Package net.bytebuddy.dynamic

Class Nexus

java.lang.Object

java.lang.ref.Reference<T>

java.lang.ref.WeakReference<java.lang.ClassLoader>

net.bytebuddy.dynamic.Nexus

public class Nexus
extends java.lang.ref.WeakReference<java.lang.ClassLoader>

This nexus is a global dispatcher for initializing classes with LoadedTypeInitializers. To do so, this class is to be loaded by the system class loader in an explicit manner. Any instrumented class is then injected a code block into its static type initializer that makes a call to this very same nexus which had the loaded type initializer registered before hand.

Note: Availability of the Nexus class and its injection into the system class loader can be disabled entirely by setting the PROPERTY system property to false.

Important: The nexus must never be accessed directly but only by the NexusAccessor which makes sure that the nexus is loaded by the system class loader. Otherwise, a class might not be able to initialize itself if it is loaded by different class loader that does not have the system class loader in its hierarchy.

Field Summary

Fields

Modifier and Type	Field	Description
private int	classLoaderHashCode	The class loader's hash code upon registration.
private int	identification	A random value that uniquely identifies a Nexus entry in order to avoid conflicts when applying the self-initialization strategy in multiple transformations.
private java.lang.String	name	The name of a type for which a loaded type initializer is registered.
private static java.lang.ref.ReferenceQueue<java.lang.ClassLoader>	NO_QUEUE	An type-safe constant for a non-operational reference queue.
static java.lang.String	PROPERTY	A system property that allows to disable the use of the Nexus class which is normally injected into the system class loader.
private static java.util.concurrent.ConcurrentMap<Nexus,java.lang.Object>	TYPE_INITIALIZERS	A map of keys identifying a loaded type by its name and class loader mapping their potential LoadedTypeInitializer where the class loader of these initializers is however irrelevant.

Constructor Summary

Constructors

Modifier	Constructor	Description
private	Nexus(java.lang.Class<?> type, int identification)	Creates a key for identifying a loaded type initializer.
private	Nexus(java.lang.String name, java.lang.ClassLoader classLoader, java.lang.ref.ReferenceQueue<? super java.lang.ClassLoader> referenceQueue, int identification)	Creates a key for identifying a loaded type initializer.

Method Summary

Modifier and Type	Method	Description
static void	clean(java.lang.ref.Reference<? super java.lang.ClassLoader> reference)	Cleans any stale entries from this nexus.
boolean	equals(java.lang.Object other)
int	hashCode()
static void	initialize(java.lang.Class<?> type, int identification)	Initializes a loaded type.
private static java.lang.String	nonAnonymous(java.lang.String typeName)	Normalizes a type name if it is loaded by an anonymous class loader.
static void	register(java.lang.String name, java.lang.ClassLoader classLoader, java.lang.ref.ReferenceQueue<? super java.lang.ClassLoader> referenceQueue, int identification, java.lang.Object typeInitializer)	Registers a new loaded type initializer.
java.lang.String	toString()

Methods inherited from class java.lang.ref.Reference

clear, clone, enqueue, get, isEnqueued, reachabilityFence

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

PROPERTY

public static final java.lang.String PROPERTY

A system property that allows to disable the use of the Nexus class which is normally injected into the system class loader.

See Also:

Constant Field Values

NO_QUEUE

@AlwaysNull
private static final java.lang.ref.ReferenceQueue<java.lang.ClassLoader> NO_QUEUE

An type-safe constant for a non-operational reference queue.

TYPE_INITIALIZERS

private static final java.util.concurrent.ConcurrentMap<Nexus,java.lang.Object> TYPE_INITIALIZERS

A map of keys identifying a loaded type by its name and class loader mapping their potential LoadedTypeInitializer where the class loader of these initializers is however irrelevant.

name

private final java.lang.String name

The name of a type for which a loaded type initializer is registered.

classLoaderHashCode

private final int classLoaderHashCode

The class loader's hash code upon registration.

identification

private final int identification

A random value that uniquely identifies a Nexus entry in order to avoid conflicts when applying the self-initialization strategy in multiple transformations.

Constructor Detail

Nexus

private Nexus(java.lang.Class<?> type,
              int identification)

Creates a key for identifying a loaded type initializer.

Parameters:

type - The loaded type for which a key is to be created.

identification - An identification for the initializer to run.

Nexus

private Nexus(java.lang.String name,
              @MaybeNull
              java.lang.ClassLoader classLoader,
              @MaybeNull
              java.lang.ref.ReferenceQueue<? super java.lang.ClassLoader> referenceQueue,
              int identification)

Creates a key for identifying a loaded type initializer.

Parameters:

name - The name of a type for which a loaded type initializer is registered.

classLoader - The class loader for which a loaded type initializer is registered.

referenceQueue - The reference queue to notify upon the class loader's collection or null if no queue should be notified.

identification - An identification for the initializer to run.

Method Detail

nonAnonymous

private static java.lang.String nonAnonymous(java.lang.String typeName)

Normalizes a type name if it is loaded by an anonymous class loader.

Parameters:

typeName - The name as returned by Class.getName().

Returns:

The non-anonymous name of the given class.

initialize

public static void initialize(java.lang.Class<?> type,
                              int identification)
                       throws java.lang.Exception

Initializes a loaded type. This method must only be invoked via the system class loader.

Important: This method must never be called directly but only by using a NexusAccessor.InitializationAppender which enforces to access this class for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders, too. Any access of the instance is done using Java reflection instead.

Parameters:

type - The loaded type to initialize.

identification - An identification for the initializer to run.

Throws:

java.lang.Exception - If an exception occurs.

register

public static void register(java.lang.String name,
                            @MaybeNull
                            java.lang.ClassLoader classLoader,
                            @MaybeNull
                            java.lang.ref.ReferenceQueue<? super java.lang.ClassLoader> referenceQueue,
                            int identification,
                            java.lang.Object typeInitializer)

Registers a new loaded type initializer.

Important: This method must never be called directly but only by using a NexusAccessor which enforces to access this class for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders, too. Any access of the instance is done using Java reflection instead.

Parameters:

name - The name of the type for the loaded type initializer.

classLoader - The class loader of the type for the loaded type initializer.

referenceQueue - The reference queue to notify upon the class loader's collection which will be enqueued a reference which can be handed to clean(Reference) or null if no reference queue should be notified.

identification - An identification for the initializer to run.

typeInitializer - The type initializer to register. The initializer must be an instance of LoadedTypeInitializer where it does however not matter which class loader loaded this latter type.

clean

public static void clean(java.lang.ref.Reference<? super java.lang.ClassLoader> reference)

Cleans any stale entries from this nexus. Entries are considered stale if their class loader was collected before a class was initialized.

Important: This method must never be called directly but only by using a NexusAccessor which enforces to access this class for the system class loader to assure a VM global singleton. This avoids a duplication of the class if this nexus is loaded by different class loaders. For this reason, the last parameter must not use a Byte Buddy specific type as those types can be loaded by different class loaders, too. Any access of the instance is done using Java reflection instead.

Parameters:

reference - The stale reference to clean.

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

equals

public boolean equals(@MaybeNull
                      java.lang.Object other)

Overrides:

equals in class java.lang.Object

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object