched as described above. The declaring class of theMethod
object passed toinvoke
will bejava.lang.Object
. Other public methods of a proxy instance inherited fromjava.lang.Object
are not overridden by a proxy class so invocations of those methods behave like they do for instances ofjava.lang.Object
.Methods Duplicated in Multiple Proxy Interfaces
When two or more interfaces of a proxy class contain a method with the same name and parameter signature the order of the proxy class's interfaces becomes significant. When such a duplicate method is invoked on a proxy instance the
Method
object passed to the invocation handler will not necessarily be the one whose declaring class is assignable from the reference type of the interface that the proxy's method was invoked through. This limitation exists because the corresponding method implementation in the generated proxy class cannot determine which interface it was invoked through. Therefore when a duplicate method is invoked on a proxy instance theMethod
object for the method in the foremost interface that contains the method (either directly or inherited through a superinterface) in the proxy class's list of interfaces is passed to the invocation handler'sinvoke
method regardless of the reference type through which the method invocation occurred.If a proxy interface contains a method with the same name and parameter signature as the
hashCode
equals
ortoString
methods ofjava.lang.Object
when such a method is invoked on a proxy instance theMethod
object passed to the invocation handler will havejava.lang.Object
as its declaring class. In other words the public non-final methods ofjava.lang.Object
logically precede all of the proxy interfaces for the determination of whichMethod
object to pass to the invocation handler.Note also that when a duplicate method is dispatched to an invocation handler the
invoke
method may only throw checked exception types that are assignable to one of the exception types in thethrows
clause of the method in all of the proxy interfaces that it can be invoked through. If theinvoke
method throws a checked exception that is not assignable to any of the exception types declared by the method in one of the the proxy interfaces that it can be invoked through then an uncheckedUndeclaredThrowableException
will be thrown by the invocation on the proxy instance. This restriction means that not all of the exception types returned by invokinggetExceptionTypes
on theMethod
object passed to theinvoke
method can necessarily be thrown successfully by theinvoke
method. @author Peter Jones @version 1.9100102/1202/0306 @see InvocationHandler @since JDK1.3
Returns theClass Proxy, Object newProxyInstance(ClassLoader, Class[], InvocationHandler)java.lang.Class
object for a proxy class given a class loader and an array of interfaces. The proxy class will be definedinby the specified class loader and will implement all of the supplied interfaces. If a proxy class for the same permutation of interfaces has already been definedinby the class loader then the existing proxy class will be returned; otherwise a proxy class for those interfaces will be generated dynamically and definedinby the class loader.There are several restrictions on the parameters that may be passed to
Proxy.getProxyClass
:
- All of the
Class
objects in theinterfaces
array must represent interfaces not classes or primitive types.- No two elements in the
interfaces
array may refer to identicalClass
objects.- All of the interface types must be visible by name through the specified class loader. In other words for class loader
cl
and every interfacei
the following expression must be true:Class.forName(i.getName() false cl) == i- All non-public interfaces must be in the same package; otherwise it would not be possible for the proxy class to implement all of the interfaces regardless of what package it is defined in.
- No two interfaces may each have a method with the same name and parameter signature but different return type.
- The resulting proxy class must not exceed any limits imposed on classes by the virtual machine. For example the VM may limit the number of interfaces that a class may implement to 65535; in that case the size of the
interfaces
array must not exceed 65535.If any of these restrictions are violated
Proxy.getProxyClass
will throw anIllegalArgumentException
. If theinterfaces
array argument or any of its elements arenull
aNullPointerException
will be thrown.Note that the order of the specified proxy interfaces is significant: two requests for a proxy class with the same combination of interfaces but in a different order will result in two distinct proxy classes. @param loader the class loader to define the proxy class
in@param interfaces the list of interfaces for the proxy class to implement @return a proxy class that is defined in the specified class loader and that implements the specified interfaces @throws IllegalArgumentException if any of the restrictions on the parameters that may be passed togetProxyClass
are violated @throws NullPointerException if theinterfaces
array argument or any of its elements arenull
Returns an instance of a proxy class for the specified interfaces that dispatches method invocations to the specified invocation handler. This method is equivalent to:Proxy.getProxyClass(loader interfaces). getConstructor(new Class[] { InvocationHandler.class }). newInstance(new Object[] { handler });
Proxy.newProxyInstance
throwsIllegalArgumentException
for the same reasons thatProxy.getProxyClass
does. @param loader the class loader to define the proxy classin@param interfaces the list of interfaces for the proxy class to implement @param h the invocation handler to dispatch method invocations to @return a proxy instance with the specified invocation handler of a proxy class that is definedinby the specified class loader and that implements the specified interfaces @throws IllegalArgumentException if any of the restrictions on the parameters that may be passed togetProxyClass
are violated @throws NullPointerException if theinterfaces
array argument or any of its elements arenull
or if the invocation handlerh
isnull
Constructs a ReflectPermission with the specified name and actions. The actions should be null; they are ignored.This constructor exists for use by the Policy object to instantiate new Permission objects.@param name the name of the ReflectPermission @param actions should be null.