SLF4J--自动绑定实现类原理（源码）

其他 2018-09-25 11:18:27 阅读次数: 0

转载自：https://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apache的log4j，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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