logfactory.java

logging日志的相关包 logging日志的相关包

            }
        }


        // 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
     *
     * @exception LogConfigurationException if a suitable <code>Log</code>
     *  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 <code>Log</code> 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 <code>Log</code>
     *  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 <code>release()</code> 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));
        }
        synchronized (factories) {
            if (classLoader == null) {
                if (nullClassLoaderFactory != null) {
                    nullClassLoaderFactory.release();
                    nullClassLoaderFactory = null;
                }
            } else {
                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 <code>release()</code> 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.");
        }
        synchronized (factories) {
            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.
     * <p>
     * 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.
     * <p>
     * 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.
     * 
     * @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;
        }
    }

    /**
     * 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.
     */
    protected static ClassLoader getContextClassLoader()
        throws LogConfigurationException {

        return (ClassLoader)AccessController.doPrivileged(
            new PrivilegedAction() {
                public Object run() {
                    return directGetContextClassLoader();
                }
            });
    }

    /**
     * Return the thread context class loader if available; otherwise return 
     * null. 
     * <p>
     * Most/all code should call getContextClassLoader rather than calling
     * this method directly.
     * <p>
     * The thread context class loader is available for JDK 1.2
     * or later, if certain security conditions are met.
     * <p>
     * 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.
     * 
     * @exception LogConfigurationException if a suitable class loader
     * cannot be identified.
     * 
     * @exception 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?
            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