simplelog.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

     *
     * @param logLevel is this level enabled?
     */
    protected boolean isLevelEnabled(int logLevel) {
        // log level are numerically ordered so can use simple numeric
        // comparison
        return (logLevel >= currentLogLevel);
    }


    // -------------------------------------------------------- Log Implementation


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_DEBUG</code>.
     *
     * @param message to log
     * @see org.apache.commons.logging.Log#debug(Object)
     */
    public final void debug(Object message) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_DEBUG)) {
            log(SimpleLog.LOG_LEVEL_DEBUG, message, null);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_DEBUG</code>.
     *
     * @param message to log
     * @param t log this cause
     * @see org.apache.commons.logging.Log#debug(Object, Throwable)
     */
    public final void debug(Object message, Throwable t) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_DEBUG)) {
            log(SimpleLog.LOG_LEVEL_DEBUG, message, t);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_TRACE</code>.
     *
     * @param message to log
     * @see org.apache.commons.logging.Log#trace(Object)
     */
    public final void trace(Object message) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_TRACE)) {
            log(SimpleLog.LOG_LEVEL_TRACE, message, null);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_TRACE</code>.
     *
     * @param message to log
     * @param t log this cause
     * @see org.apache.commons.logging.Log#trace(Object, Throwable)
     */
    public final void trace(Object message, Throwable t) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_TRACE)) {
            log(SimpleLog.LOG_LEVEL_TRACE, message, t);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_INFO</code>.
     *
     * @param message to log
     * @see org.apache.commons.logging.Log#info(Object)
     */
    public final void info(Object message) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_INFO)) {
            log(SimpleLog.LOG_LEVEL_INFO,message,null);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_INFO</code>.
     *
     * @param message to log
     * @param t log this cause
     * @see org.apache.commons.logging.Log#info(Object, Throwable)
     */
    public final void info(Object message, Throwable t) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_INFO)) {
            log(SimpleLog.LOG_LEVEL_INFO, message, t);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_WARN</code>.
     *
     * @param message to log
     * @see org.apache.commons.logging.Log#warn(Object)
     */
    public final void warn(Object message) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_WARN)) {
            log(SimpleLog.LOG_LEVEL_WARN, message, null);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_WARN</code>.
     *
     * @param message to log
     * @param t log this cause
     * @see org.apache.commons.logging.Log#warn(Object, Throwable)
     */
    public final void warn(Object message, Throwable t) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_WARN)) {
            log(SimpleLog.LOG_LEVEL_WARN, message, t);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_ERROR</code>.
     *
     * @param message to log
     * @see org.apache.commons.logging.Log#error(Object)
     */
    public final void error(Object message) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_ERROR)) {
            log(SimpleLog.LOG_LEVEL_ERROR, message, null);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_ERROR</code>.
     *
     * @param message to log
     * @param t log this cause
     * @see org.apache.commons.logging.Log#error(Object, Throwable)
     */
    public final void error(Object message, Throwable t) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_ERROR)) {
            log(SimpleLog.LOG_LEVEL_ERROR, message, t);
        }
    }


    /**
     * Log a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_FATAL</code>.
     *
     * @param message to log
     * @see org.apache.commons.logging.Log#fatal(Object)
     */
    public final void fatal(Object message) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_FATAL)) {
            log(SimpleLog.LOG_LEVEL_FATAL, message, null);
        }
    }


    /**
     * Logs a message with 
     * <code>org.apache.commons.logging.impl.SimpleLog.LOG_LEVEL_FATAL</code>.
     *
     * @param message to log
     * @param t log this cause
     * @see org.apache.commons.logging.Log#fatal(Object, Throwable)
     */
    public final void fatal(Object message, Throwable t) {

        if (isLevelEnabled(SimpleLog.LOG_LEVEL_FATAL)) {
            log(SimpleLog.LOG_LEVEL_FATAL, message, t);
        }
    }


    /**
     * <p> Are debug messages currently enabled? </p>
     *
     * <p> This allows expensive operations such as <code>String</code>
     * concatenation to be avoided when the message will be ignored by the
     * logger. </p>
     */
    public final boolean isDebugEnabled() {

        return isLevelEnabled(SimpleLog.LOG_LEVEL_DEBUG);
    }


    /**
     * <p> Are error messages currently enabled? </p>
     *
     * <p> This allows expensive operations such as <code>String</code>
     * concatenation to be avoided when the message will be ignored by the
     * logger. </p>
     */
    public final boolean isErrorEnabled() {

        return isLevelEnabled(SimpleLog.LOG_LEVEL_ERROR);
    }


    /**
     * <p> Are fatal messages currently enabled? </p>
     *
     * <p> This allows expensive operations such as <code>String</code>
     * concatenation to be avoided when the message will be ignored by the
     * logger. </p>
     */
    public final boolean isFatalEnabled() {

        return isLevelEnabled(SimpleLog.LOG_LEVEL_FATAL);
    }


    /**
     * <p> Are info messages currently enabled? </p>
     *
     * <p> This allows expensive operations such as <code>String</code>
     * concatenation to be avoided when the message will be ignored by the
     * logger. </p>
     */
    public final boolean isInfoEnabled() {

        return isLevelEnabled(SimpleLog.LOG_LEVEL_INFO);
    }


    /**
     * <p> Are trace messages currently enabled? </p>
     *
     * <p> This allows expensive operations such as <code>String</code>
     * concatenation to be avoided when the message will be ignored by the
     * logger. </p>
     */
    public final boolean isTraceEnabled() {

        return isLevelEnabled(SimpleLog.LOG_LEVEL_TRACE);
    }


    /**
     * <p> Are warn messages currently enabled? </p>
     *
     * <p> This allows expensive operations such as <code>String</code>
     * concatenation to be avoided when the message will be ignored by the
     * logger. </p>
     */
    public final boolean isWarnEnabled() {

        return isLevelEnabled(SimpleLog.LOG_LEVEL_WARN);
    }


    /**
     * Return the thread context class loader if available.
     * Otherwise return null.
     *
     * The thread context class loader is available for JDK 1.2
     * or later, if certain security conditions are met.
     *
     * @exception LogConfigurationException if a suitable class loader
     * cannot be identified.
     */
    private static ClassLoader getContextClassLoader()
    {
        ClassLoader classLoader = null;

        if (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(), 
                            (Class[]) null);
                } catch (IllegalAccessException e) {
                    ;  // ignore
                } 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
                ;  // ignore
            }
        }

        if (classLoader == null) {
            classLoader = SimpleLog.class.getClassLoader();
        }

        // Return the selected class loader
        return classLoader;
    }

    private static InputStream getResourceAsStream(final String name)
    {
        return (InputStream)AccessController.doPrivileged(
            new PrivilegedAction() {
                public Object run() {
                    ClassLoader threadCL = getContextClassLoader();

                    if (threadCL != null) {
                        return threadCL.getResourceAsStream(name);
                    } else {
                        return ClassLoader.getSystemResourceAsStream(name);
                    }
                }
            });
    }
}