logger(一)slf4j简介及其实现原理
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。用一张图来表示门面模式的结构为
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
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.21</version>
</dependency>
如下图所示，slf4j不能单独使用，比如要使用logback实现，需要导入logback的jar包
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.21</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.1.7</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.1.7</version>
</dependency>
比如要使用log4j或者 jdk自带的logging，需要使用桥接包如slf4j-jdk14.jar包
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
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.class
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);
fixSubstituteLoggers();
replayEvents();
// release all resources in SUBST_FACTORY
SUBST_FACTORY.clear();
} 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);
}
}
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StaticLoggerBinder类，仔细研究我们会发现StaticLoggerBinder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。
接下来具体分析日志实现框架 logback和log4j2。
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