org.apache.commons.logging.LogFactory Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.logging;
import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLConnection;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Properties;
/**
* Factory for creating {@link 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.
*
* @version $Id: LogFactory.java 1449064 2013-02-22 14:49:22Z tn $
*/
public abstract class LogFactory {
// Implementation note re AccessController usage
//
// It is important to keep code invoked via an AccessController to small
// auditable blocks. Such code must carefully evaluate all user input
// (parameters, system properties, config file contents, etc). As an
// example, a Log implementation should not write to its logfile
// with an AccessController anywhere in the call stack, otherwise an
// insecure application could configure the log implementation to write
// to a protected file using the privileges granted to JCL rather than
// to the calling application.
//
// Under no circumstance should a non-private method return data that is
// retrieved via an AccessController. That would allow an insecure app
// to invoke that method and obtain data that it is not permitted to have.
//
// Invoking user-supplied code with an AccessController set is not a major
// issue (eg invoking the constructor of the class specified by
// HASHTABLE_IMPLEMENTATION_PROPERTY). That class will be in a different
// trust domain, and therefore must have permissions to do whatever it
// is trying to do regardless of the permissions granted to JCL. There is
// a slight issue in that untrusted code may point that environment var
// to another trusted library, in which case the code runs if both that
// lib and JCL have the necessary permissions even when the untrusted
// caller does not. That's a pretty hard route to exploit though.
// ----------------------------------------------------- Manifest Constants
/**
* The name (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 String PRIORITY_KEY = "priority";
/**
* 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. By default, the TCCL is used.
*/
public static final String TCCL_KEY = "use_tccl";
/**
* The name (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 String FACTORY_PROPERTY = "org.apache.commons.logging.LogFactory";
/**
* The fully qualified class name of the fallback LogFactory
* implementation class to use, if no other can be found.
*/
public static final String FACTORY_DEFAULT = "org.apache.commons.logging.impl.LogFactoryImpl";
/**
* The name (commons-logging.properties) of the properties file to search for.
*/
public static final String FACTORY_PROPERTIES = "commons-logging.properties";
/**
* JDK1.3+
* 'Service Provider' specification.
*/
protected static final String SERVICE_ID =
"META-INF/services/org.apache.commons.logging.LogFactory";
/**
* 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.
*
* 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 DIAGNOSTICS_DEST_PROPERTY =
"org.apache.commons.logging.diagnostics.dest";
/**
* When null (the usual case), no diagnostic output will be
* generated by LogFactory or LogFactoryImpl. When non-null,
* interesting events will be written to the specified object.
*/
private static PrintStream diagnosticsStream = null;
/**
* 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.
*/
private static final String diagnosticPrefix;
/**
* 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.
*
* Note: LogFactory will print:
*
* [ERROR] LogFactory: Load of custom hashtable failed
*
* 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>
* 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 ;).
*/
public static final String HASHTABLE_IMPLEMENTATION_PROPERTY =
"org.apache.commons.logging.LogFactory.HashtableImpl";
/** Name used to load the weak hashtable implementation by names. */
private static final String WEAK_HASHTABLE_CLASSNAME =
"org.apache.commons.logging.impl.WeakHashtable";
/**
* A reference to the classloader that loaded this class. This is the
* same as LogFactory.class.getClassLoader(). However computing this
* value isn't quite as simple as that, as we potentially need to use
* AccessControllers etc. It's more efficient to compute it once and
* cache it here.
*/
private static final ClassLoader thisClassLoader;
// ----------------------------------------------------------- Constructors
/**
* Protected constructor that is not available for public use.
*/
protected LogFactory() {
}
// --------------------------------------------------------- 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 abstract Object getAttribute(String 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 abstract String[] getAttributeNames();
/**
* 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
* @throws LogConfigurationException if a suitable Log
* instance cannot be returned
*/
public abstract Log getInstance(Class clazz)
throws LogConfigurationException;
/**
* 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.
*
* @param 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)
* @throws LogConfigurationException if a suitable Log
* instance cannot be returned
*/
public abstract Log getInstance(String name)
throws LogConfigurationException;
/**
* Release any internal references to previously created {@link 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 release();
/**
* 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 abstract void removeAttribute(String name);
/**
* Set the configuration attribute with the specified name. Calling
* this with a null value is equivalent to calling
* removeAttribute(name).
*
* @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 abstract void setAttribute(String name, Object value);
// ------------------------------------------------------- Static Variables
/**
* The previously constructed LogFactory instances, keyed by
* the ClassLoader with which it was created.
*/
protected static Hashtable factories = null;
/**
* Previously constructed LogFactory instance as in the
* factories map, but for the case where
* getClassLoader returns null.
* This can happen when:
*
* - using JDK1.1 and the calling code is loaded via the system
* classloader (very common)
* - using JDK1.2+ and the calling code is loaded via the boot
* classloader (only likely for embedded systems work).
*
* Note that factories is a Hashtable (not a HashMap),
* and hashtables don't allow null as a key.
* @deprecated since 1.1.2
*/
protected static volatile LogFactory nullClassLoaderFactory = null;
/**
* Create the hashtable which will be used to store a map of
* (context-classloader -> logfactory-object). Version 1.2+ of Java
* supports "weak references", allowing a custom Hashtable class
* to be used which uses only weak references to its keys. Using weak
* references can fix memory leaks on webapp unload in some cases (though
* not all). Version 1.1 of Java does not support weak references, so we
* must dynamically determine which we are using. And just for fun, this
* code also supports the ability for a system property to specify an
* arbitrary Hashtable implementation name.
*
* 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 final Hashtable createFactoryStore() {
Hashtable result = null;
String storeImplementationClass;
try {
storeImplementationClass = getSystemProperty(HASHTABLE_IMPLEMENTATION_PROPERTY, null);
} catch (SecurityException ex) {
// Permissions don't allow this to be accessed. Default to the "modern"
// weak hashtable implementation if it is available.
storeImplementationClass = null;
}
if (storeImplementationClass == null) {
storeImplementationClass = WEAK_HASHTABLE_CLASSNAME;
}
try {
Class implementationClass = Class.forName(storeImplementationClass);
result = (Hashtable) implementationClass.newInstance();
} catch (Throwable t) {
handleThrowable(t); // may re-throw t
// ignore
if (!WEAK_HASHTABLE_CLASSNAME.equals(storeImplementationClass)) {
// if the user's trying to set up a custom implementation, give a clue
if (isDiagnosticsEnabled()) {
// use internal logging to issue the warning
logDiagnostic("[ERROR] LogFactory: Load of custom hashtable failed");
} else {
// we *really* want this output, even if diagnostics weren't
// explicitly enabled by the user.
System.err.println("[ERROR] LogFactory: Load of custom hashtable failed");
}
}
}
if (result == null) {
result = new Hashtable();
}
return result;
}
// --------------------------------------------------------- Static Methods
/** Utility method to safely trim a string. */
private static String trim(String src) {
if (src == null) {
return null;
}
return src.trim();
}
/**
* Checks whether the supplied Throwable is one that needs to be
* re-thrown and ignores all others.
*
* The following errors are re-thrown:
*
* - ThreadDeath
* - VirtualMachineError
*
*
* @param t the Throwable to check
*/
protected static void handleThrowable(Throwable t) {
if (t instanceof ThreadDeath) {
throw (ThreadDeath) t;
}
if (t instanceof VirtualMachineError) {
throw (VirtualMachineError) t;
}
// All other instances of Throwable will be silently ignored
}
/**
* 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.
*
*
* - The
org.apache.commons.logging.LogFactory system
* property.
* - The JDK 1.3 Service Discovery mechanism
* - Use the properties file
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.
* - Fall back to a default implementation class
* (
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.
*
* @throws LogConfigurationException if the implementation class is not
* available or cannot be instantiated.
*/
public static LogFactory getFactory() throws LogConfigurationException {
// Identify the class loader we will be using
ClassLoader contextClassLoader = getContextClassLoaderInternal();
if (contextClassLoader == null) {
// This is an odd enough situation to report about. This
// output will be a nuisance on JDK1.1, as the system
// classloader is null in that environment.
if (isDiagnosticsEnabled()) {
logDiagnostic("Context classloader is null.");
}
}
// Return any previously registered factory for this class loader
LogFactory factory = getCachedFactory(contextClassLoader);
if (factory != null) {
return factory;
}
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] LogFactory implementation requested for the first time for context classloader " +
objectId(contextClassLoader));
logHierarchy("[LOOKUP] ", contextClassLoader);
}
// Load properties file.
//
// If the properties file exists, then its contents are used as
// "attributes" on the LogFactory implementation class. One particular
// property may also control which LogFactory concrete subclass is
// used, but only if other discovery mechanisms fail..
//
// As the properties file (if it exists) will be used one way or
// another in the end we may as well look for it first.
Properties props = getConfigurationFile(contextClassLoader, FACTORY_PROPERTIES);
// Determine whether we will be using the thread context class loader to
// load logging classes or not by checking the loaded properties file (if any).
ClassLoader baseClassLoader = contextClassLoader;
if (props != null) {
String useTCCLStr = props.getProperty(TCCL_KEY);
if (useTCCLStr != null) {
// The Boolean.valueOf(useTCCLStr).booleanValue() formulation
// is required for Java 1.2 compatibility.
if (Boolean.valueOf(useTCCLStr).booleanValue() == false) {
// Don't use current context classloader when locating any
// LogFactory or Log classes, just use the class that loaded
// this abstract class. When this class is deployed in a shared
// classpath of a container, it means webapps cannot deploy their
// own logging implementations. It also means that it is up to the
// implementation whether to load library-specific config files
// from the TCCL or not.
baseClassLoader = thisClassLoader;
}
}
}
// Determine which concrete LogFactory subclass to use.
// First, try a global system property
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Looking for system property [" + FACTORY_PROPERTY +
"] to define the LogFactory subclass to use...");
}
try {
String factoryClass = getSystemProperty(FACTORY_PROPERTY, null);
if (factoryClass != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Creating an instance of LogFactory class '" + factoryClass +
"' as specified by system property " + FACTORY_PROPERTY);
}
factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
} else {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] No system property [" + FACTORY_PROPERTY + "] defined.");
}
}
} catch (SecurityException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] A security exception occurred while trying to create an" +
" instance of the custom factory class" + ": [" + trim(e.getMessage()) +
"]. Trying alternative implementations...");
}
// ignore
} catch (RuntimeException e) {
// This is not consistent with the behaviour when a bad LogFactory class is
// specified in a services file.
//
// One possible exception that can occur here is a ClassCastException when
// the specified class wasn't castable to this LogFactory type.
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] An exception occurred while trying to create an" +
" instance of the custom factory class" + ": [" +
trim(e.getMessage()) +
"] as specified by a system property.");
}
throw e;
}
// Second, try to find a service by using the JDK1.3 class
// discovery mechanism, which involves putting a file with the name
// of an interface class in the META-INF/services directory, where the
// contents of the file is a single line specifying a concrete class
// that implements the desired interface.
if (factory == null) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Looking for a resource file of name [" + SERVICE_ID +
"] to define the LogFactory subclass to use...");
}
try {
final InputStream is = getResourceAsStream(contextClassLoader, SERVICE_ID);
if( is != null ) {
// This code is needed by EBCDIC and other strange systems.
// It's a fix for bugs reported in xerces
BufferedReader rd;
try {
rd = new BufferedReader(new InputStreamReader(is, "UTF-8"));
} catch (java.io.UnsupportedEncodingException e) {
rd = new BufferedReader(new InputStreamReader(is));
}
String factoryClassName = rd.readLine();
rd.close();
if (factoryClassName != null && ! "".equals(factoryClassName)) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Creating an instance of LogFactory class " +
factoryClassName +
" as specified by file '" + SERVICE_ID +
"' which was present in the path of the context classloader.");
}
factory = newFactory(factoryClassName, baseClassLoader, contextClassLoader );
}
} else {
// is == null
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] No resource file with name '" + SERVICE_ID + "' found.");
}
}
} catch (Exception ex) {
// note: if the specified LogFactory class wasn't compatible with LogFactory
// for some reason, a ClassCastException will be caught here, and attempts will
// continue to find a compatible class.
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] A security exception occurred while trying to create an" +
" instance of the custom factory class" +
": [" + trim(ex.getMessage()) +
"]. Trying alternative implementations...");
}
// ignore
}
}
// Third try looking into the properties file read earlier (if found)
if (factory == null) {
if (props != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] Looking in properties file for entry with key '" + FACTORY_PROPERTY +
"' to define the LogFactory subclass to use...");
}
String factoryClass = props.getProperty(FACTORY_PROPERTY);
if (factoryClass != null) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] Properties file specifies LogFactory subclass '" + factoryClass + "'");
}
factory = newFactory(factoryClass, baseClassLoader, contextClassLoader);
// TODO: think about whether we need to handle exceptions from newFactory
} else {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Properties file has no entry specifying LogFactory subclass.");
}
}
} else {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] No properties file available to determine" + " LogFactory subclass from..");
}
}
}
// Fourth, try the fallback implementation class
if (factory == null) {
if (isDiagnosticsEnabled()) {
logDiagnostic(
"[LOOKUP] Loading the default LogFactory implementation '" + FACTORY_DEFAULT +
"' via the same classloader that loaded this LogFactory" +
" class (ie not looking in the context classloader).");
}
// Note: unlike the above code which can try to load custom LogFactory
// implementations via the TCCL, we don't try to load the default LogFactory
// implementation via the context classloader because:
// * that can cause problems (see comments in newFactory method)
// * no-one should be customising the code of the default class
// Yes, we do give up the ability for the child to ship a newer
// version of the LogFactoryImpl class and have it used dynamically
// by an old LogFactory class in the parent, but that isn't
// necessarily a good idea anyway.
factory = newFactory(FACTORY_DEFAULT, thisClassLoader, contextClassLoader);
}
if (factory != null) {
/**
* Always cache using context class loader.
*/
cacheFactory(contextClassLoader, factory);
if (props != null) {
Enumeration names = props.propertyNames();
while (names.hasMoreElements()) {
String name = (String) names.nextElement();
String value = props.getProperty(name);
factory.setAttribute(name, value);
}
}
}
return factory;
}
/**
* Convenience method to return a named logger, without the application
* having to care about factories.
*
* @param clazz Class from which a log name will be derived
* @throws LogConfigurationException if a suitable Log
* instance cannot be returned
*/
public static Log getLog(Class clazz) throws LogConfigurationException {
return getFactory().getInstance(clazz);
}
/**
* Convenience method to return a named logger, without the application
* having to care about factories.
*
* @param 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)
* @throws LogConfigurationException if a suitable Log
* instance cannot be returned
*/
public static Log getLog(String name) throws LogConfigurationException {
return getFactory().getInstance(name);
}
/**
* Release any internal references to previously created {@link LogFactory}
* instances that have been associated with the specified class loader
* (if any), after calling the instance method release() on
* each of them.
*
* @param classLoader ClassLoader for which to release the LogFactory
*/
public static void release(ClassLoader classLoader) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Releasing factory for classloader " + objectId(classLoader));
}
// factories is not final and could be replaced in this block.
final Hashtable factories = LogFactory.factories;
synchronized (factories) {
if (classLoader == null) {
if (nullClassLoaderFactory != null) {
nullClassLoaderFactory.release();
nullClassLoaderFactory = null;
}
} else {
final LogFactory factory = (LogFactory) factories.get(classLoader);
if (factory != null) {
factory.release();
factories.remove(classLoader);
}
}
}
}
/**
* Release any internal references to previously created {@link 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.
*/
public static void releaseAll() {
if (isDiagnosticsEnabled()) {
logDiagnostic("Releasing factory for all classloaders.");
}
// factories is not final and could be replaced in this block.
final Hashtable factories = LogFactory.factories;
synchronized (factories) {
final Enumeration elements = factories.elements();
while (elements.hasMoreElements()) {
LogFactory element = (LogFactory) elements.nextElement();
element.release();
}
factories.clear();
if (nullClassLoaderFactory != null) {
nullClassLoaderFactory.release();
nullClassLoaderFactory = null;
}
}
}
// ------------------------------------------------------ Protected Methods
/**
* Safely get access to the classloader for the specified class.
*
* 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.
*
* @since 1.1
*/
protected static ClassLoader getClassLoader(Class clazz) {
try {
return clazz.getClassLoader();
} catch (SecurityException ex) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Unable to get classloader for class '" + clazz +
"' due to security restrictions - " + ex.getMessage());
}
throw ex;
}
}
/**
* Returns the current context classloader.
*
* 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.
*
* @return 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.
* @throws SecurityException if the current java security policy doesn't
* allow this class to access the context classloader.
*/
protected static ClassLoader getContextClassLoader() throws LogConfigurationException {
return directGetContextClassLoader();
}
/**
* 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.
*
* @return 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.
* @throws SecurityException if the current java security policy doesn't
* allow this class to access the context classloader.
*/
private static ClassLoader getContextClassLoaderInternal() throws LogConfigurationException {
return (ClassLoader)AccessController.doPrivileged(
new PrivilegedAction() {
public Object run() {
return directGetContextClassLoader();
}
});
}
/**
* Return the thread context class loader if available; otherwise return null.
*
* 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.
*
* @throws LogConfigurationException if a suitable class loader
* cannot be identified.
* @throws SecurityException if the java security policy forbids
* access to the context classloader from one of the classes in the
* current call stack.
* @since 1.1
*/
protected static ClassLoader directGetContextClassLoader() throws LogConfigurationException {
ClassLoader classLoader = null;
try {
// Are we running on a JDK 1.2 or later system?
final Method method = Thread.class.getMethod("getContextClassLoader", (Class[]) null);
// Get the thread context class loader (if there is one)
try {
classLoader = (ClassLoader)method.invoke(Thread.currentThread(), (Object[]) null);
} catch (IllegalAccessException e) {
throw new LogConfigurationException
("Unexpected IllegalAccessException", e);
} catch (InvocationTargetException e) {
/**
* InvocationTargetException is thrown by 'invoke' when
* the method being invoked (getContextClassLoader) throws
* an exception.
*
* getContextClassLoader() throws SecurityException when
* the context class loader isn't an ancestor of the
* calling class's class loader, or if security
* permissions are restricted.
*
* In the first case (not related), we want to ignore and
* keep going. We cannot help but also ignore the second
* with the logic below, but other calls elsewhere (to
* obtain a class loader) will trigger this exception where
* we can make a distinction.
*/
if (e.getTargetException() instanceof SecurityException) {
// ignore
} else {
// Capture 'e.getTargetException()' exception for details
// alternate: log 'e.getTargetException()', and pass back 'e'.
throw new LogConfigurationException("Unexpected InvocationTargetException", e.getTargetException());
}
}
} catch (NoSuchMethodException e) {
// Assume we are running on JDK 1.1
classLoader = getClassLoader(LogFactory.class);
// We deliberately don't log a message here to outputStream;
// this message would be output for every call to LogFactory.getLog()
// when running on JDK1.1
//
// if (outputStream != null) {
// outputStream.println(
// "Method Thread.getContextClassLoader does not exist;"
// + " assuming this is JDK 1.1, and that the context"
// + " classloader is the same as the class that loaded"
// + " the concrete LogFactory class.");
// }
}
// Return the selected class loader
return classLoader;
}
/**
* Check cached factories (keyed by contextClassLoader)
*
* @param 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.
*
* @return the factory associated with the specified classloader if
* one has previously been created, or null if this is the first time
* we have seen this particular classloader.
*/
private static LogFactory getCachedFactory(ClassLoader contextClassLoader) {
if (contextClassLoader == null) {
// We have to handle this specially, as factories is a Hashtable
// and those don't accept null as a key value.
//
// nb: nullClassLoaderFactory might be null. That's ok.
return nullClassLoaderFactory;
} else {
return (LogFactory) factories.get(contextClassLoader);
}
}
/**
* Remember this factory, so later calls to LogFactory.getCachedFactory
* can return the previously created object (together with all its
* cached Log objects).
*
* @param classLoader should be the current context classloader. Note that
* this can be null under some circumstances; this is ok.
* @param factory should be the factory to cache. This should never be null.
*/
private static void cacheFactory(ClassLoader classLoader, LogFactory factory) {
// Ideally we would assert(factory != null) here. However reporting
// errors from within a logging implementation is a little tricky!
if (factory != null) {
if (classLoader == null) {
nullClassLoaderFactory = factory;
} else {
factories.put(classLoader, factory);
}
}
}
/**
* Return a new instance of the specified LogFactory
* implementation class, loaded by the specified class loader.
* If that fails, try the class loader used to load this
* (abstract) LogFactory.
*
*
ClassLoader conflicts
* 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.
*
* @param factoryClass Fully qualified name of the LogFactory
* implementation class
* @param classLoader ClassLoader from which to load this class
* @param contextClassLoader is the context that this new factory will
* manage logging for.
* @throws LogConfigurationException if a suitable instance
* cannot be created
* @since 1.1
*/
protected static LogFactory newFactory(final String factoryClass,
final ClassLoader classLoader,
final ClassLoader contextClassLoader)
throws LogConfigurationException {
// Note that any unchecked exceptions thrown by the createFactory
// method will propagate out of this method; in particular a
// ClassCastException can be thrown.
Object result = AccessController.doPrivileged(
new PrivilegedAction() {
public Object run() {
return createFactory(factoryClass, classLoader);
}
});
if (result instanceof LogConfigurationException) {
LogConfigurationException ex = (LogConfigurationException) result;
if (isDiagnosticsEnabled()) {
logDiagnostic("An error occurred while loading the factory class:" + ex.getMessage());
}
throw ex;
}
if (isDiagnosticsEnabled()) {
logDiagnostic("Created object " + objectId(result) + " to manage classloader " +
objectId(contextClassLoader));
}
return (LogFactory)result;
}
/**
* Method provided for backwards compatibility; see newFactory version that
* takes 3 parameters.
*
* 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(final String factoryClass,
final ClassLoader classLoader) {
return newFactory(factoryClass, classLoader, null);
}
/**
* Implements the operations described in the javadoc for newFactory.
*
* @param factoryClass
* @param 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.
* @return either a LogFactory object or a LogConfigurationException object.
* @since 1.1
*/
protected static Object createFactory(String factoryClass, ClassLoader classLoader) {
// This will be used to diagnose bad configurations
// and allow a useful message to be sent to the user
Class logFactoryClass = null;
try {
if (classLoader != null) {
try {
// First the given class loader param (thread class loader)
// Warning: must typecast here & allow exception
// to be generated/caught & recast properly.
logFactoryClass = classLoader.loadClass(factoryClass);
if (LogFactory.class.isAssignableFrom(logFactoryClass)) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Loaded class " + logFactoryClass.getName() +
" from classloader " + objectId(classLoader));
}
} else {
//
// This indicates a problem with the ClassLoader tree.
// An incompatible ClassLoader was used to load the
// implementation.
// As the same classes
// must be available in multiple class loaders,
// it is very likely that multiple JCL jars are present.
// The most likely fix for this
// problem is to remove the extra JCL jars from the
// ClassLoader hierarchy.
//
if (isDiagnosticsEnabled()) {
logDiagnostic("Factory class " + logFactoryClass.getName() +
" loaded from classloader " + objectId(logFactoryClass.getClassLoader()) +
" does not extend '" + LogFactory.class.getName() +
"' as loaded by this classloader.");
logHierarchy("[BAD CL TREE] ", classLoader);
}
}
return (LogFactory) logFactoryClass.newInstance();
} catch (ClassNotFoundException ex) {
if (classLoader == thisClassLoader) {
// Nothing more to try, onwards.
if (isDiagnosticsEnabled()) {
logDiagnostic("Unable to locate any class called '" + factoryClass +
"' via classloader " + objectId(classLoader));
}
throw ex;
}
// ignore exception, continue
} catch (NoClassDefFoundError e) {
if (classLoader == thisClassLoader) {
// Nothing more to try, onwards.
if (isDiagnosticsEnabled()) {
logDiagnostic("Class '" + factoryClass + "' cannot be loaded" +
" via classloader " + objectId(classLoader) +
" - it depends on some other class that cannot be found.");
}
throw e;
}
// ignore exception, continue
} catch (ClassCastException e) {
if (classLoader == thisClassLoader) {
// There's no point in falling through to the code below that
// tries again with thisClassLoader, because we've just tried
// loading with that loader (not the TCCL). Just throw an
// appropriate exception here.
final boolean implementsLogFactory = implementsLogFactory(logFactoryClass);
//
// Construct a good message: users may not actual expect that a custom implementation
// has been specified. Several well known containers use this mechanism to adapt JCL
// to their native logging system.
//
final StringBuffer msg = new StringBuffer();
msg.append("The application has specified that a custom LogFactory implementation ");
msg.append("should be used but Class '");
msg.append(factoryClass);
msg.append("' cannot be converted to '");
msg.append(LogFactory.class.getName());
msg.append("'. ");
if (implementsLogFactory) {
msg.append("The conflict is caused by the presence of multiple LogFactory classes ");
msg.append("in incompatible classloaders. ");
msg.append("Background can be found in http://commons.apache.org/logging/tech.html. ");
msg.append("If you have not explicitly specified a custom LogFactory then it is likely ");
msg.append("that the container has set one without your knowledge. ");
msg.append("In this case, consider using the commons-logging-adapters.jar file or ");
msg.append("specifying the standard LogFactory from the command line. ");
} else {
msg.append("Please check the custom implementation. ");
}
msg.append("Help can be found @http://commons.apache.org/logging/troubleshooting.html.");
if (isDiagnosticsEnabled()) {
logDiagnostic(msg.toString());
}
throw new ClassCastException(msg.toString());
}
// Ignore exception, continue. Presumably the classloader was the
// TCCL; the code below will try to load the class via thisClassLoader.
// This will handle the case where the original calling class is in
// a shared classpath but the TCCL has a copy of LogFactory and the
// specified LogFactory implementation; we will fall back to using the
// LogFactory implementation from the same classloader as this class.
//
// Issue: this doesn't handle the reverse case, where this LogFactory
// is in the webapp, and the specified LogFactory implementation is
// in a shared classpath. In that case:
// (a) the class really does implement LogFactory (bad log msg above)
// (b) the fallback code will result in exactly the same problem.
}
}
/* At this point, either classLoader == null, OR
* classLoader was unable to load factoryClass.
*
* In either case, we call Class.forName, which is equivalent
* to LogFactory.class.getClassLoader().load(name), ie we ignore
* the classloader parameter the caller passed, and fall back
* to trying the classloader associated with this class. See the
* javadoc for the newFactory method for more info on the
* consequences of this.
*
* Notes:
* * LogFactory.class.getClassLoader() may return 'null'
* if LogFactory is loaded by the bootstrap classloader.
*/
// Warning: must typecast here & allow exception
// to be generated/caught & recast properly.
if (isDiagnosticsEnabled()) {
logDiagnostic("Unable to load factory class via classloader " + objectId(classLoader) +
" - trying the classloader associated with this LogFactory.");
}
logFactoryClass = Class.forName(factoryClass);
return (LogFactory) logFactoryClass.newInstance();
} catch (Exception e) {
// Check to see if we've got a bad configuration
if (isDiagnosticsEnabled()) {
logDiagnostic("Unable to create LogFactory instance.");
}
if (logFactoryClass != null && !LogFactory.class.isAssignableFrom(logFactoryClass)) {
return new LogConfigurationException(
"The chosen LogFactory implementation does not extend LogFactory." +
" Please check your configuration.", e);
}
return new LogConfigurationException(e);
}
}
/**
* Determines whether the given class actually implements 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.
* @param logFactoryClass Class which may implement LogFactory
* @return true if the logFactoryClass does extend
* LogFactory when that class is loaded via the same
* classloader that loaded the logFactoryClass.
*/
private static boolean implementsLogFactory(Class logFactoryClass) {
boolean implementsLogFactory = false;
if (logFactoryClass != null) {
try {
ClassLoader logFactoryClassLoader = logFactoryClass.getClassLoader();
if (logFactoryClassLoader == null) {
logDiagnostic("[CUSTOM LOG FACTORY] was loaded by the boot classloader");
} else {
logHierarchy("[CUSTOM LOG FACTORY] ", logFactoryClassLoader);
Class factoryFromCustomLoader
= Class.forName("org.apache.commons.logging.LogFactory", false, logFactoryClassLoader);
implementsLogFactory = factoryFromCustomLoader.isAssignableFrom(logFactoryClass);
if (implementsLogFactory) {
logDiagnostic("[CUSTOM LOG FACTORY] " + logFactoryClass.getName() +
" implements LogFactory but was loaded by an incompatible classloader.");
} else {
logDiagnostic("[CUSTOM LOG FACTORY] " + logFactoryClass.getName() +
" does not implement LogFactory.");
}
}
} catch (SecurityException e) {
//
// The application is running within a hostile security environment.
// This will make it very hard to diagnose issues with JCL.
// Consider running less securely whilst debugging this issue.
//
logDiagnostic("[CUSTOM LOG FACTORY] SecurityException thrown whilst trying to determine whether " +
"the compatibility was caused by a classloader conflict: " + e.getMessage());
} catch (LinkageError e) {
//
// This should be an unusual circumstance.
// LinkageError's usually indicate that a dependent class has incompatibly changed.
// Another possibility may be an exception thrown by an initializer.
// Time for a clean rebuild?
//
logDiagnostic("[CUSTOM LOG FACTORY] LinkageError thrown whilst trying to determine whether " +
"the compatibility was caused by a classloader conflict: " + e.getMessage());
} catch (ClassNotFoundException e) {
//
// LogFactory cannot be loaded by the classloader which loaded the custom factory implementation.
// The custom implementation is not viable until this is corrected.
// Ensure that the JCL jar and the custom class are available from the same classloader.
// Running with diagnostics on should give information about the classloaders used
// to load the custom factory.
//
logDiagnostic("[CUSTOM LOG FACTORY] LogFactory class cannot be loaded by classloader which loaded " +
"the custom LogFactory implementation. Is the custom factory in the right classloader?");
}
}
return implementsLogFactory;
}
/**
* 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. In this case, we need to
* run the operation using an AccessController.
*/
private static InputStream getResourceAsStream(final ClassLoader loader, final String name) {
return (InputStream)AccessController.doPrivileged(
new PrivilegedAction() {
public Object run() {
if (loader != null) {
return loader.getResourceAsStream(name);
} else {
return ClassLoader.getSystemResourceAsStream(name);
}
}
});
}
/**
* Given a filename, return an enumeration of URLs pointing to
* all the occurrences of that filename in the classpath.
*
* 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 Enumeration getResources(final ClassLoader loader, final String name) {
PrivilegedAction action =
new PrivilegedAction() {
public Object run() {
try {
if (loader != null) {
return loader.getResources(name);
} else {
return ClassLoader.getSystemResources(name);
}
} catch (IOException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Exception while trying to find configuration file " +
name + ":" + e.getMessage());
}
return null;
} catch (NoSuchMethodError e) {
// we must be running on a 1.1 JVM which doesn't support
// ClassLoader.getSystemResources; just return null in
// this case.
return null;
}
}
};
Object result = AccessController.doPrivileged(action);
return (Enumeration) result;
}
/**
* Given a URL that refers to a .properties file, load that file.
* This 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.
*
* {@code Null} is returned if the URL cannot be opened.
*/
private static Properties getProperties(final URL url) {
PrivilegedAction action =
new PrivilegedAction() {
public Object run() {
InputStream stream = null;
try {
// We must ensure that useCaches is set to false, as the
// default behaviour of java is to cache file handles, and
// this "locks" files, preventing hot-redeploy on windows.
URLConnection connection = url.openConnection();
connection.setUseCaches(false);
stream = connection.getInputStream();
if (stream != null) {
Properties props = new Properties();
props.load(stream);
stream.close();
stream = null;
return props;
}
} catch (IOException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("Unable to read URL " + url);
}
} finally {
if (stream != null) {
try {
stream.close();
} catch (IOException e) {
// ignore exception; this should not happen
if (isDiagnosticsEnabled()) {
logDiagnostic("Unable to close stream for URL " + url);
}
}
}
}
return null;
}
};
return (Properties) AccessController.doPrivileged(action);
}
/**
* Locate a user-provided configuration file.
*
* 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 final Properties getConfigurationFile(ClassLoader classLoader, String fileName) {
Properties props = null;
double priority = 0.0;
URL propsUrl = null;
try {
Enumeration urls = getResources(classLoader, fileName);
if (urls == null) {
return null;
}
while (urls.hasMoreElements()) {
URL url = (URL) urls.nextElement();
Properties newProps = getProperties(url);
if (newProps != null) {
if (props == null) {
propsUrl = url;
props = newProps;
String priorityStr = props.getProperty(PRIORITY_KEY);
priority = 0.0;
if (priorityStr != null) {
priority = Double.parseDouble(priorityStr);
}
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Properties file found at '" + url + "'" +
" with priority " + priority);
}
} else {
String newPriorityStr = newProps.getProperty(PRIORITY_KEY);
double newPriority = 0.0;
if (newPriorityStr != null) {
newPriority = Double.parseDouble(newPriorityStr);
}
if (newPriority > priority) {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Properties file at '" + url + "'" +
" with priority " + newPriority +
" overrides file at '" + propsUrl + "'" +
" with priority " + priority);
}
propsUrl = url;
props = newProps;
priority = newPriority;
} else {
if (isDiagnosticsEnabled()) {
logDiagnostic("[LOOKUP] Properties file at '" + url + "'" +
" with priority " + newPriority +
" does not override file at '" + propsUrl + "'" +
" with priority " + priority);
}
}
}
}
}
} catch (SecurityException e) {
if (isDiagnosticsEnabled()) {
logDiagnostic("SecurityException thrown while trying to find/read config files.");
}
}
if (isDiagnosticsEnabled()) {
if (props == null) {
logDiagnostic("[LOOKUP] No properties file of name '" + fileName + "' found.");
} else {
logDiagnostic("[LOOKUP] Properties file of name '" + fileName + "' found at '" + propsUrl + '"');
}
}
return props;
}
/**
* 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.
*/
private static String getSystemProperty(final String key, final String def)
throws SecurityException {
return (String) AccessController.doPrivileged(
new PrivilegedAction() {
public Object run() {
return System.getProperty(key, def);
}
});
}
/**
* Determines whether the user wants internal diagnostic output. If so,
* returns an appropriate writer object. Users can enable diagnostic
* output by setting the system property named {@link #DIAGNOSTICS_DEST_PROPERTY} to
* a filename, or the special values STDOUT or STDERR.
*/
private static PrintStream initDiagnostics() {
String dest;
try {
dest = getSystemProperty(DIAGNOSTICS_DEST_PROPERTY, null);
if (dest == null) {
return null;
}
} catch (SecurityException ex) {
// We must be running in some very secure environment.
// We just have to assume output is not wanted..
return null;
}
if (dest.equals("STDOUT")) {
return System.out;
} else if (dest.equals("STDERR")) {
return System.err;
} else {
try {
// open the file in append mode
FileOutputStream fos = new FileOutputStream(dest, true);
return new PrintStream(fos);
} catch (IOException ex) {
// We should report this to the user - but how?
return null;
}
}
}
/**
* Indicates true if the user has enabled internal logging.
*
* By the way, sorry for the incorrect grammar, but calling this method
* areDiagnosticsEnabled just isn't java beans style.
*
* @return true if calls to logDiagnostic will have any effect.
* @since 1.1
*/
protected static boolean isDiagnosticsEnabled() {
return diagnosticsStream != null;
}
/**
* Write the specified message to the internal logging destination.
*
* 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).
*
* @param msg is the diagnostic message to be output.
*/
private static final void logDiagnostic(String msg) {
if (diagnosticsStream != null) {
diagnosticsStream.print(diagnosticPrefix);
diagnosticsStream.println(msg);
diagnosticsStream.flush();
}
}
/**
* Write the specified message to the internal logging destination.
*
* @param msg is the diagnostic message to be output.
* @since 1.1
*/
protected static final void logRawDiagnostic(String msg) {
if (diagnosticsStream != null) {
diagnosticsStream.println(msg);
diagnosticsStream.flush();
}
}
/**
* Generate useful diagnostics regarding the classloader tree for
* the specified class.
*
* 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.
*
* @param clazz is the class whose classloader + tree are to be
* output.
*/
private static void logClassLoaderEnvironment(Class clazz) {
if (!isDiagnosticsEnabled()) {
return;
}
try {
// Deliberately use System.getProperty here instead of getSystemProperty; if
// the overall security policy for the calling application forbids access to
// these variables then we do not want to output them to the diagnostic stream.
logDiagnostic("[ENV] Extension directories (java.ext.dir): " + System.getProperty("java.ext.dir"));
logDiagnostic("[ENV] Application classpath (java.class.path): " + System.getProperty("java.class.path"));
} catch (SecurityException ex) {
logDiagnostic("[ENV] Security setting prevent interrogation of system classpaths.");
}
String className = clazz.getName();
ClassLoader classLoader;
try {
classLoader = getClassLoader(clazz);
} catch (SecurityException ex) {
// not much useful diagnostics we can print here!
logDiagnostic("[ENV] Security forbids determining the classloader for " + className);
return;
}
logDiagnostic("[ENV] Class " + className + " was loaded via classloader " + objectId(classLoader));
logHierarchy("[ENV] Ancestry of classloader which loaded " + className + " is ", classLoader);
}
/**
* Logs diagnostic messages about the given classloader
* and it's hierarchy. The prefix is prepended to the message
* and is intended to make it easier to understand the logs.
* @param prefix
* @param classLoader
*/
private static void logHierarchy(String prefix, ClassLoader classLoader) {
if (!isDiagnosticsEnabled()) {
return;
}
ClassLoader systemClassLoader;
if (classLoader != null) {
final String classLoaderString = classLoader.toString();
logDiagnostic(prefix + objectId(classLoader) + " == '" + classLoaderString + "'");
}
try {
systemClassLoader = ClassLoader.getSystemClassLoader();
} catch (SecurityException ex) {
logDiagnostic(prefix + "Security forbids determining the system classloader.");
return;
}
if (classLoader != null) {
final StringBuffer buf = new StringBuffer(prefix + "ClassLoader tree:");
for(;;) {
buf.append(objectId(classLoader));
if (classLoader == systemClassLoader) {
buf.append(" (SYSTEM) ");
}
try {
classLoader = classLoader.getParent();
} catch (SecurityException ex) {
buf.append(" --> SECRET");
break;
}
buf.append(" --> ");
if (classLoader == null) {
buf.append("BOOT");
break;
}
}
logDiagnostic(buf.toString());
}
}
/**
* Returns a string that uniquely identifies the specified object, including
* its class.
*
* 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.
*
* @param o may be null.
* @return a string of form classname@hashcode, or "null" if param o is null.
* @since 1.1
*/
public static String objectId(Object o) {
if (o == null) {
return "null";
} else {
return o.getClass().getName() + "@" + System.identityHashCode(o);
}
}
// ----------------------------------------------------------------------
// Static initialiser block to perform initialisation at class load time.
//
// We can't do this in the class constructor, as there are many
// static methods on this class that can be called before any
// LogFactory instances are created, and they depend upon this
// stuff having been set up.
//
// Note that this block must come after any variable declarations used
// by any methods called from this block, as we want any static initialiser
// associated with the variable to run first. If static initialisers for
// variables run after this code, then (a) their value might be needed
// by methods called from here, and (b) they might *override* any value
// computed here!
//
// So the wisest thing to do is just to place this code at the very end
// of the class file.
// ----------------------------------------------------------------------
static {
// note: it's safe to call methods before initDiagnostics (though
// diagnostic output gets discarded).
thisClassLoader = getClassLoader(LogFactory.class);
// In order to avoid confusion where multiple instances of JCL are
// being used via different classloaders within the same app, we
// ensure each logged message has a prefix of form
// [LogFactory from classloader OID]
//
// Note that this prefix should be kept consistent with that
// in LogFactoryImpl. However here we don't need to output info
// about the actual *instance* of LogFactory, as all methods that
// output diagnostics from this class are static.
String classLoaderName;
try {
ClassLoader classLoader = thisClassLoader;
if (thisClassLoader == null) {
classLoaderName = "BOOTLOADER";
} else {
classLoaderName = objectId(classLoader);
}
} catch (SecurityException e) {
classLoaderName = "UNKNOWN";
}
diagnosticPrefix = "[LogFactory from " + classLoaderName + "] ";
diagnosticsStream = initDiagnostics();
logClassLoaderEnvironment(LogFactory.class);
factories = createFactoryStore();
if (isDiagnosticsEnabled()) {
logDiagnostic("BOOTSTRAP COMPLETED");
}
}
}