Flink Log4j 2.x使用Filter过滤日志类型（区别INFO、ERROR）
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- [Flink Log4j 2.x使用Filter过滤日志类型（区别INFO、ERROR）](#Flink Log4j 2.x使用Filter过滤日志类型（区别INFO、ERROR）)
日志级别：
ALL < TRACE < DEBUG < INFO < WARN < ERROR < FATAL < OFF
log4j官网：
https://logging.apache.org/log4j/2.x/index.html
ThresholdFilter
在官网中，有一个Filters的组件。Filters组件允许对日志事件进行评估，以确定是否或如何发布它们。Filter将在其过滤器方法之一上被调用，并将返回一个Result，这是一个Enum，具有3个值之一- ACCEPT, DENY或NEUTRAL。
如果LogEvent中的级别与配置的级别相同或更具体，则此过滤器返回onMatch结果，否则返回onMismatch值。例如，如果ThresholdFilter配置了ERROR级别，并且LogEvent包含DEBUG级别，那么onMismatch值将被返回，因为ERROR事件比DEBUG事件更高。
ThresholdFilter过滤器的原理是，如果LogEvent的日志级别被配置的高，则会执行onMatch，否则执行onMismatch。比如如果ThresholdFilter配置了INFO级别，而LogEvent是WARN、ERROR级别，那么onMatch值将会执行。而当LogEvent是DEBUG级别时，则onMismatch值将会执行。
这里有一个Threshold的过滤器，参数包含了：
- Level：要匹配的有效日志级别。
- onMatch： 当过滤器匹配时要采取的操作。可以是ACCEPT, DENY或NEUTRAL。缺省值为NEUTRAL。
- onMismatch：当过滤器不匹配时采取的操作。可以是ACCEPT, DENY或NEUTRAL。缺省值为DENY。
借助于这个Threshold过滤器，可以初步实现过滤日志的功能：
显示info 级别的日志
xml
appender.rolling.filter.threshold.type = ThresholdFilter
appender.rolling.filter.threshold.level = ERROR
appender.rolling.filter.threshold.onMatch = DENY
appender.rolling.filter.threshold.onMismatch = ACCEPT由于log4j.properties的rootLogger.level = INFO，因此最小的日志级别就已经是INFO了，所以上面的配置可以保证当前appender的输出日志只包含INFO信息。相当于是对ERROR及以上级别的日志执行onMatch=>DENY，而对小于ERROR级别，也就是INFO级别，执行onMismatch => ACCEPT。
或者xml的配置方式：
xml
<RollingFile name="RollingFileInfo" fileName="${logFilePath}/${logFileName}-info.log"
filePattern="${logFilePath}/$${date:yyyy-MM}/${logFileName}-%d{yyyy-MM-dd}_%i.log.gz">
<Filters>
<!-- onMatch:Action to take when the filter matches. The default value is NEUTRAL -->
<!-- onMismatch: Action to take when the filter does not match. The default value is DENY -->
<!-- 级别在 ERROR 之上的都拒绝输出 -->
<!-- 在组合过滤器中，接受使用 NEUTRAL（中立），被第一个过滤器接受的日志信息，会继续用后面的过滤器进行过滤，只有符合所有过滤器条件的日志信息，才会被最终写入日志文件 -->
<ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="NEUTRAL"/>
<ThresholdFilter level="INFO" onMatch="ACCEPT" onMismatch="DENY"/>
</Filters>
<PatternLayout pattern="%d{yyyy.MM.dd HH:mm:ss z} %-5level %class{36} %L %M - %msg%xEx%n"/>
<Policies>
<TimeBasedTriggeringPolicy/>
<SizeBasedTriggeringPolicy size="30MB"/>
</Policies>
</RollingFile>这种方式看着总感觉有点别扭，那有没有其他的Filter组件能更好地支持呢？
LevelMatchFilter
查询资料发现，有一个LevelMatchFilter的过滤器组件，其执行原理是：
如果日志级别等于${指定的日志级别}，则onMatch，否则onMismatch
刚好符合我们的需求，于是此时，log4j.properties的配置文件就可以变成：
################################################################################
# Licensed to the Apache Software Foundation (ASF) under one
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# distributed with this work for additional information
# regarding copyright ownership. The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
################################################################################
# Allows this configuration to be modified at runtime. The file will be checked every 30 seconds.
monitorInterval=30
# This affects logging for both user code and Flink
# This affects logging for both user code and Flink
rootLogger.level = INFO
rootLogger.appenderRef.rolling.ref = RollingFileAppender
rootLogger.appenderRef.errorLogFile.ref = errorLogFile
# Uncomment this if you want to _only_ change Flink's logging
#logger.flink.name = org.apache.flink
#logger.flink.level = INFO
# The following lines keep the log level of common libraries/connectors on
# log level INFO. The root logger does not override this. You have to manually
# change the log levels here.
logger.akka.name = akka
logger.akka.level = INFO
logger.kafka.name= org.apache.kafka
logger.kafka.level = INFO
logger.hadoop.name = org.apache.hadoop
logger.hadoop.level = INFO
logger.zookeeper.name = org.apache.zookeeper
logger.zookeeper.level = INFO
# Log all infos in the given rolling file
appender.rolling.name = RollingFileAppender
appender.rolling.type = RollingFile
appender.rolling.append = true
appender.rolling.fileName = ${sys:log.file}
appender.rolling.filePattern = ${sys:log.file}.%i
appender.rolling.layout.type = PatternLayout
appender.rolling.layout.pattern = %d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
appender.rolling.policies.type = Policies
appender.rolling.policies.size.type = SizeBasedTriggeringPolicy
appender.rolling.policies.size.size=100MB
appender.rolling.policies.startup.type = OnStartupTriggeringPolicy
appender.rolling.strategy.type = DefaultRolloverStrategy
appender.rolling.strategy.max = ${env:MAX_LOG_FILE_NUMBER:-10}
appender.rolling.filter.threshold.type = LevelMatchFilter
appender.rolling.filter.threshold.level = INFO
appender.rolling.filter.threshold.onMatch = ACCEPT
appender.rolling.filter.threshold.onMisMatch = DENY
appender.errorFile.name = errorLogFile
appender.errorFile.type = RollingFile
appender.errorFile.append = true
appender.errorFile.fileName = ${sys:log.file}.err
appender.errorFile.filePattern = ${sys:log.file}.err.%i
appender.errorFile.layout.type = PatternLayout
appender.errorFile.layout.pattern = %d{yyyy-MM-dd HH:mm:ss,SSS} %-5p %-60c %x - %m%n
appender.errorFile.policies.type = Policies
appender.errorFile.policies.size.type = SizeBasedTriggeringPolicy
appender.errorFile.policies.size.size = 100MB
appender.errorFile.policies.startup.type = OnStartupTriggeringPolicy
appender.errorFile.strategy.type = DefaultRolloverStrategy
appender.errorFile.strategy.max = ${env:MAX_LOG_FILE_NUMBER:-10}
appender.errorFile.filter.threshold.type = LevelMatchFilter
appender.errorFile.filter.threshold.level = ERROR
appender.errorFile.filter.threshold.onMatch = ACCEPT
appender.errorFile.filter.threshold.onMisMatch = DENY
# Suppress the irrelevant (wrong) warnings from the Netty channel handler
logger.netty.name = org.apache.flink.shaded.akka.org.jboss.netty.channel.DefaultChannelPipeline
logger.netty.level = OFF
大家如果在部署flink任务时有类似的需求，可以参考上面的配置进行修改，实际上主要添加的只有filter.threshold配置参数即可。
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