logfactoryimpl.java

comming logging 的源码 可以封装log4j等日志系统。 源码中使用了很多的设计模式

     * 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
     * <pre>
     * LogFactory.getFactory().setAttribute(...)
     * </pre>
     * This must be done before the first Log object is created; configuration
     * changes after that point will be ignored.
     * <p>
     * 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 <code>null</code>
     *  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.
     * <p>
     * This string will later be prefixed to each "internal logging" message
     * emitted, so that users can clearly see any unexpected behaviour.
     * <p>
     * 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;
    }


    /**
     * <p>Return the <code>Constructor</code> that can be called to instantiate
     * new {@link org.apache.commons.logging.Log} instances.</p>
     *
     * <p><strong>IMPLEMENTATION NOTE</strong> - Race conditions caused by
     * calling this method from more than one thread are ignored, because
     * the same <code>Constructor</code> instance will ultimately be derived
     * in all circumstances.</p>
     *
     * @exception LogConfigurationException if a suitable constructor
     *  cannot be returned   
     * 
     * @deprecated  Never invoked by this class; subclasses should not assume
     *              it will be.
     */
    protected Constructor getLogConstructor()
        throws LogConfigurationException {

        // Return the previously identified Constructor (if any)
        if (logConstructor == null) {
            discoverLogImplementation(getClass().getName());
        }

        return logConstructor;
    }
    

    /**
     * Is <em>JDK 1.3 with Lumberjack</em> logging available?   
     * 
     * @deprecated  Never invoked by this class; subclasses should not assume
     *              it will be.
     */
    protected boolean isJdk13LumberjackAvailable() {
        return isLogLibraryAvailable(
                "Jdk13Lumberjack",
                "org.apache.commons.logging.impl.Jdk13LumberjackLogger");
    }


    /**
     * <p>Return <code>true</code> if <em>JDK 1.4 or later</em> logging
     * is available.  Also checks that the <code>Throwable</code> class
     * supports <code>getStackTrace()</code>, which is required by
     * Jdk14Logger.</p>  
     * 
     * @deprecated  Never invoked by this class; subclasses should not assume
     *              it will be.
     */
    protected boolean isJdk14Available() {
        return isLogLibraryAvailable(
                "Jdk14",
                "org.apache.commons.logging.impl.Jdk14Logger");
    }


    /**
     * Is a <em>Log4J</em> implementation available? 
     * 
     * @deprecated  Never invoked by this class; subclasses should not assume
     *              it will be.
     */
    protected boolean isLog4JAvailable() {
        return isLogLibraryAvailable(
                "Log4J",
                LOGGING_IMPL_LOG4J_LOGGER);
    }


    /**
     * Create and return a new {@link org.apache.commons.logging.Log}
     * instance for the specified name.
     *
     * @param name Name of the new logger
     *
     * @exception LogConfigurationException if a new instance cannot
     *  be created
     */
    protected Log newInstance(String name) throws LogConfigurationException {

        Log instance = null;
        try {
            if (logConstructor == null) {
                instance = discoverLogImplementation(name);
            }
            else {
                Object params[] = { name };
                instance = (Log) logConstructor.newInstance(params);
            }
            
            if (logMethod != null) {
                Object params[] = { this };
                logMethod.invoke(instance, params);
            }
            
            return (instance);
            
        } catch (LogConfigurationException lce) {
            
            // this type of exception means there was a problem in discovery
            // and we've already output diagnostics about the issue, etc.; 
            // just pass it on
            throw (LogConfigurationException) lce;
            
        } catch (InvocationTargetException e) {
            // A problem occurred invoking the Constructor or Method 
            // previously discovered
            Throwable c = e.getTargetException();
            if (c != null) {
                throw new LogConfigurationException(c);
            } else {
                throw new LogConfigurationException(e);
            }
        } catch (Throwable t) {
            // A problem occurred invoking the Constructor or Method 
            // previously discovered
            throw new LogConfigurationException(t);
        }
    }
    

    //  ------------------------------------------------------ Private Methods
    
    /**
     * 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 LogFactory.directGetContextClassLoader();
                }
            });
    }

    /**
     * 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.
     * <p>
     * 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);
                    }
                });
    }

    /**
     * Fetch the parent classloader of a specified classloader.
     * <p>
     * If a SecurityException occurs, null is returned.
     * <p>
     * Note that this method is non-static merely so logDiagnostic is available.
     */
    private ClassLoader getParentClassLoader(final ClassLoader cl) {
        try {
            return (ClassLoader)AccessController.doPrivileged(
                    new PrivilegedAction() {
                        public Object run() {
                            return cl.getParent();
                        }
                    });
        } catch(SecurityException ex) {
            logDiagnostic("[SECURITY] Unable to obtain parent classloader");
            return null;
        }
        
    }

    /**
     * Utility method to check whether a particular logging library is
     * present and available for use. Note that this does <i>not</i>
     * affect the future behaviour of this class.
     */
    private boolean isLogLibraryAvailable(String name, String classname) {
        if (isDiagnosticsEnabled()) {
            logDiagnostic("Checking for '" + name + "'.");
        }
        try {
            Log log = createLogFromClass(
                        classname, 
                        this.getClass().getName(), // dummy category
                        false);

            if (log == null) {
                if (isDiagnosticsEnabled()) {
                    logDiagnostic("Did not find '" + name + "'.");
                }
                return false;
            } else {
                if (isDiagnosticsEnabled()) {
                    logDiagnostic("Found '" + name + "'.");
                }
                return true;
            }
        } catch(LogConfigurationException e) {
            if (isDiagnosticsEnabled()) {
                logDiagnostic("Logging system '" + name + "' is available but not useable.");
            }
            return false;
        }
    }

    /**
     * Attempt to find an attribute (see method setAttribute) or a 
     * system property with the provided name and return its value.
     * <p>
     * The attributes associated with this object are checked before
     * system properties in case someone has explicitly called setAttribute,