- Logger
- Appender
- Layout
1) Logger:
Logger methods are used to generate log statements in a java class instead of sopln.
We must create Logger object right after our class name.
While creating a Logger object we need to pass current class object as a parameter for which we are going to use Log4j.
Eg.
1 2 3 4 5 6 7 8 | public class Client { static Logger l = Logger.getLogger(Client.class.getName()); public static void main(String[] args) { // Our logic will goes here } } |
Logger object has some methods, We use these methods to print the status of our application.
We have 5 methods in Logger class starting from highest priority
- debug()
- info()
- warn()
- error()
- fetal()
Note: The purpose of all these methods is same ie. to print logs in a file. Only names are different.
If you mention warn in log4j.properties file then methods from and below warn() will be executed.
2) Appender:
Appender job is to write the messages into the external file or database or smtp
Appender is an interface.
In log4j we have different Appender implementation classes.
- FileAppender [ writing into a file ]
- ConsoleAppender [ Writing into console ]
- JDBCAppender [ For Databases ]
- SMTPAppender [ Mails ]
- SocketAppender [ For remote storage ]
- SocketHubAppender
- SyslogAppendersends
- TelnetAppender
1) DailyRollingFileAppender - Rotates based on dateFormat
2) RollingFileAppender - Rotates based on a maximum file size.
Layout:
This component specifies the format in which the log statements are written into the destination repository by the appender
We have different type of layout classes in log4j
- SimpleLayout
- PatternLayout
- HTMLLayout
- XMLLayout
Note: The PatternLayout defaults to %m%n which means print your-supplied message in a newline. This is exactly the same as printed out by Java's System.out.println(...) method
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