How to get java Logger output to file by default [duplicate]

Answer 1

You have to define where the log is writting in the logger configuration file. For example, if you use log4j, a log4j.xml (or log4j.properties) file will contain such information.

For example, here is a simple log4j.xml file that logs directly into a file (my-app.log) and in the console:

<?xml version="1.0" encoding="UTF-8"?>
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="rolling" class="org.apache.log4j.DailyRollingFileAppender">
        <param name="File" value="my-app.log" />
        <param name="DatePattern" value=".yyyy-MM-dd" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern"
                value="%d{yyyy-MM-dd HH:mm:ss} %-5p [%C] [IP=%X{ipAddress}] [user=%X{user}] %m%n" />
        </layout>
    </appender>

    <appender name="console" class="org.apache.log4j.ConsoleAppender">
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern"
                value="%d{yyyy-MM-dd HH:mm:ss} %-5p [%C] [user=%X{user}] %m%n" />
        </layout>
    </appender>

    <root>
        <priority value="info" />
        <appender-ref ref="console" />
        <appender-ref ref="rolling" />
    </root>

</log4j:configuration>

Answer 2

I just add the following at startup

Handler handler = new FileHandler("test.log", LOG_SIZE, LOG_ROTATION_COUNT);
Logger.getLogger("").addHandler(handler);

You can specify your own values for LOG_SIZE and LOG_ROTATION_COUNT

You may need adjust the logging level to suit.