Package org.apache.logging.log4j.util

Class LoaderUtil

java.lang.Object

org.apache.logging.log4j.util.LoaderUtil

@InternalApi
public final class LoaderUtil
extends Object

Consider this class private. Utility class for ClassLoaders.

Since:

2.0.1

See Also:

ClassLoader, RuntimePermission, Thread.getContextClassLoader(), ClassLoader.getSystemClassLoader()

Field Summary

Fields

Modifier and Type	Field	Description
static String	IGNORE_TCCL_PROPERTY	System property to set to ignore the thread context ClassLoader.

Method Summary

Modifier and Type	Method	Description
static Collection<URL>	findResources(String resource)	Finds classpath resources.
static ClassLoader	getClassLoader()	Returns the ClassLoader to use.
static ClassLoader	getClassLoader(Class<?> class1, Class<?> class2)
static ClassLoader	getThreadContextClassLoader()	Looks up the ClassLoader for this current thread.
static boolean	isClassAvailable(String className)	Determines if a named Class can be loaded or not.
static Class<?>	loadClass(String className)	Loads a class by name.
static Class<?>	loadClassUnchecked(String className)	Loads and initializes a class given its fully qualified class name.
static <T> T	newCheckedInstanceOf(String className, Class<T> clazz)	Loads and instantiates a derived class using its default constructor.
static <T> T	newCheckedInstanceOfProperty(String propertyName, Class<T> clazz)	Loads and instantiates a class given by a property name.
static <T> T	newCheckedInstanceOfProperty(String propertyName, Class<T> clazz, Supplier<T> defaultSupplier)	Loads and instantiates a class given by a property name.
static <T> T	newInstanceOf(Class<T> clazz)	Loads and instantiates a Class using the default constructor.
static <T> T	newInstanceOf(String className)	Loads and instantiates a Class using the default constructor.
static <T> T	newInstanceOfUnchecked(Class<T> clazz)	Creates an instance of the provided class using the default constructor.
static <T> T	newInstanceOfUnchecked(String className)	Loads and instantiates a class by name using its default constructor.
static <T> T	newInstanceOfUnchecked(String className, Class<T> supertype)	Loads the provided class by name as a checked subtype of the given class.

Methods inherited from class java.lang.Object

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

Field Detail

IGNORE_TCCL_PROPERTY

public static final String IGNORE_TCCL_PROPERTY

System property to set to ignore the thread context ClassLoader.

Since:

2.1

See Also:

Constant Field Values

Method Detail

getClassLoader

public static ClassLoader getClassLoader()

Returns the ClassLoader to use.

Returns:

the ClassLoader.

Since:

2.22.0

getClassLoader

public static ClassLoader getClassLoader(Class<?> class1,
                                         Class<?> class2)

Since:

2.22.0

getThreadContextClassLoader

public static ClassLoader getThreadContextClassLoader()

Looks up the ClassLoader for this current thread. If this class does not have the runtime permission getClassLoader, then the only ClassLoader this attempts to look up is the loader behind this class. When a SecurityManager is installed, this attempts to make a privileged call to get the current thread context ClassLoader, falling back to either the ClassLoader of this class or the system ClassLoader. When no SecurityManager is present, the same lookups are performed without use of AccessController. If none of these strategies can obtain a ClassLoader, then this returns null.

Returns:

the current thread's ClassLoader, a fallback loader, or null if no fallback can be determined

isClassAvailable

public static boolean isClassAvailable(String className)

Determines if a named Class can be loaded or not.

Parameters:

className - The class name.

Returns:

true if the class could be found or false otherwise.

Since:

2.7

loadClass

public static Class<?> loadClass(String className)
                          throws ClassNotFoundException

Loads a class by name. This method respects the IGNORE_TCCL_PROPERTY Log4j property. If this property is specified and set to anything besides false, then the default ClassLoader will be used.

Parameters:

className - fully qualified class name to load

Returns:

the loaded class

Throws:

ClassNotFoundException - if the specified class name could not be found

ExceptionInInitializerError - if an exception is thrown during class initialization

LinkageError - if the linkage of the class fails for any other reason

Since:

2.1

loadClassUnchecked

public static Class<?> loadClassUnchecked(String className)

Loads and initializes a class given its fully qualified class name. All checked reflective operation exceptions are translated into equivalent LinkageError classes.

Parameters:

className - fully qualified class name to load

Returns:

the loaded class

Throws:

NoClassDefFoundError - if the specified class name could not be found

ExceptionInInitializerError - if an exception is thrown during class initialization

LinkageError - if the linkage of the class fails for any other reason

Since:

2.22.0

See Also:

loadClass(String)

newInstanceOf

public static <T> T newInstanceOf(Class<T> clazz)
                           throws InstantiationException,
                                  IllegalAccessException,
                                  InvocationTargetException,
                                  NoSuchMethodException

Loads and instantiates a Class using the default constructor.

Type Parameters:

T - the type of the class modeled by the Class object.

Parameters:

clazz - The class.

Returns:

new instance of the class.

Throws:

NoSuchMethodException - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

IllegalAccessException - if the class can't be instantiated through a public constructor

InstantiationException - if the provided class is abstract or an interface

InvocationTargetException - if an exception is thrown by the constructor

ExceptionInInitializerError - if an exception was thrown while initializing the class

Since:

2.7

newInstanceOfUnchecked

public static <T> T newInstanceOfUnchecked(Class<T> clazz)

Creates an instance of the provided class using the default constructor. All checked reflective operation exceptions are translated into LinkageError or InternalException.

Type Parameters:

T - the type of the object being instantiated

Parameters:

clazz - class to instantiate

Returns:

instance of the class

Throws:

NoSuchMethodError - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

InternalException - if an exception is thrown by the constructor

InstantiationError - if the provided class is abstract or an interface

IllegalAccessError - if the class cannot be accessed

Since:

2.22.0

newInstanceOf

public static <T> T newInstanceOf(String className)
                           throws ClassNotFoundException,
                                  IllegalAccessException,
                                  InstantiationException,
                                  InvocationTargetException,
                                  NoSuchMethodException

Loads and instantiates a Class using the default constructor.

Type Parameters:

T - type the class must be compatible with

Parameters:

className - fully qualified class name to load, initialize, and construct

Returns:

new instance of the class

Throws:

ClassNotFoundException - if the class isn't available to the usual ClassLoaders

ExceptionInInitializerError - if an exception was thrown while initializing the class

LinkageError - if the linkage of the class fails for any other reason

ClassCastException - if the class is not compatible with the generic type parameter provided

NoSuchMethodException - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

IllegalAccessException - if the class can't be instantiated through a public constructor

InstantiationException - if the provided class is abstract or an interface

InvocationTargetException - if an exception is thrown by the constructor

Since:

2.1

newCheckedInstanceOfProperty

public static <T> T newCheckedInstanceOfProperty(String propertyName,
                                                 Class<T> clazz)
                                          throws ClassNotFoundException,
                                                 InvocationTargetException,
                                                 InstantiationException,
                                                 IllegalAccessException,
                                                 NoSuchMethodException

Loads and instantiates a class given by a property name.

Type Parameters:

T - The type to cast it to.

Parameters:

propertyName - The property name to look up a class name for.

clazz - The class to cast it to.

Returns:

new instance of the class given in the property or null if the property was unset.

Throws:

ClassNotFoundException - if the class isn't available to the usual ClassLoaders

ExceptionInInitializerError - if an exception was thrown while initializing the class

LinkageError - if the linkage of the class fails for any other reason

ClassCastException - if the class is not compatible with the generic type parameter provided

NoSuchMethodException - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

IllegalAccessException - if the class can't be instantiated through a public constructor

InstantiationException - if the provided class is abstract or an interface

InvocationTargetException - if an exception is thrown by the constructor

Since:

2.5

newCheckedInstanceOfProperty

public static <T> T newCheckedInstanceOfProperty(String propertyName,
                                                 Class<T> clazz,
                                                 Supplier<T> defaultSupplier)
                                          throws ClassNotFoundException,
                                                 InvocationTargetException,
                                                 InstantiationException,
                                                 IllegalAccessException,
                                                 NoSuchMethodException

Loads and instantiates a class given by a property name.

Type Parameters:

T - The type to cast it to.

Parameters:

propertyName - The property name to look up a class name for.

clazz - The class to cast it to.

defaultSupplier - Supplier of a default value if the property is not present.

Returns:

new instance of the class given in the property or null if the property was unset.

Throws:

ClassNotFoundException - if the class isn't available to the usual ClassLoaders

ExceptionInInitializerError - if an exception was thrown while initializing the class

LinkageError - if the linkage of the class fails for any other reason

ClassCastException - if the class is not compatible with the generic type parameter provided

NoSuchMethodException - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

IllegalAccessException - if the class can't be instantiated through a public constructor

InstantiationException - if the provided class is abstract or an interface

InvocationTargetException - if an exception is thrown by the constructor

Since:

2.22.0

newInstanceOfUnchecked

public static <T> T newInstanceOfUnchecked(String className)

Loads and instantiates a class by name using its default constructor. All checked reflective operation exceptions are translated into corresponding LinkageError classes.

Type Parameters:

T - type the class must be compatible with

Parameters:

className - fully qualified class name to load, initialize, and construct

Returns:

new instance of the class

Throws:

NoClassDefFoundError - if the specified class name could not be found

ExceptionInInitializerError - if an exception is thrown during class initialization

ClassCastException - if the class is not compatible with the generic type parameter provided

NoSuchMethodError - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

InternalException - if an exception is thrown by the constructor

InstantiationError - if the provided class is abstract or an interface

IllegalAccessError - if the class cannot be accessed

LinkageError - if the linkage of the class fails for any other reason

Since:

2.22.0

newCheckedInstanceOf

public static <T> T newCheckedInstanceOf(String className,
                                         Class<T> clazz)
                                  throws ClassNotFoundException,
                                         InvocationTargetException,
                                         InstantiationException,
                                         IllegalAccessException,
                                         NoSuchMethodException

Loads and instantiates a derived class using its default constructor.

Type Parameters:

T - The type of the class to check.

Parameters:

className - The class name.

clazz - The class to cast it to.

Returns:

new instance of the class cast to T

Throws:

ClassNotFoundException - if the class isn't available to the usual ClassLoaders

ExceptionInInitializerError - if an exception is thrown during class initialization

LinkageError - if the linkage of the class fails for any other reason

ClassCastException - if the constructed object isn't type compatible with T

NoSuchMethodException - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

IllegalAccessException - if the class can't be instantiated through a public constructor

InstantiationException - if the provided class is abstract or an interface

InvocationTargetException - if there was an exception whilst constructing the class

Since:

2.1

newInstanceOfUnchecked

public static <T> T newInstanceOfUnchecked(String className,
                                           Class<T> supertype)

Loads the provided class by name as a checked subtype of the given class. All checked reflective operation exceptions are translated into corresponding LinkageError classes.

Type Parameters:

T - type of instance to return

Parameters:

className - fully qualified class name to load

supertype - supertype of the class being loaded

Returns:

new instance of the requested class

Throws:

NoClassDefFoundError - if the provided class name could not be found

ExceptionInInitializerError - if an exception is thrown during class initialization

ClassCastException - if the loaded class is not a subtype of the provided class

NoSuchMethodError - if no zero-arg constructor exists

SecurityException - if this class is not allowed to access declared members of the provided class

InternalException - if an exception is thrown by the constructor

InstantiationError - if the provided class is abstract or an interface

IllegalAccessError - if the class cannot be accessed

LinkageError - if the linkage of the class fails for any other reason

Since:

2.22.0

findResources

public static Collection<URL> findResources(String resource)

Finds classpath resources.

Parameters:

resource - the name of the resource to find.

Returns:

a Collection of URLs matching the resource name. If no resources could be found, then this will be empty.

Since:

2.1