Factory for creating Log instances, with discovery and configuration features similar to that employed by standard Java APIs such as JAXP.
IMPLEMENTATION NOTE - This implementation is heavily based on the SAXParserFactory and DocumentBuilderFactory implementations (corresponding to the JAXP pluggability APIs) found in Apache Xerces.
Craig- R. McClanahan
Richard- A. Sitze
$- Revision: 593798 $ $Date: 2007-11-10 18:40:43 +0100 $
|public static final String||PRIORITY_KEY||The name (|
|public static final String||TCCL_KEY||The name (|
|public static final String||FACTORY_PROPERTY||The name (|
|public static final String||FACTORY_DEFAULT||The fully qualified class name of the fallback |
|public static final String||FACTORY_PROPERTIES||The name (|
|protected static final String||SERVICE_ID||JDK1.3+ 'Service Provider' specification.|
|public static final String||DIAGNOSTICS_DEST_PROPERTY||The name (|
If a system property of this name is set then the value is assumed to be the name of a file. The special strings STDOUT or STDERR (case-sensitive) indicate output to System.out and System.err respectively.
Diagnostic logging should be used only to debug problematic configurations and should not be set in normal production use.
|public static final String||HASHTABLE_IMPLEMENTATION_PROPERTY|
Setting this system property
Usage: Set this property when Java is invoked
A typical use case is to allow a custom Hashtable implementation using weak references to be substituted. This will allow classloaders to be garbage collected without the need to release them (on 1.3+ JVMs only, of course ;)
|protected static Hashtable||factories||The previously constructed |
|protected static LogFactory||nullClassLoaderFactory||Prevously constructed |
|Method from org.apache.commons.logging.LogFactory Summary:|
|createFactory, directGetContextClassLoader, getAttribute, getAttributeNames, getClassLoader, getContextClassLoader, getFactory, getInstance, getInstance, getLog, getLog, isDiagnosticsEnabled, logRawDiagnostic, newFactory, newFactory, objectId, release, release, releaseAll, removeAttribute, setAttribute|
|Methods from java.lang.Object:|
|equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait|
|Method from org.apache.commons.logging.LogFactory Detail:|
protected static Object createFactory(String factoryClass, ClassLoader classLoader)
protected static ClassLoader directGetContextClassLoader() throws LogConfigurationException
Most/all code should call getContextClassLoaderInternal rather than calling this method directly.
The thread context class loader is available for JDK 1.2 or later, if certain security conditions are met.
Note that no internal logging is done within this method because this method is called every time LogFactory.getLogger() is called, and we don't want too much output generated here.
abstract public Object getAttribute(String name)
abstract public String getAttributeNames()
protected static ClassLoader getClassLoader(Class clazz)
Theoretically, calling getClassLoader can throw a security exception, and so should be done under an AccessController in order to provide maximum flexibility. However in practice people don't appear to use security policies that forbid getClassLoader calls. So for the moment all code is written to call this method rather than Class.getClassLoader, so that we could put AccessController stuff in this method without any disruption later if we need to.
Even when using an AccessController, however, this method can still throw SecurityException. Commons-logging basically relies on the ability to access classloaders, ie a policy that forbids all classloader access will also prevent commons-logging from working: currently this method will throw an exception preventing the entire app from starting up. Maybe it would be good to detect this situation and just disable all commons-logging? Not high priority though - as stated above, security policies that prevent classloader access aren't common.
Note that returning an object fetched via an AccessController would technically be a security flaw anyway; untrusted code that has access to a trusted JCL library could use it to fetch the classloader for a class even when forbidden to do so directly.
protected static ClassLoader getContextClassLoader() throws LogConfigurationException
In versions prior to 1.1, this method did not use an AccessController. In version 1.1, an AccessController wrapper was incorrectly added to this method, causing a minor security flaw.
In version 1.1.1 this change was reverted; this method no longer uses an AccessController. User code wishing to obtain the context classloader must invoke this method via AccessController.doPrivileged if it needs support for that.
public static LogFactory getFactory() throws LogConfigurationException
Construct (if necessary) and return a
NOTE - If the properties file method of identifying the
NOTE - In a multithreaded environment it is possible that two different instances will be returned for the same classloader environment.
abstract public Log getInstance(Class clazz) throws LogConfigurationException
abstract public Log getInstance(String name) throws LogConfigurationException
Construct (if necessary) and return a
NOTE - Depending upon the implementation of
public static Log getLog(Class clazz) throws LogConfigurationException
public static Log getLog(String name) throws LogConfigurationException
protected static boolean isDiagnosticsEnabled()
By the way, sorry for the incorrect grammar, but calling this method areDiagnosticsEnabled just isn't java beans style.
protected static final void logRawDiagnostic(String msg)
protected static LogFactory newFactory(String factoryClass, ClassLoader classLoader)
This method would only ever be called in some rather odd situation. Note that this method is static, so overriding in a subclass doesn't have any effect unless this method is called from a method in that subclass. However this method only makes sense to use from the getFactory method, and as that is almost always invoked via LogFactory.getFactory, any custom definition in a subclass would be pointless. Only a class with a custom getFactory method, then invoked directly via CustomFactoryImpl.getFactory or similar would ever call this. Anyway, it's here just in case, though the "managed class loader" value output to the diagnostics will not report the correct value.
protected static LogFactory newFactory(String factoryClass, ClassLoader classLoader, ClassLoader contextClassLoader) throws LogConfigurationException
ClassLoader conflictsNote that there can be problems if the specified ClassLoader is not the same as the classloader that loaded this class, ie when loading a concrete LogFactory subclass via a context classloader.
The problem is the same one that can occur when loading a concrete Log subclass via a context classloader.
The problem occurs when code running in the context classloader calls class X which was loaded via a parent classloader, and class X then calls LogFactory.getFactory (either directly or via LogFactory.getLog). Because class X was loaded via the parent, it binds to LogFactory loaded via the parent. When the code in this method finds some LogFactoryYYYY class in the child (context) classloader, and there also happens to be a LogFactory class defined in the child classloader, then LogFactoryYYYY will be bound to LogFactory@childloader. It cannot be cast to LogFactory@parentloader, ie this method cannot return the object as the desired type. Note that it doesn't matter if the LogFactory class in the child classloader is identical to the LogFactory class in the parent classloader, they are not compatible.
The solution taken here is to simply print out an error message when this occurs then throw an exception. The deployer of the application must ensure they remove all occurrences of the LogFactory class from the child classloader in order to resolve the issue. Note that they do not have to move the custom LogFactory subclass; that is ok as long as the only LogFactory class it can find to bind to is in the parent classloader.
The returned string is of form "classname@hashcode", ie is the same as the return value of the Object.toString() method, but works even when the specified object's class has overidden the toString method.
abstract public void release()
public static void release(ClassLoader classLoader)
public static void releaseAll()
abstract public void removeAttribute(String name)
abstract public void setAttribute(String name, Object value)