slf4j简介和技术选型
市面上的日志框架：
JUL、JCL、Jboss-logging、logback、log4j、log4j2、slf4j....
| 日志实现 | |
|---|---|
| Log4j JUL（java.util.logging） Log4j2 |
左边选一个门面（抽象层）、右边来选一个实现；
日志门面： SLF4J；
日志实现：Logback；
SpringBoot：底层是Spring框架，Spring框架默认是用JCL；‘
SpringBoot选用 SLF4j和logback；
一、slf4j简介
slf4j(Simple logging facade for Java)是对所有日志框架制定的一种规范、标准、接口，并不是一个框架的具体的实现，因为接口并不能独立使用，需要和具体的日志框架实现配合使用
slf4j是门面模式的典型应用，外部与一个子系统的通信必须通过一个统一的外观对象进行，使得子系统更易于使用。
日志实现(log4j、logback、log4j2)
- log4j是apache实现的一个开源日志组件
- logback同样是由log4j的作者设计完成的，拥有更好的特性，用来取代log4j的一个日志框架，是slf4j的原生实现
- log4j2是log4j 1.x和logback的改进版，据说采用了一些新技术（无锁异步、等等），使得日志的吞吐量、性能比log4j 1.x提高10倍，并解决了一些死锁的bug，而且配置更加简单灵活。
为什么要使用slf4j
- SLF4J提供了统一的记录日志的接口，对不同日志系统的具体实现进行了抽象化，只要按照其提供的方法记录即可，最终日志的格式、记录级别、输出方式等通过绑定具体的日志系统来实现。在项目中使用了SLF4J记录日志，并且绑定了log4j，则日志会以log4j的风格输出；后期需要改为以logback的风格输出日志，只需要将jar包log4j替换成logback即可，不用修改项目中的代码。
- SLF4J支持
{}作为占位符，等价于C语言中的%s，而不必再进行字符串的拼接，效率有显著的提升
maven jar包
springBoot版本：
<!--boot版本:--> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.2.13.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <!--使用的log版本是（boot这一个就可以了）：以下内容会自动导入--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-logging</artifactId> <version>2.2.13.RELEASE</version> </dependency> <!--logback-classic和logback-core版本是：--> <dependency> <groupId>ch.qos.logback</groupId> <artifactId>logback-classic</artifactId> <version>1.2.3</version> <scope>compile</scope> </dependency> <dependency> <groupId>ch.qos.logback</groupId> <artifactId>logback-core</artifactId> <version>1.2.3</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.slf4j</groupId> <artifactId>jul-to-slf4j</artifactId> <version>1.7.30</version> <scope>compile</scope> </dependency>
二、实现原理
slf4j只是一个日志标准，并不是日志系统的具体实现。slf4j只提做两件事情：Logger类用来打日志，LoggerFactory类用来获取Logger;
- 提供日志接口 (Logger.class)
- 提供获取具体日志对象的方法 (LoggerFactory.class)
Logger.class
/** * Copyright (c) 2004-2011 QOS.ch * All rights reserved. * * Permission is hereby granted, free of charge, to any person obtaining * a copy of this software and associated documentation files (the * "Software"), to deal in the Software without restriction, including * without limitation the rights to use, copy, modify, merge, publish, * distribute, sublicense, and/or sell copies of the Software, and to * permit persons to whom the Software is furnished to do so, subject to * the following conditions: * * The above copyright notice and this permission notice shall be * included in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. * */ package org.slf4j; /** * The org.slf4j.Logger interface is the main user entry point of SLF4J API. * It is expected that logging takes place through concrete implementations * of this interface. * <p/> * <h3>Typical usage pattern:</h3> * <pre> * import org.slf4j.Logger; * import org.slf4j.LoggerFactory; * * public class Wombat { * * <span style="color:green">final static Logger logger = LoggerFactory.getLogger(Wombat.class);</span> * Integer t; * Integer oldT; * * public void setTemperature(Integer temperature) { * oldT = t; * t = temperature; * <span style="color:green">logger.debug("Temperature set to {}. Old temperature was {}.", t, oldT);</span> * if(temperature.intValue() > 50) { * <span style="color:green">logger.info("Temperature has risen above 50 degrees.");</span> * } * } * } * </pre> * * Be sure to read the FAQ entry relating to <a href="../../../faq.html#logging_performance">parameterized * logging</a>. Note that logging statements can be parameterized in * <a href="../../../faq.html#paramException">presence of an exception/throwable</a>. * * <p>Once you are comfortable using loggers, i.e. instances of this interface, consider using * <a href="MDC.html">MDC</a> as well as <a href="Marker.html">Markers</a>.</p> * * @author Ceki Gülcü */ public interface Logger { /** * Case insensitive String constant used to retrieve the name of the root logger. * * @since 1.3 */ final public String ROOT_LOGGER_NAME = "ROOT"; /** * Return the name of this <code>Logger</code> instance. * @return name of this logger instance */ public String getName(); /** * Is the logger instance enabled for the TRACE level? * * @return True if this Logger is enabled for the TRACE level, * false otherwise. * @since 1.4 */ public boolean isTraceEnabled(); /** * Log a message at the TRACE level. * * @param msg the message string to be logged * @since 1.4 */ public void trace(String msg); /** * Log a message at the TRACE level according to the specified format * and argument. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the TRACE level. </p> * * @param format the format string * @param arg the argument * @since 1.4 */ public void trace(String format, Object arg); /** * Log a message at the TRACE level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the TRACE level. </p> * * @param format the format string * @param arg1 the first argument * @param arg2 the second argument * @since 1.4 */ public void trace(String format, Object arg1, Object arg2); /** * Log a message at the TRACE level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous string concatenation when the logger * is disabled for the TRACE level. However, this variant incurs the hidden * (and relatively small) cost of creating an <code>Object[]</code> before invoking the method, * even if this logger is disabled for TRACE. The variants taking {@link #trace(String, Object) one} and * {@link #trace(String, Object, Object) two} arguments exist solely in order to avoid this hidden cost.</p> * * @param format the format string * @param arguments a list of 3 or more arguments * @since 1.4 */ public void trace(String format, Object... arguments); /** * Log an exception (throwable) at the TRACE level with an * accompanying message. * * @param msg the message accompanying the exception * @param t the exception (throwable) to log * @since 1.4 */ public void trace(String msg, Throwable t); /** * Similar to {@link #isTraceEnabled()} method except that the * marker data is also taken into account. * * @param marker The marker data to take into consideration * @return True if this Logger is enabled for the TRACE level, * false otherwise. * * @since 1.4 */ public boolean isTraceEnabled(Marker marker); /** * Log a message with the specific Marker at the TRACE level. * * @param marker the marker data specific to this log statement * @param msg the message string to be logged * @since 1.4 */ public void trace(Marker marker, String msg); /** * This method is similar to {@link #trace(String, Object)} method except that the * marker data is also taken into consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg the argument * @since 1.4 */ public void trace(Marker marker, String format, Object arg); /** * This method is similar to {@link #trace(String, Object, Object)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg1 the first argument * @param arg2 the second argument * @since 1.4 */ public void trace(Marker marker, String format, Object arg1, Object arg2); /** * This method is similar to {@link #trace(String, Object...)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param argArray an array of arguments * @since 1.4 */ public void trace(Marker marker, String format, Object... argArray); /** * This method is similar to {@link #trace(String, Throwable)} method except that the * marker data is also taken into consideration. * * @param marker the marker data specific to this log statement * @param msg the message accompanying the exception * @param t the exception (throwable) to log * @since 1.4 */ public void trace(Marker marker, String msg, Throwable t); /** * Is the logger instance enabled for the DEBUG level? * * @return True if this Logger is enabled for the DEBUG level, * false otherwise. */ public boolean isDebugEnabled(); /** * Log a message at the DEBUG level. * * @param msg the message string to be logged */ public void debug(String msg); /** * Log a message at the DEBUG level according to the specified format * and argument. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the DEBUG level. </p> * * @param format the format string * @param arg the argument */ public void debug(String format, Object arg); /** * Log a message at the DEBUG level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the DEBUG level. </p> * * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void debug(String format, Object arg1, Object arg2); /** * Log a message at the DEBUG level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous string concatenation when the logger * is disabled for the DEBUG level. However, this variant incurs the hidden * (and relatively small) cost of creating an <code>Object[]</code> before invoking the method, * even if this logger is disabled for DEBUG. The variants taking * {@link #debug(String, Object) one} and {@link #debug(String, Object, Object) two} * arguments exist solely in order to avoid this hidden cost.</p> * * @param format the format string * @param arguments a list of 3 or more arguments */ public void debug(String format, Object... arguments); /** * Log an exception (throwable) at the DEBUG level with an * accompanying message. * * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void debug(String msg, Throwable t); /** * Similar to {@link #isDebugEnabled()} method except that the * marker data is also taken into account. * * @param marker The marker data to take into consideration * @return True if this Logger is enabled for the DEBUG level, * false otherwise. */ public boolean isDebugEnabled(Marker marker); /** * Log a message with the specific Marker at the DEBUG level. * * @param marker the marker data specific to this log statement * @param msg the message string to be logged */ public void debug(Marker marker, String msg); /** * This method is similar to {@link #debug(String, Object)} method except that the * marker data is also taken into consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg the argument */ public void debug(Marker marker, String format, Object arg); /** * This method is similar to {@link #debug(String, Object, Object)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void debug(Marker marker, String format, Object arg1, Object arg2); /** * This method is similar to {@link #debug(String, Object...)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arguments a list of 3 or more arguments */ public void debug(Marker marker, String format, Object... arguments); /** * This method is similar to {@link #debug(String, Throwable)} method except that the * marker data is also taken into consideration. * * @param marker the marker data specific to this log statement * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void debug(Marker marker, String msg, Throwable t); /** * Is the logger instance enabled for the INFO level? * * @return True if this Logger is enabled for the INFO level, * false otherwise. */ public boolean isInfoEnabled(); /** * Log a message at the INFO level. * * @param msg the message string to be logged */ public void info(String msg); /** * Log a message at the INFO level according to the specified format * and argument. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the INFO level. </p> * * @param format the format string * @param arg the argument */ public void info(String format, Object arg); /** * Log a message at the INFO level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the INFO level. </p> * * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void info(String format, Object arg1, Object arg2); /** * Log a message at the INFO level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous string concatenation when the logger * is disabled for the INFO level. However, this variant incurs the hidden * (and relatively small) cost of creating an <code>Object[]</code> before invoking the method, * even if this logger is disabled for INFO. The variants taking * {@link #info(String, Object) one} and {@link #info(String, Object, Object) two} * arguments exist solely in order to avoid this hidden cost.</p> * * @param format the format string * @param arguments a list of 3 or more arguments */ public void info(String format, Object... arguments); /** * Log an exception (throwable) at the INFO level with an * accompanying message. * * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void info(String msg, Throwable t); /** * Similar to {@link #isInfoEnabled()} method except that the marker * data is also taken into consideration. * * @param marker The marker data to take into consideration * @return true if this logger is warn enabled, false otherwise */ public boolean isInfoEnabled(Marker marker); /** * Log a message with the specific Marker at the INFO level. * * @param marker The marker specific to this log statement * @param msg the message string to be logged */ public void info(Marker marker, String msg); /** * This method is similar to {@link #info(String, Object)} method except that the * marker data is also taken into consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg the argument */ public void info(Marker marker, String format, Object arg); /** * This method is similar to {@link #info(String, Object, Object)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void info(Marker marker, String format, Object arg1, Object arg2); /** * This method is similar to {@link #info(String, Object...)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arguments a list of 3 or more arguments */ public void info(Marker marker, String format, Object... arguments); /** * This method is similar to {@link #info(String, Throwable)} method * except that the marker data is also taken into consideration. * * @param marker the marker data for this log statement * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void info(Marker marker, String msg, Throwable t); /** * Is the logger instance enabled for the WARN level? * * @return True if this Logger is enabled for the WARN level, * false otherwise. */ public boolean isWarnEnabled(); /** * Log a message at the WARN level. * * @param msg the message string to be logged */ public void warn(String msg); /** * Log a message at the WARN level according to the specified format * and argument. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the WARN level. </p> * * @param format the format string * @param arg the argument */ public void warn(String format, Object arg); /** * Log a message at the WARN level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous string concatenation when the logger * is disabled for the WARN level. However, this variant incurs the hidden * (and relatively small) cost of creating an <code>Object[]</code> before invoking the method, * even if this logger is disabled for WARN. The variants taking * {@link #warn(String, Object) one} and {@link #warn(String, Object, Object) two} * arguments exist solely in order to avoid this hidden cost.</p> * * @param format the format string * @param arguments a list of 3 or more arguments */ public void warn(String format, Object... arguments); /** * Log a message at the WARN level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the WARN level. </p> * * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void warn(String format, Object arg1, Object arg2); /** * Log an exception (throwable) at the WARN level with an * accompanying message. * * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void warn(String msg, Throwable t); /** * Similar to {@link #isWarnEnabled()} method except that the marker * data is also taken into consideration. * * @param marker The marker data to take into consideration * @return True if this Logger is enabled for the WARN level, * false otherwise. */ public boolean isWarnEnabled(Marker marker); /** * Log a message with the specific Marker at the WARN level. * * @param marker The marker specific to this log statement * @param msg the message string to be logged */ public void warn(Marker marker, String msg); /** * This method is similar to {@link #warn(String, Object)} method except that the * marker data is also taken into consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg the argument */ public void warn(Marker marker, String format, Object arg); /** * This method is similar to {@link #warn(String, Object, Object)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void warn(Marker marker, String format, Object arg1, Object arg2); /** * This method is similar to {@link #warn(String, Object...)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arguments a list of 3 or more arguments */ public void warn(Marker marker, String format, Object... arguments); /** * This method is similar to {@link #warn(String, Throwable)} method * except that the marker data is also taken into consideration. * * @param marker the marker data for this log statement * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void warn(Marker marker, String msg, Throwable t); /** * Is the logger instance enabled for the ERROR level? * * @return True if this Logger is enabled for the ERROR level, * false otherwise. */ public boolean isErrorEnabled(); /** * Log a message at the ERROR level. * * @param msg the message string to be logged */ public void error(String msg); /** * Log a message at the ERROR level according to the specified format * and argument. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the ERROR level. </p> * * @param format the format string * @param arg the argument */ public void error(String format, Object arg); /** * Log a message at the ERROR level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous object creation when the logger * is disabled for the ERROR level. </p> * * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void error(String format, Object arg1, Object arg2); /** * Log a message at the ERROR level according to the specified format * and arguments. * <p/> * <p>This form avoids superfluous string concatenation when the logger * is disabled for the ERROR level. However, this variant incurs the hidden * (and relatively small) cost of creating an <code>Object[]</code> before invoking the method, * even if this logger is disabled for ERROR. The variants taking * {@link #error(String, Object) one} and {@link #error(String, Object, Object) two} * arguments exist solely in order to avoid this hidden cost.</p> * * @param format the format string * @param arguments a list of 3 or more arguments */ public void error(String format, Object... arguments); /** * Log an exception (throwable) at the ERROR level with an * accompanying message. * * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void error(String msg, Throwable t); /** * Similar to {@link #isErrorEnabled()} method except that the * marker data is also taken into consideration. * * @param marker The marker data to take into consideration * @return True if this Logger is enabled for the ERROR level, * false otherwise. */ public boolean isErrorEnabled(Marker marker); /** * Log a message with the specific Marker at the ERROR level. * * @param marker The marker specific to this log statement * @param msg the message string to be logged */ public void error(Marker marker, String msg); /** * This method is similar to {@link #error(String, Object)} method except that the * marker data is also taken into consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg the argument */ public void error(Marker marker, String format, Object arg); /** * This method is similar to {@link #error(String, Object, Object)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arg1 the first argument * @param arg2 the second argument */ public void error(Marker marker, String format, Object arg1, Object arg2); /** * This method is similar to {@link #error(String, Object...)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param format the format string * @param arguments a list of 3 or more arguments */ public void error(Marker marker, String format, Object... arguments); /** * This method is similar to {@link #error(String, Throwable)} * method except that the marker data is also taken into * consideration. * * @param marker the marker data specific to this log statement * @param msg the message accompanying the exception * @param t the exception (throwable) to log */ public void error(Marker marker, String msg, Throwable t); }
LoggerFactory.classs
/** * Copyright (c) 2004-2011 QOS.ch * All rights reserved. * * Permission is hereby granted, free of charge, to any person obtaining * a copy of this software and associated documentation files (the * "Software"), to deal in the Software without restriction, including * without limitation the rights to use, copy, modify, merge, publish, * distribute, sublicense, and/or sell copies of the Software, and to * permit persons to whom the Software is furnished to do so, subject to * the following conditions: * * The above copyright notice and this permission notice shall be * included in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. * */ package org.slf4j; import java.io.IOException; import java.net.URL; import java.util.ArrayList; import java.util.Arrays; import java.util.Enumeration; import java.util.LinkedHashSet; import java.util.List; import java.util.Set; import java.util.concurrent.LinkedBlockingQueue; import org.slf4j.event.SubstituteLoggingEvent; import org.slf4j.helpers.NOPLoggerFactory; import org.slf4j.helpers.SubstituteLogger; import org.slf4j.helpers.SubstituteLoggerFactory; import org.slf4j.helpers.Util; import org.slf4j.impl.StaticLoggerBinder; /** * The <code>LoggerFactory</code> is a utility class producing Loggers for * various logging APIs, most notably for log4j, logback and JDK 1.4 logging. * Other implementations such as {@link org.slf4j.impl.NOPLogger NOPLogger} and * {@link org.slf4j.impl.SimpleLogger SimpleLogger} are also supported. * <p/> * <p/> * <code>LoggerFactory</code> is essentially a wrapper around an * {@link ILoggerFactory} instance bound with <code>LoggerFactory</code> at * compile time. * <p/> * <p/> * Please note that all methods in <code>LoggerFactory</code> are static. * * * @author Alexander Dorokhine * @author Robert Elliot * @author Ceki Gülcü * */ public final class LoggerFactory { static final String CODES_PREFIX = "http://www.slf4j.org/codes.html"; static final String NO_STATICLOGGERBINDER_URL = CODES_PREFIX + "#StaticLoggerBinder"; static final String MULTIPLE_BINDINGS_URL = CODES_PREFIX + "#multiple_bindings"; static final String NULL_LF_URL = CODES_PREFIX + "#null_LF"; static final String VERSION_MISMATCH = CODES_PREFIX + "#version_mismatch"; static final String SUBSTITUTE_LOGGER_URL = CODES_PREFIX + "#substituteLogger"; static final String LOGGER_NAME_MISMATCH_URL = CODES_PREFIX + "#loggerNameMismatch"; static final String REPLAY_URL = CODES_PREFIX + "#replay"; static final String UNSUCCESSFUL_INIT_URL = CODES_PREFIX + "#unsuccessfulInit"; static final String UNSUCCESSFUL_INIT_MSG = "org.slf4j.LoggerFactory in failed state. Original exception was thrown EARLIER. See also " + UNSUCCESSFUL_INIT_URL; static final int UNINITIALIZED = 0; static final int ONGOING_INITIALIZATION = 1; static final int FAILED_INITIALIZATION = 2; static final int SUCCESSFUL_INITIALIZATION = 3; static final int NOP_FALLBACK_INITIALIZATION = 4; static volatile int INITIALIZATION_STATE = UNINITIALIZED; static final SubstituteLoggerFactory SUBST_FACTORY = new SubstituteLoggerFactory(); static final NOPLoggerFactory NOP_FALLBACK_FACTORY = new NOPLoggerFactory(); // Support for detecting mismatched logger names. static final String DETECT_LOGGER_NAME_MISMATCH_PROPERTY = "slf4j.detectLoggerNameMismatch"; static final String JAVA_VENDOR_PROPERTY = "java.vendor.url"; static boolean DETECT_LOGGER_NAME_MISMATCH = Util.safeGetBooleanSystemProperty(DETECT_LOGGER_NAME_MISMATCH_PROPERTY); /** * It is LoggerFactory's responsibility to track version changes and manage * the compatibility list. * <p/> * <p/> * It is assumed that all versions in the 1.6 are mutually compatible. */ static private final String[] API_COMPATIBILITY_LIST = new String[] { "1.6", "1.7" }; // private constructor prevents instantiation private LoggerFactory() { } /** * Force LoggerFactory to consider itself uninitialized. * <p/> * <p/> * This method is intended to be called by classes (in the same package) for * testing purposes. This method is internal. It can be modified, renamed or * removed at any time without notice. * <p/> * <p/> * You are strongly discouraged from calling this method in production code. */ static void reset() { INITIALIZATION_STATE = UNINITIALIZED; } private final static void performInitialization() { bind(); if (INITIALIZATION_STATE == SUCCESSFUL_INITIALIZATION) { versionSanityCheck(); } } private static boolean messageContainsOrgSlf4jImplStaticLoggerBinder(String msg) { if (msg == null) return false; if (msg.contains("org/slf4j/impl/StaticLoggerBinder")) return true; if (msg.contains("org.slf4j.impl.StaticLoggerBinder")) return true; return false; } private final static void bind() { try { Set<URL> staticLoggerBinderPathSet = null; // skip check under android, see also // http://jira.qos.ch/browse/SLF4J-328 if (!isAndroid()) { staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet(); reportMultipleBindingAmbiguity(staticLoggerBinderPathSet); } // the next line does the binding StaticLoggerBinder.getSingleton(); INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION; reportActualBinding(staticLoggerBinderPathSet); } catch (NoClassDefFoundError ncde) { String msg = ncde.getMessage(); if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) { INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION; Util.report("Failed to load class "org.slf4j.impl.StaticLoggerBinder"."); Util.report("Defaulting to no-operation (NOP) logger implementation"); Util.report("See " + NO_STATICLOGGERBINDER_URL + " for further details."); } else { failedBinding(ncde); throw ncde; } } catch (java.lang.NoSuchMethodError nsme) { String msg = nsme.getMessage(); if (msg != null && msg.contains("org.slf4j.impl.StaticLoggerBinder.getSingleton()")) { INITIALIZATION_STATE = FAILED_INITIALIZATION; Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding."); Util.report("Your binding is version 1.5.5 or earlier."); Util.report("Upgrade your binding to version 1.6.x."); } throw nsme; } catch (Exception e) { failedBinding(e); throw new IllegalStateException("Unexpected initialization failure", e); } finally { postBindCleanUp(); } } private static void postBindCleanUp() { fixSubstituteLoggers(); replayEvents(); // release all resources in SUBST_FACTORY SUBST_FACTORY.clear(); } private static void fixSubstituteLoggers() { synchronized (SUBST_FACTORY) { SUBST_FACTORY.postInitialization(); for (SubstituteLogger substLogger : SUBST_FACTORY.getLoggers()) { Logger logger = getLogger(substLogger.getName()); substLogger.setDelegate(logger); } } } static void failedBinding(Throwable t) { INITIALIZATION_STATE = FAILED_INITIALIZATION; Util.report("Failed to instantiate SLF4J LoggerFactory", t); } private static void replayEvents() { final LinkedBlockingQueue<SubstituteLoggingEvent> queue = SUBST_FACTORY.getEventQueue(); final int queueSize = queue.size(); int count = 0; final int maxDrain = 128; List<SubstituteLoggingEvent> eventList = new ArrayList<SubstituteLoggingEvent>(maxDrain); while (true) { int numDrained = queue.drainTo(eventList, maxDrain); if (numDrained == 0) break; for (SubstituteLoggingEvent event : eventList) { replaySingleEvent(event); if (count++ == 0) emitReplayOrSubstituionWarning(event, queueSize); } eventList.clear(); } } private static void emitReplayOrSubstituionWarning(SubstituteLoggingEvent event, int queueSize) { if (event.getLogger().isDelegateEventAware()) { emitReplayWarning(queueSize); } else if (event.getLogger().isDelegateNOP()) { // nothing to do } else { emitSubstitutionWarning(); } } private static void replaySingleEvent(SubstituteLoggingEvent event) { if (event == null) return; SubstituteLogger substLogger = event.getLogger(); String loggerName = substLogger.getName(); if (substLogger.isDelegateNull()) { throw new IllegalStateException("Delegate logger cannot be null at this state."); } if (substLogger.isDelegateNOP()) { // nothing to do } else if (substLogger.isDelegateEventAware()) { substLogger.log(event); } else { Util.report(loggerName); } } private static void emitSubstitutionWarning() { Util.report("The following set of substitute loggers may have been accessed"); Util.report("during the initialization phase. Logging calls during this"); Util.report("phase were not honored. However, subsequent logging calls to these"); Util.report("loggers will work as normally expected."); Util.report("See also " + SUBSTITUTE_LOGGER_URL); } private static void emitReplayWarning(int eventCount) { Util.report("A number (" + eventCount + ") of logging calls during the initialization phase have been intercepted and are"); Util.report("now being replayed. These are subject to the filtering rules of the underlying logging system."); Util.report("See also " + REPLAY_URL); } private final static void versionSanityCheck() { try { String requested = StaticLoggerBinder.REQUESTED_API_VERSION; boolean match = false; for (String aAPI_COMPATIBILITY_LIST : API_COMPATIBILITY_LIST) { if (requested.startsWith(aAPI_COMPATIBILITY_LIST)) { match = true; } } if (!match) { Util.report("The requested version " + requested + " by your slf4j binding is not compatible with " + Arrays.asList(API_COMPATIBILITY_LIST).toString()); Util.report("See " + VERSION_MISMATCH + " for further details."); } } catch (java.lang.NoSuchFieldError nsfe) { // given our large user base and SLF4J's commitment to backward // compatibility, we cannot cry here. Only for implementations // which willingly declare a REQUESTED_API_VERSION field do we // emit compatibility warnings. } catch (Throwable e) { // we should never reach here Util.report("Unexpected problem occured during version sanity check", e); } } // We need to use the name of the StaticLoggerBinder class, but we can't // reference // the class itself. private static String STATIC_LOGGER_BINDER_PATH = "org/slf4j/impl/StaticLoggerBinder.class"; static Set<URL> findPossibleStaticLoggerBinderPathSet() { // use Set instead of list in order to deal with bug #138 // LinkedHashSet appropriate here because it preserves insertion order // during iteration 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 boolean isAmbiguousStaticLoggerBinderPathSet(Set<URL> binderPathSet) { return binderPathSet.size() > 1; } /** * Prints a warning message on the console if multiple bindings were found * on the class path. No reporting is done otherwise. * */ 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 boolean isAndroid() { String vendor = Util.safeGetSystemProperty(JAVA_VENDOR_PROPERTY); if (vendor == null) return false; return vendor.toLowerCase().contains("android"); } 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() + "]"); } } /** * Return a logger named according to the name parameter using the * statically bound {@link ILoggerFactory} instance. * * @param name * The name of the logger. * @return logger */ public static Logger getLogger(String name) { ILoggerFactory iLoggerFactory = getILoggerFactory(); return iLoggerFactory.getLogger(name); } /** * Return a logger named corresponding to the class passed as parameter, * using the statically bound {@link ILoggerFactory} instance. * * <p> * In case the the <code>clazz</code> parameter differs from the name of the * caller as computed internally by SLF4J, a logger name mismatch warning * will be printed but only if the * <code>slf4j.detectLoggerNameMismatch</code> system property is set to * true. By default, this property is not set and no warnings will be * printed even in case of a logger name mismatch. * * @param clazz * the returned logger will be named after clazz * @return logger * * * @see <a * href="http://www.slf4j.org/codes.html#loggerNameMismatch">Detected * logger name mismatch</a> */ public static Logger getLogger(Class<?> clazz) { Logger logger = getLogger(clazz.getName()); if (DETECT_LOGGER_NAME_MISMATCH) { Class<?> autoComputedCallingClass = Util.getCallingClass(); if (autoComputedCallingClass != null && nonMatchingClasses(clazz, autoComputedCallingClass)) { Util.report(String.format("Detected logger name mismatch. Given name: "%s"; computed name: "%s".", logger.getName(), autoComputedCallingClass.getName())); Util.report("See " + LOGGER_NAME_MISMATCH_URL + " for an explanation"); } } return logger; } private static boolean nonMatchingClasses(Class<?> clazz, Class<?> autoComputedCallingClass) { return !autoComputedCallingClass.isAssignableFrom(clazz); } /** * Return the {@link ILoggerFactory} instance in use. * <p/> * <p/> * ILoggerFactory instance is bound with this class at compile time. * * @return the ILoggerFactory instance in use */ 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(); 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"); } }
这里看下获取getLogger函数的源码，我们发现LoggerFactory.getLogger()首先获取一个ILoggerFactory接口，然后使用该接口获取具体的Logger。
获取ILoggerFactory的时候用到了一个 LoggerContext 类，仔细研究我们会发现LoggerContext 这个类并不是slf4j-api这个包中的类，而是实现日志框架里的类，所有的实现框架都需要定义该类，提供具体的Logger实现。
三、SLF4j使用
以后开发的时候，日志记录方法的调用，不应该来直接调用日志的实现类，而是调用日志抽象层里面的方法；
给系统里面导入slf4j的jar和 logback的实现jar
import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class HelloWorld { public static void main(String[] args) { Logger logger = LoggerFactory.getLogger(HelloWorld.class); logger.info("Hello World"); } }
a（slf4j+logback）: Spring（commons-logging）、Hibernate（jboss-logging）、MyBatis、xxxx
统一日志记录，即使是别的框架和我一起统一使用slf4j进行输出？
如何让系统中所有的日志都统一到slf4j；
1、将系统中其他日志框架先排除出去；
2、用中间包来替换原有的日志框架；
3、我们导入slf4j其他的实现
<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.2.13.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent>
SpringBoot使用它来做日志功能：
<!--不需要导入--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-logging</artifactId> <version>2.2.13.RELEASE</version> </dependency>
底层依赖关系
貌似新版本的 boot 不需要导入 jcl-over-self4j
总结：
1）、SpringBoot底层也是使用slf4j+logback的方式进行日志记录
2）、SpringBoot也把其他的日志都替换成了slf4j；
3）、中间替换包？
@SuppressWarnings("rawtypes")
public abstract class LogFactory {
static String UNSUPPORTED_OPERATION_IN_JCL_OVER_SLF4J = "http://www.slf4j.org/codes.html#unsupported_operation_in_jcl_over_slf4j";
static LogFactory logFactory = new SLF4JLogFactory();
4）、如果我们普通的 maven 项目要引入其他框架？一定要把spring框架的默认日志依赖移除掉？
Spring框架用的是commons-logging；
<dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <exclusions> <exclusion> <groupId>commons-logging</groupId> <artifactId>commons-logging</artifactId> </exclusion> </exclusions> </dependency>
SpringBoot能自动适配所有的日志，而且底层使用slf4j+logback的方式记录日志，引入其他框架的时候，只需要把这个框架依赖的日志框架排除掉即可
三、logback简介
logback是log4j创始人写的，性能比log4j要好，目前主要分为3个模块
- logback-core:核心代码模块
- logback-classic:log4j的一个改良版本，同时实现了
slf4j的接口，这样你如果之后要切换其他日志组件也是一件很容易的事 - logback-access:访问模块与Servlet容器集成提供通过Http来访问日志的功能
三、日志使用
1、logback-spring.xml配置
<?xml version="1.0" encoding="UTF-8"?> <!-- scan：当此属性设置为true时,配置文件如果发生改变,将会被重新加载,默认值为true。 scanPeriod：设置监测配置文件是否有修改的时间间隔,如果没有给出时间单位,默认单位是毫秒当scan为true时,此属性生效。默认的时间间隔为1分钟。 debug：当此属性设置为true时,将打印出logback内部日志信息,实时查看logback运行状态。默认值为false。 --> <configuration scan="false" scanPeriod="60 seconds" debug="false"> <!-- 定义日志的根目录为项目的根目录,前面不要加"/",加了会默认会认为是根目录,提示 classnotfond --> <property name="LOG_HOME" value="app/log"/> <!-- 定义日志文件名称 --> <property name="appName" value="logbackBootText"/> <!-- ConsoleAppender 用于控制台输出 --> <appender name="stdout" class="ch.qos.logback.core.ConsoleAppender"> <!-- 日志输出格式： %d表示日期时间, %thread表示线程名, %-5level：级别从左显示5个字符宽度 %logger{50} 表示logger名字最长50个字符,否则按照句点分割。 %msg：日志消息, %n是换行符 --> <layout class="ch.qos.logback.classic.PatternLayout"> <!--springProfile可以指定某段配置只在某个环境下生效--> <!--如果使用logback.xml作为日志配置文件,还要使用profile功能,会有以下错误no applicable action for [springProfile]--> <springProfile name="dev"> <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} ----> [%thread] ---> %-5level %logger{50} - %msg%n</pattern> </springProfile> <springProfile name="!dev"> <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} ==== [%thread] ==== %-5level %logger{50} - %msg%n</pattern> </springProfile> </layout> </appender> <!-- 滚动记录文件,先将日志记录到指定文件,当符合某个条件时,将日志记录到其他文件 --> <appender name="appLogAppender" class="ch.qos.logback.core.rolling.RollingFileAppender"> <!--定义日志输出的路径和名称--> <!-- 指定日志文件的名称 --> <!--这里的scheduler.manager.server.home 没有在上面的配置中设定,所以会使用java启动时配置的值--> <!--比如通过 java -Dscheduler.manager.server.home=/path/to XXXX 配置该属性--> <!--<file>${scheduler.manager.server.home}/${LOG_HOME}/${appName}.log</file>--> <!--当发生滚动时,决定 RollingFileAppender 的行为,涉及文件移动和重命名 TimeBasedRollingPolicy： 最常用的滚动策略,它根据时间来制定滚动策略,既负责滚动也负责出发滚动。“%d”可以包含一个java.text.SimpleDateFormat指定的时间格式,--> <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"> <!--滚动时产生的文件的存放位置及文件名称 %d{yyyy-MM-dd}：按天进行日志滚动 %i：当文件大小超过maxFileSize时,按照i进行文件滚动--> <fileNamePattern>${LOG_HOME}/${appName}-%d{yyyy-MM-dd}-%i.log</fileNamePattern> <!--可选节点,控制保留的归档文件的最大数量,超出数量就删除旧文件。假设设置每天滚动, 且maxHistory是365,则只保存最近365天的文件,删除之前的旧文件。注意,删除旧文件是, 那些为了归档而创建的目录也会被删除。--> <MaxHistory>365</MaxHistory> <!-- 该属性在 1.1.6版本后 才开始支持,日志量最大20GB--> <totalSizeCap>20GB</totalSizeCap> <!--当日志文件超过maxFileSize指定的大小是,根据上面提到的%i进行日志文件滚动 注意此处配置 SizeBasedTriggeringPolicy 是无法实现按文件大小进行滚动的,必须配置 timeBasedFileNamingAndTriggeringPolicy--> <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP"> <maxFileSize>100MB</maxFileSize> </timeBasedFileNamingAndTriggeringPolicy> </rollingPolicy> <!-- 日志输出格式： --> <layout class="ch.qos.logback.classic.PatternLayout"> <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [ %thread ] ->> [ %-5level ] [ %logger{50} : %line ] ->> %msg%n </pattern> </layout> </appender> <!-- 滚动记录文件,先将日志记录到指定文件,当符合某个条件时,将日志记录到其他文件 --> <appender name="appLogAppenderBoot" class="ch.qos.logback.core.rolling.RollingFileAppender"> <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"> <fileNamePattern>${LOG_HOME}/boot-${appName}-%d{yyyy-MM-dd}-%i.log</fileNamePattern> <MaxHistory>365</MaxHistory> <timeBasedFileNamingAndTriggeringPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP"> <maxFileSize>100MB</maxFileSize> </timeBasedFileNamingAndTriggeringPolicy> </rollingPolicy> <layout class="ch.qos.logback.classic.PatternLayout"> <pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [ %thread ] -> [ %-5level ] [ %logger{50} : %line ] -> %msg%n</pattern> </layout> </appender> <!--root是默认的logger,root与logger是父子关系,没有特别定义则默认为root,任何一个类只会和一个logger对应, 要么是定义的logger,要么是root,判断的关键在于找到这个logger,然后判断这个logger的appender和level。 --> <root level="DEBUG"> <!--定义了三个appender,日志会通过往这这些appender里面写--> <appender-ref ref="stdout"/> <appender-ref ref="appLogAppender"/> <appender-ref ref="appLogAppenderBoot"/> </root> <!--logger主要用于存放日志对象,也可以定义日志类型、级别--> <!--name：表示匹配的logger类型前缀,也就是包的前半部分--> <!--level：要记录的日志级别,包括 TRACE < DEBUG < INFO < WARN < ERROR 越往后越精简--> <!--additivity：作用在于children-logger是否使用 rootLogger配置的appender进行输出,--> <!--false：表示只用当前logger的appender-ref,true：表示当前logger的appender-ref和rootLogger的appender-ref都有效--> <!-- Spring framework logger 记录 spring 的日志 --> <logger name="org.springframework.boot" level="debug" additivity="false"> <appender-ref ref="appLogAppenderBoot"/> </logger> <!--通过 LoggerFactory.getLogger("mytest") 可以获取到这个logger--> <!--由于这个logger自动继承了root的appender，root中已经有stdout的appender了，自己这边又引入了stdout的appender--> <!--如果没有设置 additivity="false" ,就会导致一条日志在控制台输出两次的情况,原因是:没有写additivity会用 rootlogger 输出日志,而它下面有三个appender,单appLogAppenderBoot经过自定义,不会输出,stdout则会打印两遍--> <!--additivity表示要不要使用rootLogger配置的appender进行输出--> <logger name="com.tuniu" level="debug" additivity="false"> <!--即输出到appLogAppender,又输出到stdout--> <appender-ref ref="appLogAppender"/> <appender-ref ref="stdout"/> </logger> <!--对于类路径以 com.tuniu 开头的Logger,输出级别设置为 warn,--> <!--这个logger没有指定appender，它会继承root节点中定义的那些appender--> <!--注意,如果名称相同,两个 logger 会有属性互补机制;而且以最后一个加载的属性为准,可以理解为 boot的 bootstrap.properties与 application.yml--> <!-- <logger name="com.tuniu" level="warn"/> 如果将上面的这段配置放开,就如同写了: <logger name="com.tuniu" level="warn" additivity="false"> <appender-ref ref="appLogAppender"/> </logger> --> <!--由于设置了 additivity="false" ，所以输出时不会使用rootLogger的appender--> <!--但是这个logger本身又没有配置 appender，所以使用这个logger输出日志的话就不会输出到任何地方--> <!-- <logger name="mytest2" level="info" additivity="false"/>--> </configuration>
后续有源码阅读部分