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Log4j Example : A simple way to show possibility of providing
various appenders in a single log4j.properties file



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I have used Three appenders from Log4j 1.2.14, such as 
ConsoleAppender, FileAppender and JDBCAppender.

This example will try to show how to use multiple Logger
and combination of appenders for various purpose and depending
on logging requirement.

Now in this example I shall try to configure three Loggers and
three appenders, such as shown below:


log4j.rootLogger=A B C
log4j.logger.A=DEBUG, A1
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %C - %m%n

log4j.logger.B=DEBUG, A2
log4j.appender.A2=org.apache.log4j.FileAppender
log4j.appender.A2.file=sample-log.txt
log4j.appender.A2.layout=org.apache.log4j.PatternLayout
log4j.appender.A2.layout.ConversionPattern=%d [%t] %-5p %C - %m%n

log4j.logger.C=ERROR, A3
log4j.appender.A3=org.apache.log4j.jdbc.JDBCAppender
log4j.appender.A3.Driver=org.hsqldb.jdbcDriver
log4j.appender.A3.URL=jdbc:hsqldb:hsql://localhost/
log4j.appender.A3.User=sa
log4j.appender.A3.Password=
log4j.appender.A3.layout=org.apache.log4j.PatternLayout
log4j.appender.A3.layout.ConversionPattern=
       insert into LogTable(log_detail) values('%d [%t] %-5p %C - %m%n')


I shall try to explain this log4j properties file,
In this example, there are three loggers with names A, B, C
and these loggers are defined in rootLogger property.
Each logger has various levels such as for A and B loggers, level is DEBUG
and for C logger, Level is ERROR.

Logger A has consoleAppender
Logger B has FileAppender
and Logger C has JDBCAppender.

As the value after comma separated level in logger definition, is that of
Appender, so Logger A has A1 appender, Logger B has A2 and Logger C has A3
as appender.

Each appender has to have some log destination  and Layout with pattern.
Interestingly for JDBCAppender (in this example, appender A3), database
table with insert statement , along with database driver and url with login
credential required. But there are ways to provide database Connection from
some other DataSource with connection Pooling capabilities as well.
This can be done by overriding default JDBCAppender getConnection method.

For this example, I have used HSQLDB as database and following Table to
hold log messages:

create table LogTable
(log_detail varchar(300))


And the Java Main application is as follows:

import org.apache.log4j.*;

public class TestLog4j
{
    private static Logger logger = Logger.getLogger("B");
    public TestLog4j() {
        testLogging();
    }
    public void testLogging() {
        logger.debug("starting testLogging method....");
        for(int i=0;i<10;i++) {
            logger.info("counting work ..."+i);
        }
        logger.debug("closing testLogging method....");
        logger.error("some error occured....");
    }
    public static void main(String[] args) 
    {
        new TestLog4j();
    }
}


Just notice the RED part in bold above, it shows that I am selecting
logger B and with Appender A2. So all DEBUG level logs will go to
Log file "sample-log.txt".
Now if I want to send all debug logs to filesystem and to database 
table, then one can use two appenders A2 and A3 with Logger B.

like 
log4j.logger.B=DEBUG, A2,  A3

Hope this example helps in understanding a basic usage of Log4j
as logging framework.



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While using Log4j 1.2.x version, JDBCAppender has following method setBufferSize(int newBufferSize), reference http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/jdbc/JDBCAppender.html So I guess by adding following line to the log4j.properties file, one can set buffer size and subsequently alter frequency of writing log statement to database. log4j.appender.A3= Can you please try this out and let me know if this works?

One can look at the SMTP appender from Javadoc api of Log4j http://logging.apache.org/log4j/1.2/apidocs/index.html?org/apache/log4j/net/SMTPAppender.html I think you can read the explaination of buffersize for Log4j 1.2.15, and use accordingly. To my understanding this Buffersize is the cyclic buffer of events those are stored in internal buffer before flushing out at some predefined numbers reached (as set by the bufferSize attribute in log4j properties for SMTPAppender) Please correct me if I am wrong.

hi arunlepuru, With respect to your first question regarding sending an email when some error (runtime I guess) occurs in any class, I would suggest you to go through the Apache Log4j Javadoc api, as pointed out below: SMTPAppender And try to do some sort of prototype using this and you may need to configure or pass any already configured SMTP server to be used along with your prototype. And I think Buffersize is the internal storage capacity to hold on with log messages, and once the capacity is full, then those logged messages are done with as per the configuration setting in log4j.properties file. Hope this answers your questions. used all at

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