项目打印日志使用的是log4j,并且是项目启动的时候加载log4j.xml配置文件初始化log4j,为了排查问题方便,修改log4j.xml,增加日志输出到控制台,但之前不小心改过一次,时间久了再使用就不不打印日志到控制台了,也没找到原因,今天看了下log4j的源码,才发现问题!
#log4j.xml配置
如下是我使用的log4j.xml的具体配置(关键部分),相信对log4j.xml比较熟悉的很容易就看出问题所在,但当时还真没看出来
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="console" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d %-5p: %c.%M:%L - %m%n" />
layout>
appender>
<appender name="SQL_DEBUG"
class="com.xxx.sims.uspc.platform.log.TimeSizeRollingFileAppender">
<param name="File" value="uspc/sql/debug.log" />
<param name="MaxBackupIndex" value="300" />
<param name="Encoding" value="GB2312" />
<param name="MaxFileSize" value="50MB" />
<param name="DatePattern" value="'.'yyyy-MM-dd" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="%d{ISO8601} %p [%c] - [%m]%n" />
layout>
<filter class="org.apache.log4j.varia.LevelRangeFilter">
<param name="LevelMin" value="debug" />
<param name="LevelMax" value="debug" />
<param name="acceptOnMatch" value="true" />
filter>
appender>
<appender name="SQL_INFO"
class="com.xxx.sims.uspc.platform.log.TimeSizeRollingFileAppender">
<param name="File" value="uspc/sql/info.log" />
<param name="MaxBackupIndex" value="300" />
<param name="Encoding" value="GB2312" />
<param name="MaxFileSize" value="50MB" />
<param name="DatePattern" value="'.'yyyy-MM-dd" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="%d{ISO8601} %p [%c] - [%m]%n" />
layout>
<filter class="org.apache.log4j.varia.LevelRangeFilter">
<param name="LevelMin" value="info" />
<param name="LevelMax" value="info" />
<param name="acceptOnMatch" value="true" />
filter>
appender>
<appender name="SQL_ERROR"
class="com.xxx.xxx.xxx.xxx.log.TimeSizeRollingFileAppender">
<param name="File" value="uspc/sql/error.log" />
<param name="MaxBackupIndex" value="300" />
<param name="Encoding" value="GB2312" />
<param name="MaxFileSize" value="50MB" />
<param name="DatePattern" value="'.'yyyy-MM-dd" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern"
value="%d{ISO8601} %p [%c] - [%m]%n" />
layout>
<filter class="org.apache.log4j.varia.LevelRangeFilter">
<param name="LevelMin" value="error" />
<param name="LevelMax" value="error" />
<param name="acceptOnMatch" value="true" />
filter>
appender>
中间省略其他appender配置
<logger name="com.ibatis" additivity="false">
<level value="info" />
<appender-ref ref="SQL_DEBUG" />
<appender-ref ref="SQL_INFO" />
<appender-ref ref="SQL_ERROR" />
logger>
<logger name="org.mybatis" additivity="false">
<level value="info" />
<appender-ref ref="SQL_DEBUG" />
<appender-ref ref="SQL_INFO" />
<appender-ref ref="SQL_ERROR" />
logger>
<logger name="java.sql" additivity="false">
<level value="info" />
<appender-ref ref="SQL_DEBUG" />
<appender-ref ref="SQL_INFO" />
<appender-ref ref="SQL_ERROR" />
logger>
<logger name="com.xxx" additivity="false">
<level value="info" />
<appender-ref ref="simsuspcDebug" />
<appender-ref ref="simsuspcInfo" />
<appender-ref ref="simsuspcError" />
logger>
<logger name="org.quartz" additivity="false">
<level value="info" />
<appender-ref ref="QUARTZ_DEBUG" />
<appender-ref ref="QUARTZ_INFO" />
<appender-ref ref="QUARTZ_ERROR" />
logger>
<root>
<level value="info" />
<appender-ref ref="console" />
<appender-ref ref="OTHER_DEBUG" />
<appender-ref ref="OTHER_INFO" />
<appender-ref ref="OTHER_ERROR" />
root>
log4j:configuration>
晃眼一看,
配置了名称为console的appender,但却没有打印出来,原因是要打印的包路径的
要么没有配置
,要么additivity="false"
。
注意上面代码的和
additivity="false"
,前者在logger标签被注释并且additivity配置为false,意味着这个logger对应的日志不会被打印到控制台并且不会把日志传递到root来进来打印。
此处解决方案有两种
,这样可以将logger的日志单独打印
也可以,但需要指定additivity=true,意思是日志传递到root标签打印,root配置了
,因此会打印到控制台关键行:第2行,打印入口
if (logger.isInfoEnabled()) {
logger.info("重发操作结束。重发=" + id);
}
继承关系:public class Logger extends Category{…}
关键行:第4行
public void info(Object message) {
if (!this.repository.isDisabled(20000)) {
if (Level.INFO.isGreaterOrEqual(this.getEffectiveLevel())) {
this.forcedLog(FQCN, Level.INFO, message, (Throwable)null);
}
}
}
关键行:第2行
protected void forcedLog(String fqcn, Priority level, Object message, Throwable t) {
this.callAppenders(new LoggingEvent(fqcn, this, level, message, t));
}
关键行:第7行
注意:
c.aai的aai属性是org.apache.log4j.helpers.AppenderAttachableImpl类型,包含一个Vector类型的appenderList,这个就是我们logger或者root标签配置的appender列表
public void callAppenders(LoggingEvent event) {
int writes = 0;
for(Category c = this; c != null; c = c.parent) {
synchronized(c) {
if (c.aai != null) {
writes += c.aai.appendLoopOnAppenders(event);
}
if (!c.additive) {
break;
}
}
}
if (writes == 0) {
this.repository.emitNoAppenderWarning(this);
}
}
关键行:第8行 appender.doAppend(event)
public int appendLoopOnAppenders(LoggingEvent event) {
int size = 0;
if (this.appenderList != null) {
size = this.appenderList.size();
for(int i = 0; i < size; ++i) {
Appender appender = (Appender)this.appenderList.elementAt(i);
appender.doAppend(event);
}
}
return size;
}
关键行:第10行
public interface Appender {
void addFilter(Filter var1);
Filter getFilter();
void clearFilters();
void close();
void doAppend(LoggingEvent var1);
String getName();
void setErrorHandler(ErrorHandler var1);
ErrorHandler getErrorHandler();
void setLayout(Layout var1);
Layout getLayout();
void setName(String var1);
boolean requiresLayout();
}
关键行:第22行 this.append(event)
public synchronized void doAppend(LoggingEvent event) {
if (this.closed) {
LogLog.error("Attempted to append to closed appender named [" + this.name + "].");
} else if (this.isAsSevereAsThreshold(event.getLevel())) {
Filter f = this.headFilter;
while(true) {
if (f != null) {
switch(f.decide(event)) {
case -1:
return;
case 0:
f = f.getNext();
continue;
case 1:
break;
default:
continue;
}
}
this.append(event);
return;
}
}
}
抽象类AppenderSkeleton继承Appender接口实现了doAppend方法逻辑,doAppend方法调用了自身的一个抽象方法this.append(event),而这个抽象方法具体由AppenderSkeleton抽象类的子类来实现。
org.apache.log4j.Appender接口的体系如下图
关键行:第3行
public void append(LoggingEvent event) {
if (this.checkEntryConditions()) {
this.subAppend(event);
}
}
由上面的继承体系可以看出,控制台打印输出的ConsoleAppender是直接继承的WriterAppender来的,而ConsoleAppender并没有重写subAppend方法,因此最终打印输出的逻辑就在这个subAppend方法。
关键行:
protected void subAppend(LoggingEvent event) {
this.qw.write(super.layout.format(event));
if (super.layout.ignoresThrowable()) {
String[] s = event.getThrowableStrRep();
if (s != null) {
int len = s.length;
for(int i = 0; i < len; ++i) {
this.qw.write(s[i]);
this.qw.write(Layout.LINE_SEP);
}
}
}
if (this.immediateFlush) {
this.qw.flush();
}
}
由上面的代码可以看出,打印刷新缓冲区用的是this.qw,这个qw在这里是QuietWriter
public void flush() {
try {
super.out.flush();
} catch (IOException var2) {
this.errorHandler.error("Failed to flush writer,", var2, 2);
}
}