Log level and priority in Log4j: all < debug < info < warn < error < fatal < off. By defining the level of each log information, we can more carefully control the log generation process.

log4j.properties configuration file:

# Global logging configuration

# Set the log output level and output destination. You can set multiple output destinations. In the development environment, the log level should be set to DEBUG or ERROR

# Write the log level in front, and write the output destination after the comma: corresponding to the destination set below, separated by commas

# log4j.rootLogger = [level],appenderName1,appenderName2,...

log4j.rootLogger=DEBUG,CONSOLE,LOGFILE



#### console output  ####

log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender

# Output to console

log4j.appender.CONSOLE.Target = System.out

# Specify console output log level

log4j.appender.CONSOLE.Threshold = DEBUG

# The default value is true, indicating whether to output immediately

log4j.appender.CONSOLE.ImmediateFlush = true

# Set encoding method

log4j.appender.CONSOLE.Encoding = UTF-8

# Log output layout

log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout

# If the log output layout is at the PatternLayout custom level, you need to use ConversionPattern to specify the output format

log4j.appender.CONSOLE.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %5p (%c:%L) - %m%n



#### Output error message to file ####

log4j.appender.LOGFILE=org.apache.log4j.FileAppender

# Specify the output file path

#log4j.appender.LOGFILE.File =F://Intellij idea/logs/error.log 

log4j.appender.LOGFILE.File =./logs/error.log 



#Log output to file. The default value is true

log4j.appender.LOGFILE.Append = true

# Specify the output log level

log4j.appender.LOGFILE.Threshold = ERROR

# Whether to output immediately. The default value is true,

log4j.appender.LOGFILE.ImmediateFlush = true

# Set encoding method

log4j.appender.LOGFILE.Encoding = UTF-8

# Log output layout

log4j.appender.LOGFILE.layout = org.apache.log4j.PatternLayout

# If the log output layout is at the PatternLayout custom level, you need to use ConversionPattern to specify the output format

log4j.appender.LOGFILE.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n 

Test query operation:

Log4j three components

• Logger: logger, the core class of logging, which is used to output messages at different log levels.

• Appender: log output destination, used to specify the destination of log output, such as console, file, etc.

• Layout: log formatter, used to specify the format of log output. It is the formatter of log output.

Appender: the destination used to control log output in Log4j. Each appender represents an output target. There are the following types:

• ConsoleAppender: output to the console;

• FileAppender: output to the specified file;

• Daily rolling file appender: generate a separate log file every day;

• RollingFileAppender: limit the size of the log file and generate a new log file whenever the size limit is reached;

• WriterAppender: send log information to any specified place in stream format;

Layout: log output format. Log4j provides the following layouts:

• org.apache.log4j.HTMLLayout (layout in HTML table form),

• org.apache.log4j.PatternLayout (layout mode can be flexibly specified),

• org.apache.log4j.SimpleLayout (contains the level and information string of log information),

• org.apache.log4j.TTCCLayout (including log generation time, thread, category, etc.)

Logger: the logger is the core class used by Log4j. Through the logger class, you can set the output level, output destination and output format of log messages;

Basic use

1. Introduce related dependencies: log4j

<dependency>

    <groupId>log4j</groupId>

    <artifactId>log4j</artifactId>

    <version>1.2.12</version>

</dependency> 

2. Import package: org apache. log4j. Logger

3. Create log object: static final logger logger = logger getLogger(XXX.class); // The parameter is the class file of the current class

summary

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