Dubbo Logger适配器模式使用分析

适配器模式

模式动机

在软件开发中采用类似于电源适配器的设计和编码技巧被称为适配器模式。
通常情况下，客户端可以通过目标类的接口访问它所提供的服务。有时，现有的类可以满足客户类的功能需要，但是它所提供的接口不一定是客户类所期望的，这可能是因为现有类中方法名与目标类中定义的方法名不一致等原因所导致的。
在这种情况下，现有的接口需要转化为客户类期望的接口，这样保证了对现有类的重用。如果不进行这样的转化，客户类就不能利用现有类所提供的功能，适配器模式可以完成这样的转化。
在适配器模式中可以定义一个包装类，包装不兼容接口的对象，这个包装类指的就是适配器(Adapter)，它所包装的对象就是适配者(Adaptee)，即被适配的类。
适配器提供客户类需要的接口，适配器的实现就是把客户类的请求转化为对适配者的相应接口的调用。也就是说：当客户类调用适配器的方法时，在适配器类的内部将调用适配者类的方法，而这个过程对客户类是透明的，客户类并不直接访问适配者类。因此，适配器可以使由于接口不兼容而不能交互的类可以一起工作。这就是适配器模式的模式动机。

模式定义

适配器模式(Adapter Pattern) ：将一个接口转换成客户希望的另一个接口，适配器模式使接口不兼容的那些类可以一起工作，其别名为包装器(Wrapper)。适配器模式既可以作为类结构型模式，也可以作为对象结构型模式。

模式结构

适配器模式包含如下角色：

Target：目标抽象类
Adapter：适配器类
Adaptee：适配者类
Client：客户类
适配器模式有对象适配器和类适配器两种实现：

对象适配器：

类适配器：

时序图

Dubbo中的使用

Logger的定义

Dubbo中首先定义了Logger接口对象，Dubbo内部的所有日志相关接口都是通过Logger接口进行操作的。

/**
 * Logger interface
 * <p>
 * This interface is referred from commons-logging
 */
public interface Logger {

    /**
     * Logs a message with trace log level.
     *
     * @param msg log this message
     */
    void trace(String msg);

    /**
     * Logs an error with trace log level.
     *
     * @param e log this cause
     */
    void trace(Throwable e);

    /**
     * Logs an error with trace log level.
     *
     * @param msg log this message
     * @param e   log this cause
     */
    void trace(String msg, Throwable e);

    /**
     * Logs a message with debug log level.
     *
     * @param msg log this message
     */
    void debug(String msg);

    /**
     * Logs an error with debug log level.
     *
     * @param e log this cause
     */
    void debug(Throwable e);

    /**
     * Logs an error with debug log level.
     *
     * @param msg log this message
     * @param e   log this cause
     */
    void debug(String msg, Throwable e);

    /**
     * Logs a message with info log level.
     *
     * @param msg log this message
     */
    void info(String msg);

    /**
     * Logs an error with info log level.
     *
     * @param e log this cause
     */
    void info(Throwable e);

    /**
     * Logs an error with info log level.
     *
     * @param msg log this message
     * @param e   log this cause
     */
    void info(String msg, Throwable e);

    /**
     * Logs a message with warn log level.
     *
     * @param msg log this message
     */
    void warn(String msg);

    /**
     * Logs a message with warn log level.
     *
     * @param e log this message
     */
    void warn(Throwable e);

    /**
     * Logs a message with warn log level.
     *
     * @param msg log this message
     * @param e   log this cause
     */
    void warn(String msg, Throwable e);

    /**
     * Logs a message with error log level.
     *
     * @param msg log this message
     */
    void error(String msg);

    /**
     * Logs an error with error log level.
     *
     * @param e log this cause
     */
    void error(Throwable e);

    /**
     * Logs an error with error log level.
     *
     * @param msg log this message
     * @param e   log this cause
     */
    void error(String msg, Throwable e);

    /**
     * Is trace logging currently enabled?
     *
     * @return true if trace is enabled
     */
    boolean isTraceEnabled();

    /**
     * Is debug logging currently enabled?
     * 
     * @return true if debug is enabled
     */
    boolean isDebugEnabled();

    /**
     * Is info logging currently enabled?
     *
     * @return true if info is enabled
     */
    boolean isInfoEnabled();

    /**
     * Is warn logging currently enabled?
     *
     * @return true if warn is enabled
     */
    boolean isWarnEnabled();

    /**
     * Is error logging currently enabled?
     *
     * @return true if error is enabled
     */
    boolean isErrorEnabled();

}

dubbo中Logger的实现类如下图：

Slf4jLogger实现如下：

public class Slf4jLogger implements Logger, Serializable {

    private static final long serialVersionUID = 1L;

    private static final String FQCN = FailsafeLogger.class.getName();

    private final org.slf4j.Logger logger;

    private final LocationAwareLogger locationAwareLogger;

    public Slf4jLogger(org.slf4j.Logger logger) {
        if (logger instanceof LocationAwareLogger) {
            locationAwareLogger = (LocationAwareLogger) logger;
        } else {
            locationAwareLogger = null;
        }
        this.logger = logger;
    }

    @Override
    public void trace(String msg) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.TRACE_INT, msg, null, null);
            return;
        }
        logger.trace(msg);
    }

    @Override
    public void trace(Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.TRACE_INT, e.getMessage(), null, e);
            return;
        }
        logger.trace(e.getMessage(), e);
    }

    @Override
    public void trace(String msg, Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.TRACE_INT, msg, null, e);
            return;
        }
        logger.trace(msg, e);
    }

    @Override
    public void debug(String msg) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.DEBUG_INT, msg, null, null);
            return;
        }
        logger.debug(msg);
    }

    @Override
    public void debug(Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.DEBUG_INT, e.getMessage(), null, e);
            return;
        }
        logger.debug(e.getMessage(), e);
    }

    @Override
    public void debug(String msg, Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.DEBUG_INT, msg, null, e);
            return;
        }
        logger.debug(msg, e);
    }

    @Override
    public void info(String msg) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.INFO_INT, msg, null, null);
            return;
        }
        logger.info(msg);
    }

    @Override
    public void info(Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.INFO_INT, e.getMessage(), null, e);
            return;
        }
        logger.info(e.getMessage(), e);
    }

    @Override
    public void info(String msg, Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.INFO_INT, msg, null, e);
            return;
        }
        logger.info(msg, e);
    }

    @Override
    public void warn(String msg) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.WARN_INT, msg, null, null);
            return;
        }
        logger.warn(msg);
    }

    @Override
    public void warn(Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.WARN_INT, e.getMessage(), null, e);
            return;
        }
        logger.warn(e.getMessage(), e);
    }

    @Override
    public void warn(String msg, Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.WARN_INT, msg, null, e);
            return;
        }
        logger.warn(msg, e);
    }

    @Override
    public void error(String msg) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.ERROR_INT, msg, null, null);
            return;
        }
        logger.error(msg);
    }

    @Override
    public void error(Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.ERROR_INT, e.getMessage(), null, e);
            return;
        }
        logger.error(e.getMessage(), e);
    }

    @Override
    public void error(String msg, Throwable e) {
        if (locationAwareLogger != null) {
            locationAwareLogger.log(null, FQCN, LocationAwareLogger.ERROR_INT, msg, null, e);
            return;
        }
        logger.error(msg, e);
    }

    @Override
    public boolean isTraceEnabled() {
        return logger.isTraceEnabled();
    }

    @Override
    public boolean isDebugEnabled() {
        return logger.isDebugEnabled();
    }

    @Override
    public boolean isInfoEnabled() {
        return logger.isInfoEnabled();
    }

    @Override
    public boolean isWarnEnabled() {
        return logger.isWarnEnabled();
    }

    @Override
    public boolean isErrorEnabled() {
        return logger.isErrorEnabled();
    }

}

Slf4jLogger中通过组合的方式引入了org.slf4j.Logger对象。具体的实际操作动作最终使用slf4j接口的对象。

到此，对应的不同的Logger第三方日志，都统一适配成dubbo中的Logger接口

LoggerAdapter 作为dubbo中统一对外提供的日志管理器，具体代码如下所示：

接口具体定义如下：

public class Slf4jLoggerAdapter implements LoggerAdapter {

    private Level level;
    private File file;

    @Override
    public Logger getLogger(String key) {
        return new Slf4jLogger(org.slf4j.LoggerFactory.getLogger(key));
    }

    @Override
    public Logger getLogger(Class<?> key) {
        return new Slf4jLogger(org.slf4j.LoggerFactory.getLogger(key));
    }

    @Override
    public Level getLevel() {
        return level;
    }

    @Override
    public void setLevel(Level level) {
        this.level = level;
    }

    @Override
    public File getFile() {
        return file;
    }

    @Override
    public void setFile(File file) {
        this.file = file;
    }

}

最后通过工厂类对外提供日志服务：

在这个工厂类中，所有的日志，都被重新封装成FailsafeLogger，用作不抛出异常的安全类。

public class FailsafeLogger implements Logger {

    private Logger logger;

    public FailsafeLogger(Logger logger) {
        this.logger = logger;
    }

    public Logger getLogger() {
        return logger;
    }

    public void setLogger(Logger logger) {
        this.logger = logger;
    }

    private String appendContextMessage(String msg) {
        return " [DUBBO] " + msg + ", dubbo version: " + Version.getVersion() + ", current host: " + NetUtils.getLocalHost();
    }

    @Override
    public void trace(String msg, Throwable e) {
        try {
            logger.trace(appendContextMessage(msg), e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void trace(Throwable e) {
        try {
            logger.trace(e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void trace(String msg) {
        try {
            logger.trace(appendContextMessage(msg));
        } catch (Throwable t) {
        }
    }

    @Override
    public void debug(String msg, Throwable e) {
        try {
            logger.debug(appendContextMessage(msg), e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void debug(Throwable e) {
        try {
            logger.debug(e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void debug(String msg) {
        try {
            logger.debug(appendContextMessage(msg));
        } catch (Throwable t) {
        }
    }

    @Override
    public void info(String msg, Throwable e) {
        try {
            logger.info(appendContextMessage(msg), e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void info(String msg) {
        try {
            logger.info(appendContextMessage(msg));
        } catch (Throwable t) {
        }
    }

    @Override
    public void warn(String msg, Throwable e) {
        try {
            logger.warn(appendContextMessage(msg), e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void warn(String msg) {
        try {
            logger.warn(appendContextMessage(msg));
        } catch (Throwable t) {
        }
    }

    @Override
    public void error(String msg, Throwable e) {
        try {
            logger.error(appendContextMessage(msg), e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void error(String msg) {
        try {
            logger.error(appendContextMessage(msg));
        } catch (Throwable t) {
        }
    }

    @Override
    public void error(Throwable e) {
        try {
            logger.error(e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void info(Throwable e) {
        try {
            logger.info(e);
        } catch (Throwable t) {
        }
    }

    @Override
    public void warn(Throwable e) {
        try {
            logger.warn(e);
        } catch (Throwable t) {
        }
    }

    @Override
    public boolean isTraceEnabled() {
        try {
            return logger.isTraceEnabled();
        } catch (Throwable t) {
            return false;
        }
    }

    @Override
    public boolean isDebugEnabled() {
        try {
            return logger.isDebugEnabled();
        } catch (Throwable t) {
            return false;
        }
    }

    @Override
    public boolean isInfoEnabled() {
        try {
            return logger.isInfoEnabled();
        } catch (Throwable t) {
            return false;
        }
    }

    @Override
    public boolean isWarnEnabled() {
        try {
            return logger.isWarnEnabled();
        } catch (Throwable t) {
            return false;
        }
    }

    @Override
    public boolean isErrorEnabled() {
        try {
            return logger.isErrorEnabled();
        } catch (Throwable t) {
            return false;
        }
    }

}

最后LoggerFactory的实现如下：

/**
 * Logger factory
 */
public class LoggerFactory {

    private static final ConcurrentMap<String, FailsafeLogger> LOGGERS = new ConcurrentHashMap<>();
    private static volatile LoggerAdapter LOGGER_ADAPTER;

    // search common-used logging frameworks
    static {
        String logger = System.getProperty("dubbo.application.logger", "");
        switch (logger) {
            case "slf4j":
                setLoggerAdapter(new Slf4jLoggerAdapter());
                break;
            case "jcl":
                setLoggerAdapter(new JclLoggerAdapter());
                break;
            case "log4j":
                setLoggerAdapter(new Log4jLoggerAdapter());
                break;
            case "jdk":
                setLoggerAdapter(new JdkLoggerAdapter());
                break;
            case "log4j2":
                setLoggerAdapter(new Log4j2LoggerAdapter());
                break;
            default:
                List<Class<? extends LoggerAdapter>> candidates = Arrays.asList(
                        Log4jLoggerAdapter.class,
                        Slf4jLoggerAdapter.class,
                        Log4j2LoggerAdapter.class,
                        JclLoggerAdapter.class,
                        JdkLoggerAdapter.class
                );
                for (Class<? extends LoggerAdapter> clazz : candidates) {
                    try {
                        setLoggerAdapter(clazz.newInstance());
                        break;
                    } catch (Throwable ignored) {
                    }
                }
        }
    }

    private LoggerFactory() {
    }

    public static void setLoggerAdapter(String loggerAdapter) {
        if (loggerAdapter != null && loggerAdapter.length() > 0) {
            setLoggerAdapter(ExtensionLoader.getExtensionLoader(LoggerAdapter.class).getExtension(loggerAdapter));
        }
    }

    /**
     * Set logger provider
     *
     * @param loggerAdapter logger provider
     */
    public static void setLoggerAdapter(LoggerAdapter loggerAdapter) {
        if (loggerAdapter != null) {
            Logger logger = loggerAdapter.getLogger(LoggerFactory.class.getName());
            logger.info("using logger: " + loggerAdapter.getClass().getName());
            LoggerFactory.LOGGER_ADAPTER = loggerAdapter;
            for (Map.Entry<String, FailsafeLogger> entry : LOGGERS.entrySet()) {
                entry.getValue().setLogger(LOGGER_ADAPTER.getLogger(entry.getKey()));
            }
        }
    }

    /**
     * Get logger provider
     *
     * @param key the returned logger will be named after clazz
     * @return logger
     */
    public static Logger getLogger(Class<?> key) {
        return LOGGERS.computeIfAbsent(key.getName(), name -> new FailsafeLogger(LOGGER_ADAPTER.getLogger(name)));
    }

    /**
     * Get logger provider
     *
     * @param key the returned logger will be named after key
     * @return logger provider
     */
    public static Logger getLogger(String key) {
        return LOGGERS.computeIfAbsent(key, k -> new FailsafeLogger(LOGGER_ADAPTER.getLogger(k)));
    }

    /**
     * Get logging level
     *
     * @return logging level
     */
    public static Level getLevel() {
        return LOGGER_ADAPTER.getLevel();
    }

    /**
     * Set the current logging level
     *
     * @param level logging level
     */
    public static void setLevel(Level level) {
        LOGGER_ADAPTER.setLevel(level);
    }

    /**
     * Get the current logging file
     *
     * @return current logging file
     */
    public static File getFile() {
        return LOGGER_ADAPTER.getFile();
    }

}