Class LogFactoryImpl
LogFactory that implements the
following algorithm to dynamically select a logging implementation
class to instantiate a wrapper for:
- Use a factory configuration attribute named
org.apache.commons.logging.Logto identify the requested implementation class. - Use the
org.apache.commons.logging.Logsystem property to identify the requested implementation class. - If Log4J is available, return an instance of
org.apache.commons.logging.impl.Log4JLogger. - If JDK 1.4 or later is available, return an instance of
org.apache.commons.logging.impl.Jdk14Logger. - Otherwise, return an instance of
org.apache.commons.logging.impl.SimpleLog.
If the selected Log implementation class has a
setLogFactory() method that accepts a LogFactory
parameter, this method will be called on each newly created instance
to identify the associated factory. This makes factory configuration
attributes available to the Log instance, if it so desires.
This factory will remember previously created Log instances
for the same name, and will return them on repeated requests to the
getInstance() method.
- Version:
- $Id: LogFactoryImpl.java 1449064 2013-02-22 14:49:22Z tn $
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Field Summary
FieldsModifier and TypeFieldDescriptionstatic final StringThe name (org.apache.commons.logging.Log.allowFlawedContext) of the system property which can be set true/false to determine system behaviour when a bad context-classloader is encountered.static final StringThe name (org.apache.commons.logging.Log.allowFlawedDiscovery) of the system property which can be set true/false to determine system behaviour when a bad logging adapter class is encountered during logging discovery.static final StringThe name (org.apache.commons.logging.Log.allowFlawedHierarchy) of the system property which can be set true/false to determine system behaviour when a logging adapter class is encountered which has bound to the wrong Log class implementation.private booleanSee getBaseClassLoader and initConfiguration.private booleanSee handleFlawedDiscovery and initConfiguration.private booleanSee handleFlawedHierarchy and initConfiguration.protected HashtableConfiguration attributes.private static final String[]The names of classes that will be tried (in order) as logging adapters.private StringThe string prefixed to every message output by the logDiagnostic method.protected HashtableTheLoginstances that have already been created, keyed by logger name.static final StringThe name (org.apache.commons.logging.Log) of the system property identifying ourLogimplementation class.protected static final StringThe deprecated system property used for backwards compatibility with old versions of JCL.private StringName of the class implementing the Log interface.protected ConstructorThe one-argument constructor of theLogimplementation class that will be used to create new instances.protected Class[]The signature of the Constructor to be used.private static final StringJdk14Logger class nameprivate static final StringLog4JLogger class nameprivate static final StringJdk13LumberjackLogger class nameprivate static final StringSimpleLog class nameprotected MethodThe one-argumentsetLogFactorymethod of the selectedLogmethod, if it exists.protected Class[]The signature of thesetLogFactorymethod to be used.private static final Stringprivate static final intprivate booleanDetermines whether logging classes should be loaded using the thread-context classloader, or via the classloader that loaded this LogFactoryImpl class.Fields inherited from class org.apache.commons.logging.LogFactory
DIAGNOSTICS_DEST_PROPERTY, factories, FACTORY_DEFAULT, FACTORY_PROPERTIES, FACTORY_PROPERTY, HASHTABLE_IMPLEMENTATION_PROPERTY, nullClassLoaderFactory, PRIORITY_KEY, SERVICE_ID, TCCL_KEY -
Constructor Summary
ConstructorsConstructorDescriptionPublic no-arguments constructor required by the lookup mechanism. -
Method Summary
Modifier and TypeMethodDescriptionprivate LogcreateLogFromClass(String logAdapterClassName, String logCategory, boolean affectState) Attempts to load the given class, find a suitable constructor, and instantiate an instance of Log.private LogdiscoverLogImplementation(String logCategory) Attempts to create a Log instance for the given category name.private StringChecks system properties and the attribute map for a Log implementation specified by the user under the property namesLOG_PROPERTYorLOG_PROPERTY_OLD.getAttribute(String name) Return the configuration attribute with the specified name (if any), ornullif there is no such attribute.String[]Return an array containing the names of all currently defined configuration attributes.private ClassLoaderReturn the classloader from which we should try to load the logging adapter classes.private booleangetBooleanConfiguration(String key, boolean dflt) Get the setting for the user-configurable behaviour specified by key.protected static ClassLoadergetClassLoader(Class clazz) Workaround for bug in Java1.2; in theory this method is not needed.private StringgetConfigurationValue(String property) Attempt to find an attribute (see method setAttribute) or a system property with the provided name and return its value.protected static ClassLoaderGets the context classloader.private static ClassLoaderCalls LogFactory.directGetContextClassLoader under the control of an AccessController class.getInstance(Class clazz) Convenience method to derive a name from the specified class and callgetInstance(String)with it.getInstance(String name) Construct (if necessary) and return aLoginstance, using the factory's current set of configuration attributes.protected StringDeprecated.Never invoked by this class; subclasses should not assume it will be.protected ConstructorDeprecated.Never invoked by this class; subclasses should not assume it will be.private ClassLoaderGiven two related classloaders, return the one which is a child of the other.private ClassLoaderFetch the parent classloader of a specified classloader.private static StringgetSystemProperty(String key, String def) Read the specified system property, using an AccessController so that the property can be read if JCL has been granted the appropriate security rights even if the calling code has not.private voidhandleFlawedDiscovery(String logAdapterClassName, ClassLoader classLoader, Throwable discoveryFlaw) Generates an internal diagnostic logging of the discovery failure and then throws aLogConfigurationExceptionthat wraps the passedThrowable.private voidhandleFlawedHierarchy(ClassLoader badClassLoader, Class badClass) Report a problem loading the log adapter, then either return (if the situation is considered recoverable) or throw a LogConfigurationException.private voidinformUponSimilarName(StringBuffer messageBuffer, String name, String candidate) Appends message if the given name is similar to the candidate.private voidInitialize a number of variables that control the behaviour of this class and that can be tweaked by the user.private voidCalculate and cache a string that uniquely identifies this instance, including which classloader the object was loaded from.protected static booleanWorkaround for bug in Java1.2; in theory this method is not needed.protected booleanDeprecated.Never invoked by this class; subclasses should not assume it will be.protected booleanDeprecated.Never invoked by this class; subclasses should not assume it will be.protected booleanDeprecated.Never invoked by this class; subclasses should not assume it will be.private booleanisLogLibraryAvailable(String name, String classname) Utility method to check whether a particular logging library is present and available for use.protected voidlogDiagnostic(String msg) Output a diagnostic message to a user-specified destination (if the user has enabled diagnostic logging).protected LognewInstance(String name) Create and return a newLoginstance for the specified name.voidrelease()Release any internal references to previously createdLoginstances returned by this factory.voidremoveAttribute(String name) Remove any configuration attribute associated with the specified name.voidsetAttribute(String name, Object value) Set the configuration attribute with the specified name.Methods inherited from class org.apache.commons.logging.LogFactory
createFactory, directGetContextClassLoader, getFactory, getLog, getLog, handleThrowable, logRawDiagnostic, newFactory, newFactory, objectId, release, releaseAll
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Field Details
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LOGGING_IMPL_LOG4J_LOGGER
Log4JLogger class name- See Also:
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LOGGING_IMPL_JDK14_LOGGER
Jdk14Logger class name- See Also:
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LOGGING_IMPL_LUMBERJACK_LOGGER
Jdk13LumberjackLogger class name- See Also:
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LOGGING_IMPL_SIMPLE_LOGGER
SimpleLog class name- See Also:
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PKG_IMPL
- See Also:
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PKG_LEN
private static final int PKG_LEN -
LOG_PROPERTY
The name (org.apache.commons.logging.Log) of the system property identifying ourLogimplementation class.- See Also:
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LOG_PROPERTY_OLD
The deprecated system property used for backwards compatibility with old versions of JCL.- See Also:
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ALLOW_FLAWED_CONTEXT_PROPERTY
The name (org.apache.commons.logging.Log.allowFlawedContext) of the system property which can be set true/false to determine system behaviour when a bad context-classloader is encountered. When set to false, a LogConfigurationException is thrown if LogFactoryImpl is loaded via a child classloader of the TCCL (this should never happen in sane systems). Default behaviour: true (tolerates bad context classloaders) See also method setAttribute.- See Also:
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ALLOW_FLAWED_DISCOVERY_PROPERTY
The name (org.apache.commons.logging.Log.allowFlawedDiscovery) of the system property which can be set true/false to determine system behaviour when a bad logging adapter class is encountered during logging discovery. When set to false, an exception will be thrown and the app will fail to start. When set to true, discovery will continue (though the user might end up with a different logging implementation than they expected).Default behaviour: true (tolerates bad logging adapters) See also method setAttribute.
- See Also:
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ALLOW_FLAWED_HIERARCHY_PROPERTY
The name (org.apache.commons.logging.Log.allowFlawedHierarchy) of the system property which can be set true/false to determine system behaviour when a logging adapter class is encountered which has bound to the wrong Log class implementation. When set to false, an exception will be thrown and the app will fail to start. When set to true, discovery will continue (though the user might end up with a different logging implementation than they expected).Default behaviour: true (tolerates bad Log class hierarchy) See also method setAttribute.
- See Also:
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classesToDiscover
The names of classes that will be tried (in order) as logging adapters. Each class is expected to implement the Log interface, and to throw NoClassDefFound or ExceptionInInitializerError when loaded if the underlying logging library is not available. Any other error indicates that the underlying logging library is available but broken/unusable for some reason. -
useTCCL
private boolean useTCCLDetermines whether logging classes should be loaded using the thread-context classloader, or via the classloader that loaded this LogFactoryImpl class. -
diagnosticPrefix
The string prefixed to every message output by the logDiagnostic method. -
attributes
Configuration attributes. -
instances
TheLoginstances that have already been created, keyed by logger name. -
logClassName
Name of the class implementing the Log interface. -
logConstructor
The one-argument constructor of theLogimplementation class that will be used to create new instances. This value is initialized bygetLogConstructor(), and then returned repeatedly. -
logConstructorSignature
The signature of the Constructor to be used. -
logMethod
The one-argumentsetLogFactorymethod of the selectedLogmethod, if it exists. -
logMethodSignature
The signature of thesetLogFactorymethod to be used. -
allowFlawedContext
private boolean allowFlawedContextSee getBaseClassLoader and initConfiguration. -
allowFlawedDiscovery
private boolean allowFlawedDiscoverySee handleFlawedDiscovery and initConfiguration. -
allowFlawedHierarchy
private boolean allowFlawedHierarchySee handleFlawedHierarchy and initConfiguration.
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Constructor Details
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LogFactoryImpl
public LogFactoryImpl()Public no-arguments constructor required by the lookup mechanism.
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Method Details
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getAttribute
Return the configuration attribute with the specified name (if any), ornullif there is no such attribute.- Specified by:
getAttributein classLogFactory- Parameters:
name- Name of the attribute to return
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getAttributeNames
Return an array containing the names of all currently defined configuration attributes. If there are no such attributes, a zero length array is returned.- Specified by:
getAttributeNamesin classLogFactory
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getInstance
Convenience method to derive a name from the specified class and callgetInstance(String)with it.- Specified by:
getInstancein classLogFactory- Parameters:
clazz- Class for which a suitable Log name will be derived- Throws:
LogConfigurationException- if a suitableLoginstance cannot be returned
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getInstance
Construct (if necessary) and return a
Loginstance, using the factory's current set of configuration attributes.NOTE - Depending upon the implementation of the
LogFactoryyou are using, theLoginstance you are returned may or may not be local to the current application, and may or may not be returned again on a subsequent call with the same name argument.- Specified by:
getInstancein classLogFactory- Parameters:
name- Logical name of theLoginstance to be returned (the meaning of this name is only known to the underlying logging implementation that is being wrapped)- Throws:
LogConfigurationException- if a suitableLoginstance cannot be returned
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release
public void release()Release any internal references to previously createdLoginstances returned by this factory. This is useful in environments like servlet containers, which implement application reloading by throwing away a ClassLoader. Dangling references to objects in that class loader would prevent garbage collection.- Specified by:
releasein classLogFactory
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removeAttribute
Remove any configuration attribute associated with the specified name. If there is no such attribute, no action is taken.- Specified by:
removeAttributein classLogFactory- Parameters:
name- Name of the attribute to remove
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setAttribute
Set the configuration attribute with the specified name. Calling this with anullvalue is equivalent to callingremoveAttribute(name).This method can be used to set logging configuration programmatically rather than via system properties. It can also be used in code running within a container (such as a webapp) to configure behaviour on a per-component level instead of globally as system properties would do. To use this method instead of a system property, call
LogFactory.getFactory().setAttribute(...)
This must be done before the first Log object is created; configuration changes after that point will be ignored.This method is also called automatically if LogFactory detects a commons-logging.properties file; every entry in that file is set automatically as an attribute here.
- Specified by:
setAttributein classLogFactory- Parameters:
name- Name of the attribute to setvalue- Value of the attribute to set, ornullto remove any setting for this attribute
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getContextClassLoader
Gets the context classloader. This method is a workaround for a java 1.2 compiler bug.- Throws:
LogConfigurationException- Since:
- 1.1
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isDiagnosticsEnabled
protected static boolean isDiagnosticsEnabled()Workaround for bug in Java1.2; in theory this method is not needed. See LogFactory.isDiagnosticsEnabled. -
getClassLoader
Workaround for bug in Java1.2; in theory this method is not needed. See LogFactory.getClassLoader.- Since:
- 1.1
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initDiagnostics
private void initDiagnostics()Calculate and cache a string that uniquely identifies this instance, including which classloader the object was loaded from.This string will later be prefixed to each "internal logging" message emitted, so that users can clearly see any unexpected behaviour.
Note that this method does not detect whether internal logging is enabled or not, nor where to output stuff if it is; that is all handled by the parent LogFactory class. This method just computes its own unique prefix for log messages.
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logDiagnostic
Output a diagnostic message to a user-specified destination (if the user has enabled diagnostic logging).- Parameters:
msg- diagnostic message- Since:
- 1.1
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getLogClassName
Deprecated.Never invoked by this class; subclasses should not assume it will be.Return the fully qualified Java classname of theLogimplementation we will be using. -
getLogConstructor
Deprecated.Never invoked by this class; subclasses should not assume it will be.Return the
Constructorthat can be called to instantiate newLoginstances.IMPLEMENTATION NOTE - Race conditions caused by calling this method from more than one thread are ignored, because the same
Constructorinstance will ultimately be derived in all circumstances.- Throws:
LogConfigurationException- if a suitable constructor cannot be returned
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isJdk13LumberjackAvailable
protected boolean isJdk13LumberjackAvailable()Deprecated.Never invoked by this class; subclasses should not assume it will be.Is JDK 1.3 with Lumberjack logging available? -
isJdk14Available
protected boolean isJdk14Available()Deprecated.Never invoked by this class; subclasses should not assume it will be.Returntrueif JDK 1.4 or later logging is available. Also checks that theThrowableclass supportsgetStackTrace(), which is required by Jdk14Logger. -
isLog4JAvailable
protected boolean isLog4JAvailable()Deprecated.Never invoked by this class; subclasses should not assume it will be.Is a Log4J implementation available? -
newInstance
Create and return a newLoginstance for the specified name.- Parameters:
name- Name of the new logger- Throws:
LogConfigurationException- if a new instance cannot be created
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getContextClassLoaderInternal
Calls LogFactory.directGetContextClassLoader under the control of an AccessController class. This means that java code running under a security manager that forbids access to ClassLoaders will still work if this class is given appropriate privileges, even when the caller doesn't have such privileges. Without using an AccessController, the the entire call stack must have the privilege before the call is allowed.- Returns:
- the context classloader associated with the current thread, or null if security doesn't allow it.
- Throws:
LogConfigurationException- if there was some weird error while attempting to get the context classloader.SecurityException- if the current java security policy doesn't allow this class to access the context classloader.
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getSystemProperty
Read the specified system property, using an AccessController so that the property can be read if JCL has been granted the appropriate security rights even if the calling code has not.Take care not to expose the value returned by this method to the calling application in any way; otherwise the calling app can use that info to access data that should not be available to it.
- Throws:
SecurityException
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getParentClassLoader
Fetch the parent classloader of a specified classloader.If a SecurityException occurs, null is returned.
Note that this method is non-static merely so logDiagnostic is available.
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isLogLibraryAvailable
Utility method to check whether a particular logging library is present and available for use. Note that this does not affect the future behaviour of this class. -
getConfigurationValue
Attempt to find an attribute (see method setAttribute) or a system property with the provided name and return its value.The attributes associated with this object are checked before system properties in case someone has explicitly called setAttribute, or a configuration property has been set in a commons-logging.properties file.
- Returns:
- the value associated with the property, or null.
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getBooleanConfiguration
Get the setting for the user-configurable behaviour specified by key. If nothing has explicitly been set, then return dflt. -
initConfiguration
private void initConfiguration()Initialize a number of variables that control the behaviour of this class and that can be tweaked by the user. This is done when the first logger is created, not in the constructor of this class, because we need to give the user a chance to call method setAttribute in order to configure this object. -
discoverLogImplementation
Attempts to create a Log instance for the given category name. Follows the discovery process described in the class javadoc.- Parameters:
logCategory- the name of the log category- Throws:
LogConfigurationException- if an error in discovery occurs, or if no adapter at all can be instantiated
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informUponSimilarName
Appends message if the given name is similar to the candidate.- Parameters:
messageBuffer-StringBufferthe message should be appended to, not nullname- the (trimmed) name to be test against the candidate, not nullcandidate- the candidate name (not null)
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findUserSpecifiedLogClassName
Checks system properties and the attribute map for a Log implementation specified by the user under the property namesLOG_PROPERTYorLOG_PROPERTY_OLD.- Returns:
- classname specified by the user, or
null
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createLogFromClass
private Log createLogFromClass(String logAdapterClassName, String logCategory, boolean affectState) throws LogConfigurationException Attempts to load the given class, find a suitable constructor, and instantiate an instance of Log.- Parameters:
logAdapterClassName- classname of the Log implementationlogCategory- argument to pass to the Log implementation's constructoraffectState-trueif this object's state should be affected by this method call,falseotherwise.- Returns:
- an instance of the given class, or null if the logging library associated with the specified adapter is not available.
- Throws:
LogConfigurationException- if there was a serious error with configuration and the handleFlawedDiscovery method decided this problem was fatal.
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getBaseClassLoader
Return the classloader from which we should try to load the logging adapter classes.This method usually returns the context classloader. However if it is discovered that the classloader which loaded this class is a child of the context classloader and the allowFlawedContext option has been set then the classloader which loaded this class is returned instead.
The only time when the classloader which loaded this class is a descendant (rather than the same as or an ancestor of the context classloader) is when an app has created custom classloaders but failed to correctly set the context classloader. This is a bug in the calling application; however we provide the option for JCL to simply generate a warning rather than fail outright.
- Throws:
LogConfigurationException
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getLowestClassLoader
Given two related classloaders, return the one which is a child of the other.- Parameters:
c1- is a classloader (including the null classloader)c2- is a classloader (including the null classloader)- Returns:
- c1 if it has c2 as an ancestor, c2 if it has c1 as an ancestor, and null if neither is an ancestor of the other.
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handleFlawedDiscovery
private void handleFlawedDiscovery(String logAdapterClassName, ClassLoader classLoader, Throwable discoveryFlaw) Generates an internal diagnostic logging of the discovery failure and then throws aLogConfigurationExceptionthat wraps the passedThrowable.- Parameters:
logAdapterClassName- is the class name of the Log implementation that could not be instantiated. Cannot benull.classLoader- is the classloader that we were trying to load the logAdapterClassName from when the exception occurred.discoveryFlaw- is the Throwable created by the classloader- Throws:
LogConfigurationException- ALWAYS
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handleFlawedHierarchy
private void handleFlawedHierarchy(ClassLoader badClassLoader, Class badClass) throws LogConfigurationException Report a problem loading the log adapter, then either return (if the situation is considered recoverable) or throw a LogConfigurationException.There are two possible reasons why we successfully loaded the specified log adapter class then failed to cast it to a Log object:
- the specific class just doesn't implement the Log interface (user screwed up), or
- the specified class has bound to a Log class loaded by some other classloader; Log@classloaderX cannot be cast to Log@classloaderY.
Here we try to figure out which case has occurred so we can give the user some reasonable feedback.
- Parameters:
badClassLoader- is the classloader we loaded the problem class from, ie it is equivalent to badClass.getClassLoader().badClass- is a Class object with the desired name, but which does not implement Log correctly.- Throws:
LogConfigurationException- when the situation should not be recovered from.
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