List of appenders
The logger allows you to save data to several files at once. Such output data streams are called appenders (from append). There are quite a few standard appenders, so we will only cover the most popular ones:
| Appenders | Description | |
|---|---|---|
| 1 | Console | Prints data to the console |
| 2 | file | Outputs data to a file |
| 3 | DailyRollingFile | Outputs data to a file, the file is cyclically overwritten |
| 4 | Async | Allows you to write data to another appender asynchronously |
| 5 | Socket | Writes data to a specific socket |
| 6 | JDBC | Writes messages to the database using the JDBC protocol |
| 7 | JPA | Writes messages to the database using the JPA protocol |
| 8 | http | Sends events via HTTP protocol to a remote server |
| 9 | SMTP | Stores messages in a buffer, and then sends them as an email |
Good documentation for all appenders is on their official website
And below we will consider the most popular and simple of them.
ConsoleAppender
The simplest appender isConsoleApender . As you may have guessed, he simply writes his messages to the console. It has several interesting parameters for us:
| Attributes | ||
|---|---|---|
| 1 | name | Appender name |
| 2 | filter | Allows you to filter some messages |
| 3 | layout | Specifies the formatting of messages when output |
| 4 | target | Specifies where to write: SYTEM_OUTorSYSTEM_ERR |
It's very easy to configure it:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
<Appenders>
<Console name="STDOUT" target="SYSTEM_OUT">
<PatternLayout pattern="%m%n"/>
</Console>
</Appenders>
<Loggers>
<Root level="error">
<AppenderRef ref="STDOUT"/>
</Root>
</Loggers>
</Configuration>
FileAppender
The most useful appender isFileAppender . Unlike ConsoleAppenderhe writes his messages to a file. Which is very useful when your application is running somewhere on the server. It has a lot of parameters, because it must be able to write files on different operating systems.
But we will consider only the most popular of them.
| 1 | name | Specifies the name of the appender |
| 2 | filter | Allows you to filter some messages |
| 3 | layout | Specifies the formatting of messages when output |
| 4 | fileName | Specifies the name of the file where to write messages |
| 5 | append | If true, then the messages will be added to the old log, if false- the log file will be recreated each time the application is started. |
| 6 | bufferSize | Sets the buffer size in bytes |
| 7 | immediateFlush | If true, then each message is actually written to disk immediately (without a buffer). The log starts to work slowly, but this saves you from losing data when the program crashes. |
You already know how to work well with files, so these settings are nothing new to you. Configuring such a logger is even easier than a console logger:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
<Appenders>
<File name="MyFile" fileName="logs/app.log">
<PatternLayout>
<Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
</PatternLayout>
</File>
</Appenders>
<Loggers>
<Root level="error">
<AppenderRef ref="MyFile"/>
</Root>
</Loggers>
</Configuration>
RollingFileAppender
The most popular appender isRollingFileAppender . Unlike FileAppenderit, it allows you to split the log into many small files. This is very important for large logs. In addition, it allows you to set rules for what to do with old files after new ones have started to be written.
And this appender has almost a hundred different settings. You can find out more about them at the link .
Consider the most popular attributes of this appender:
| Attributes | ||
|---|---|---|
| 1 | name | Specifies the name of the appender |
| 2 | filter | Allows you to filter some messages |
| 3 | layout | Specifies the formatting of messages when output |
| 4 | fileName | Specifies the name of the file where to write messages |
| 5 | filePattern | Specifies a naming pattern for archive files that are no longer written |
| 6 | policy | Specifies the condition when the file should start being overwritten |
| 7 | strategy | Describes what to do with old files: archive, history for how many days to keep, etc. |
Here is a good example:
<Configuration status="warn" name="MyApp" packages="">
<Appenders>
<RollingFile name="RollingFile" fileName="logs/app.log" filePattern="logs/app-%d{MM-dd-yyyy}-%i.log.gz">
<PatternLayout>
<Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
</PatternLayout>
<Policies>
<TimeBasedTriggeringPolicy />
<SizeBasedTriggeringPolicy size="250 MB"/>
</Policies>
</RollingFile>
</Appenders>
<Loggers>
<Root level="error">
<AppenderRef ref="RollingFile"/>
</Root>
</Loggers>
</Configuration>
The parameter filePatternspecifies a template for archives of old logs. There are also two, when triggered, a new file will be written:
TimeBasedTriggeringPolicy– will work if a new day starts (the current date changes)SizeBasedTriggeringPolicy– will work if the file size reaches 250MB
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