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[最新] SLF4J--自动绑定实现类原理(源码)

szztlingpeng 1月前 0

转载自:http://www.cnblogs.com/Anidot/articles/7744018.html

一、概述

  slf4j(全称是Simple Loging Facade For Java)是一个为Java程序提供日志输出的统一接口,并不是一个具体的日志实现方案,就好像我们经常使用的JDBC一样,只是一种接口规则定义而已,使用了slf4j可以对客户端应用解耦。因为当我们在代码实现中引入log日志的时候,用的是接口,所以可以实时的更具情况来调换具体的日志实现类。这就是slf4j的作用。基于SLF4J日志实现方案,比如apachelog4j,log4j2,logback,jdk自带的java.util.logging.Logger等等。

  其中对应的实现jar包:

    slf4j-log4j12-x.x.x.jar/log4j-slf4j-impl是使用org.apache.log4j.Logger提供的驱动

    slf4j-jdk14-x.x.x.jar是使用java.util.logging提供的驱动

    slf4j-simple-x.x.x.jar直接绑定System.err

    slf4j-jcl-x.x.x.jar是使用commons-logging提供的驱动

    logback-classic-x.x.x.jar是使用logback提供的驱动

二、工作原理窥探

  1. 简单实现
     1 package com.test.slf4j;
     2 import org.slf4j.Logger;
     3 import org.slf4j.LoggerFactory;
     4 public class TestLog4j {
     5 private static final Logger LOGGER = LoggerFactory.getLogger(TestLog4j.class);
     6
     7 public static void main(String[] args) {
     8         String message = "服务器出错啦.";
     9         LOGGER.info("Error message is: {}", message);
    10     }
    11 }
  2. 通过LoggerFactory类的静态getLogger()获取logger。slf4j-api作为slf4j的接口类,使用在程序代码中,这个包提供了一个Logger类和LoggerFactory类,Logger类用来打日志,LoggerFactory类用来获取Logger;比如说:slf4j-log4j,这个包是连接slf4j和log4j的桥梁,怎么连接的呢?我们看看slf4j的LoggerFactory类的getLogger函数的源码:
        public static Logger getLogger(String name) {
            ILoggerFactory iLoggerFactory = getILoggerFactory();
            return iLoggerFactory.getLogger(name);
        }
        
        public static ILoggerFactory getILoggerFactory() {
            if (INITIALIZATION_STATE == UNINITIALIZED) {
                synchronized (LoggerFactory.class) {
                    if (INITIALIZATION_STATE == UNINITIALIZED) {
                        INITIALIZATION_STATE = ONGOING_INITIALIZATION;
                        performInitialization();
                    }
                }
            }
            switch (INITIALIZATION_STATE) {
            case SUCCESSFUL_INITIALIZATION:
                return StaticLoggerBinder.getSingleton().getLoggerFactory(); // StaticLoggerBinder非SLF4J提供,是由具体的实现包,如log4j,logback来提供
            case NOP_FALLBACK_INITIALIZATION:
                return NOP_FALLBACK_FACTORY;
            case FAILED_INITIALIZATION:
                throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
            case ONGOING_INITIALIZATION:
                // support re-entrant behavior.
                // See also http://jira.qos.ch/browse/SLF4J-97
                return SUBST_FACTORY;
            }
            throw new IllegalStateException("Unreachable code");
        }
    
        

     

  3. 我本地同时引入了log4j2和logback包,即可看到实现。可以看出log4j-slf4j提供了该org.slf4j.impl.StaticLoggerBinder静态类来实现slf4和log4j的桥接
  4. 再看看slf4j-log4j包种的这个StaticLoggerBinder类创建ILoggerFactory长什么样子
    package org.slf4j.impl;
    
    import org.apache.logging.slf4j.Log4jLoggerFactory;
    import org.slf4j.ILoggerFactory;
    import org.slf4j.spi.LoggerFactoryBinder;
    
    public final class StaticLoggerBinder implements LoggerFactoryBinder {
        public static String REQUESTED_API_VERSION = "1.6";
        private static final String LOGGER_FACTORY_CLASS_STR = Log4jLoggerFactory.class.getName();
        private static final StaticLoggerBinder SINGLETON = new StaticLoggerBinder();
        private final ILoggerFactory loggerFactory = new Log4jLoggerFactory();
    
        private StaticLoggerBinder() {
        }
    
        public static StaticLoggerBinder getSingleton() {
            return SINGLETON;
        }
    
        public ILoggerFactory getLoggerFactory() {
            return this.loggerFactory;
        }
    
        public String getLoggerFactoryClassStr() {
            return LOGGER_FACTORY_CLASS_STR;
        }
    }
  5. 可以看到slf4j-log4j中的StaticLoggerBinder类创建的ILoggerFactory其实是一个org.slf4j.impl.Log4jLoggerFactory,这个类的getLogger函数代码如下:

    package org.apache.logging.slf4j;
    
    import org.apache.logging.log4j.LogManager;
    import org.apache.logging.log4j.spi.AbstractLoggerAdapter;
    import org.apache.logging.log4j.spi.LoggerContext;
    import org.apache.logging.log4j.util.StackLocatorUtil;
    import org.apache.logging.slf4j.Log4jLogger;
    import org.slf4j.ILoggerFactory;
    import org.slf4j.Logger;
    
    public class Log4jLoggerFactory extends AbstractLoggerAdapter<Logger> implements ILoggerFactory {
        private static final String FQCN = Log4jLoggerFactory.class.getName();
        private static final String PACKAGE = "org.slf4j";
    
        public Log4jLoggerFactory() {
        }
    
        protected Logger newLogger(String name, LoggerContext context) {
            String key = "ROOT".equals(name)?"":name;
            return new Log4jLogger(context.getLogger(key), name);
        }
    
        protected LoggerContext getContext() {
            Class anchor = StackLocatorUtil.getCallerClass(FQCN, "org.slf4j");
            return anchor == null?LogManager.getContext():this.getContext(StackLocatorUtil.getCallerClass(anchor));
        }
    }

三、slf4j加载实现类顺序问题

  1. 默认来说,slf4j的加载实现类是随机的,如发现有多个org.slf4j.impl.StaticLoggerBinder,启动应用的时候会出现下面警告:
  2. 从源码上来看,在getILoggerFactory()方法中,初始化会调用performInitialization方法进行检测实现类,最终会调用reportMultipleBindingAmbiguity方法打印出警告信息
        static Set<URL> findPossibleStaticLoggerBinderPathSet() {
            Set<URL> staticLoggerBinderPathSet = new LinkedHashSet<URL>();
            try {
                ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader();
                Enumeration<URL> paths;
                if (loggerFactoryClassLoader == null) {
                    paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH);
                } else {
                    paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH);
                }
                while (paths.hasMoreElements()) {
                    URL path = paths.nextElement();
                    staticLoggerBinderPathSet.add(path);
                }
            } catch (IOException ioe) {
                Util.report("Error getting resources from path", ioe);
            }
            return staticLoggerBinderPathSet;
        }
    
        private static void reportMultipleBindingAmbiguity(Set<URL> binderPathSet) {
            if (isAmbiguousStaticLoggerBinderPathSet(binderPathSet)) {
                Util.report("Class path contains multiple SLF4J bindings.");
                for (URL path : binderPathSet) {
                    Util.report("Found binding in [" + path + "]");
                }
                Util.report("See " + MULTIPLE_BINDINGS_URL + " for an explanation.");
            }
        }
    
        private static void reportActualBinding(Set<URL> binderPathSet) {
            // binderPathSet can be null under Android
            if (binderPathSet != null && isAmbiguousStaticLoggerBinderPathSet(binderPathSet)) {
                Util.report("Actual binding is of type [" + StaticLoggerBinder.getSingleton().getLoggerFactoryClassStr() + "]");
            }
        }

四、log4j2简单例子

  1. log4j2的MDC配置
    public final class ContextLog4j2Util {
    
        /**
         * 将上下文环境变量信息加入到MDC中,以便打印到日志
         */
        public static void addContext2MDC() {
            MDC.put(ContextConstKey.REQUEST_NO, StringUtils.isEmpty(context.getRequestNo()) ? "" : context.getRequestNo());
            MDC.put(ContextConstKey.CONSUMER_IP, StringUtils.isEmpty(context.getConsumerIp()) ? "" : context.getConsumerIp());
            MDC.put(ContextConstKey.CHANNEL_CODE, StringUtils.isEmpty(context.getChannelCode()) ? "" : context.getChannelCode());
            MDC.put(ContextConstKey.LOCAL_IP, NetUtils.getLocalHost());
        }
    
        /**
         * 从MDC清理对象
         */
        public static void removeContextFromMDC() {
            MDC.remove(ContextConstKey.REQUEST_NO);
            MDC.remove(ContextConstKey.CONSUMER_IP);
            MDC.remove(ContextConstKey.CHANNEL_CODE);
            MDC.remove(ContextConstKey.REMOTE_IP);
            MDC.remove(ContextConstKey.LOCAL_IP);
        }
    }
  2. log4j2.xml配置
    <?xml version="1.0" encoding="UTF-8"?>
    <configuration status="WARN" shutdownHook="disable">
        <Properties>
            <Property name="sysName">test-app</Property>
            <Property name="bizLogLevel">INFO</Property>
            <Property name="otherLogLevel">INFO</Property>
            <Property name="logFilePath">/home/q/test/test-app/logs</Property>
            <Property name="logSize">1000 MB</Property>
            <Property name="maxFile">100</Property>
            <Property name="errorLogFile">${sysName}_err</Property>
            <Property name="bizLogFile">${sysName}_biz</Property>
            <Property name="allLogFile">${sysName}_all</Property>
            <Property name="monitorLogFile">${sysName}_monitor</Property>
            <Property name="ioLogFile">${sysName}_io</Property>
            <Property name="dcLogFile">${sysName}_dc</Property>
            <Property name="rdsLogFile">${sysName}_rds</Property>
            <Property name="threadLogFile">${sysName}_thread</Property>
            <Property name="tempLogFile">${sysName}_temp</Property>
        </Properties>
        <appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <ThresholdFilter level="INFO" onMatch="ACCEPT" onMismatch="DENY"/>
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
            </Console>
            <RollingFile name="ErrorRollingFile" fileName="${logFilePath}/${errorLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${errorLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
                <ThresholdFilter level="ERROR" onMatch="ACCEPT" onMismatch="DENY"/>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
            <RollingFile name="BizRollingFile" fileName="${logFilePath}/${bizLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${bizLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
                <Filters>
                    <ThresholdFilter level="${bizLogLevel}"/>
                    <ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="NEUTRAL"/>
                </Filters>
                <Policies>
                    <TimeBasedTriggeringPolicy />
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
            <RollingFile name="AllRollingFile" fileName="${logFilePath}/${allLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${allLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
            <RollingFile name="MonitorRollingFile" fileName="${logFilePath}/${monitorLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${monitorLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout pattern="%date{yyyy-MM-dd HH:mm:ss.SSS}|%-5level|%msg%n"/>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
            <RollingFile name="IORollingFile" fileName="${logFilePath}/${ioLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${ioLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
                <Filters>
                    <ThresholdFilter level="${bizLogLevel}"/>
                    <ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="NEUTRAL"/>
                </Filters>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
            <RollingFile name="DcRollingFile" fileName="${logFilePath}/${dcLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${dcLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
                <Filters>
                    <ThresholdFilter level="${bizLogLevel}"/>
                </Filters>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
    
            <RollingFile name="RdsRollingFile" fileName="${logFilePath}/${rdsLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${rdsLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
                <Filters>
                    <ThresholdFilter level="${bizLogLevel}"/>
                </Filters>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
    
            <RollingFile name="ThreadRollingFile" fileName="${logFilePath}/${threadLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${threadLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout pattern="%date{yyyy-MM-dd HH:mm:ss.SSS}|%-5level|%msg%n"/>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
    
            <RollingFile name="TempRollingFile" fileName="${logFilePath}/${tempLogFile}.log"
                         filePattern="${logFilePath}/$${date:yyyy-MM}/${tempLogFile}-%d{MM-dd-yyyy}-%i.log.gz">
                <PatternLayout charset="UTF-8"
                               pattern="%date{yyyy-MM-dd HH:mm:ss.SSS} %-5level [%t] [%X{requestNo}|%X{consumerIp}|%X{sysChannelCode}|%X{localIp}] [%c:%line] - %msg%n"/>
                <Filters>
                    <ThresholdFilter level="${bizLogLevel}"/>
                    <ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="NEUTRAL"/>
                </Filters>
                <Policies>
                    <TimeBasedTriggeringPolicy/>
                    <SizeBasedTriggeringPolicy size="${logSize}"/>
                </Policies>
                <DefaultRolloverStrategy max="${maxFile}"/>
            </RollingFile>
    
            <CatAppender name="CatAppender"/>
        </appenders>
        <loggers>
            <logger name="com.app.msf.core.annotation.log.InputOutputLogger" level="${bizLogLevel}" additivity="false">
                <appender-ref ref="IORollingFile"/>
            </logger>
    
            <logger name="com.app.msf.core.annotation.log" level="${bizLogLevel}" additivity="false">
                <appender-ref ref="MonitorRollingFile"/>
            </logger>
    
            <logger name="com.app.test" level="${bizLogLevel}" additivity="false">
                <appender-ref ref="ErrorRollingFile" />
                <appender-ref ref="BizRollingFile"/>
                <appender-ref ref="CatAppender"/>
            </logger>
    
            <logger name="com.app.msf.rmq.consumer.impl.ConsumerServiceImpl" level="${bizLogLevel}" additivity="false">
                <appender-ref ref="BizRollingFile"/>
                <appender-ref ref="AllRollingFile"/>
            </logger>
    
            <logger name="com.app.test.modules.cust.dao" level="DEBUG" additivity="false">
                <appender-ref ref="ErrorRollingFile" />
                <appender-ref ref="BizRollingFile"/>
                <appender-ref ref="CatAppender"/>
            </logger>
    
            <logger name="com.app.test.modules.user.dao" level="DEBUG" additivity="false">
                <appender-ref ref="ErrorRollingFile" />
                <appender-ref ref="BizRollingFile"/>
                <appender-ref ref="CatAppender"/>
            </logger>
    
            <logger name="com.app.msf.threadpool" level="${bizLogLevel}"
                    additivity="false">
                <appender-ref ref="ThreadRollingFile"/>
            </logger>
            <logger name="com.alibaba.dubbo.common.threadpool" level="${bizLogLevel}"
                    additivity="false">
                <appender-ref ref="ThreadRollingFile"/>
            </logger>
    
            <logger name="tempLog" level="${bizLogLevel}"
                    additivity="false">
                <appender-ref ref="TempRollingFile"/>
            </logger>
    
            <root level="${otherLogLevel}">
                <appender-ref ref="AllRollingFile"/>
                <appender-ref ref="ErrorRollingFile"/>
                <appender-ref ref="CatAppender"/>
            </root>
        </loggers>
    </configuration>

五、工作中遇到的问题

   在生产上web应用中,catalina.out文件打印了DEBUG日志,经发现是因为包冲突,spring框架选用了slf4j的logback日志实现导致的。
两个方案:

  1. 添加logback的日志配置文件,默认为warn
  2. 排除logback实现包,但是以后新加包也可能会间接依赖导致问题再次发生(不使用该方案,slf4j的实现包太多,很容易被间接依赖,所以不仅仅是排除logback的实现)
  3. logback的空实现
    <?xml version="1.0" encoding="UTF-8"?>
    <configuration debug="false">
        <!-- 控制台输出 -->
        <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
            <encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
                <!--格式化输出:%d表示日期,%thread表示线程名,%-5level:级别从左显示5个字符宽度%msg:日志消息,%n是换行符-->
                <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern>
            </encoder>
        </appender>
        <!-- 日志输出级别 -->
        <root level="WARN">
            <appender-ref ref="STDOUT"/>
        </root>
    </configuration>
            <!-- ************************************************************* -->
            <!-- ************************************************************* -->
            <!-- ************************************************************* -->
            <!-- logback空配置文件防止应用把日志打印到console:******************* -->
            <!-- 1,web应用的catalina.out************************************** -->
            <!-- 2,app应用的启动脚本stdout.log********************************* -->
            <!-- ************************************************************* -->
            <!-- ************************************************************* -->
            <!-- ************************************************************* -->

     

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