commons-logging.jar 和 log4j.jar 的关系
在用springmvc开发项目的时候,在日志管理这一块,我们一般用的都是log4j进行日志管理,但是我们在导入spring相关的jar的时候,都会看到commons-logging.jar包,为什么我们使用log4j的同时还要引入commons-logging.jar包,它们到底是一种什么关系呢?
接下来我们看看commons-logging中的org.apache.commons.logging.Log的源码
/*** Eclipse Class Decompiler plugin, copyright (c) 2016 Chen Chao (cnfree2000@hotmail.com) ***/
package org.apache.commons.logging; public abstract interface Log {
public abstract void debug(Object paramObject); public abstract void debug(Object paramObject, Throwable paramThrowable); public abstract void error(Object paramObject); public abstract void error(Object paramObject, Throwable paramThrowable); public abstract void fatal(Object paramObject); public abstract void fatal(Object paramObject, Throwable paramThrowable); public abstract void info(Object paramObject); public abstract void info(Object paramObject, Throwable paramThrowable); public abstract boolean isDebugEnabled(); public abstract boolean isErrorEnabled(); public abstract boolean isFatalEnabled(); public abstract boolean isInfoEnabled(); public abstract boolean isTraceEnabled(); public abstract boolean isWarnEnabled(); public abstract void trace(Object paramObject); public abstract void trace(Object paramObject, Throwable paramThrowable); public abstract void warn(Object paramObject); public abstract void warn(Object paramObject, Throwable paramThrowable);
}
很显然,commons-logging中j的log类就是一个接口,只要实现了该接j它口,那么它就是一个logger组件,继续看commons-logging下的org.apache.commons.logging.impl.Log4JLogger源码
/*** Eclipse Class Decompiler plugin, copyright (c) 2016 Chen Chao (cnfree2000@hotmail.com) ***/
package org.apache.commons.logging.impl; import java.io.Serializable;
import java.lang.reflect.Field;
import org.apache.commons.logging.Log;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
import org.apache.log4j.Priority; public class Log4JLogger implements Log, Serializable {
private static final long serialVersionUID = 5160705895411730424L;
private static final String FQCN = Log4JLogger.class.getName(); private volatile transient Logger logger = null;
private final String name;
private static final Priority traceLevel; public Log4JLogger() {
this.name = null;
} public Log4JLogger(String name) {
this.name = name;
this.logger = getLogger();
} public Log4JLogger(Logger logger) {
if (logger == null) {
throw new IllegalArgumentException(
"Warning - null logger in constructor; possible log4j misconfiguration.");
} this.name = logger.getName();
this.logger = logger;
} public void trace(Object message) {
getLogger().log(FQCN, traceLevel, message, null);
} public void trace(Object message, Throwable t) {
getLogger().log(FQCN, traceLevel, message, t);
} public void debug(Object message) {
getLogger().log(FQCN, Level.DEBUG, message, null);
} public void debug(Object message, Throwable t) {
getLogger().log(FQCN, Level.DEBUG, message, t);
} public void info(Object message) {
getLogger().log(FQCN, Level.INFO, message, null);
} public void info(Object message, Throwable t) {
getLogger().log(FQCN, Level.INFO, message, t);
} public void warn(Object message) {
getLogger().log(FQCN, Level.WARN, message, null);
} public void warn(Object message, Throwable t) {
getLogger().log(FQCN, Level.WARN, message, t);
} public void error(Object message) {
getLogger().log(FQCN, Level.ERROR, message, null);
} public void error(Object message, Throwable t) {
getLogger().log(FQCN, Level.ERROR, message, t);
} public void fatal(Object message) {
getLogger().log(FQCN, Level.FATAL, message, null);
} public void fatal(Object message, Throwable t) {
getLogger().log(FQCN, Level.FATAL, message, t);
} public Logger getLogger() {
Logger result = this.logger;
if (result == null) {
synchronized (this) {
result = this.logger;
if (result == null) {
this.logger = (result = Logger.getLogger(this.name));
}
}
}
return result;
} public boolean isDebugEnabled() {
return getLogger().isDebugEnabled();
} public boolean isErrorEnabled() {
return getLogger().isEnabledFor(Level.ERROR);
} public boolean isFatalEnabled() {
return getLogger().isEnabledFor(Level.FATAL);
} public boolean isInfoEnabled() {
return getLogger().isInfoEnabled();
} public boolean isTraceEnabled() {
return getLogger().isEnabledFor(traceLevel);
} public boolean isWarnEnabled() {
return getLogger().isEnabledFor(Level.WARN);
} static {
if (!(Priority.class.isAssignableFrom(Level.class))) {
throw new InstantiationError("Log4J 1.2 not available");
} Priority _traceLevel;
try {
_traceLevel = (Priority) Level.class.getDeclaredField("TRACE").get(
null);
} catch (Exception ex) {
_traceLevel = Level.DEBUG;
}
traceLevel = _traceLevel;
}
}
/*** Eclipse Class Decompiler plugin, copyright (c) 2016 Chen Chao (cnfree2000@hotmail.com) ***/
package org.apache.commons.logging.impl; import java.io.Serializable;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.apache.commons.logging.Log; public class Jdk14Logger implements Log, Serializable {
private static final long serialVersionUID = 4784713551416303804L;
protected static final Level dummyLevel = Level.FINE; protected transient Logger logger = null; protected String name = null; public Jdk14Logger(String name) {
this.name = name;
this.logger = getLogger();
} protected void log(Level level, String msg, Throwable ex) {
Logger logger = getLogger();
if (!(logger.isLoggable(level)))
return;
Throwable dummyException = new Throwable();
StackTraceElement[] locations = dummyException.getStackTrace(); String cname = this.name;
String method = "unknown"; if ((locations != null) && (locations.length > 2)) {
StackTraceElement caller = locations[2];
method = caller.getMethodName();
}
if (ex == null)
logger.logp(level, cname, method, msg);
else
logger.logp(level, cname, method, msg, ex);
} public void debug(Object message) {
log(Level.FINE, String.valueOf(message), null);
} public void debug(Object message, Throwable exception) {
log(Level.FINE, String.valueOf(message), exception);
} public void error(Object message) {
log(Level.SEVERE, String.valueOf(message), null);
} public void error(Object message, Throwable exception) {
log(Level.SEVERE, String.valueOf(message), exception);
} public void fatal(Object message) {
log(Level.SEVERE, String.valueOf(message), null);
} public void fatal(Object message, Throwable exception) {
log(Level.SEVERE, String.valueOf(message), exception);
} public Logger getLogger() {
if (this.logger == null) {
this.logger = Logger.getLogger(this.name);
}
return this.logger;
} public void info(Object message) {
log(Level.INFO, String.valueOf(message), null);
} public void info(Object message, Throwable exception) {
log(Level.INFO, String.valueOf(message), exception);
} public boolean isDebugEnabled() {
return getLogger().isLoggable(Level.FINE);
} public boolean isErrorEnabled() {
return getLogger().isLoggable(Level.SEVERE);
} public boolean isFatalEnabled() {
return getLogger().isLoggable(Level.SEVERE);
} public boolean isInfoEnabled() {
return getLogger().isLoggable(Level.INFO);
} public boolean isTraceEnabled() {
return getLogger().isLoggable(Level.FINEST);
} public boolean isWarnEnabled() {
return getLogger().isLoggable(Level.WARNING);
} public void trace(Object message) {
log(Level.FINEST, String.valueOf(message), null);
} public void trace(Object message, Throwable exception) {
log(Level.FINEST, String.valueOf(message), exception);
} public void warn(Object message) {
log(Level.WARNING, String.valueOf(message), null);
} public void warn(Object message, Throwable exception) {
log(Level.WARNING, String.valueOf(message), exception);
}
}
我们看到有两个类,一个是Jdk14Logger,另一个是Log4JLogger。到这里我们应该知道,真正记录日志的是Jdk14Logger类和Log4JLogger类。而 commons-logging 把这两个(实际上,在 org.apache.commons.logging.impl 包下,commons-logging 仅仅为我们封装了 log4j 和 sun logger)记录日志的工具重新封装了一遍(Log4JLogger.java 和 Jdk14Logger.java),可以认为 org.apache.commons.logging.Log 是个傀儡,它只是提供了对外的统一接口。因此我们只要能拿到 org.apache.commons.logging.Log,而不用关注到底使用的是 log4j 还是 sun logger。正如我们经常在项目中这样写:
private static final Log logger = LogFactory.getLog(Run.class);
既然如此,我们的项目有两个jar包,那么我们用的是log4j 还是 Jdk14Logger呢?我们在配置spring的web.xml文件时,经常会有如下配置:
<listener>
<listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
</listener>
终于找到了 org.springframework.util.Log4jConfigurer,这正是 log4j 提供给我们的初始化日志的类。至此,我们终于明白了我们系统的的确确使用的是 log4j 的日志工具。
可是问题又来了,org.apache.commons.logging.Log 和 org.apache.log4j.Logger 这两个类,通过包名我们可以发现它们都是 apache 的项目,既然如下,为何要动如此大的动作搞两个东西(指的是 commons-logging 和 log4j)出来呢?事实上,在 sun 开发 logger 前,apache 项目已经开发了功能强大的 log4j 日志工具,并向 sun 推荐将其纳入到 jdk 的一部分,可是 sun 拒绝了 apache 的提议,sun 后来自己开发了一套记录日志的工具。可是现在的开源项目都使用的是 log4j,log4j 已经成了事实上的标准,但由于又有一部分开发者在使用 sun logger,因此 apache 才推出 commons-logging,使得我们不必关注我们正在使用何种日志工具。
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