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log4j2中LevelRangeFilter的注意点

LevelRangeFilter的注意点

在log4j2中,LevelRangeFilter的minLevel,maxLevel的配置是和log4j 1.x相反的;minLevel需要配置的是高级别,maxLevel配置的是低级别,如下:

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<LevelRangeFilter minLevel="fatal" maxLevel="info" onMatch="ACCEPT" onMismatch="DENY"/>

如上边的配置,是打印info到fatal级别的log,如果配置反过来,则不会输出任何log。

如果不配置minLevel、maxLevel、onMatch和onMismatch的值,则会为其设置默认值,在LevelRangeFilter中的源码实现如下:

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@PluginFactory
public static LevelRangeFilter createFilter(
// @formatter:off
@PluginAttribute("minLevel") final Level minLevel,
@PluginAttribute("maxLevel") final Level maxLevel,
@PluginAttribute("onMatch") final Result match,
@PluginAttribute("onMismatch") final Result mismatch) {
// @formatter:on
final Level actualMinLevel = minLevel == null ? Level.ERROR : minLevel;
final Level actualMaxLevel = maxLevel == null ? Level.ERROR : maxLevel;
final Result onMatch = match == null ? Result.NEUTRAL : match;
final Result onMismatch = mismatch == null ? Result.DENY : mismatch;
return new LevelRangeFilter(actualMinLevel, actualMaxLevel, onMatch, onMismatch);
}

至于为什么把最大最小level的值配置反了就会无法输出,是因为在LevelRangeFilter中的源码实现如下:

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private Result filter(final Level level) {
return level.isInRange(this.minLevel, this.maxLevel) ? onMatch : onMismatch;
}

可以看到,在调用filter方法进行过滤时,是调用了level#isInRange()来判断是否匹配该filter的。而在该方法中,实现如下:

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public boolean isInRange(final Level minLevel, final Level maxLevel) {
return this.intLevel >= minLevel.intLevel && this.intLevel <= maxLevel.intLevel;
}

这里通过对比Level对象的intLevel值(int)来判断是否匹配,而这些Level对象也在Level这个类里进行里实例化:

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static {
OFF = new Level("OFF", StandardLevel.OFF.intLevel());
FATAL = new Level("FATAL", StandardLevel.FATAL.intLevel());
ERROR = new Level("ERROR", StandardLevel.ERROR.intLevel());
WARN = new Level("WARN", StandardLevel.WARN.intLevel());
INFO = new Level("INFO", StandardLevel.INFO.intLevel());
DEBUG = new Level("DEBUG", StandardLevel.DEBUG.intLevel());
TRACE = new Level("TRACE", StandardLevel.TRACE.intLevel());
ALL = new Level("ALL", StandardLevel.ALL.intLevel());
}

可以看到,这些Level对象的intLevel值是由另一个枚举类StandardLevel来提供的:

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/**
* No events will be logged.
*/
OFF(0),

/**
* A severe error that will prevent the application from continuing.
*/
FATAL(100),

/**
* An error in the application, possibly recoverable.
*/
ERROR(200),

/**
* An event that might possible lead to an error.
*/
WARN(300),

/**
* An event for informational purposes.
*/
INFO(400),

/**
* A general debugging event.
*/
DEBUG(500),

/**
* A fine-grained debug message, typically capturing the flow through the application.
*/
TRACE(600),

/**
* All events should be logged.
*/
ALL(Integer.MAX_VALUE);

可以看到,Level级别越高,其对应的intLevel值越小,可以这样理解:级别越高,能打印出来的日志信息就越少,所以其intLevel值就越小。

如果我们把LevelRangeFilter的minLevel、maxLevel配置反了,会导致level#isInRange()返回false,最终也就没有任何日志得以输出了。

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