log实例

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>

### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### direct messages to file hibernate.log ###
#log4j.appender.file=org.apache.log4j.FileAppender
#log4j.appender.file.File=hibernate.log
#log4j.appender.file.layout=org.apache.log4j.PatternLayout
#log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### set log levels - for more verbose logging change ‘info‘ to ‘debug‘ ###

log4j.rootLogger=error, A1, R
log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
 
# Print the date in ISO 8601 format
#log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n
#log4j.appender.A1.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %m%n 
log4j.appender.A1.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %l "#" %m%n
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=logs/elec.log
log4j.appender.R.MaxFileSize=1000KB
# Keep one backup file
log4j.appender.R.MaxBackupIndex=10
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %l "#" %m%n

public class MyException extends RuntimeException{
    public MyException(String msg) {
        super(msg);
    }
}

public class TestExc {

    private static Logger log = Logger.getLogger(TestExc.class);

    public static void main(String[] args) throws NoSuchMethodException,
            SecurityException {
        try {
            hehe("a");
        } catch (Exception e) {
            String errorMsg = "a";
            if (e instanceof RuntimeException) {
                RuntimeException re = (RuntimeException) e;
                errorMsg = re.getMessage().trim();
            }
            log.error(errorMsg, e);
        }
    }

    static void hehe(String s) {
        throw new MyException("aaa");
    }
}

2016-04-14 13:15:12,028 excel.TestExc.main(TestExc.java:24) "#" aaa
excel.MyException: aaa
    at excel.TestExc.hehe(TestExc.java:29)
    at excel.TestExc.main(TestExc.java:17)