Class OverridingClassLoader

java.lang.Object

java.lang.ClassLoader

org.springframework.core.DecoratingClassLoader

org.springframework.core.OverridingClassLoader

Direct Known Subclasses:

SimpleInstrumentableClassLoader, SimpleThrowawayClassLoader

public class OverridingClassLoader
extends DecoratingClassLoader

ClassLoader that does not always delegate to the parent loader as normal class loaders do. This enables, for example, instrumentation to be forced in the overriding ClassLoader, or a "throwaway" class loading behavior where selected application classes are temporarily loaded in the overriding ClassLoader for introspection purposes before eventually loading an instrumented version of the class in the given parent ClassLoader.

Since:

2.0.1

Author:

Rod Johnson, Juergen Hoeller

Field Summary

Fields

Modifier and Type	Field	Description
static final String[]	DEFAULT_EXCLUDED_PACKAGES	Packages that are excluded by default.

Constructor Summary

Constructors

Constructor	Description
OverridingClassLoader(@Nullable ClassLoader parent)	Create a new OverridingClassLoader for the given ClassLoader.
OverridingClassLoader(@Nullable ClassLoader parent, @Nullable ClassLoader overrideDelegate)	Create a new OverridingClassLoader for the given ClassLoader.

Method Summary

Modifier and Type	Method	Description
protected boolean	isEligibleForOverriding(String className)	Determine whether the specified class is eligible for overriding by this class loader.
protected byte @Nullable []	loadBytesForClass(String name)	Load the defining bytes for the given class, to be turned into a Class object through a ClassLoader.defineClass(byte[], int, int) call.
Class<?>	loadClass(String name)
protected Class<?>	loadClass(String name, boolean resolve)
protected @Nullable Class<?>	loadClassForOverriding(String name)	Load the specified class for overriding purposes in this ClassLoader.
protected @Nullable InputStream	openStreamForClass(String name)	Open an InputStream for the specified class.
protected byte[]	transformIfNecessary(String name, byte[] bytes)	Transformation hook to be implemented by subclasses.

Methods inherited from class DecoratingClassLoader

excludeClass, excludePackage, isExcluded

Methods inherited from class ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findClass, findClass, findLibrary, findLoadedClass, findResource, findResource, findResources, findSystemClass, getClassLoadingLock, getDefinedPackage, getDefinedPackages, getName, getPackage, getPackages, getParent, getPlatformClassLoader, getResource, getResourceAsStream, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, getUnnamedModule, isRegisteredAsParallelCapable, registerAsParallelCapable, resolveClass, resources, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class Object

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

Field Details

DEFAULT_EXCLUDED_PACKAGES

public static final String[] DEFAULT_EXCLUDED_PACKAGES

Packages that are excluded by default.

Constructor Details

OverridingClassLoader

public OverridingClassLoader(@Nullable ClassLoader parent)

Create a new OverridingClassLoader for the given ClassLoader.

Parameters:

parent - the ClassLoader to build an overriding ClassLoader for

OverridingClassLoader

public OverridingClassLoader(@Nullable ClassLoader parent,
 @Nullable ClassLoader overrideDelegate)

Create a new OverridingClassLoader for the given ClassLoader.

Parameters:

parent - the ClassLoader to build an overriding ClassLoader for

overrideDelegate - the ClassLoader to delegate to for overriding

Since:

4.3

Method Details

loadClass

public Class<?> loadClass(String name)
                   throws ClassNotFoundException

Overrides:

loadClass in class ClassLoader

Throws:

ClassNotFoundException

loadClass

protected Class<?> loadClass(String name,
 boolean resolve)
                      throws ClassNotFoundException

Overrides:

loadClass in class ClassLoader

Throws:

ClassNotFoundException

isEligibleForOverriding

protected boolean isEligibleForOverriding(String className)

Determine whether the specified class is eligible for overriding by this class loader.

Parameters:

className - the class name to check

Returns:

whether the specified class is eligible

See Also:

• DecoratingClassLoader.isExcluded(String)

loadClassForOverriding

protected @Nullable Class<?> loadClassForOverriding(String name)
                                             throws ClassNotFoundException

Load the specified class for overriding purposes in this ClassLoader.

The default implementation delegates to ClassLoader.findLoadedClass(String), loadBytesForClass(String) and ClassLoader.defineClass(byte[], int, int).

Parameters:

name - the name of the class

Returns:

the Class object, or null if no class defined for that name

Throws:

ClassNotFoundException - if the class for the given name couldn't be loaded

loadBytesForClass

protected byte @Nullable [] loadBytesForClass(String name)
                                       throws ClassNotFoundException

Load the defining bytes for the given class, to be turned into a Class object through a ClassLoader.defineClass(byte[], int, int) call.

The default implementation delegates to openStreamForClass(String) and transformIfNecessary(String, byte[]).

Parameters:

name - the name of the class

Returns:

the byte content (with transformers already applied), or null if no class defined for that name

Throws:

ClassNotFoundException - if the class for the given name couldn't be loaded

openStreamForClass

protected @Nullable InputStream openStreamForClass(String name)

Open an InputStream for the specified class.

The default implementation loads a standard class file through the parent ClassLoader's getResourceAsStream method.

Parameters:

name - the name of the class

Returns:

the InputStream containing the byte code for the specified class

transformIfNecessary

protected byte[] transformIfNecessary(String name,
 byte[] bytes)

Transformation hook to be implemented by subclasses.

The default implementation simply returns the given bytes as-is.

Parameters:

name - the fully-qualified name of the class being transformed

bytes - the raw bytes of the class

Returns:

the transformed bytes (never null; same as the input bytes if the transformation produced no changes)