org.apache.logging.log4j.core.util

Class Loader

java.lang.Object

org.apache.logging.log4j.core.util.Loader

public final class Loader
extends Object

Load resources (or images) from various sources.

Method Summary

Modifier and Type	Method and Description
static ClassLoader	getClassLoader() Returns the ClassLoader to use.
static ClassLoader	getClassLoader(Class<?> class1, Class<?> class2)
static URL	getResource(String resource, ClassLoader defaultLoader) This method will search for resource in different places.
static InputStream	getResourceAsStream(String resource, ClassLoader defaultLoader) This method will search for resource in different places.
static ClassLoader	getThreadContextClassLoader() Returns the ClassLoader of current thread if possible, or falls back to the system ClassLoader if none is available.
static Class<?>	initializeClass(String className, ClassLoader loader) Loads and initializes a named Class using a given ClassLoader.
static boolean	isClassAvailable(String className) Determines if a named Class can be loaded or not.
static boolean	isJansiAvailable()
static Class<?>	loadClass(String className) Loads a class by name.
static Class<?>	loadClass(String className, ClassLoader loader) Loads a named Class using a given ClassLoader.
static Class<?>	loadSystemClass(String className) Load a Class in the java.* namespace by name.
static <T> T	newCheckedInstanceOf(String className, Class<T> clazz) Loads, instantiates, and casts a Class using the default constructor.
static <T> T	newCheckedInstanceOfProperty(String propertyName, Class<T> clazz) Loads and instantiates a class given by a property name.
static <T> T	newInstanceOf(String className) Loads and instantiates a Class using the default constructor.

Methods inherited from class java.lang.Object

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

Method Detail

getClassLoader

public static ClassLoader getClassLoader()

Returns the ClassLoader to use.

Returns:

the ClassLoader.

getThreadContextClassLoader

public static ClassLoader getThreadContextClassLoader()

Returns the ClassLoader of current thread if possible, or falls back to the system ClassLoader if none is available.

Returns:

the TCCL.

See Also:

LoaderUtil.getThreadContextClassLoader()

getClassLoader

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

getResource

public static URL getResource(String resource,
                              ClassLoader defaultLoader)

This method will search for resource in different places. The search order is as follows:

1. Search for resource using the thread context class loader under Java2. If that fails, search for resource using the class loader that loaded this class (Loader). Under JDK 1.1, only the the class loader that loaded this class (Loader) is used.
2. Try one last time with ClassLoader.getSystemResource(resource), that is is using the system class loader in JDK 1.2 and virtual machine's built-in class loader in JDK 1.1.

Parameters:

resource - The resource to load.

defaultLoader - The default ClassLoader.

Returns:

A URL to the resource.

getResourceAsStream

public static InputStream getResourceAsStream(String resource,
                                              ClassLoader defaultLoader)

This method will search for resource in different places. The search order is as follows:

1. Search for resource using the thread context class loader under Java2. If that fails, search for resource using the class loader that loaded this class (Loader). Under JDK 1.1, only the the class loader that loaded this class (Loader) is used.
2. Try one last time with ClassLoader.getSystemResource(resource), that is is using the system class loader in JDK 1.2 and virtual machine's built-in class loader in JDK 1.1.

Parameters:

resource - The resource to load.

defaultLoader - The default ClassLoader.

Returns:

An InputStream to read the resouce.

initializeClass

public static Class<?> initializeClass(String className,
                                       ClassLoader loader)
                                throws ClassNotFoundException

Loads and initializes a named Class using a given ClassLoader.

Parameters:

className - The class name.

loader - The class loader.

Returns:

The class.

Throws:

ClassNotFoundException - if the class could not be found.

loadClass

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

Loads a named Class using a given ClassLoader.

Parameters:

className - The class name.

loader - The class loader.

Returns:

The class, or null if loader is null.

Throws:

ClassNotFoundException - if the class could not be found.

loadSystemClass

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

Load a Class in the java.* namespace by name. Useful for peculiar scenarios typically involving Google App Engine.

Parameters:

className - The class name.

Returns:

The Class.

Throws:

ClassNotFoundException - if the Class could not be found.

newInstanceOf

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

Loads and instantiates a Class using the default constructor.

Parameters:

className - The class name.

Returns:

new instance of the class.

Throws:

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

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

InstantiationException - if there was an exception whilst instantiating the class

NoSuchMethodException - if there isn't a no-args constructor on the class

InvocationTargetException - if there was an exception whilst constructing the class

newCheckedInstanceOf

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

Loads, instantiates, and casts a Class using the default constructor.

Type Parameters:

T - The type to cast it to.

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

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

InstantiationException - if there was an exception whilst instantiating the class

NoSuchMethodException - if there isn't a no-args constructor on the class

InvocationTargetException - if there was an exception whilst constructing the class

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

newCheckedInstanceOfProperty

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

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

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

InstantiationException - if there was an exception whilst instantiating the class

NoSuchMethodException - if there isn't a no-args constructor on the class

InvocationTargetException - if there was an exception whilst constructing the class

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

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.

isJansiAvailable

public static boolean isJansiAvailable()

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 - The class name.

Returns:

the Class for the given name.

Throws:

ClassNotFoundException - if the specified class name could not be found