Concrete subclass of {@link LogFactory} that implements the * following algorithm to dynamically select a logging implementation * class to instantiate a wrapper for.
*org.apache.commons.logging.Log to identify the
* requested implementation class.org.apache.commons.logging.Log system property
* to identify the requested implementation class.org.apache.commons.logging.impl.Log4JLogger.org.apache.commons.logging.impl.Jdk14Logger.org.apache.commons.logging.impl.SimpleLog.If the selected {@link Log} implementation class has a
* setLogFactory() method that accepts a {@link 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.
org.apache.commons.logging.Log) of the system
* property identifying our {@link Log} implementation class.
*/
public static final String LOG_PROPERTY =
"org.apache.commons.logging.Log";
/**
* The deprecated system property used for backwards compatibility with
* old versions of JCL.
*/
protected static final String LOG_PROPERTY_OLD =
"org.apache.commons.logging.log";
/**
* 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.
*/
public static final String ALLOW_FLAWED_CONTEXT_PROPERTY =
"org.apache.commons.logging.Log.allowFlawedContext";
/**
* 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.
*/
public static final String ALLOW_FLAWED_DISCOVERY_PROPERTY =
"org.apache.commons.logging.Log.allowFlawedDiscovery";
/**
* 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.
*/
public static final String ALLOW_FLAWED_HIERARCHY_PROPERTY =
"org.apache.commons.logging.Log.allowFlawedHierarchy";
/**
* 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.
*/
private static final String[] classesToDiscover = {
LOGGING_IMPL_LOG4J_LOGGER,
"org.apache.commons.logging.impl.Jdk14Logger",
"org.apache.commons.logging.impl.Jdk13LumberjackLogger",
"org.apache.commons.logging.impl.SimpleLog"
};
// ----------------------------------------------------- Instance Variables
/**
* Determines whether logging classes should be loaded using the thread-context
* classloader, or via the classloader that loaded this LogFactoryImpl class.
*/
private boolean useTCCL = true;
/**
* The string prefixed to every message output by the logDiagnostic method.
*/
private String diagnosticPrefix;
/**
* Configuration attributes.
*/
protected Hashtable attributes = new Hashtable();
/**
* The {@link org.apache.commons.logging.Log} instances that have
* already been created, keyed by logger name.
*/
protected Hashtable instances = new Hashtable();
/**
* Name of the class implementing the Log interface.
*/
private String logClassName;
/**
* The one-argument constructor of the
* {@link org.apache.commons.logging.Log}
* implementation class that will be used to create new instances.
* This value is initialized by getLogConstructor(),
* and then returned repeatedly.
*/
protected Constructor logConstructor = null;
/**
* The signature of the Constructor to be used.
*/
protected Class logConstructorSignature[] =
{ java.lang.String.class };
/**
* The one-argument setLogFactory method of the selected
* {@link org.apache.commons.logging.Log} method, if it exists.
*/
protected Method logMethod = null;
/**
* The signature of the setLogFactory method to be used.
*/
protected Class logMethodSignature[] =
{ LogFactory.class };
/**
* See getBaseClassLoader and initConfiguration.
*/
private boolean allowFlawedContext;
/**
* See handleFlawedDiscovery and initConfiguration.
*/
private boolean allowFlawedDiscovery;
/**
* See handleFlawedHierarchy and initConfiguration.
*/
private boolean allowFlawedHierarchy;
// --------------------------------------------------------- Public Methods
/**
* Return the configuration attribute with the specified name (if any),
* or null if there is no such attribute.
*
* @param name Name of the attribute to return
*/
public Object getAttribute(String name) {
return (attributes.get(name));
}
/**
* Return an array containing the names of all currently defined
* configuration attributes. If there are no such attributes, a zero
* length array is returned.
*/
public String[] getAttributeNames() {
Vector names = new Vector();
Enumeration keys = attributes.keys();
while (keys.hasMoreElements()) {
names.addElement((String) keys.nextElement());
}
String results[] = new String[names.size()];
for (int i = 0; i < results.length; i++) {
results[i] = (String) names.elementAt(i);
}
return (results);
}
/**
* Convenience method to derive a name from the specified class and
* call getInstance(String) with it.
*
* @param clazz Class for which a suitable Log name will be derived
*
* @exception LogConfigurationException if a suitable Log
* instance cannot be returned
*/
public Log getInstance(Class clazz) throws LogConfigurationException {
return (getInstance(clazz.getName()));
}
/**
* Construct (if necessary) and return a 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.
Log instance to be
* returned (the meaning of this name is only known to the underlying
* logging implementation that is being wrapped)
*
* @exception LogConfigurationException if a suitable Log
* instance cannot be returned
*/
public Log getInstance(String name) throws LogConfigurationException {
Log instance = (Log) instances.get(name);
if (instance == null) {
instance = newInstance(name);
instances.put(name, instance);
}
return (instance);
}
/**
* Release any internal references to previously created
* {@link org.apache.commons.logging.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 void release() {
logDiagnostic("Releasing all known loggers");
instances.clear();
}
/**
* Remove any configuration attribute associated with the specified name.
* If there is no such attribute, no action is taken.
*
* @param name Name of the attribute to remove
*/
public void removeAttribute(String name) {
attributes.remove(name);
}
/**
* Set the configuration attribute with the specified name. Calling
* this with a null value is equivalent to calling
* removeAttribute(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.
*
* @param name Name of the attribute to set
* @param value Value of the attribute to set, or null
* to remove any setting for this attribute
*/
public void setAttribute(String name, Object value) {
if (logConstructor != null) {
logDiagnostic("setAttribute: call too late; configuration already performed.");
}
if (value == null) {
attributes.remove(name);
} else {
attributes.put(name, value);
}
if (name.equals(TCCL_KEY)) {
useTCCL = Boolean.valueOf(value.toString()).booleanValue();
}
}
// ------------------------------------------------------
// Static Methods
//
// These methods only defined as workarounds for a java 1.2 bug;
// theoretically none of these are needed.
// ------------------------------------------------------
/**
* Gets the context classloader.
* This method is a workaround for a java 1.2 compiler bug.
* @since 1.1
*/
protected static ClassLoader getContextClassLoader() throws LogConfigurationException {
return LogFactory.getContextClassLoader();
}
/**
* Workaround for bug in Java1.2; in theory this method is not needed.
* See LogFactory.isDiagnosticsEnabled.
*/
protected static boolean isDiagnosticsEnabled() {
return LogFactory.isDiagnosticsEnabled();
}
/**
* Workaround for bug in Java1.2; in theory this method is not needed.
* See LogFactory.getClassLoader.
* @since 1.1
*/
protected static ClassLoader getClassLoader(Class clazz) {
return LogFactory.getClassLoader(clazz);
}
// ------------------------------------------------------ Protected Methods
/**
* 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. */ private void initDiagnostics() { // It would be nice to include an identifier of the context classloader // that this LogFactoryImpl object is responsible for. However that // isn't possible as that information isn't available. It is possible // to figure this out by looking at the logging from LogFactory to // see the context & impl ids from when this object was instantiated, // in order to link the impl id output as this object's prefix back to // the context it is intended to manage. // Note that this prefix should be kept consistent with that // in LogFactory. Class clazz = this.getClass(); ClassLoader classLoader = getClassLoader(clazz); String classLoaderName; try { if (classLoader == null) { classLoaderName = "BOOTLOADER"; } else { classLoaderName = objectId(classLoader); } } catch(SecurityException e) { classLoaderName = "UNKNOWN"; } diagnosticPrefix = "[LogFactoryImpl@" + System.identityHashCode(this) + " from " + classLoaderName + "] "; } /** * Output a diagnostic message to a user-specified destination (if the * user has enabled diagnostic logging). * * @param msg diagnostic message * @since 1.1 */ protected void logDiagnostic(String msg) { if (isDiagnosticsEnabled()) { logRawDiagnostic(diagnosticPrefix + msg); } } /** * Return the fully qualified Java classname of the {@link Log} * implementation we will be using. * * @deprecated Never invoked by this class; subclasses should not assume * it will be. */ protected String getLogClassName() { if (logClassName == null) { discoverLogImplementation(getClass().getName()); } return logClassName; } /** *
Return the Constructor that can be called to instantiate
* new {@link org.apache.commons.logging.Log} instances.
IMPLEMENTATION NOTE - Race conditions caused by
* calling this method from more than one thread are ignored, because
* the same Constructor instance will ultimately be derived
* in all circumstances.
Return true if JDK 1.4 or later logging
* is available. Also checks that the Throwable class
* supports getStackTrace(), which is required by
* Jdk14Logger.
* 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.
*
* @return the value associated with the property, or null.
*/
private String getConfigurationValue(String property) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[ENV] Trying to get configuration for item " + property);
}
Object valueObj = getAttribute(property);
if (valueObj != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[ENV] Found LogFactory attribute [" + valueObj + "] for " + property);
}
return valueObj.toString();
}
if (isDiagnosticsEnabled()) {
logDiagnostic("[ENV] No LogFactory attribute found for " + property);
}
try {
String value = System.getProperty(property);
if (value != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[ENV] Found system property [" + value + "] for " + property);
}
return value;
}
if (isDiagnosticsEnabled()) {
logDiagnostic("[ENV] No system property found for property " + property);
}
} catch (SecurityException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[ENV] Security prevented reading system property " + property);
}
}
if (isDiagnosticsEnabled()) {
logDiagnostic("[ENV] No configuration defined for item " + property);
}
return null;
}
/**
* Get the setting for the user-configurable behaviour specified by key.
* If nothing has explicitly been set, then return dflt.
*/
private boolean getBooleanConfiguration(String key, boolean dflt) {
String val = getConfigurationValue(key);
if (val == null)
return dflt;
return Boolean.valueOf(val).booleanValue();
}
/**
* 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.
*/
private void initConfiguration() {
allowFlawedContext = getBooleanConfiguration(ALLOW_FLAWED_CONTEXT_PROPERTY, true);
allowFlawedDiscovery = getBooleanConfiguration(ALLOW_FLAWED_DISCOVERY_PROPERTY, true);
allowFlawedHierarchy = getBooleanConfiguration(ALLOW_FLAWED_HIERARCHY_PROPERTY, true);
}
/**
* Attempts to create a Log instance for the given category name.
* Follows the discovery process described in the class javadoc.
*
* @param logCategory the name of the log category
*
* @throws LogConfigurationException if an error in discovery occurs,
* or if no adapter at all can be instantiated
*/
private Log discoverLogImplementation(String logCategory)
throws LogConfigurationException
{
if (isDiagnosticsEnabled()) {
logDiagnostic("Discovering a Log implementation...");
}
initConfiguration();
Log result = null;
// See if the user specified the Log implementation to use
String specifiedLogClassName = findUserSpecifiedLogClassName();
if (specifiedLogClassName != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Attempting to load user-specified log class '" +
specifiedLogClassName + "'...");
}
result = createLogFromClass(specifiedLogClassName,
logCategory,
true);
if (result == null) {
StringBuffer messageBuffer = new StringBuffer("User-specified log class '");
messageBuffer.append(specifiedLogClassName);
messageBuffer.append("' cannot be found or is not useable.");
// Mistyping or misspelling names is a common fault.
// Construct a good error message, if we can
if (specifiedLogClassName != null) {
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LOG4J_LOGGER);
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_JDK14_LOGGER);
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_LUMBERJACK_LOGGER);
informUponSimilarName(messageBuffer, specifiedLogClassName, LOGGING_IMPL_SIMPLE_LOGGER);
}
throw new LogConfigurationException(messageBuffer.toString());
}
return result;
}
// No user specified log; try to discover what's on the classpath
//
// Note that we deliberately loop here over classesToDiscover and
// expect method createLogFromClass to loop over the possible source
// classloaders. The effect is:
// for each discoverable log adapter
// for each possible classloader
// see if it works
//
// It appears reasonable at first glance to do the opposite:
// for each possible classloader
// for each discoverable log adapter
// see if it works
//
// The latter certainly has advantages for user-installable logging
// libraries such as log4j; in a webapp for example this code should
// first check whether the user has provided any of the possible
// logging libraries before looking in the parent classloader.
// Unfortunately, however, Jdk14Logger will always work in jvm>=1.4,
// and SimpleLog will always work in any JVM. So the loop would never
// ever look for logging libraries in the parent classpath. Yet many
// users would expect that putting log4j there would cause it to be
// detected (and this is the historical JCL behaviour). So we go with
// the first approach. A user that has bundled a specific logging lib
// in a webapp should use a commons-logging.properties file or a
// service file in META-INF to force use of that logging lib anyway,
// rather than relying on discovery.
if (isDiagnosticsEnabled()) {
logDiagnostic(
"No user-specified Log implementation; performing discovery" +
" using the standard supported logging implementations...");
}
for(int i=0; (i
* 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.
*
*/
private ClassLoader getBaseClassLoader() throws LogConfigurationException {
ClassLoader thisClassLoader = getClassLoader(LogFactoryImpl.class);
if (useTCCL == false) {
return thisClassLoader;
}
ClassLoader contextClassLoader = getContextClassLoader();
ClassLoader baseClassLoader = getLowestClassLoader(
contextClassLoader, thisClassLoader);
if (baseClassLoader == null) {
// The two classloaders are not part of a parent child relationship.
// In some classloading setups (e.g. JBoss with its
// UnifiedLoaderRepository) this can still work, so if user hasn't
// forbidden it, just return the contextClassLoader.
if (allowFlawedContext) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[WARNING] the context classloader is not part of a"
+ " parent-child relationship with the classloader that"
+ " loaded LogFactoryImpl.");
}
// If contextClassLoader were null, getLowestClassLoader() would
// have returned thisClassLoader. The fact we are here means
// contextClassLoader is not null, so we can just return it.
return contextClassLoader;
}
else {
throw new LogConfigurationException(
"Bad classloader hierarchy; LogFactoryImpl was loaded via"
+ " a classloader that is not related to the current context"
+ " classloader.");
}
}
if (baseClassLoader != contextClassLoader) {
// We really should just use the contextClassLoader as the starting
// point for scanning for log adapter classes. However it is expected
// that there are a number of broken systems out there which create
// custom classloaders but fail to set the context classloader so
// we handle those flawed systems anyway.
if (allowFlawedContext) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"Warning: the context classloader is an ancestor of the"
+ " classloader that loaded LogFactoryImpl; it should be"
+ " the same or a descendant. The application using"
+ " commons-logging should ensure the context classloader"
+ " is used correctly.");
}
} else {
throw new LogConfigurationException(
"Bad classloader hierarchy; LogFactoryImpl was loaded via"
+ " a classloader that is not related to the current context"
+ " classloader.");
}
}
return baseClassLoader;
}
/**
* Given two related classloaders, return the one which is a child of
* the other.
*
* @param c1 is a classloader (including the null classloader)
* @param c2 is a classloader (including the null classloader)
*
* @return 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.
*/
private ClassLoader getLowestClassLoader(ClassLoader c1, ClassLoader c2) {
// TODO: use AccessController when dealing with classloaders here
if (c1 == null)
return c2;
if (c2 == null)
return c1;
ClassLoader current;
// scan c1's ancestors to find c2
current = c1;
while (current != null) {
if (current == c2)
return c1;
current = current.getParent();
}
// scan c2's ancestors to find c1
current = c2;
while (current != null) {
if (current == c1)
return c2;
current = current.getParent();
}
return null;
}
/**
* Generates an internal diagnostic logging of the discovery failure and
* then throws a
* There are two possible reasons why we successfully loaded the
* specified log adapter class then failed to cast it to a Log object:
*
* Here we try to figure out which case has occurred so we can give the
* user some reasonable feedback.
*
* @param badClassLoader is the classloader we loaded the problem class from,
* ie it is equivalent to badClass.getClassLoader().
*
* @param 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.
*/
private void handleFlawedHierarchy(ClassLoader badClassLoader, Class badClass)
throws LogConfigurationException {
boolean implementsLog = false;
String logInterfaceName = Log.class.getName();
Class interfaces[] = badClass.getInterfaces();
for (int i = 0; i < interfaces.length; i++) {
if (logInterfaceName.equals(interfaces[i].getName())) {
implementsLog = true;
break;
}
}
if (implementsLog) {
// the class does implement an interface called Log, but
// it is in the wrong classloader
if (isDiagnosticsEnabled()) {
try {
ClassLoader logInterfaceClassLoader = getClassLoader(Log.class);
logDiagnostic(
"Class '" + badClass.getName()
+ "' was found in classloader "
+ objectId(badClassLoader)
+ ". It is bound to a Log interface which is not"
+ " the one loaded from classloader "
+ objectId(logInterfaceClassLoader));
} catch (Throwable t) {
logDiagnostic(
"Error while trying to output diagnostics about"
+ " bad class '" + badClass + "'");
}
}
if (!allowFlawedHierarchy) {
StringBuffer msg = new StringBuffer();
msg.append("Terminating logging for this context ");
msg.append("due to bad log hierarchy. ");
msg.append("You have more than one version of '");
msg.append(Log.class.getName());
msg.append("' visible.");
if (isDiagnosticsEnabled()) {
logDiagnostic(msg.toString());
}
throw new LogConfigurationException(msg.toString());
}
if (isDiagnosticsEnabled()) {
StringBuffer msg = new StringBuffer();
msg.append("Warning: bad log hierarchy. ");
msg.append("You have more than one version of '");
msg.append(Log.class.getName());
msg.append("' visible.");
logDiagnostic(msg.toString());
}
} else {
// this is just a bad adapter class
if (!allowFlawedDiscovery) {
StringBuffer msg = new StringBuffer();
msg.append("Terminating logging for this context. ");
msg.append("Log class '");
msg.append(badClass.getName());
msg.append("' does not implement the Log interface.");
if (isDiagnosticsEnabled()) {
logDiagnostic(msg.toString());
}
throw new LogConfigurationException(msg.toString());
}
if (isDiagnosticsEnabled()) {
StringBuffer msg = new StringBuffer();
msg.append("[WARNING] Log class '");
msg.append(badClass.getName());
msg.append("' does not implement the Log interface.");
logDiagnostic(msg.toString());
}
}
}
}
null
*/
private String findUserSpecifiedLogClassName()
{
if (isDiagnosticsEnabled()) {
logDiagnostic("Trying to get log class from attribute '" + LOG_PROPERTY + "'");
}
String specifiedClass = (String) getAttribute(LOG_PROPERTY);
if (specifiedClass == null) { // @deprecated
if (isDiagnosticsEnabled()) {
logDiagnostic("Trying to get log class from attribute '" +
LOG_PROPERTY_OLD + "'");
}
specifiedClass = (String) getAttribute(LOG_PROPERTY_OLD);
}
if (specifiedClass == null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Trying to get log class from system property '" +
LOG_PROPERTY + "'");
}
try {
specifiedClass = System.getProperty(LOG_PROPERTY);
} catch (SecurityException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("No access allowed to system property '" +
LOG_PROPERTY + "' - " + e.getMessage());
}
}
}
if (specifiedClass == null) { // @deprecated
if (isDiagnosticsEnabled()) {
logDiagnostic("Trying to get log class from system property '" +
LOG_PROPERTY_OLD + "'");
}
try {
specifiedClass = System.getProperty(LOG_PROPERTY_OLD);
} catch (SecurityException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("No access allowed to system property '" +
LOG_PROPERTY_OLD + "' - " + e.getMessage());
}
}
}
// Remove any whitespace; it's never valid in a classname so its
// presence just means a user mistake. As we know what they meant,
// we may as well strip the spaces.
if (specifiedClass != null) {
specifiedClass = specifiedClass.trim();
}
return specifiedClass;
}
/**
* Attempts to load the given class, find a suitable constructor,
* and instantiate an instance of Log.
*
* @param logAdapterClassName classname of the Log implementation
*
* @param logCategory argument to pass to the Log implementation's
* constructor
*
* @param affectState true if this object's state should
* be affected by this method call, false otherwise.
*
* @return 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.
*/
private Log createLogFromClass(String logAdapterClassName,
String logCategory,
boolean affectState)
throws LogConfigurationException {
if (isDiagnosticsEnabled()) {
logDiagnostic("Attempting to instantiate '" + logAdapterClassName + "'");
}
Object[] params = { logCategory };
Log logAdapter = null;
Constructor constructor = null;
Class logAdapterClass = null;
ClassLoader currentCL = getBaseClassLoader();
for(;;) {
// Loop through the classloader hierarchy trying to find
// a viable classloader.
logDiagnostic(
"Trying to load '"
+ logAdapterClassName
+ "' from classloader "
+ objectId(currentCL));
try {
if (isDiagnosticsEnabled()) {
// Show the location of the first occurrence of the .class file
// in the classpath. This is the location that ClassLoader.loadClass
// will load the class from -- unless the classloader is doing
// something weird.
URL url;
String resourceName = logAdapterClassName.replace('.', '/') + ".class";
if (currentCL != null) {
url = currentCL.getResource(resourceName );
} else {
url = ClassLoader.getSystemResource(resourceName + ".class");
}
if (url == null) {
logDiagnostic("Class '" + logAdapterClassName + "' [" + resourceName + "] cannot be found.");
} else {
logDiagnostic("Class '" + logAdapterClassName + "' was found at '" + url + "'");
}
}
Class c = null;
try {
c = Class.forName(logAdapterClassName, true, currentCL);
} catch (ClassNotFoundException originalClassNotFoundException) {
// The current classloader was unable to find the log adapter
// in this or any ancestor classloader. There's no point in
// trying higher up in the hierarchy in this case..
String msg = "" + originalClassNotFoundException.getMessage();
logDiagnostic(
"The log adapter '"
+ logAdapterClassName
+ "' is not available via classloader "
+ objectId(currentCL)
+ ": "
+ msg.trim());
try {
// Try the class classloader.
// This may work in cases where the TCCL
// does not contain the code executed or JCL.
// This behaviour indicates that the application
// classloading strategy is not consistent with the
// Java 1.2 classloading guidelines but JCL can
// and so should handle this case.
c = Class.forName(logAdapterClassName);
} catch (ClassNotFoundException secondaryClassNotFoundException) {
// no point continuing: this adapter isn't available
msg = "" + secondaryClassNotFoundException.getMessage();
logDiagnostic(
"The log adapter '"
+ logAdapterClassName
+ "' is not available via the LogFactoryImpl class classloader: "
+ msg.trim());
break;
}
}
constructor = c.getConstructor(logConstructorSignature);
Object o = constructor.newInstance(params);
// Note that we do this test after trying to create an instance
// [rather than testing Log.class.isAssignableFrom(c)] so that
// we don't complain about Log hierarchy problems when the
// adapter couldn't be instantiated anyway.
if (o instanceof Log) {
logAdapterClass = c;
logAdapter = (Log) o;
break;
}
// Oops, we have a potential problem here. An adapter class
// has been found and its underlying lib is present too, but
// there are multiple Log interface classes available making it
// impossible to cast to the type the caller wanted. We
// certainly can't use this logger, but we need to know whether
// to keep on discovering or terminate now.
//
// The handleFlawedHierarchy method will throw
// LogConfigurationException if it regards this problem as
// fatal, and just return if not.
handleFlawedHierarchy(currentCL, c);
} catch (NoClassDefFoundError e) {
// We were able to load the adapter but it had references to
// other classes that could not be found. This simply means that
// the underlying logger library is not present in this or any
// ancestor classloader. There's no point in trying higher up
// in the hierarchy in this case..
String msg = "" + e.getMessage();
logDiagnostic(
"The log adapter '"
+ logAdapterClassName
+ "' is missing dependencies when loaded via classloader "
+ objectId(currentCL)
+ ": "
+ msg.trim());
break;
} catch (ExceptionInInitializerError e) {
// A static initializer block or the initializer code associated
// with a static variable on the log adapter class has thrown
// an exception.
//
// We treat this as meaning the adapter's underlying logging
// library could not be found.
String msg = "" + e.getMessage();
logDiagnostic(
"The log adapter '"
+ logAdapterClassName
+ "' is unable to initialize itself when loaded via classloader "
+ objectId(currentCL)
+ ": "
+ msg.trim());
break;
} catch(LogConfigurationException e) {
// call to handleFlawedHierarchy above must have thrown
// a LogConfigurationException, so just throw it on
throw e;
} catch(Throwable t) {
// handleFlawedDiscovery will determine whether this is a fatal
// problem or not. If it is fatal, then a LogConfigurationException
// will be thrown.
handleFlawedDiscovery(logAdapterClassName, currentCL, t);
}
if (currentCL == null) {
break;
}
// try the parent classloader
currentCL = currentCL.getParent();
}
if ((logAdapter != null) && affectState) {
// We've succeeded, so set instance fields
this.logClassName = logAdapterClassName;
this.logConstructor = constructor;
// Identify the setLogFactory method (if there is one)
try {
this.logMethod = logAdapterClass.getMethod("setLogFactory",
logMethodSignature);
logDiagnostic("Found method setLogFactory(LogFactory) in '"
+ logAdapterClassName + "'");
} catch (Throwable t) {
this.logMethod = null;
logDiagnostic(
"[INFO] '" + logAdapterClassName
+ "' from classloader " + objectId(currentCL)
+ " does not declare optional method "
+ "setLogFactory(LogFactory)");
}
logDiagnostic(
"Log adapter '" + logAdapterClassName
+ "' from classloader " + objectId(logAdapterClass.getClassLoader())
+ " has been selected for use.");
}
return logAdapter;
}
/**
* Return the classloader from which we should try to load the logging
* adapter classes.
* LogConfigurationException that wraps
* the passed Throwable.
*
* @param logAdapterClassName is the class name of the Log implementation
* that could not be instantiated. Cannot be null.
*
* @param classLoader is the classloader that we were trying to load the
* logAdapterClassName from when the exception occurred.
*
* @param discoveryFlaw is the Throwable created by the classloader
*
* @throws LogConfigurationException ALWAYS
*/
private void handleFlawedDiscovery(String logAdapterClassName,
ClassLoader classLoader,
Throwable discoveryFlaw) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Could not instantiate Log '"
+ logAdapterClassName + "' -- "
+ discoveryFlaw.getClass().getName() + ": "
+ discoveryFlaw.getLocalizedMessage());
}
if (!allowFlawedDiscovery) {
throw new LogConfigurationException(discoveryFlaw);
}
}
/**
* Report a problem loading the log adapter, then either return
* (if the situation is considered recoverable) or throw a
* LogConfigurationException.
*
*
*