public abstract class LogFactory
extends java.lang.Object
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.
Modifier and Type | Field and Description |
---|---|
private static java.lang.String |
diagnosticPrefix
A string that gets prefixed to every message output by the
logDiagnostic method, so that users can clearly see which
LogFactory class is generating the output.
|
static java.lang.String |
DIAGNOSTICS_DEST_PROPERTY
The name (
org.apache.commons.logging.diagnostics.dest )
of the property used to enable internal commons-logging
diagnostic output, in order to get information on what logging
implementations are being discovered, what classloaders they
are loaded through, etc. |
private static java.io.PrintStream |
diagnosticsStream
When null (the usual case), no diagnostic output will be
generated by LogFactory or LogFactoryImpl.
|
protected static java.util.Hashtable |
factories
The previously constructed
LogFactory instances, keyed by
the ClassLoader with which it was created. |
static java.lang.String |
FACTORY_DEFAULT
The fully qualified class name of the fallback
LogFactory
implementation class to use, if no other can be found. |
static java.lang.String |
FACTORY_PROPERTIES
The name (
commons-logging.properties ) of the properties file to search for. |
static java.lang.String |
FACTORY_PROPERTY
The name (
org.apache.commons.logging.LogFactory ) of the property
used to identify the LogFactory implementation
class name. |
static java.lang.String |
HASHTABLE_IMPLEMENTATION_PROPERTY
Setting this system property
(
org.apache.commons.logging.LogFactory.HashtableImpl )
value allows the Hashtable used to store
classloaders to be substituted by an alternative implementation. |
protected static LogFactory |
nullClassLoaderFactory
Deprecated.
since 1.1.2
|
static java.lang.String |
PRIORITY_KEY
The name (
priority ) of the key in the config file used to
specify the priority of that particular config file. |
protected static java.lang.String |
SERVICE_ID
JDK1.3+
'Service Provider' specification.
|
static java.lang.String |
TCCL_KEY
The name (
use_tccl ) of the key in the config file used
to specify whether logging classes should be loaded via the thread
context class loader (TCCL), or not. |
private static java.lang.ClassLoader |
thisClassLoader
A reference to the classloader that loaded this class.
|
private static java.lang.String |
WEAK_HASHTABLE_CLASSNAME
Name used to load the weak hashtable implementation by names.
|
Modifier | Constructor and Description |
---|---|
protected |
LogFactory()
Protected constructor that is not available for public use.
|
Modifier and Type | Method and Description |
---|---|
private static void |
cacheFactory(java.lang.ClassLoader classLoader,
LogFactory factory)
Remember this factory, so later calls to LogFactory.getCachedFactory
can return the previously created object (together with all its
cached Log objects).
|
protected static java.lang.Object |
createFactory(java.lang.String factoryClass,
java.lang.ClassLoader classLoader)
Implements the operations described in the javadoc for newFactory.
|
private static java.util.Hashtable |
createFactoryStore()
Create the hashtable which will be used to store a map of
(context-classloader -> logfactory-object).
|
protected static java.lang.ClassLoader |
directGetContextClassLoader()
Return the thread context class loader if available; otherwise return null.
|
abstract java.lang.Object |
getAttribute(java.lang.String name)
Return the configuration attribute with the specified name (if any),
or
null if there is no such attribute. |
abstract java.lang.String[] |
getAttributeNames()
Return an array containing the names of all currently defined
configuration attributes.
|
private static LogFactory |
getCachedFactory(java.lang.ClassLoader contextClassLoader)
Check cached factories (keyed by contextClassLoader)
|
protected static java.lang.ClassLoader |
getClassLoader(java.lang.Class clazz)
Safely get access to the classloader for the specified class.
|
private static java.util.Properties |
getConfigurationFile(java.lang.ClassLoader classLoader,
java.lang.String fileName)
Locate a user-provided configuration file.
|
protected static java.lang.ClassLoader |
getContextClassLoader()
Returns the current context classloader.
|
private static java.lang.ClassLoader |
getContextClassLoaderInternal()
Calls LogFactory.directGetContextClassLoader under the control of an
AccessController class.
|
static LogFactory |
getFactory()
Construct (if necessary) and return a
LogFactory
instance, using the following ordered lookup procedure to determine
the name of the implementation class to be loaded. |
abstract Log |
getInstance(java.lang.Class clazz)
Convenience method to derive a name from the specified class and
call
getInstance(String) with it. |
abstract Log |
getInstance(java.lang.String name)
Construct (if necessary) and return a
Log instance,
using the factory's current set of configuration attributes. |
static Log |
getLog(java.lang.Class clazz)
Convenience method to return a named logger, without the application
having to care about factories.
|
static Log |
getLog(java.lang.String name)
Convenience method to return a named logger, without the application
having to care about factories.
|
private static java.util.Properties |
getProperties(java.net.URL url)
Given a URL that refers to a .properties file, load that file.
|
private static java.io.InputStream |
getResourceAsStream(java.lang.ClassLoader loader,
java.lang.String name)
Applets may run in an environment where accessing resources of a loader is
a secure operation, but where the commons-logging library has explicitly
been granted permission for that operation.
|
private static java.util.Enumeration |
getResources(java.lang.ClassLoader loader,
java.lang.String name)
Given a filename, return an enumeration of URLs pointing to
all the occurrences of that filename in the classpath.
|
private static java.lang.String |
getSystemProperty(java.lang.String key,
java.lang.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.
|
protected static void |
handleThrowable(java.lang.Throwable t)
Checks whether the supplied Throwable is one that needs to be
re-thrown and ignores all others.
|
private static boolean |
implementsLogFactory(java.lang.Class logFactoryClass)
Determines whether the given class actually implements
LogFactory . |
private static java.io.PrintStream |
initDiagnostics()
Determines whether the user wants internal diagnostic output.
|
protected static boolean |
isDiagnosticsEnabled()
Indicates true if the user has enabled internal logging.
|
private static void |
logClassLoaderEnvironment(java.lang.Class clazz)
Generate useful diagnostics regarding the classloader tree for
the specified class.
|
private static void |
logDiagnostic(java.lang.String msg)
Write the specified message to the internal logging destination.
|
private static void |
logHierarchy(java.lang.String prefix,
java.lang.ClassLoader classLoader)
Logs diagnostic messages about the given classloader
and it's hierarchy.
|
protected static void |
logRawDiagnostic(java.lang.String msg)
Write the specified message to the internal logging destination.
|
protected static LogFactory |
newFactory(java.lang.String factoryClass,
java.lang.ClassLoader classLoader)
Method provided for backwards compatibility; see newFactory version that
takes 3 parameters.
|
protected static LogFactory |
newFactory(java.lang.String factoryClass,
java.lang.ClassLoader classLoader,
java.lang.ClassLoader contextClassLoader)
Return a new instance of the specified
LogFactory
implementation class, loaded by the specified class loader. |
static java.lang.String |
objectId(java.lang.Object o)
Returns a string that uniquely identifies the specified object, including
its class.
|
abstract void |
release()
Release any internal references to previously created
Log
instances returned by this factory. |
static void |
release(java.lang.ClassLoader classLoader)
Release any internal references to previously created
LogFactory
instances that have been associated with the specified class loader
(if any), after calling the instance method release() on
each of them. |
static void |
releaseAll()
Release any internal references to previously created
LogFactory
instances, after calling the instance method release() on
each of them. |
abstract void |
removeAttribute(java.lang.String name)
Remove any configuration attribute associated with the specified name.
|
abstract void |
setAttribute(java.lang.String name,
java.lang.Object value)
Set the configuration attribute with the specified name.
|
private static java.lang.String |
trim(java.lang.String src)
Utility method to safely trim a string.
|
public static final java.lang.String PRIORITY_KEY
priority
) of the key in the config file used to
specify the priority of that particular config file. The associated value
is a floating-point number; higher values take priority over lower values.public static final java.lang.String TCCL_KEY
use_tccl
) of the key in the config file used
to specify whether logging classes should be loaded via the thread
context class loader (TCCL), or not. By default, the TCCL is used.public static final java.lang.String FACTORY_PROPERTY
org.apache.commons.logging.LogFactory
) of the property
used to identify the LogFactory implementation
class name. This can be used as a system property, or as an entry in a
configuration properties file.public static final java.lang.String FACTORY_DEFAULT
LogFactory
implementation class to use, if no other can be found.public static final java.lang.String FACTORY_PROPERTIES
commons-logging.properties
) of the properties file to search for.protected static final java.lang.String SERVICE_ID
public static final java.lang.String DIAGNOSTICS_DEST_PROPERTY
org.apache.commons.logging.diagnostics.dest
)
of the property used to enable internal commons-logging
diagnostic output, in order to get information on what logging
implementations are being discovered, what classloaders they
are loaded through, etc.
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.
private static java.io.PrintStream diagnosticsStream
private static final java.lang.String diagnosticPrefix
public static final java.lang.String HASHTABLE_IMPLEMENTATION_PROPERTY
org.apache.commons.logging.LogFactory.HashtableImpl
)
value allows the Hashtable
used to store
classloaders to be substituted by an alternative implementation.
Note: LogFactory
will print:
[ERROR] LogFactory: Load of custom hashtable failedto system error and then continue using a standard Hashtable.
Usage: Set this property when Java is invoked
and LogFactory
will attempt to load a new instance
of the given implementation class.
For example, running the following ant scriplet:
<java classname="${test.runner}" fork="yes" failonerror="${test.failonerror}"> ... <sysproperty key="org.apache.commons.logging.LogFactory.HashtableImpl" value="org.apache.commons.logging.AltHashtable"/> </java>will mean that
LogFactory
will load an instance of
org.apache.commons.logging.AltHashtable
.
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 ;).
private static final java.lang.String WEAK_HASHTABLE_CLASSNAME
private static final java.lang.ClassLoader thisClassLoader
protected static java.util.Hashtable factories
LogFactory
instances, keyed by
the ClassLoader
with which it was created.protected static volatile LogFactory nullClassLoaderFactory
LogFactory
instance as in the
factories
map, but for the case where
getClassLoader
returns null
.
This can happen when:
factories
is a Hashtable (not a HashMap),
and hashtables don't allow null as a key.protected LogFactory()
public abstract java.lang.Object getAttribute(java.lang.String name)
null
if there is no such attribute.name
- Name of the attribute to returnpublic abstract java.lang.String[] getAttributeNames()
public abstract Log getInstance(java.lang.Class clazz) throws LogConfigurationException
getInstance(String)
with it.clazz
- Class for which a suitable Log name will be derivedLogConfigurationException
- if a suitable Log
instance cannot be returnedpublic abstract Log getInstance(java.lang.String name) throws LogConfigurationException
Log
instance,
using the factory's current set of configuration attributes.
NOTE - Depending upon the implementation of
the LogFactory
you are using, the Log
instance 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.
name
- Logical name of the Log
instance to be
returned (the meaning of this name is only known to the underlying
logging implementation that is being wrapped)LogConfigurationException
- if a suitable Log
instance cannot be returnedpublic abstract void release()
Log
instances 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.public abstract void removeAttribute(java.lang.String name)
name
- Name of the attribute to removepublic abstract void setAttribute(java.lang.String name, java.lang.Object value)
null
value is equivalent to calling
removeAttribute(name)
.name
- Name of the attribute to setvalue
- Value of the attribute to set, or null
to remove any setting for this attributeprivate static final java.util.Hashtable createFactoryStore()
Note that the correct way to ensure no memory leaks occur is to ensure that LogFactory.release(contextClassLoader) is called whenever a webapp is undeployed.
private static java.lang.String trim(java.lang.String src)
protected static void handleThrowable(java.lang.Throwable t)
t
- the Throwable to checkpublic static LogFactory getFactory() throws LogConfigurationException
LogFactory
instance, using the following ordered lookup procedure to determine
the name of the implementation class to be loaded.
org.apache.commons.logging.LogFactory
system
property.commons-logging.properties
file, if found in the class path of this class. The configuration
file is in standard java.util.Properties
format and
contains the fully qualified name of the implementation class
with the key being the system property defined above.org.apache.commons.logging.impl.LogFactoryImpl
).
NOTE - If the properties file method of identifying the
LogFactory
implementation class is utilized, all of the
properties defined in this file will be set as configuration attributes
on the corresponding LogFactory
instance.
NOTE - In a multi-threaded environment it is possible that two different instances will be returned for the same classloader environment.
LogConfigurationException
- if the implementation class is not
available or cannot be instantiated.public static Log getLog(java.lang.Class clazz) throws LogConfigurationException
clazz
- Class from which a log name will be derivedLogConfigurationException
- if a suitable Log
instance cannot be returnedpublic static Log getLog(java.lang.String name) throws LogConfigurationException
name
- Logical name of the Log
instance to be
returned (the meaning of this name is only known to the underlying
logging implementation that is being wrapped)LogConfigurationException
- if a suitable Log
instance cannot be returnedpublic static void release(java.lang.ClassLoader classLoader)
LogFactory
instances that have been associated with the specified class loader
(if any), after calling the instance method release()
on
each of them.classLoader
- ClassLoader for which to release the LogFactorypublic static void releaseAll()
LogFactory
instances, after calling the instance method release()
on
each of them. 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.protected static java.lang.ClassLoader getClassLoader(java.lang.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 java.lang.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.
LogConfigurationException
- if there was some weird error while
attempting to get the context classloader.private static java.lang.ClassLoader getContextClassLoaderInternal() throws LogConfigurationException
LogConfigurationException
- if there was some weird error while
attempting to get the context classloader.protected static java.lang.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.
null
if the java security
policy forbids access to the context classloader from one of the classes
in the current call stack.LogConfigurationException
- if a suitable class loader
cannot be identified.private static LogFactory getCachedFactory(java.lang.ClassLoader contextClassLoader)
contextClassLoader
- is the context classloader associated
with the current thread. This allows separate LogFactory objects
per component within a container, provided each component has
a distinct context classloader set. This parameter may be null
in JDK1.1, and in embedded systems where jcl-using code is
placed in the bootclasspath.private static void cacheFactory(java.lang.ClassLoader classLoader, LogFactory factory)
classLoader
- should be the current context classloader. Note that
this can be null under some circumstances; this is ok.factory
- should be the factory to cache. This should never be null.protected static LogFactory newFactory(java.lang.String factoryClass, java.lang.ClassLoader classLoader, java.lang.ClassLoader contextClassLoader) throws LogConfigurationException
LogFactory
implementation class, loaded by the specified class loader.
If that fails, try the class loader used to load this
(abstract) LogFactory.
Note 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.
factoryClass
- Fully qualified name of the LogFactory
implementation classclassLoader
- ClassLoader from which to load this classcontextClassLoader
- is the context that this new factory will
manage logging for.LogConfigurationException
- if a suitable instance
cannot be createdprotected static LogFactory newFactory(java.lang.String factoryClass, java.lang.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 java.lang.Object createFactory(java.lang.String factoryClass, java.lang.ClassLoader classLoader)
factoryClass
- classLoader
- used to load the specified factory class. This is
expected to be either the TCCL or the classloader which loaded this
class. Note that the classloader which loaded this class might be
"null" (ie the bootloader) for embedded systems.private static boolean implementsLogFactory(java.lang.Class logFactoryClass)
LogFactory
.
Diagnostic information is also logged.
Usage: to diagnose whether a classloader conflict is the cause
of incompatibility. The test used is whether the class is assignable from
the LogFactory
class loaded by the class's classloader.
logFactoryClass
- Class
which may implement LogFactory
logFactoryClass
does extend
LogFactory
when that class is loaded via the same
classloader that loaded the logFactoryClass
.private static java.io.InputStream getResourceAsStream(java.lang.ClassLoader loader, java.lang.String name)
private static java.util.Enumeration getResources(java.lang.ClassLoader loader, java.lang.String name)
This is just like ClassLoader.getResources except that the operation is done under an AccessController so that this method will succeed when this jarfile is privileged but the caller is not. This method must therefore remain private to avoid security issues.
If no instances are found, an Enumeration is returned whose hasMoreElements method returns false (ie an "empty" enumeration). If resources could not be listed for some reason, null is returned.
private static java.util.Properties getProperties(java.net.URL url)
Null
is returned if the URL cannot be opened.
private static final java.util.Properties getConfigurationFile(java.lang.ClassLoader classLoader, java.lang.String fileName)
The classpath of the specified classLoader (usually the context classloader) is searched for properties files of the specified name. If none is found, null is returned. If more than one is found, then the file with the greatest value for its PRIORITY property is returned. If multiple files have the same PRIORITY value then the first in the classpath is returned.
This differs from the 1.0.x releases; those always use the first one found. However as the priority is a new field, this change is backwards compatible.
The purpose of the priority field is to allow a webserver administrator to override logging settings in all webapps by placing a commons-logging.properties file in a shared classpath location with a priority > 0; this overrides any commons-logging.properties files without priorities which are in the webapps. Webapps can also use explicit priorities to override a configuration file in the shared classpath if needed.
private static java.lang.String getSystemProperty(java.lang.String key, java.lang.String def) throws java.lang.SecurityException
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.
java.lang.SecurityException
private static java.io.PrintStream initDiagnostics()
DIAGNOSTICS_DEST_PROPERTY
to
a filename, or the special values STDOUT or STDERR.protected static boolean isDiagnosticsEnabled()
By the way, sorry for the incorrect grammar, but calling this method areDiagnosticsEnabled just isn't java beans style.
private static final void logDiagnostic(java.lang.String msg)
Note that this method is private; concrete subclasses of this class should not call it because the diagnosticPrefix string this method puts in front of all its messages is LogFactory@...., while subclasses should put SomeSubClass@...
Subclasses should instead compute their own prefix, then call logRawDiagnostic. Note that calling isDiagnosticsEnabled is fine for subclasses.
Note that it is safe to call this method before initDiagnostics is called; any output will just be ignored (as isDiagnosticsEnabled will return false).
msg
- is the diagnostic message to be output.protected static final void logRawDiagnostic(java.lang.String msg)
msg
- is the diagnostic message to be output.private static void logClassLoaderEnvironment(java.lang.Class clazz)
As an example, if the specified class was loaded via a webapp's classloader, then you may get the following output:
Class com.acme.Foo was loaded via classloader 11111 ClassLoader tree: 11111 -> 22222 (SYSTEM) -> 33333 -> BOOT
This method returns immediately if isDiagnosticsEnabled() returns false.
clazz
- is the class whose classloader + tree are to be
output.private static void logHierarchy(java.lang.String prefix, java.lang.ClassLoader classLoader)
prefix
- classLoader
- public static java.lang.String objectId(java.lang.Object o)
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.
o
- may be null.Copyright 2002-2013 The Apache Software Foundation.