net.sf.cglib.proxy

Class Enhancer

java.lang.Object

net.sf.cglib.core.AbstractClassGenerator

net.sf.cglib.proxy.Enhancer

All Implemented Interfaces:

ClassGenerator

public class Enhancer
extends AbstractClassGenerator

Generates dynamic subclasses to enable method interception. This class started as a substitute for the standard Dynamic Proxy support included with JDK 1.3, but one that allowed the proxies to extend a concrete base class, in addition to implementing interfaces. The dynamically generated subclasses override the non-final methods of the superclass and have hooks which callback to user-defined interceptor implementations.

The original and most general callback type is the MethodInterceptor, which in AOP terms enables "around advice"--that is, you can invoke custom code both before and after the invocation of the "super" method. In addition you can modify the arguments before calling the super method, or not call it at all.

Although MethodInterceptor is generic enough to meet any interception need, it is often overkill. For simplicity and performance, additional specialized callback types, such as LazyLoader are also available. Often a single callback will be used per enhanced class, but you can control which callback is used on a per-method basis with a CallbackFilter.

The most common uses of this class are embodied in the static helper methods. For advanced needs, such as customizing the ClassLoader to use, you should create a new instance of Enhancer. Other classes within CGLIB follow a similar pattern.

All enhanced objects implement the Factory interface, unless setUseFactory(boolean) is used to explicitly disable this feature. The Factory interface provides an API to change the callbacks of an existing object, as well as a faster and easier way to create new instances of the same type.

For an almost drop-in replacement for java.lang.reflect.Proxy, see the Proxy class.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Enhancer.EnhancerKey Internal interface, only public due to ClassLoader issues.

Nested classes/interfaces inherited from class net.sf.cglib.core.AbstractClassGenerator

AbstractClassGenerator.Source

Constructor Summary

Constructors

Constructor and Description
Enhancer() Create a new Enhancer.

Method Summary

Methods

Modifier and Type	Method and Description
Object	create() Generate a new class if necessary and uses the specified callbacks (if any) to create a new object instance.
Object	create(Class[] argumentTypes, Object[] arguments) Generate a new class if necessary and uses the specified callbacks (if any) to create a new object instance.
static Object	create(Class type, Callback callback) Helper method to create an intercepted object.
static Object	create(Class superclass, Class[] interfaces, Callback callback) Helper method to create an intercepted object.
static Object	create(Class superclass, Class[] interfaces, CallbackFilter filter, Callback[] callbacks) Helper method to create an intercepted object.
Class	createClass() Generate a new class if necessary and return it without creating a new instance.
protected void	filterConstructors(Class sc, List constructors) Filter the list of constructors from the superclass.
protected Object	firstInstance(Class type)
void	generateClass(org.objectweb.asm.ClassVisitor v)
protected ClassLoader	getDefaultClassLoader()
static void	getMethods(Class superclass, Class[] interfaces, List methods) Finds all of the methods that will be extended by an Enhancer-generated class using the specified superclass and interfaces.
static boolean	isEnhanced(Class type) Determine if a class was generated using Enhancer.
protected Object	nextInstance(Object instance)
static void	registerCallbacks(Class generatedClass, Callback[] callbacks) Call this method to register the Callback array to use before creating a new instance of the generated class via reflection.
static void	registerStaticCallbacks(Class generatedClass, Callback[] callbacks) Similar to registerCallbacks(java.lang.Class, net.sf.cglib.proxy.Callback[]), but suitable for use when multiple threads will be creating instances of the generated class.
void	setCallback(Callback callback) Set the single Callback to use.
void	setCallbackFilter(CallbackFilter filter) Set the CallbackFilter used to map the generated class' methods to a particular callback index.
void	setCallbacks(Callback[] callbacks) Set the array of callbacks to use.
void	setCallbackType(Class callbackType) Set the single type of Callback to use.
void	setCallbackTypes(Class[] callbackTypes) Set the array of callback types to use.
void	setInterceptDuringConstruction(boolean interceptDuringConstruction) Set whether methods called from within the proxy's constructer will be intercepted.
void	setInterfaces(Class[] interfaces) Set the interfaces to implement.
void	setSerialVersionUID(Long sUID) Insert a static serialVersionUID field into the generated class.
void	setSuperclass(Class superclass) Set the class which the generated class will extend.
void	setUseFactory(boolean useFactory) Set whether the enhanced object instances should implement the Factory interface.

Methods inherited from class net.sf.cglib.core.AbstractClassGenerator

create, getAttemptLoad, getClassLoader, getClassName, getCurrent, getNamingPolicy, getStrategy, getUseCache, setAttemptLoad, setClassLoader, setNamePrefix, setNamingPolicy, setStrategy, setUseCache

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Enhancer

public Enhancer()

Create a new Enhancer. A new Enhancer object should be used for each generated object, and should not be shared across threads. To create additional instances of a generated class, use the Factory interface.

See Also:

Factory

Method Detail

setSuperclass

public void setSuperclass(Class superclass)

Set the class which the generated class will extend. As a convenience, if the supplied superclass is actually an interface, setInterfaces will be called with the appropriate argument instead. A non-interface argument must not be declared as final, and must have an accessible constructor.

Parameters:

superclass - class to extend or interface to implement

See Also:

setInterfaces(Class[])

setInterfaces

public void setInterfaces(Class[] interfaces)

Set the interfaces to implement. The Factory interface will always be implemented regardless of what is specified here.

Parameters:

interfaces - array of interfaces to implement, or null

See Also:

Factory

setCallbackFilter

public void setCallbackFilter(CallbackFilter filter)

Set the CallbackFilter used to map the generated class' methods to a particular callback index. New object instances will always use the same mapping, but may use different actual callback objects.

Parameters:

filter - the callback filter to use when generating a new class

See Also:

setCallbacks(net.sf.cglib.proxy.Callback[])

setCallback

public void setCallback(Callback callback)

Set the single Callback to use. Ignored if you use createClass().

Parameters:

callback - the callback to use for all methods

See Also:

setCallbacks(net.sf.cglib.proxy.Callback[])

setCallbacks

public void setCallbacks(Callback[] callbacks)

Set the array of callbacks to use. Ignored if you use createClass(). You must use a CallbackFilter to specify the index into this array for each method in the proxied class.

Parameters:

callbacks - the callback array

See Also:

setCallbackFilter(net.sf.cglib.proxy.CallbackFilter), setCallback(net.sf.cglib.proxy.Callback)

setUseFactory

public void setUseFactory(boolean useFactory)

Set whether the enhanced object instances should implement the Factory interface. This was added for tools that need for proxies to be more indistinguishable from their targets. Also, in some cases it may be necessary to disable the Factory interface to prevent code from changing the underlying callbacks.

Parameters:

useFactory - whether to implement Factory; default is true

setInterceptDuringConstruction

public void setInterceptDuringConstruction(boolean interceptDuringConstruction)

Set whether methods called from within the proxy's constructer will be intercepted. The default value is true. Unintercepted methods will call the method of the proxy's base class, if it exists.

Parameters:

interceptDuringConstruction - whether to intercept methods called from the constructor

setCallbackType

public void setCallbackType(Class callbackType)

Set the single type of Callback to use. This may be used instead of setCallback(net.sf.cglib.proxy.Callback) when calling createClass(), since it may not be possible to have an array of actual callback instances.

Parameters:

callbackType - the type of callback to use for all methods

See Also:

setCallbackTypes(java.lang.Class[])

setCallbackTypes

public void setCallbackTypes(Class[] callbackTypes)

Set the array of callback types to use. This may be used instead of setCallbacks(net.sf.cglib.proxy.Callback[]) when calling createClass(), since it may not be possible to have an array of actual callback instances. You must use a CallbackFilter to specify the index into this array for each method in the proxied class.

Parameters:

callbackTypes - the array of callback types

create

public Object create()

Generate a new class if necessary and uses the specified callbacks (if any) to create a new object instance. Uses the no-arg constructor of the superclass.

Returns:

a new instance

create

public Object create(Class[] argumentTypes,
            Object[] arguments)

Generate a new class if necessary and uses the specified callbacks (if any) to create a new object instance. Uses the constructor of the superclass matching the argumentTypes parameter, with the given arguments.

Parameters:

argumentTypes - constructor signature

arguments - compatible wrapped arguments to pass to constructor

Returns:

a new instance

createClass

public Class createClass()

Generate a new class if necessary and return it without creating a new instance. This ignores any callbacks that have been set. To create a new instance you will have to use reflection, and methods called during the constructor will not be intercepted. To avoid this problem, use the multi-arg create method.

See Also:

create(Class[], Object[])

setSerialVersionUID

public void setSerialVersionUID(Long sUID)

Insert a static serialVersionUID field into the generated class.

Parameters:

sUID - the field value, or null to avoid generating field.

getDefaultClassLoader

protected ClassLoader getDefaultClassLoader()

Specified by:

getDefaultClassLoader in class AbstractClassGenerator

getMethods

public static void getMethods(Class superclass,
              Class[] interfaces,
              List methods)

Finds all of the methods that will be extended by an Enhancer-generated class using the specified superclass and interfaces. This can be useful in building a list of Callback objects. The methods are added to the end of the given list. Due to the subclassing nature of the classes generated by Enhancer, the methods are guaranteed to be non-static, non-final, and non-private. Each method signature will only occur once, even if it occurs in multiple classes.

Parameters:

superclass - the class that will be extended, or null

interfaces - the list of interfaces that will be implemented, or null

methods - the list into which to copy the applicable methods

generateClass

public void generateClass(org.objectweb.asm.ClassVisitor v)
                   throws Exception

Throws:

Exception

filterConstructors

protected void filterConstructors(Class sc,
                      List constructors)

Filter the list of constructors from the superclass. The constructors which remain will be included in the generated class. The default implementation is to filter out all private constructors, but subclasses may extend Enhancer to override this behavior.

Parameters:

sc - the superclass

constructors - the list of all declared constructors from the superclass

Throws:

IllegalArgumentException - if there are no non-private constructors

firstInstance

protected Object firstInstance(Class type)
                        throws Exception

Specified by:

firstInstance in class AbstractClassGenerator

Throws:

Exception

nextInstance

protected Object nextInstance(Object instance)

Specified by:

nextInstance in class AbstractClassGenerator

registerCallbacks

public static void registerCallbacks(Class generatedClass,
                     Callback[] callbacks)

Call this method to register the Callback array to use before creating a new instance of the generated class via reflection. If you are using an instance of Enhancer or the Factory interface to create new instances, this method is unnecessary. Its primary use is for when you want to cache and reuse a generated class yourself, and the generated class does not implement the Factory interface.

Note that this method only registers the callbacks on the current thread. If you want to register callbacks for instances created by multiple threads, use registerStaticCallbacks(java.lang.Class, net.sf.cglib.proxy.Callback[]).

The registered callbacks are overwritten and subsequently cleared when calling any of the create methods (such as create()), or any Factory newInstance method. Otherwise they are not cleared, and you should be careful to set them back to null after creating new instances via reflection if memory leakage is a concern.

Parameters:

generatedClass - a class previously created by Enhancer

callbacks - the array of callbacks to use when instances of the generated class are created

See Also:

setUseFactory(boolean)

registerStaticCallbacks

public static void registerStaticCallbacks(Class generatedClass,
                           Callback[] callbacks)

Similar to registerCallbacks(java.lang.Class, net.sf.cglib.proxy.Callback[]), but suitable for use when multiple threads will be creating instances of the generated class. The thread-level callbacks will always override the static callbacks. Static callbacks are never cleared.

Parameters:

generatedClass - a class previously created by Enhancer

callbacks - the array of callbacks to use when instances of the generated class are created

isEnhanced

public static boolean isEnhanced(Class type)

Determine if a class was generated using Enhancer.

Parameters:

type - any class

Returns:

whether the class was generated using Enhancer

create

public static Object create(Class type,
            Callback callback)

Helper method to create an intercepted object. For finer control over the generated instance, use a new instance of Enhancer instead of this static method.

Parameters:

type - class to extend or interface to implement

callback - the callback to use for all methods

create

public static Object create(Class superclass,
            Class[] interfaces,
            Callback callback)

Helper method to create an intercepted object. For finer control over the generated instance, use a new instance of Enhancer instead of this static method.

Parameters:

type - class to extend or interface to implement

interfaces - array of interfaces to implement, or null

callback - the callback to use for all methods

create

public static Object create(Class superclass,
            Class[] interfaces,
            CallbackFilter filter,
            Callback[] callbacks)

Helper method to create an intercepted object. For finer control over the generated instance, use a new instance of Enhancer instead of this static method.

Parameters:

type - class to extend or interface to implement

interfaces - array of interfaces to implement, or null

filter - the callback filter to use when generating a new class

callbacks - callback implementations to use for the enhanced object