logfactory.java

logging日志的相关包 logging日志的相关包

             * 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 <code>LogFactory</code>.
     * Diagnostic information is also logged.
     * <p>
     * <strong>Usage:</strong> to diagnose whether a classloader conflict is the cause
     * of incompatibility. The test used is whether the class is assignable from
     * the <code>LogFactory</code> class loaded by the class's classloader.
     * @param logFactoryClass <code>Class</code> which may implement <code>LogFactory</code>
     * @return true if the <code>logFactoryClass</code> does extend
     * <code>LogFactory</code> when that class is loaded via the same
     * classloader that loaded the <code>logFactoryClass</code>.
     */
    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.
     * <p>
     * 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.
     * <p>
     * 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.
     * <p>
     * Null is returned if the URL cannot be opened.
     */
    private static Properties getProperties(final URL url) {
        PrivilegedAction action = 
            new PrivilegedAction() {
                public Object run() {
                    try {
                        InputStream stream = url.openStream();
                        if (stream != null) {
                            Properties props = new Properties();
                            props.load(stream);
                            stream.close();
                            return props;
                        }
                    } catch(IOException e) {
                        if (isDiagnosticsEnabled()) {
                            logDiagnostic("Unable to read URL " + url);
                        }
                    }

                    return null;
                }
            };
        return (Properties) AccessController.doPrivileged(action);
    }

    /**
     * Locate a user-provided configuration file.
     * <p>
     * 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.
     * <p> 
     * 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.
     * <p>
     * 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 '" + fileNam